GB2565887A

GB2565887A - Moving method of shroud head, upper guide rod, and suspension tool

Info

Publication number: GB2565887A
Application number: GB1810062.8A
Authority: GB
Inventors: Takano Shintaro; Sawahata Sadakatsu; Tanaka Hidenori
Original assignee: Hitachi GE Nuclear Energy Ltd
Current assignee: Hitachi GE Nuclear Energy Ltd
Priority date: 2017-06-30
Filing date: 2018-06-19
Publication date: 2019-02-27
Also published as: GB201810062D0; JP2019012018A

Abstract

A method of moving a shroud head 8 and an attached steam separator 9 between the reactor pressure vessel (RPV) 1 of a boiling water reactor, located within a reactor well 19, and a steam dryer/separator pit 22 is disclosed. The method comprises connecting a lower end portion of an upper guide rod 17 to an upper end portion of a lower guide rod 16 installed on an inner surface of the RPV, the top of the upper guide rod extending upwards to a point level with the bottom 23A of a passage 23 between the reactor well and storage pit 22. A suspension tool 25 attached to an overhead travelling crane 28 is used to raise/lower the shroud head along the lower and upper guide rods, as well as laterally into the storage pit. The suspension tool may also comprise a plurality of floating members (30, Fig. 7).

Description

MOVING METHOD OF SHROUD HEAD, UPPER GUIDE ROD, AND SUSPENSION

TOOL

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to a moving method of a shroud head, an upper guide rod, and a suspension tool, and particularly relates to a moving method of a shroud head suitable for moving the shroud head installed inside a reactor pressure vessel configuring a reactor of a boiling water reactor power plant and having a steam separator attached thereto, an upper guide rod, and a suspension tool.

BACKGROUND ART

A reactor of a boiling water reactor power plant is configured so that a reactor pressure vessel internally has a core plate, a top guide, a plurality of fuel assemblies, a plurality of control rods, a core shroud, a shroud head, a steam separator, and a steam dryer . The plurality of fuel assemblies are arranged inside the core shroud installed inside the reactor pressure vessel, thereby configuring a core. Each lower end portion of the fuel assemblies penetrates the core plate attached to the core shroud, and is supported by fuel support metal fittings held by an upper end of a control rod guide pipe . Each upper end portion of the fuel assemblies is held by the top guide attached to the core shroud. Each of the plurality of control rods is put in and out between the fuel assemblies from below. The shroud head for covering the core is detachably attached to the upper end portion of the top guide, and the steam separator is attached to an upper surface of the shroud head, and extends upward. Above the steam separator, the steam dryer is detachably attached to an inner surface of the reactor pressure vessel. An upper lid is attached to a flange of the upper end portion of the reactor pressure vessel so as to hermetically seal the reactor pressure vessel.

Furthermore, in a state where a plurality of guide rods extend in an axial direction of the reactor pressure vessel, the plurality of guide rods are installed on the inner surface of the reactor pressure vessel at different positions (two locations at an interval of 180°) in a circumferential direction of the reactor pressure vessel. When reactor internal structures such as the shroud head, the steam separator, and the steam dryer which are located above the core shroud are detached from the reactor pressure vessel in order to carry out replacement work for the fuel assemblies during a periodic inspection of the boiling water reactor power plant, and further when the reactor internal structures are loaded into and lowered to the reactor pressure vessel, the guide rods have a role to guide the reactor internal structures. In particular, when the reactor internal structures are loaded into and lowered to the reactor pressure vessel, the guide rods have a function to specify an installation position of the reactor internal structures in the circumferential direction of the reactor pressure vessel.

JP-A-2-126766 shows an example of the guide rod installed on the inner surface of the reactor pressure vessel. A lower end of the guide rod is located in an upper end portion of a core shroud head, and an upper end thereof is located in the vicinity of the flange of the upper end portion of the reactor pressure vessel.

The guide rod disclosed in JP-A-8-327769, which is installed on the inner surface of the reactor pressure vessel, is divided into an upper guide rod and a lower guide rod. The upper guide rod is located above the lower guide rod on an extension line of the lower guide rod.

JP-A-1-210900 also discloses the guide rod divided into the upper guide rod and the lower guide rod. A lower end of the lower guide rod is located in the upper end portion of the core shroud head. An upper end of the lower guide rod is located in the vicinity of a lower bracket installed on the inner surface of the reactor pressure vessel, at a position of a lower end portion of the steam dryer installed inside the reactor pressure vessel, and is fixed to the inner surface of the reactor pressure vessel. The upper guide rod is located above the lower guide rod on the extension line of the lower guide rod, and the lower end portion of the upper guide rod is detachably connected to the upper end portion of the lower guide rod.

According to JP-A-1-210900, in a state where the upper lid is detached from the flange of the upper end portion of the reactor pressure vessel, the upper end portion of the upper guide rod extends upward of an upper surface of the flange, and is attached to a support member which is detachably installed in the flange. The upper end portion of the upper guide rod is inclined toward the upper end portion of the support member .

Aperiodic inspection of the boiling water reactor power plant is carried out after an operation of the boiling water reactor power plant is stopped in one certain operation cycle. During a period of this periodic inspection, fuel exchange is performed on some fuel assemblies inside the core.

According to JP-A-1-210900, during the periodic inspection of the boiling water reactor power plant, the reactor pressure vessel is opened by detaching the upper lid attached to the flange of the reactor pressure vessel, and the support member is detachably installed in the upper end portion of the flange. The upper guide rod is attached to the support member, and the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod fixed to the inner surface of the reactor pressure vessel.

The steam dryer located above inside the reactor pressure vessel is detached from the reactor pressure vessel. As illustrated in Fig. 5 of JP-A-1-210900, the steam dryer is suspended at four locations by a suspension tool serving as a suspension balance suspended by an overhead traveling crane inside a reactor building. Thereafter, the detached steam dryer is suspended and lifted together with the suspension tool by the overhead traveling crane, and is raised along the upper guide rod. Then, the steam dryer reaches a predetermined position inside a reactor well formed above the reactor pressure vessel. In this case, the reactor pressure vessel is internally filled with cooling water up to a position of the upper surface of the flange formed in the upper end portion of the reactor pressure vessel. This steam dryer is moved in a horizontal direction from the reactor well to a steam dryer steam separator pit through a passage allowing the reactor well and the steam dryer steam separator pit to communicate with each other, and is stored inside the steam dryer steam separator pit. Subsequently, the shroud head having the steam separator attached thereto is detached from the core shroud. Similar to the steam dryer, the shroud head is suspended up to the predetermined position inside the reactor well by the overhead traveling crane. Furthermore, the shroud head is moved to the steam dryer steam separator pit in the horizontal direction, and is stored in the cooling water inside the steam dryer steam separator pit.

After the above-described periodic inspection is carried out, the shroud head having the steam separator attached thereto and the steam dryer are moved in this order from the steam dryer steam separator pit to a position directly above the reactor pressure vessel inside the reactor well by the overhead traveling crane using the above-described suspension tool, and is lowered to the predetermined posit ion inside the reactor pressure vessel Then, both of these are installed at the predetermined position inside the reactor pressure vessel. Thereafter, the upper lid is attached to the flange of the reactor pressure vessel, and the reactor pressure vessel is hermetically sealed. Then, in order to perform the operation in the subsequent operation cycle, the boiling water reactor power plant is restarted.

When the steam dryer and the shroud head having the steam separator attached thereto are detached from the reactor pressure vessel, and when the steam dryer and the shroud head are loaded into the reactor pressure vessel, these are suspended by the overhead traveling crane. In some cases, these may be located at a position considerably far above the flange of the reactor pressure vessel in the axial direction of the reactor pressure vessel, directly above the core inside the reactor pressure vessel. This position in the axial direction of the reactor pressure vessel is located considerably far above the upper end of the upper guide rod supported by the support member attached to the flange of the upper end portion of the reactor pressure vessel, which is disclosed in JP-A-1-210900.

Ina state where the shroud head having the steam separator attached thereto is present at a high position (position above a bottom surface of the passage (first passage) allowing the steam dryer steam separator pit and the reactor well to communicate with each other in the axial direction of the reactor pressure vessel) as described above inside the reactor well directly above the core inside the reactor pressure vessel, in a case where a wire suspending the shroud head from the overhead traveling crane is cut off, a falling accident occurs in the shroud head. In a case where the shroud head falls while being rotated in this falling accident, there is a possibility that the fuel assembly inside the core may be damaged due to the shroud head which falls while being rotated. The damage to the fuel assembly has to be avoided.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a moving method of a shroud head which can prevent a fuel assembly from being damaged due to fall of the shroud head when the shroud head is moved.

