WO1999063548A1

WO1999063548A1 - A cleaning device for a nuclear power plant

Info

Publication number: WO1999063548A1
Application number: PCT/SE1999/000867
Authority: WO
Inventors: Sune Flink; Roland Ivars; Anders Rosengren; Lennart Von Der Burg; Ilija Bijelovic
Original assignee: Abb Atom Ab
Priority date: 1998-06-02
Filing date: 1999-05-21
Publication date: 1999-12-09
Also published as: SE510806C2; AU4662399A; SE9801985L; SE9801985D0

Abstract

The present invention relates to a cleaning device (4) for a nuclear power plant for cleaning of water which is contaminated by radioactive particles and/or radioactive ions. The cleaning device comprises a filtering member arranged in a container (5). A pump means is arranged connected to the cleaning device for circulation of water therethrough. The container (5) is made as a substantially straight cylinder which is sealed at both ends and which exhibits an outer geometry which corresponds to the outer shape of a fuel assembly intended for the nuclear power plant in question.

Description

A cleaning device for a nuclear power plant

TECHNICAL FIELD

The present invention relates to a cleaning device for cleaning of water which contains contaminants in the form of radioactive particles and/or ions. Such water, contaminated with radioactive particles, occurs, for example, in a pool in a nuclear power plant.

BACKGROUND ART

A conventional nuclear power plant comprises a reactor pool arranged in hydraulic connection with at least one fuel pool, usually two fuel pools. The reactor pool comprises a reactor vessel which, in turn, comprises a moderator tank comprising a core with fuel assemblies containing nuclear fuel. When the nuclear reactor has been in operation for a certain period of time, it is taken out of operation, is shut down, for carrying out refuelling, inspection and service work. When the reactor is shut down, internal reactor parts and fuel assemblies are stored in the fuel pool. Service work is carried out, for example, on the parts which are arranged in the reactor pool and the fuel pool, respectively, and in the reactor vessel. Such service work consists, for example, of repair, inspection, machining by cutting, and welding under water. During the service work, contaminants are released from, for example, grinding and spark machining. The contaminants are in the form of, for example, radioactive particles and/or ions and they are spread in the water in the reactor and fuel pools, respectively. Other sources of the released particles and/or the ions are the reactor vessel and the fuel in which radioactive corrosion products, so-called crud, are released as a result of the temperature reduction when the nuclear reactor is shut down, or when transferring the fuel to the fuel pool . Most currently known devices for cleaning of the contaminated water are arranged at such a large distance from the source that the contaminants have time to spread over a large area in the pools before they reach a cleaning device. During service work in progress, where release of particles occurs, some form of suction nozzle is therefore usually arranged in the vicinity of the place where the radioactive particles are released. The suction nozzle is arranged for suction of at least the main part of the contaminated water to a cleaning plant.

After completed service work, the reactor and fuel pools are emptied of the water which is carried off via the cleaning plant, whereupon, for example, the fuel walls and the reactor vessel are cleaned before filling in clean water and putting the nuclear reactor into operation again.

For cleaning of the water, a cleaning plant comprising a filter is usually used. These filters are often in the form of so-called ion exchange filters. A filter of ion exchange type comprises an ion exchange resin which is enclosed by a container. When the ion exchange resin is consumed, it is replaced by new ion exchange resin while the container is reused. One disadvantage of the ion exchange resin is that it is voluminous, which leads to large amounts of waste. The radioactivity emitted by the particles absorbed in the ion exchange resin may break down the ion exchange resin, which is usually a polymer. Such a breakdown of the ion exchange resin may lead to release of radioactivity and breakdown products which may be corrosive to the pipe system and vessels or the final waste container.

One known device for cleaning of water containing radioactive particles comprises a suction nozzle connected to a bag-like member placed in a container which is temporarily arranged in the pool. The container is, for example, made of stainless steel and has, for example, the shape of a circular cylinder. The bag-like member comprises an inlet for water to be cleaned, an outlet for cleaned water and a filter, arranged between the inlet and the outlet, for cleaning the water. After completed cleaning, the bag-like member together with the container are raised to the surface and placed in a concrete mould. The mould is then filled With some cast mixture, for example cement.