According to an aspect of the present invention, there isprovidedamovingmethodof a shroudhead. The method includes opening a reactor pressure vessel by detaching an upper lid from the reactor pressure vessel, connecting a lower end portion of an upper guide rod to an upper end portion of a lower guide rodinstalledonan inner surface of the reactor pressure vessel, extending the upper guide rod upward of the lower guide rod in a state where the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod, causing an upper end of the upper guide rod to reach a position of a bottom surface of a passage allowing a reactor well formed directly above the reactor pressure vessel and a steam dryer steam separator pit formed adjacent to the reactor well to communicate with each other in an axial direction of the reactor pressure vessel, moving the shroud head, having a steam separator attached thereto, to be installed inside the reactor pressure vessel above a core located inside the reactor pressure vessel so as to be detachable from the reactor pressure vessel into the passage allowing the reactor well and the steam separator to communicate with each other, between an installation position of the shroud head and the steam dryer steam separator pit inside the reactor pressure vessel, and moving the shroud head further along the upper guide rod whose upper end reaches a position of the bottom surface of the passage.

The upper end of the upper guide rod connected to the upper end portion of the lower guide rod reaches the position of the bottom surface of the passage allowing the reactor well and the steam dryer steam separator pit to communicate with each other in the axial direction of the reactor pressure vessel. Accordingly, when the shroud head is located at a position above the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel, inside the reactor well, directly above the core, between the installationposition of the shroud head and the steam dryer steam separator pit inside the reactor pressure vessel, in which the shroud head to be installed inside the reactor pressure vessel above the core so as to be detachable from the reactor pressure vessel, even in a case where the shroud head falls from the position, the falling shroud head can be lowered while being guided by the upper guide rod and the lower guide rod. Accordingly, the rotation of the falling shroud head is prevented by the upper guide rod and the lower guide rod. Therefore, it is possible to prevent a fuel assembly loaded into the core from being damaged by the falling shroud head.

The above-described object can be achieved as follows. The reactor pressure vessel is opened by detaching the upper lid. Thereafter, the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod installed on the inner surface of the reactor pressure vessel. In a state where the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod, the upper guide rod extends upward of the lower guide rod. In a state where the shroud head is suspended by the suspension tool having the floating member, the shroud head having the steam separator attached thereto is moved inside the passage allowing the reactor well and the steam dryer steam separator pit to communicate with each other, between the installation position of the shroud head inside the reactor pressure vessel and the steam dryer steam separator pit formed adjacent to the reactor well formed directly above the reactor pressure vessel, in which the shroud head to be installed inside the reactor pressure vessel above the core located inside the reactor pressure vessel so as to be detachable from the reactor pressure vessel is moved. Furthermore, the shroud head is moved along the upper guide rod and the lower guide rod.

In a case where the shroud head suspended by the suspension tool having the floating member directly above the core inside the reactor well falls together with the suspension tool having the floating member, each falling speed of the shroud head and the suspension tool is considerably reduced by an operation effect of the floating member disposed in the suspension tool. Therefore, it is possible to prevent the fuel assembly loaded into the core from being damaged by the shroud head and the suspension tool which fall toward the reactor pressure vessel.

According to the aspect of the present invention, it is possible to prevent the fuel assembly located inside the core from being damaged by the falling shroud head.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. lisa view for describing a moving method of a shroud head according to Embodiment 1 serving as a preferred embodiment of the present invention.

Fig. 2 is a longitudinal sectional view of a reactor of a boiling water reactor power plant to which the moving method of the shroud head according to Embodiment 1 is applicable.

Fig. 3 is a structural diagram of a lower guide rod installed inside the reactor illustrated in Fig. 2.

Fig. 4 is a view for describing a state where an upper guide rod is connected to an upper end portion of the lower guide rod installed inside the reactor.

Fig. 5 is a structural diagram of the upper guide rod illustrated in Fig. 4.

Fig. 6 is a view for describing a moving method of a shroud head according to Embodiment 2 serving as another preferred embodiment of the present invention.

Fig. 7 is a structural diagram of a suspension tool used for a moving method of a shroud head according to Embodiment 3 serving as still another preferred embodiment of the present invention.

Fig. 8 is a view for describing a state where an upper guide rod used for the moving method of the shroud head according to Embodiment 3 is installed in a reactor pressure vessel.

Fig. 9 is a view for describing a moving method of a shroud head according to Embodiment 4 serving as still another pref erred embodiment of the present invention.

Fig. 10 is a view for describing a schematic structure of fastening between the upper guide rod and a bracket.

DETAILED DESCRIPTION OF THE INVENTION

In various ways, the inventors have examined a moving method of a shroud head which can prevent a fuel assembly loaded into a core inside a reactor pressure vessel from being damaged even if the moving shroud head falls during the movement of the shroud head detached from the reactor pressure vessel and having a steam separator attached thereto. Results of the examination will be described below.

In the shroud head detached from the reactor pressure vessel, after the shroud head is detached from the reactor pressure vessel, when the shroud head is loaded into the reactor pressure vessel, the shroud head is moved through a passage allowing a reactor well and a steam dryer steam separator pit to communicate with each other, between the reactor well and the steam dryer steam separator pit. When the shroud head is moved, the reactor well, the steam dryer steam separator pit, and the passage are filled with cooling water. Accordingly, the shroud head is moved through the cooling water. When a steam dryer is moved, the reactor pressure vessel is internally filled with the cooling water up to an upper surface of a flange of the reactor pressure vessel, and the cooling water is not present inside the reactor well, the steam dryer steam separator pit, and the above-described communication passage . Therefore, the steam dryer moving between the reactor pressure vessel and the steam dryer steam separator pit is moved in the air. In order to move the above-described communication passage, the shroud head and the steam dryer need to be located above a bottom surface of the passage in an axial direction of the reactor pressure vessel, directly above the core inside the reactor pressure vessel inside the reactor well.

In this way, when the shroud head having the steam separator attached thereto is located above the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core inside the reactor pressure vessel inside the reactor well, even if a falling accident occurs in the shroud head as described above, the fuel assembly located inside the core has to avoid damage caused by the falling shroud head. Through the above-described examination, the inventors have found out the following solution to prevent the fuel assembly located inside the core from being damaged by the fall of the shroud head. That is, this solution is as follows. The reactor pressure vessel is opened by detaching an upper lid. Thereafter, a lower end portion of the upper guide rod is connected to an upper end portion of the lower guide rod installed on an inner surface of the reactor pressure vessel. In a state where the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod, an upper end of the upper guide rod is caused to reach a position of a bottom surface of the passage allowing the reactor well formed directly above the reactor pressure vessel and the steam dryer steam separator pit formed adj acent to the reactor well to communicate with each other, in the axial direction of the reactor pressure vessel. The shroud head is moved inside the passage allowing the reactor well and the steam dryer steam separator pit, between a position inside the reactor pressure vessel and steam dryer steam separator pit, in which the shroud head to be installed inside the reactor pressure vessel above the core located inside the reactor pressure vessel so as to be detachable from the reactor pressure vessel is moved. Furthermore, the shroud head is moved along the upper guide rod whose upper end reaches the position of the bottom surface of the passage.

As another solution, the inventors have found out that the floating member is attached to the suspension tool suspending the shroud head. Even if the suspension tool suspending the shroud head falls into the cooling water together with the shroud head, the falling speed of the shroud head and the suspension tool in the cooling water is reduced by an operation effect of the floating member installed in the suspension tool, thereby preventing the rotation of the shroud head. Therefore, the fuel assembly located inside the core is prevented from being damaged by the falling shroud head.

The steam dryer is also moved between the reactor pressure vessel and the steam dryer steam separator pit. During this movement, the steam dryer is located above the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core inside the reactor pressure vessel inside the reactor well. Inthis state, even if a falling accident occurs, the falling steam dryer falls onto the steam separator attached to the shroud head installed on a top guide covering the core shroud. Therefore, the fuel assembly loaded into the core below the shroud head is not damaged by the falling steam dryer.

Each embodiment reflecting each solution found out through the above-described examination will be described below.

Embodiment 1

Hereinafter, a moving method of a shroud head according to Embodiment 1 serving as a preferred embodiment of the present invention will be described with reference to Figs. 1 to 5.

First, a structure of a boiling water reactor power plant to which the present embodiment is applicable will be described with reference to Figs . 1 and 2 . For example, the boiling water reactor power plant is an advanced boiling water reactor power plant (ABWR power plant) . Fig. 2 illustrates a structure of a reactor of the boiling water reactor power plant. The reactor includes a reactor pressure vessel 1, and a core shroud 3, a core 4, a core plate 6, a top guide 7, a shroud head 8, a steam separator 9, and a steam dryer 10 which are arranged inside the reactor pressure vessel 1. The core shroud 3 is installed inside the reactor pressure vessel 1. The core plate 6 is located inside the core shroud 3, and is attached to the core shroud

3. The top guide 7 is attached to an upper end of the core shroud 3, and is located above the core plate 6. The top guide 7 has a grid member 7A, a cylindrical portion 7B, and a flange 29. The grid member 7A is attached to a lower end of the cylindrical portion 7B, and the flange 29 is attached to an upper end of the cylindrical portion 7B.

A control rod driving mechanism housing 14 for internally installing a control rod driving mechanism (not illustrated) operating a control rod (not illustrated) is disposed in a bottom portion of the reactor pressure vessel 1, and extends downward from the bottom portion. Apluralityof control rod guide pipes 31 are arranged below the core plate 6 inside the reactor pressure vessel 1. A lower end of each control rod guide pipe 31 is attached to an upper end of each control rod driving mechanism housing 14 inside the reactor pressure vessel 1. A plurality of fuel support metal fittings (not illustrated) respectively penetrate the core plate 6, and are supported by an upper end of the respective control rod guide pipes 31.

Each lower end portion of a plurality of fuel assemblies 5 containing a nuclear fuel material is supported by the fuel support metal fitting, and each upper end portion of the fuel assemblies 5 is held by the grid member 7A of the top guide . These fuel assemblies 5 configure the core 4, and the core shroud 3 encloses the core 4. One fuel support metal fitting supports a lower end portion of the four fuel assemblies 5, and one control rod located inside one control rod guide pipe 31 is driven by operating the control rod driving mechanism. In this manner, the control rod is inserted between the four fuel assemblies 5 supported by the fuel support metal fittings through the fuel support metal fittings from the inside of the control rod guide pipe 31.

The shroud head 8 is attached to the flange 29 present in an upper end portion of the top guide 7 . The steam separator 9 is installed on a curved portion of an upper end portion of the shroud head 8. The steam dryer 10 is located above the steam separator 9 inside the reactor pressure vessel 1, and is installed in the reactor pressure vessel 1. An upper lid 2 is attached to a flange 1A of the upper end portion of the reactor pressure vessel 1, thereby hermetically sealing the reactor pressure vessel 1. A main steam nozzle 15 to which a main steam pipe (not illustrated) for guiding steam generated in the core 4 to a turbine (not illustrated) is connected is formed in the vicinity of the upper end portion of the reactor pressure vessel 1. Apluralityof internal pumps 13 for boosting the cooling water inside an annular downcomer formed between the reactor pressure vessel 1 and the core shroud and for supplying the cooling water to the respective fuel assemblies are disposed in a bottom portion of the reactor pressure vessel

1.

In a state where a plurality of lower guide rods 16 illustrated in Fig. 3 extend in an axial direction of the reactor pressure vessel 1, the plurality of lower guide rods 16 are arranged facing an inner surface of the reactor pressure vessel 1 at different positions (two locations at an interval of 180°) in a circumferential direction of the reactor pressure vessel

1. A lower end portion of the lower guide rod 16 is attached to the flange 29 of the upper end portion of the top guide 7, and an upper end portion of the lower guide rod 16 is attached to a lower bracket 11 disposed on the inner surface of the reactor pressure vessel 1. Lugs (not illustrated) which are as many as the lower guide rods 16 are attached to each outer peripheral portion of the steam dryer 10 and the shroud head 8 and an outer peripheral portion of a support ring (not illustrated) disposed in the steam separator 9 attached to the shroud head 8 . These lugs have a cutout portion into which the lower guide rod 16 is inserted. Each of the lower guide rods 16 is inserted into the cutout portion formed in the lug attached to each support ring disposed in the steam dryer 10, the shroud head 8, and the steam separator 9. In this manner, the steam dryer 10, the shroud head 8, and the steam separator 9 are respectively positioned in the circumferential direction of the reactor pressure vessel 1.

The reactor pressure vessel 1 is installed inside a reactor container (not illustrated) to be installed inside a reactor building (not illustrated) . Inside the reactor building, a reactor well 19 is formed directly above the reactor pressure vessel 1 as illustrated in Fig. 1. A steam dryer steam separator pit (dryer separator pit) 22 and a fuel storage pit (not illustrated) are arranged adjacent to both sides of the reactor well 19. The reactor well 19, the steam dryer steam separator pit 22, and the fuel storage pit are linearly arranged in this order, and are enclosed by an operation floor 21. During a periodic inspection when an operation the boiling water reactor power plant is stopped, the reactor well 19 and the steam dryer steam separator pit 22 are allowed to communicate with each other by a first passage 23. The reactor well 19 and the fuel storage pit are allowed to communicate with each other by a second passage (not illustrated). Although not illustrated, each of the first passage 23 and the second passage is blocked by a plurality of stacked throttle plugs (gate members) during the operation of the boiling water reactor power plant.

A baffle plate 20 serving as a portion of a bottom portion of the reactor well 19 is located between the reactor pressure vessel 1 and the reactor container, and the baffle plate 20 is attached to the reactor pressure vessel 1 and the reactor container .

When the boiling water reactor power plant is completely operated in one certain operation cycle, the operation of the boiling water reactor power plant is stopped. After the operation is stopped, a periodic inspection is carried out for the boiling water reactor power plant. During a period of the periodic inspection, maintenance inspection is performed on equipment and pipes on the boiling water reactor power plant, and fuel exchange work is carried out to refuel some of the fuel assembly loaded into the core 4. When the maintenance inspection is performed on a reactor internal structure installed inside the reactor pressure vessel 1, for example, the core shroud 3, and when the fuel exchange work is carried out, first, a shielding plug (not illustrated) installed on the operation floor 21, which is located above the container head so as to cover the reactor well 19 is removed by an overhead traveling crane (not illustrated), and the reactor well 19 is released. Next, the container head covering the upper lid 2 of the reactor container is detached from the flange 1A of the reactor pressure vessel 1, and is unloaded outward of the reactor well 19 by the overhead traveling crane. The upper lid 2 is detached from the flange 1A of the reactor pressure vessel 1, and is unloaded outward of the reactor well 19 by the overhead traveling crane, similarly to the container head. Each of the detached container head and upper lid2 isplacedon the operation floor 21.

After the upper lid 2 is unloaded from the reactor well

19, each lower end portion of the upper guide rod 17 illustrated in Fig. 5 is connected to the upper end portion of each lower guide rod 16 installed inside the reactor pressure vessel 1. A lower guide rod stud 36 having a projection-shaped tip is disposed in the upper end portion of each lower guide rod 16. An upper guide rod connector 37 having a recess shape into which the lower guide rod stud 36 is inserted is disposed in the lower end portion of the upper guide rod 17. The upper guide rod 17 has a coupler 38 to be connected to a bracket 12. An example of work for connecting the upper guide rod 17 to the upper end portion of the lower guide rod 16 will be described below.

In order to carry out this connection work, a fuel exchange machine (not illustrated) is used which is located across the reactor well 19 and is movably installed on the operation floor

21. Amounting tool for suspending the upper guide rod 17 is attached to a fuel gripping tool of the fuel exchange machine. One upper guide rod 17 is suspended by the mounting tool, and a traveling carriage and a traversing carriage of the fuel exchange machine are operated. In this manner, the upper guide rod 17 is located directly above one lower guide rod 16, and the upper guide rod 17 is lowered by lowering the fuel gripping tool. Then, the lower end portion of the lowered upper guide rod 17 is connected to the upper end portion of the lower guide rod 16. The connected upper guide rod 17 is held by an upper bracket 12 disposed on the inner surface of the reactor pressure vessel 1 in the vicinity of the flange 1A. After the lower end portion of the upper guide rod 17 is connected to the lower guide rod 16, the mounting tool attached to the fuel gripping tool is detached from the upper guide rod 17, and the mounting tool is lifted up together with the fuel gripping tool. The lower end portion of the other one upper guide rod 17 is similarly connected to the upper end portion of the other one lower guide rod 16. The upper end of the upper guide rod 17 connected to the upper end portion of the lower guide rod 16 is located at apositionofa bottom surface2 3Aof the first passage 2 3 allowing the reactor well 19 and the steam dryer steam separator pit to communicate with each other in the axial direction of the reactor pressure vessel 1. Each connected upper guide rod 17 is supported by a support member 18 located inside the reactor well 19 . The support member 18 extends in a horizontal direction, and is located below the bottom surface 23A of the first passage in the axial direction of the reactor pressure vessel 1. One end portion of the support member 18 is attached to a side surface of the reactor well 19, and the other end portion of the support member 18 is attached to the upper guide rod 17 (refer to Fig. 4) . The support member 18 prevents the upper guide rod 17 from falling down.