One difficulty with conventional filters is the handling of the filters after the water in the pool has been cleaned. Due to their design, conventional filters must be handled and transported in specially-designed containers, usually large and heavy ones, which are very expensive.

Another difficulty is that the personnel which handle the filters after completed use receive a certain radiation dose from the radioactive particles which have accumulated in the used filter.. A particularly delicate moment is when the polluted filters have been raised above the water surface. In addition, personnel may be subjected to radioactive radiation in those cases where the radioactive particles are not taken care of directly at the source. The radioactive particles may accumulate in places such as in gaps, passages with lower water flow, valves or in pipe bends which are arranged connected to the pools . When personnel carry out service work in such places, they are subjected to radioactive radiation.

SUMMARY OF THE INVENTION

The present invention relates to a cleaning device for cleaning of water containing corrosion products in the form of radioactive particles and/or ions, such as crud from nuclear fuel or radioactive contaminants from service tasks which have been carried out or which are in progress. The cleaning device comprises a container which is designed in such a way that its outer shape corresponds to the outer shape of a fuel assembly intended for use in the nuclear reactor in question. Further, the container comprises, at that end which is normally arranged as the upper end in the reactor, a member shaped as a handle for cooperation with a lifting member such that the container may be handled as a fuel assembly intended for use in the nuclear reactor in question. Further, the container comprises, at that end which is normally arranged as the lower end in the pool, a bottom support intended to make possible utilization of existing supporting members, such as fuel stands, for fuel assemblies arranged in the pools .

That end of the container, which is normally arranged as the upper end, further comprises an opening for inlet of water which is to be cleaned and outlet for cleaned water. At least the main part of the space which is surrounded by the container is filled up by a filter for cleaning of the water which is contaminated by radioactive particles and/or ions. The filter as such is preferably a filter conventionally used for this cleaning purpose.

The advantage of the present invention is that, by designing the container in such a way that its outside dimensions correspond to the outside dimensions of a nuclear fuel assembly used in the nuclear reactor in question, the cleaning device may be handled with handling equipment present in the nuclear power plant, intended for handling of fuel assemblies or other internal reactor parts .

Further, the design of the container permits use of the system, which is intended for transport of radioactive core components, for transferring radioactive internal parts from the reactor vessel to, for example, a storage placed in a plant separated from the nuclear power plant, for example a plant for ultimate waste disposal. By making it possible to use already-existing handling equipment and transport systems for fuel assemblies, the costs for handling and transport of the device according to the invention are considerably reduced.

The radiation dose, to which personnel risk being subjected, is reduced by means of the present invention in that the radioactive particles and/or the ions are accumulated at the source and are brought to a filter arranged in a container which accompanies the filter to ultimate waste disposal in the same way as the fuel assemblies of the nuclear reactor plant referred to here.

The container in the device according to the invention may, for example, be given the same outer shape as a fuel element intended for a BWR, a PWR or a WER reactor. One advantage of this is that the location of the cleaning device in an ultimate storage is facilitated by its design. The shape of the cleaning device permits already-existing supporting means adapted for ultimate storage of the fuel assemblies to be used.

The container is preferably made in a length of the order of magnitude of four metres, that is, the length of the con- tainers corresponds substantially to the length of the fuel assemblies which are to be used in the nuclear reactor plant. The container may also be made considerably shorter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with reference to the accompanying drawings .

Figure la schematically shows, in a view from above, a nuclear power plant comprising a cleaning device according to the invention. Figure lb shows the nuclear reactor plant of Figure la in a view from the side.

Figure 2 schematically shows, in a view from the side, a cleaning device for cleaning of water containing radioactive particles .

Figure 3 shows a cleaning device according to the invention in a section A-A in Figure 2.

Figure 4 shows a schematic embodiment of a cleaning plant comprising a plurality of cleaning devices according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figures la, lb show a reactor vessel 1 arranged in a normally water-filled reactor pool 2. At each side of the reactor pool 2, a fuel pool 3 is arranged. A cleaning device 4 according to the invention is arranged at an arbitrary location in one or more of the pools. Further, a handling machine M is shown, arranged adjacent to the pools. The handling machine M is of a conventional type and intended for, for example, lifting and handling of fuel assemblies into and out of the reactor vessel 1 and between the reactor pool 2 and one of the fuel pools 3, respectively.