An example of work for attaching the support member 18 to the side surface of the reactor well 19 and the upper guide rod 17 will be described below. Before this attachment work starts, cooling water 24 is supplied into the reactor pressure vessel 1 so that a water level of the cooling water 24 reaches a position of the upper surface of the flange 1A of the reactor pressure vessel 1. When the water level of the cooling water 24 reaches the position of the upper surface of the flange 1A (refertoFig. 4) , supplying the cooling water 2 4 into the reactor pressure vessel 1 is stopped.

In order to carry out the attachment work of the support member 18, for example, a platform whose upper end portion was released is used. This platform has a flat floor so that a worker is likely to ride thereon. A radiation shielding body for radiation shielding frombelow is installed under the floor, and a radiation shielding wall for radiation shielding is also disposed around the floor. The platform on which the support member 18 is placed and a plurality of workers ride is suspended at four locations by a suspension balance suspended by the overhead traveling crane. The platform is suspended and lowered from the operation floor 21 into the reactor well 19 by the operation of the overhead traveling crane. When the upper end of the platform is lowered to the vicinity of an installation location of the support member 18, lowering the platform is stopped. Thereafter, in a state where the water level of the cooling water 24 is maintained at the position of the upper surface of the flange 1A of the reactor pressure vessel 1, one end portion of the support member 18 is attached to the side surface of the reactor well 19, and the other end portion of the support member 18 is attached to the upper guide rod 17 by the worker riding on the platform. After the support member 18 is attached to each upper guide rod 17, the platform is raised by the overhead traveling crane, and is moved onto the operation floor 21. In this way, attaching the support member 18 to each upper guide rod 17 is completed. The support member 18 is attached to the upper guide rod 17 so as not to obstruct the movement of the steam dryer 10 and the shroud head 8 which are raised and lowered while being guided by the upper guide rod 17.

In a state where the water level of the cooling water 24 is maintained at the position of the upper surface of the flange 1A of the reactor pressure vessel 1, a radiation dose of the worker who carries out the work for attaching the support member 18 to the side surface of the reactor well 19 and the upper guide rod 17 on the platform can be significantly suppressed by installing the radiation shielding body and the radiation shielding wall in the platform as described above. The radiation shielding body and the radiation shielding wall which are installed in the platform suppress the radiation dose of the worker who carries out the work on the platform, even when work for detaching the support member 18 from the side surface of the reactor well 19 and the upper guide rod 17 is carried out.

The worker riding on the platform wears a safety belt. One end portion of the safety belt is attached to the platform, and the other end portion is attached to the body of the worker. In a case where the worker falls from the platform when carrying out the attachment work / detachment work of the support member 18, the safety belt prevents the worker from falling to the bottom surface of the reactor well 19, and prevents the worker falling to the bottom surface from being injured.

Each unloading work starts for the steam dryer 10 and the shroud head 8 having the steam separator 9 attached thereto . The steam dryer 10 located above the steam separator 9 is detachably attached to the inner surface of the reactor pressure vessel 1. The core shroud 3 is fixed to the inner surface of the bottom port ion of the reactor pressure vessel 1 by a plurality of shroud support legs (not illustrated) attached to the lower end of the core shroud 3. Therefore, the shroud head 8 to be detachably attached to the upper end of the core shroud 3 and having the steam separator 9 attached thereto is consequently detachably attached to the reactor pressure vessel 1.

Before the unloading work of the steam dryer 10 starts, a plurality of throttle plugs blocking the first passage 23 are removed. At this time, the water level of the cooling water 24 is maintained at the position of the upper surface of the flange 1A of the reactor pressure vessel 1. Even during the unloading work of the steam dryer 10, the water level of the cooling water 24 is present at the position of the upper surface of the flange 1A.

First, the steam dryer 10 is detached from the reactor pressure vessel 1, and is suspended and lifted by the overhead traveling crane. This steam dryer 10 is suspended using four wires 27 by the suspension tool 25 serving as the suspension balance suspended by the overhead traveling crane. The suspension tool 25 has a beam 26. For example, as illustrated in Fig. 3 of JP-A-1-210900, two beams 26 are used, and two beams 26 are combined so as to be orthogonal to each other. The suspension tool 25 may employ a structure in which four beams 26 arranged in a square shape are coupled to each other instead of the two orthogonal beams 26.

The lower guide rod 16 is inserted into the cutout portion of each lug attached to the steam dryer 10. Accordingly, the steam dryer 10 suspended and lifted by the overhead traveling crane using the suspension tool 25 is guided by each lower guide rod 16, and rises inside the reactor pressure vessel 1. When the steam dryer 10 rises until each lug attached to the steam dryer 10 faces the lower guide rod 16 from the upper guide rod 17, each upper guide rod 17 is inserted into the cutout portion of each lug attached to the steam dryer 10. Subsequently, the steam dryer 10 rises while being guided by each upper guide rod 17.

When the lower end surface of the steam dryer 10 reaches a position above the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4 inside the reactor well 19 from the inside of the reactor pressure vessel 1, the steam dryer 10 stops rising. At this time, each lug attached to the steam dryer 10 is detached from each upper guide rod 17, and the lower surface of the steam dryer 10 is located above the upper end of the upper guide rod 17. Thereafter, the steam dryer 10 is moved in the horizontal direction toward the steam dryer steam separator pit 22 by the overhead traveling crane. Specifically, the steam dryer 10 is moved in the air to a predetermined position inside the steam dryer steam separator pit 22 from a position directly above the core 4 inside the reactor well 19 through the first passage 23. The steam dryer 10 is placed on the bottom surface of the steam dryer steam separator pit 22 at the predetermined position inside the steam dryer steam separator pit 22, and is stored inside the steam dryer steam separator pit 22 until the steam dryer 10 returns to the inside of the reactor pressure vessel 1.

Next, the unloading work is carried out for the shroud head 8 having the steam separator 9 attached thereto. Before this unloading work starts, the reactor well 19, the first passage 23 from which the throttle plug is removed, and the inside of the steam dryer steam separator pit 22 are filled with the cooling water 24 until the water level reaches a set water level above the upper endof the upper guide rod 17 connected to the upper end portion of the upper guide rod 16 (refer to Fig. 1) . The shroud head 8 having the steam separator 9 attached thereto is detached from the core shroud 3. Similar to the steam dryer 10, the shroud head 8 is suspended by the suspension tool 25, and is raised inside the reactor pressure vessel 1 and the reactor well 19 by the overhead traveling crane. The shroud head 8 is also raised while being guided by each of the lower guide rod 16 and the upper guide rod 17 inserted into the cutout portion of each lug disposed in the support ring of the shroud head 8 and the steam separator 9. When the lower end surface of the shroud head 8 reaches the position above the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4 inside the reactor well 19, raising the shroud head 8 having the steam separator 9 attached thereto and the steam separator 9 is stopped.

Thereafter, the shroud head 8 having the steam separator 9 attached thereto, which is immersed in the cooling water 24 inside the reactor well 19, is moved in the horizontal direction toward the steam dryer steam separator pit 22 by the overhead traveling crane. The shroud head 8 having the steam separator 9 attached thereto is moved in the cooling water 24 from the reactor well 19 to a predetermined position inside the steam dryer steam separator pit 22 through the first passage 23. The shroud head 8 having the steam separator 9 attached thereto isplacedon the bottom surface of the steam dryer steam separator pit 22 at the predetermined position inside the steam dryer steam separator pit 22, and is stored in the cooling water 24 inside steam dryer steam separator pit 22 until the shroud head 8 returns to the inside of the reactor pressure vessel 1.

After the steam dryer 10 and the shroud head 8 having the steam separator 9 attached thereto are completely unloaded from the reactor pressure vessel 1 to the steam dryer steam separator pit 22, fuel exchange work is carried out for exchanging a portion of the fuel assembly 5 (used fuel assembly) which is loaded into the core 4 and whose life is finished, with a new fuel assembly having a burnup rate of 0 GWd/t. The fuel exchange machine moving on the operation floor 21 is operated, and the fuel gripping tool is lowered. The used fuel assembly inside the core 4 is gripped with the fuel gripping tool, and the fuel gripping tool is raised. The used fuel assembly inside the core 4 is raised together with the fuel gripping tool, and is moved from the reactor pressure vessel 1 to a predetermined level inside the reactor well 19. The plurality of throttle plugs blocking the second pas sage allowing the reactor well 19 and the fuel storage pit to communicate with each other are previously removed.

The used fuel assembly which reaches a predetermined level inside the reactor well 19 is moved in the horizontal direction toward the fuel storage pit by the fuel exchange machine. The used fuel assembly moved from the reactor well 19 to the fuel storage pit through the second passage by the fuel exchange machine is accommodated in a fuel storage rack stored in the cooling water inside the fuel storage pit. The new fuel assembly having the burnup rate of 0 GWd/t which is accommodated in another fuel storage rack is gripped by the fuel gripping tool of the fuel exchange machine, and is moved from the fuel storage pit to the reactor well 19 through the second passage . Furthermore, the new fuel assembly is loaded into the core 4 inside the reactor pressure vessel 1.

Before the fuel exchange work starts or after the fuel exchange work is completely carried out, the plurality of fuel assemblies 5 loaded in a peripheral portion of the core 4 are moved to the fuel storage pit. After the fuel assemblies are moved, maintenance inspection is performed on the core shroud 3 (for example, detecting a flaw of the core shroud 3 by using an ultrasound flaw detector or applying compression residual stress to the inner surface of the core shroud 3 by using a water j et peening method) . Furthermore, concurrently with the fuel exchange work, the maintenance inspection is performed on pipes and equipment which are connected to the reactor pressure vessel 1.

After the fuel exchange work and the maintenance inspection work inside the reactor pressure vessel 1 are completely carried out, the shroud head 8 having the steam separator 9 attached thereto, which is stored inside the steam dryer steam separator pit 22, and the steam dryer 10 are sequentially loaded into the reactor pressure vessel 1. First, the shroud head 8 having the steam separator 9 attached thereto inside the steam dryer steam separator pit 22 is suspended by the suspension tool 25 suspended from the overhead traveling crane . The shroud head 8 is suspended and lifted from the bottom surface of the steam dryer steam separator pit 22 by the overhead traveling crane. The shroud head 8 is moved in the cooling water 24 to a position directly above the core 4 inside the reactor well 19 through the first passage 23, above the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1. The movement of the shroud head 8 in the horizontal direction is stopped at the position directly above the core 4 inside the reactor well

19. At this time, the lower surface of the shroud head 8 is located above the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, above the upper end of each upper guide rod 17. The shroud head 8 and the cutout portion formed in each lug attached to each support ring disposed in the steam separator 9 are located directly above each upper guide rod 17.

The overhead traveling crane is operated so that the shroud head 8 is lowered toward the inside of the reactor pressure vessel 1 from the position where the movement of the shroud head 8 in the horizontal direction is stopped. As the shroud head 8 is lowered, each upper guide rod 17 is inserted into the cutout portion formed in each lug. The lowered shroud head 8 and steam separator 9 are guided by each upper guide rod 17. Each lower guide rod 16 connected to the lower end portion of each upper guide rod 17 is inserted into the cutout portion formed in each lug. Thereafter, the lowered shroud head 8 and steam separator 9 are guided by each lower guide rod 16. Then, the lower surface of the shroud head 8 is seated on the upper surface of the flange 29 of the top guide 7. The shroud head 8 is attached to the flange 29.

After the shroud head 8 is attached to the flange 29, the cooling water 24 inside the reactor well 19 is discharged, and the water level of the cooling water 24 reaches the position of the upper surface of the flange 1A of the reactor pressure vessel 1. Thereafter, the steam dryer 10 inside the steam dryer steam separator pit 22 is suspended by the suspension tool 25 suspended by the overhead traveling crane, similarly to the shroud head 8. The overhead traveling crane is operated so that the steam dryer 10 is moved in the air to the position directly above the core 4 inside the reactor well 19 through the first passage 23. At that position, the movement of the steam dryer 10 stops in the horizontal direction is stopped. The cutout portion formed in each lug attached to the steam dryer 10 in a stopped state is located directly above each upper guide rods 17 . If the steam dryer 10 is lowered by the overhead traveling crane, each upper guide rod 17 is inserted into the cutout portion formed in each lug disposed in the steam dryer 10, and the steam dryer 10 is guided and lowered by the upper guide rod 17. Similar to the shroud head 8, the steam dryer 10 is further guided by the lower guide rod 16. When the steam dryer 10 is lowered to a predetermined position above the steam separator 9 inside the reactor pressure vessel 1, lowering the steam dryer 10 is stopped, and the steam dryer 10 is installed in the reactor pressure vessel 1.

The upper guide rod 17 connected to the lower guide rod 16 attached to the inner surface of the reactor pressure vessel 1 and the support member 18 attached to the side surface of the reactor well 19 and the upper guide rod 17 are arranged inside the reactor well 19 at least during a period from when the upper guide rod 17 is connected to the lower guide rod 16 before the unloading work of the steam dryer 10 from the reactor pressure vessel 1 starts until the steam dryer 10 is completely installed inside the reactor pressure vessel 1.

After the steam dryer 10 is completely installed inside the reactor pressure vessel 1, in a state where the water level of the cooling water 24 is maintained at the position of the upper surface of the flange 1A (refer to Fig. 4), the above-described platform suspended by the suspension balance is lowered by the overhead traveling crane, to the vicinity of the position where the support member 18 is attached to the inner surface of the reactor well 19 and the upper guide rod

17. First, a worker who rides on the platform carries out decontamination work for each of the support member 18 and the vicinity of the position where the upper guide rod 17 and the inner surface of the reactor well 19 are attached to the support member 18. Thereafter, the worker detaches the support member 18 from the upper guide rod 17 and the side surface of the reactor well 19. The platform having the detached support member 18 is moved onto the operation floor 21.

Thereafter, the fuel exchange machine is operated so that the mounting tool attached to the fuel gripping tool of the fuel exchange machine is lowered from the position directly above the upper guide rod 17 to the vicinity of the upper end of the upper guide rod 17. After the upper guide rod 17 is suspended by the attachment portion, the fuel gripping tool is raised. A connection state between the upper guide rod 17 and the lower guide rod 16 is released, and the upper guide rod 17 is lifted up to the position of the fuel exchange machine . The upper guide rod 17 is moved from the fuel gripping tool to the overhead traveling crane, and is moved onto the operation floor 21. Similarly, the remaining upper guide rod 17 is moved onto the operation floor 21.

The cooling water inside the reactor well 19 is discharged, and the water level of the cooling water inside the reactor pressure vessel 1 is lowered below the main steam nozzle 15 and the steam dryer 10 . The upper lid 2 is moved onto the flange 1A of the reactor pressure vessel 1 while being suspended by the overhead traveling crane, and is attached to the flange 1A of the reactor pressure vessel 1. After the upper lid 2 is moved onto the flange 1A and is completely attached to the flange 1A of the reactor pressure vessel 1, the plurality of throttle plugs are installed inside the first passage 23, and the first passage 23 is closed. The container head covers the upper lid 2, and is attached to the reactor container. Thereafter, the shielding plug covers the reactor well 19, and is installed on the operation floor 21.

After the periodic inspection is completely performed on the boiling water reactor power plant, the boiling water reactor power plant is started so as to perform an operation in the subsequent operation cycle.

According to the present embodiment, after the reactor pressure vessel 1 is opened, the lower end portion of the upper guide rod 17 is connected to the upper end portion of the lower guide rod 16 installed on the inner surface of the reactor pressure vessel 1. In a state where the lower end portion of the upper guide rod 17 is connected to the upper end portion of the lower guide rod 16, the upper end of the upper guide rod 17 reaches the position of the bottom surface 23A of the first passage 23 allowing the reactor well 19 and the steam dryer steam separator pit 22 to communicate with each other in the axial direction of the reactor pressure vessel 1 inside the reactor well 19 . Accordingly, when the shroud head 8 having the steam separator 9 attached thereto is moved between the steam dryer steam separator pit 22 and the reactor pressure vessel 1, and when the shroud head 8 is located the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4, for example, in a case where the wire 27 is cut off and the shroud head 8 having the steam separator 9 attached thereto falls, before the falling shroud head 8 having the steam separator 9 is rotated along the axial direction of the reactor pressure vessel 1, each upper guide rod 17 is inserted into the cutout formed in each lug attached to the falling shroud head 8 having the steam separator 9 attached thereto. Therefore, the falling shroud head 8 is lowered while being guided by the upper guide rod 17 and the lower guide rod 16.

Therefore, the rotation of the falling shroud head 8 is prevented by the upper guide rod 17 and the lower guide rod

16. The fuel assembly 5 loaded to the core 4 can be prevented from being damaged by the falling shroud head 8.

The upper guide rod 17 connected to the lower guide rod 16 is supported by the support member 18 attached to the side surface of the reactor well 19 inside the reactor well 19.

Accordingly, the upper guide rod 17 can be prevented from falling down due to the falling shroud head 8, and the falling shroud head 8 can be guided along the upper guide rod 17.

Even in a case where the above-described falling accident does not occur, the upper guide rod 17 connected to the lower guide rod 16 can guide the steam dryer 10 unloaded from the reactor pressure vessel 1 to the steam dryer steam separator pit 22 and the shroud head 8 having the steam separator 9 attached thereto, and further the shroud head 8 having the steam separator 9 attached thereto loaded into the reactor pressure vessel 1 from the steam dryer steam separator pit 22 and the steam dryer

10.

As in the upper guide rod illustrated in Fig. 3 of JP-A-1-210900, the upper end portion of each upper guide rod 17 may be inclined so as to be closer to the side surface of the reactor well 19 as the upper end portion goes toward the upper end of the upper guide rod 17 . Since the upper end portion of each upper guide rod 17 is inclined in this manner, when the steam dryer 10 and the shroud head 8 which are moved from the steam dryer steam separator pit 22 to directly above the core 4 inside the reactor well 19 are moved downward, the steam dryer 10 and the shroud head 8 can be smoothly moved toward a vertical portion of the upper guide rod 17 along the inclined portion of the upper end portion of the upper guide rod 17. Therefore, the vertical portion of the upper guide rod 17 is easily inserted into the cutout portion of each lug disposed in each of the steam dryer 10 and the shroud head 8 . The lowered steam dryer 10 and shroud head 8 are guided by the vertical portion of the upper guide rod 17 to a predetermined installation position. Furthermore, when the shroud head 8 is located above the core 4 above the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4, even in a case where the shroud head 8 falls, the shroud head 8 can be smoothly moved toward the vertical portion of the upper guide rod 17 along the inclined portion of the upper end portion of the upper guide rod 17. The vertical portion of the upper guide rod 17 can be easily inserted into the cutout portion of each lug disposed in the shroud head 8. Therefore, the fallen shroud head 8 can also be guided by the upper guide rod 17.

The upper end of the upper guide rod 17 connected to the lower guide rod 16 and extending upward is located at the position of the bottom surface 23A of the first passage 23 allowing the reactor well 19 and the steam dryer steam separator pit 22 to communicate with each other in the axial direction of the reactor pressure vessel 1. Accordingly, without being hindered by the upper guide rod 17, the shroud head 8 or the steam dryer 10 can be easily moved between the steam dryer steam separator pit 22 and the position directly above the core 4 of the reactor well 19 through the first passage 23.

The upper end of the upper guide rod 17 is located at the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1. Accordingly, during the fuel exchange, each movement of the fuel assembly and the used fuel assembly and the new fuel assembly between the core 4 and the fuel storage pit is not hindered by the upper guide rod 17. In the reactor well 19 and the fuel storage pit in the axial direction of the reactor pressure vessel 1, the position of the bottom surface of the second passage is the same as the position of the bottom surface 23A of the first passage 23.

Embodiment 2

Hereinafter, a moving method of a shroud head according to Embodiment 2 serving as another preferred embodiment of the present invention will be described with reference to Fig. 6.

The moving method of the shroud head according to the present embodiment is performed in a state where the reactor pressure vessel 1 is covered with an iron-made radiation shielding plate (radiation shielding member) 32 by attaching the radiation shielding plate 32 to the upper surface of the flange 1A of the reactor pressure vessel 1 in the moving method of the shroud head according to Embodiment 1.

In the moving method of the shroud head according to Embodiment 1, when the attachment work of the support member 18 is carried out, shielding of upward radiation from the inside of the reactor pressure vessel 1 is performed using the cooling water 24 present up to the position of the upper end of the flange 1A inside the reactor pressure vessel 1.

In contrast, according to the present embodiment, when the attachment work is carried out to attach the support member 18 to the upper guide rod 17, the shielding of the radiation is performed using the cooling water 2 4 present up to the position of the upper end of the flange 1A inside the reactor pressure vessel 1 and the radiation shielding plate 32 covering the reactor pressure vessel 1 located in the upper end of the flange 1A and covering the reactor pressure vessel 1.

Except for the above-described point, the moving method of the shroud head according the present embodiment is the same as the moving method of the shroud head according to Embodiment

1. A point different between the moving method of the shroud head according to the present embodiment and the moving method of the shroud head according to Embodiment 1 will be described in detail.

After the shielding plug, the container head, and the upper lid 2 are detached, similar to Embodiment 1, the lower end portion of the upper guide rod 17 is connected to the upper end portion of the lower guiderodl6 installedinside the reactor pressure vessel 1. At this time, the water level of the cooling water 24 is present at the position of the upper end of the flange 1A of the reactor pressure vessel 1, and the reactor pressure vessel 1 is internally filled with the cooling water 24.

The iron-made circular radiation shielding plate 32 having two cutout portions 33 into which the two upper guide rods 17 are inserted is suspended by the overhead traveling crane, and is lowered into the reactor well 19. Similar to the upper guide rod 17, the two cutout portions 33 formed to penetrate the radiation shielding plate 32 in the thickness direction of the radiation shielding plate 32 are formed at an interval of 180 degrees in the circumferential direction of the radiation shielding plate 32 . As the radiation shielding plate 32 is lowered, each upper guide rods 17 is inserted into each cutout portion 33. The radiation shielding plate 32 is lowered along the upper guide rod 17, and then, is seated on the upper surface of the flange 1A. The radiation shielding plate 32 placed on the upper surface covers the reactor pressure vessel 1, and is detachably attached to the flange 1A.

In a state where the radiation shielding plate 32 is attached to the flange 1A, similar to Embodiment 1, the support member 18 located below the bottom surface 23A of the first passage 23 is attached to the side surface of the reactor well 19 and the upper guide rod 17 (refer to Fig. 6) . After the support member 18 is attached to the upper guide rod 17, the radiation shielding plate 32 detached from the flange 1A is suspended and lifted by the overhead traveling crane so as to be moved onto the operation floor 21. Each cutout portion 33 is formed to be elongated from the insertion position of the upper guide rod 17 toward the side surface of the radiation shielding plate 32 in the radial direction of the radiation shielding plate 32 so that the support member 18 can pass through the inside of the cutout portion 33 of the radiation shielding plate 32. The cutout portion 33 is open not only on the upper surface and the lower surface of the radiation shielding plate 32 but also on the side surface of the radiation shielding plate 32. The width of the cutout portion 33 in the horizontal direction is slightly wider than the width of the support member 18 in the horizontal direction.

After the radiation shielding plate 32 is moved onto the operation floor 21, similar to Embodiment 1, the steam dryer 10 detached from the reactor pressure vessel 1 is suspended and lifted by the overhead traveling crane, and is raised along each of the lower guide rod 16 and the upper guide rod 17. The steam dryer 10 is moved in the air to the steam dryer steam separator pit 22 through each of the reactor well 19 and the first passage 23 from which the throttle plug is detached.

Thereafter, the reactor well 19, the first passage 23, and the steam dryer steam separator pit 22 are filled with the cooling water 24 so that the water level reaches the above-described set water level. Similar to Embodiment 1, the shroud head 8 which is detached from the core shroud 3 and from which the steam separator 9 is detached is raised along each of the lower guide rod 16 and the upper guide rod 17, and is moved in the cooling water 24 to the steam dryer steam separator pit 22 through each of the reactor well 19 and the first passage

23.

After the fuel exchange work and the maintenance inspection work inside the reactor pressure vessel 1 are completely carried out, the shroud head 8 having the steam separator 9 attached thereto is moved in the cooling water 24 from the steam dryer steam separator pit 22 into the reactor pressure vessel 1 through the first passage 23 and the reactor well 19. The shroud head 8 reaching the inside of the reactor well 19 is lowered along the upper guide rod 17 and the lower guide rod, and is attached to the flange 2 9 . After the attachment, the cooling water 24 inside the reactor well 19 is discharged, and the water level of the cooling water 24 is lowered to the position of the upper end of the flange 1A. Then, the steam dryer 10 is moved in the air from the steam dryer steam separator pit 22 to the reactor well 19 through the first passage 23. The steam dryer 10 which reaches the inside of the reactor well 19 and which is present in the air is lowered along the upper guide rod 17 and the lower guide rod, and is attached to the predetermined position inside the reactor pressure vessel 1, which is above the steam separator 9.

The radiation shielding plate 32 is lowered inside the reactor well 19 by the overhead traveling crane. Each upper guide rod 17 is inserted into each cutout portion 33, and the radiation shielding plate 32 is lowered along the upper guide rod 17. The radiation shielding plate 32 lowered to the upper end of the flange 1A is attached to the flange 1A. In a state where the radiation shielding plate 32 is attached to the flange 1A, similar to Embodiment 1, the support member 18 is detached from the side surface of the reactor well 19 and the upper guide rod 17. Thereafter, similar to Embodiment 1, the upper guide rod 17 is detached from the lower guide rod 16.

The upper lid 2 is attached to the flange 1A, the throttle plug is installed into the first passage 23, the container head is attached to the reactor container, and the shielding plug is attached to the operation floor 21, in this order.

The present embodiment can achieve each advantageous effect realized according to Embodiment 1. In the present embodiment, in order to carry out the attachment work for attaching the support member 18 to the upper guide rod 17 and the detachment work for detaching the support member 18 from the upper guide rod 17, the radiation shielding plate 32 is attached to the flange 1A so as to cover the reactor pressure vessel 1 with the radiation shielding plate 32. Therefore, a worker can be shielded against the radiation from the reactor pressure vessel 1 by using the radiation shielding plate 32, and the attachment work of the support member 18 is carried out. The above-described radiation dose of the worker riding on the platform can be further reduced by the radiation shielding plate 32, compared to Embodiment 1.

Embodiment 3

Hereinafter, a moving method of a shroud head according to Embodiment 3 serving as another preferred embodiment of the present invention will be described with reference to Fig. 7.

In the moving method of the shroud head according to the present embodiment, a suspension tool 25A illustrated in Fig. 7 is used instead of the suspension tool 25 illustrated in Fig.

1. The suspension tool 25A has a structure in which a plurality of floating members 30 are disposed in the suspension tool 25. The plurality of floating members 30 are attached to each beam 26 of the suspension tool 25A. The floating member 30 has a hollow member internally having a space, and is configured so that the internal space of the hollow member is hermetically sealed while being filled with compressed air. A hook box 28 is fastened to the overhead traveling crane, and is connected to each beam 26 via a wire 27. An end portion of each beam 26 is configured to include a connector 40 for being fastened to the shroud head 8 or the steam dryer 10. The length of each beam 26 is configured to be a proper length which meets a size of the shroud head 8 or the steam dryer 10.

In the present embodiment, the upper lid 2 is also detached, and the reactor pressure vessel 1 is released. Similar to

Embodiment 1, a lower end portion of an upper guide rod 17A is connected to the upper end portion of the lower guide rod 16 installed inside the reactor pressure vessel 1 (refer to Fig. 8) . In the present embodiment, the upper end of the upper guide rod 17A connected to the lower guide rod 16 extends slightly upward from the upper surface of the flange 1A of the reactor pressure vessel 1 as illustrated in Fig. 8. The upper end of the upper guide rod 17A is located considerably far below the upper end of the upper guide rod 17 connected to the upper end portion of the lower guide rod 16 according to Embodiment 1, which reaches the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1.

Similar to Embodiment 1, the steam dryer 10 detached from the reactor pressure vessel 1 and the shroud head 8 detached from the core shroud 3 and having the steam separator 9 attached thereto are sequentially unloaded from the reactor pressure vessel 1 to the reactor well 19, and are moved to the steam dryer steam separator pit 22 through the first passage 23. Furthermore, the shroud head 8 having the steam separator 9 attached thereto and the steam dryer 10 are sequentially moved from the steam dryer steam separator pit 22 into the reactor well 19 through the first passage 23, and are loaded from the reactor well 19 into the reactor pressure vessel 1. When unloaded from the reactor pressure vessel 1 or when loaded into the reactor pressure vessel 1, the shroud head 8 or the steam dryer 10 is suspended by the suspension tool 25A suspended by the overhead traveling crane, and is moved while being guided by the upper guide rod 17A connected to the upper end portion of the lower guide rod 16 and the lower guide rod 16 inside the reactor pressure vessel 1.

When the above-described shroud head 8 or steam dryer 10 is unloaded from the reactor pressure vessel 1 or when the shroud head 8 or the steam dryer 10 is loaded into the reactor pressure vessel 1, the shroud head 8 having the steam separator attached thereto or the steam dryer 10 in a state of being suspended by the suspension tool 25A is moved between the installation position of the shroud head 8 or the steam dryer and the steam dryer steam separator pit 22 inside the reactor pressure vessel 1.

When the shroud head 8 having the steam separator 9 attached thereto is unloaded from the reactor pressure vessel 1 or when loaded into the reactor pressure vessel 1, the shroud head 8 suspended by the overhead traveling crane is located above the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4 inside the reactor well 19 filled with the cooling water 24. At this time, in a case where the wire 27 is cut off and the shroud head 8 falls together with the suspension tool 25A, even if the shroud head 8 is rotated and comes into contact with the upper end portion of the fuel assembly 5 loaded into the core 4, the falling speedof the shroudhead 8 is extremely reduced by the floating member 30 disposed in the suspension tool 25A, and the rotation is suppressed. The reduced falling speed prevents the fuel assembly 5 loaded into the core 4 from being damaged.

When a central axis of the falling shroud head 8 having the steam separator 9 attached thereto is horizontal in the vicinity of the upper surface of the flange 1A of the reactor pressure vessel 1 due to the rotation of the shroud head 8 along the axial direction of the reactor pressure vessel 1, the shroud head 8 having the steam separator 9 attached thereto has a certain width in a direction of the central axis. Accordingly, the falling shroud head 8 is prevented from falling further downward by the flange 1A of the reactor pressure vessel 1, thereby avoiding damage to the fuel assembly 5 inside the core 4. When the central axis of the falling shroud head 8 is inclined within a certain angular range which is different from a horizontal state, the falling shroud head 8 enters the inside of the reactor pressure vessel 1, and is lowered into the reactor pressure vessel 1 due to its own weight. When the angular range of the central axis of the shroud head 8 which enters the inside of the reactor pressure vessel 1 and further falls is a portion of the above-described certain angular range, the flange 29 of the top guide 7 inhibits the falling shroud head 8 from being lowered. In this manner, the damage to the fuel assembly 5 inside the core 4 can be avoided. However, when the angular range of the central axis of the shroud head 8 which enters the inside of the reactor pressure vessel 1 and further falls is the other angle within the above-described certain angular range, the falling shroud head 8 collides with the flange 29 of the top guide 7, and is deformed. Accordingly, the shroud head 8 is not inhibited from being lowered, and there is a possibility that the fuel assembly inside the core may be damaged However, as described above, the falling speed of the shroud head 8 is significantly reduced by the floating member 30 of the suspension tool 25A. Accordingly, an impact force applied to the fuel assembly 5 inside the core 4 by the falling shroud head 8 is considerably reduced, and the fuel assembly 5 inside the core 4 is less deformed. Therefore, it is possible to prevent the fuel assembly 5 inside the core 4 from being damaged by the falling shroud head 8.

The falling speed of the falling shroud head 8 is adjusted in advance by the pressure of the compressed air filling the space inside the hollow member of the floating member 30 installed in the suspension tool 25A.

Embodiment 4

Hereinafter, a moving method of a shroud head according to Embodiment 4 serving as another preferred embodiment of the present invention will be described with reference to Fig. 9.

The moving method of the shroud head according to the present embodiment employs the suspension tool 25A (refer to Fig. 7) used according to Embodiment 3 in the moving method of the shroud head according to Embodiment 1. That is, the moving method of the shroud head according to the present embodiment employs the suspension tool 25A illustrated in Fig. 6 instead of the suspension tool 25 illustrated in Fig. 1 . The suspension tool 25A has a structure in which a plurality of floating members 30 are disposed in the suspension tool 25. The plurality of floating members 30 are attached to each beam 26 of the suspension tool 25A. The floating member 30 has a hollow member internally having a space, and is configured so that the internal space of the hollow member is hermetically sealed while being filled with compressed air.

According to the present embodiment, similar to Embodiment 1, the steam dryer 10 detached from the reactor pressure vessel 1 and the shroud head 8 detached from the core shroud 3 and having the steam separator 9 attached thereto are sequentially unloaded from the reactor pressure vessel 1 to the reactor well 19, and are moved to the steam dryer steam separator pit 22 through the first passage 23. Furthermore, the shroud head 8 having the steam separator 9 attached thereto and the steam dryer 10 are sequentially moved from the steam dryer steam separator pit 22 into the reactor well 19 through the first passage 23, and are loaded from the reactor well 19 into the reactor pressure vessel 1. When unloaded from the reactor pressure vessel 1 or when loaded into the reactor pressure vessel 1, the shroud head 8 or the steam dryer 10 is suspended by the suspension tool 25A suspended by the overhead traveling crane. Similar to Embodiment 1, the shroud head 8 or the steam dryer 10 is moved while being guided by each of the upper guide rod 17 connected to the upper end portion of the lower guide rod 16 and extending upward and the lower guide rod 16 . Similar to Embodiment 1, the upper guide rod 17 connected to the upper end portion of the lower guide rod 16 after the upper lid 2 is detached and the reactor pressure vessel 1 is released extends to the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1.

When the shroud head 8 suspended by the suspension tool 25A is located at the position above the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1, directly above the core 4 inside the reactor well 19 filled with the cooling water 24, even if the wire 27 is cut off and accordingly the shroud head 8 falls, the upper guide rod 17 extends to the position of the bottom surface 23A of the first passage 23 in the axial direction of the reactor pressure vessel 1. Accordingly, similar to Embodiment 1, the falling shroud head 8 is lowered while being guided by the upper guide rod 17 and the lower guide rod 16. Therefore, it is possible to prevent the fuel assembly loaded into the core 4 from being damaged by the falling shroud head 8.

The present embodiment can achieve another advantageous effect realized according to Embodiment 1. Furthermore, according to the present embodiment, the floating members 30 are disposed in the suspension tool 25A. Accordingly, similar to Embodiment 3, the falling speed of the shroud head 8 is significantly reduced by the floating members 30. Therefore, it is possible to more reliably prevent the fuel assembly 5 inside the core 4 from being damaged by the falling shroud head 8 .

The moving method of the shroud head according to Embodiment 4 may employ the suspension tool 25A used according Embodiment 3.

Finally, fastening between the upper guide rods 17 and 17A and the upper bracket 12 which are described in Embodiments 1 to 4 will be described with reference to views for describing a schematic structure of the fastening between the upper guide rod and the bracket in Fig. 10. The upper bracket 12 disposed on the inner surface of the flange of the reactor pressure vessel has a hollow cylindrical portion 39. A coupler 38 connected to the upper bracket 12 is disposed in the vicinity of the intermediate portion of the upper guide rod 17. The coupler 38 internally has a cutout portion 41 which is partially cut out. The upper bracket 12 is inserted into the cutout portion

41, and the hollow cylindrical portion 39 of the upper bracket 12 is inserted into a coupler internal stud 42 (illustrated by a broken line in the drawing) disposed inside the coupler 38. In this manner, the fastening is performed. Since the coupler 38 has the cutout portion 41, the upper bracket 12 is easily inserted into the cutout portion 41.

The present invention is not limited to the above-described embodiments, and includes various modification examples. For example, the embodiments have been described above in detail in order to facilitate the understanding of the present invention. The present invention is not necessarily limited to those including all of the above-described configurations. Configurations according to a certain embodiment can be partially substituted with configurations according to the other embodiment. The configurations according to the other embodiment can be added to the configurations of the certain embodiment. Additions, deletions, and substitutions of the other configurations can be made for some of the configurations according to the respective embodiments.

Claims

What is claimed is:

1. A moving method of a shroud head, the method comprising:

opening a reactor pressure vessel by detaching an upper lid from the reactor pressure vessel;

connecting a lower end portion of an upper guide rod to an upper end portion of a lower guide rod installed on an inner surface of the reactor pressure vessel;

extending the upper guide rod upward of the lower guide rod in a state where the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod;

causing an upper end of the upper guide rod to reach a position of a bottom surface of a passage allowing a reactor well formed directly above the reactor pressure vessel and a steam dryer steam separator pit formed adjacent to the reactor well to communicate with each other in an axial direction of the reactor pressure vessel;

moving the shroud head, having a steam separator attached thereto, to be installed inside the reactor pressure vessel above a core located inside the reactor pressure vessel so as to be detachable from the reactor pressure vessel into the passage between an installation position of the shroud head and the steam dryer steam separator pit inside the reactor pressure vessel; and moving the shroud head further along the upper guide rod whose upper end reaches a position of the bottom surface of the passage.

2 . The moving method of a shroud head according to claim

1, further comprising:

attaching a support member to each of a side surface of the reactor well and the upper guide rod, below the bottom surface of the passage inside the reactor well, after the upper guide rod is connected to the lower guide rod.

3 . The moving method of a shroud head according to claim

2, further comprising:

filling the inside of the reactor pressure vessel with cooling water up to a position of an upper surface of a flange to which the upper lid is attached in the reactor pressure vessel; and attaching the support member to each of the side surface of the reactor well and the upper guide rod in a state where the reactor pressure vessel is filled with the cooling water up to the position of the upper surface of the flange.

4 . The moving method of a shroud head according to claim

2, further comprising:

installing a radiation shielding member in an upper end of the reactor pressure vessel from which the upper lid is detached; and attaching the support member to each of the side surface of the reactor well and the upper guide rod, in a state where the upper guide rod connected to the lower guide rod penetrates the radiation shielding member installed in the upper end of the reactor pressure vessel and extends upward of the radiation shielding member.

5. The moving method of a shroud head according to claim

1 or 2, wherein when the shroud head detached from the reactor pressure vessel is moved to the steam dryer steam separator pit from the installation position inside the reactor pressure vessel, the shroud head moved along the upper guide rod is the shroud head detached from the reactor pressure vessel, and wherein the detached shroud head is raised along the upper guide rod, and is moved to above the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core.

6. The moving method of a shroud head according to claim

1 or 2, wherein when the shroud head is moved to the installation position inside the reactor pressure vessel from the steam dryer steam separator pit, the shroud head moved along the upper guide rod is the shroud head to be installed at the installation position inside the reactor pressure vessel, and wherein the shroud head to be installedat the installation position is lowered along the upper guide rod from a position above the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core, and is moved to the installation position inside the reactor pressure vessel.

7. A moving method of a shroud head, comprising:

moving the shroud head to be installed inside the reactor pressure vessel above a core located inside the reactor pressure vessel so as to be detachable from the reactor pressure vessel into a passage allowing a reactor well and a steam dryer steam separator pit to communicate with each other, in a state where the shroud head is suspended by a suspension tool having a floating member, between an installation position of the shroud head inside the reactor pressure vessel and the steam dryer steam separator pit formed adjacent to the reactor well formed directly above the reactor pressure vessel; and moving the shroud head further along the upper guide rod and the lower guide rod.

8 . The moving method of a shroud head according to claim

7, wherein when the shroud head is moved from the steam dryer steam separator pit to the installation position inside the reactor pressure vessel, the shroud head moved while being suspended by the suspension tool having the floating member is the shroud head detached from the reactor pressure vessel, and wherein in a state where the detached shroud head is suspended by the suspension tool having the floating member, the shroud head is raised along the upper guide rod, and is moved to a position directly above the core inside the reactor well.

9. The moving method of a shroud head according to claim

7, wherein when the shroud head is moved from the steam dryer steam separator pit to the installation position inside the reactor pressure vessel, the shroud head moved while being suspended by the suspension tool having the floating member is the shroud head to be installed at the installation position inside the reactor pressure vessel, and wherein in a state where the shroud head to be installed at the installation position is suspended by the suspension tool having the floating member, the shroud head is lowered along the upper guide rod, and is moved to the installation position inside the reactor pressure vessel.

10 . The moving method of a shroud head according to claim

7, wherein in a state where the lower end portion of the upper guide rod is connected to the upper end portion of the lower guide rod, the upper end of the upper guide rod further reaches a position of a bottom surface of the passage in an axial direction of the reactor pressure vessel, and wherein when the shroud head is moved along the upper guide rod, in a state where the shroud head is suspended by the suspension tool having the floating member, the shroud head is moved along the upper guide rod whose upper end reaches the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel.

11. The moving method of a shroud head according to claim

10, wherein after the upper guide rod is connected to the lower guide rod, the upper guide rod is attached to a side surface of the reactor well, inside the reactor well.

12 . The moving method of a shroud head according to claim 10 or 11, wherein when the shroud head detached from the reactor pressure vessel is moved to the steam dryer steam separator pit from the installation position inside the reactor pressure vessel, the shroud head moved along the upper guide rod is the shroud head detached from the reactor pressure vessel, and wherein the detached shroud head is raised along the upper guide rod, and is moved to above the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core.

13 . The moving method of a shroud head according to claim 10 or 11, wherein when the shroud head is moved to the installation position inside the reactor pressure vessel from the steam dryer steam separator pit, the shroud head moved along the upper guide rod is the shroud head to be installed at the installation position inside the reactor pressure vessel, and wherein the shroud head to be installedat the installation position is lowered along the upper guide rod from a position above the position of the bottom surface of the passage in the axial direction of the reactor pressure vessel, directly above the core, and is moved to the installation position inside the reactor pressure vessel.

14. An upper guide rod used for a moving method of a shroud head, the upper guide rod comprising:

a recess-shaped upper guide rod connector that is an end portion of the upper guide rod, and that is connected to a lower guide rod stud of a lower guide rod;

a coupler that is an intermediate portion of the upper guide rod, and that has a cutout portion connected to an upper bracket disposed on an inner surface of a flange of a reactor pressure vessel; and a coupler internal stud that is located inside the cutout portion of the coupler, and that is inserted into a hollow cylindrical portion of the upper bracket.

15. A suspension tool comprising:

a hook box connected to an overhead traveling crane;

a plurality of wires connected to the hook box;

a beam disposed across the plurality of wires;

a connector fastened to a shroud head or a steam dryer disposed in the beam; and a plurality of floating members disposed in the beam, wherein the floatingmember has a hollowmember internally having a space, and the space is hermetically sealed while being filled with compressed air.