Figure 2 shows a cleaning device 4 according to the invention designed with an outer shape which corresponds to the outer shape of a fuel assembly, chosen for the embodiment, for a boiling water reactor. In case the cleaning device is to be used in a pressurized-water reactor or a WER-type reactor, it has an appearance like the one shown in the figure but with the outside dimensions modified so as to correspond to the outside dimensions of fuel assemblies for use in these types of reactors. Internally, there is no significant difference between the various embodiments of the invention.

The cleaning device 4 comprises a container 5 in the form of a substantially straight cylinder with a substantially rectangular cross section. The normally downward end of the container 5 is sealed by means of a bottom part 6, and its normally upward end is sealed by means of a top part 7. The top part 7 is made with a handle 7a for lifting and handling by means of the handling machine M. The bottom part 6 has been given a shape corresponding to the shape of the bottom part of a fuel assembly intended for the nuclear reactor in question, the shape of which permits location in a fuel stand arranged in at least one of the pools.

The top part 7 is provided with an inlet opening 8 for inlet of water which is to be cleaned with respect to contaminants in the form of radioactive particles and/or ions in the cleaning device 4, and an outlet opening 9 for outlet of water which has been cleaned.

The inlet opening 8 is associated with a hose means 10, the inlet opening of which, in turn, is formed with a suction nozzle-like member 11 for sucking in water to be cleaned for further transport via the hose means 10 and the inlet opening 8 to the cleaning device 4. The suction nozzle-like member 11 of the hose means 10 is preferably placed in the vicinity of that location in the pools, or in the reactor vessel 1, where the radioactive particles and/or the ions are released for achieving an efficient collection of the contaminants. In an alternative embodiment, the cleaning device is arranged in a closed system comprising an object, for example a fuel assembly, which is arranged for decontamination. The water which is passed through, for example, the fuel assembly for decontamination thereof is thus passed to the cleaning device according to the invention for cleaning before it is returned to the water in the pool .

Figure 3 shows a section of the container 5, its bottom part 6 and its top part 7. The filtering member is, in this embodiment, made in the form of eight filter units 12 for filtering the contaminated water in four 'stages . During operation of the cleaning device 4, the device is normally vertically arranged and immersed into the water in the pools.

The embodiment shown in Figure 3 relates to a cleaning device 4 in which the container 5, in its normally arranged upper part, comprises filter units 12 with a filter structure which permits capture of the relatively larger particles, from the size point of view, for example with a diameter of the order of size of ten micrometers or larger. Further, the normally arranged lower part of the container 5 comprises filter units 12 with a filter structure for capturing the relatively smaller particles, from the size point of view, for example with a diameter of the order of size of one micrometer. When the water passes through the filter units 12, a pressure drop arises. The pressure drop inside the container 5 constitutes a measure of the degree to which radioactive particles have adhered to the filter units 12. When a certain pressure drop has been obtained, the filter unit 12 and hence the cleaning device 4 are consumed, whereby it is replaced with a new one.

The filter units 12 have an extent in the axial direction of the container 5 which substantially corresponds to half the length of the container 5 in the axial direction. The space enclosed by the container 5 is divided into two substantially equally large parts, arranged axially separated by a partition 13.

The filter units 12 which are placed in the normally arranged upper space 13a of the container 5 are arranged in a parallel manner. The filter units 12 in the normally arranged lower space ,13b of the container 5 are arranged in the same parallel manner.

The water which is filtered through the filter units 12 arranged in the upper container space 13a is passed to the lower container space 13b through a passa'ge opening 14 arranged in the partition 13. In one embodiment of the invention, partitions with an axial extent are also arranged (not shown) for separating the filter units 12 from one another.

After cleaning by the filter units 12 arranged in the lower container space 13b, the cleaned water is passed to a collection space 15 arranged adjacent to the bottom part 6. An outlet conduit 16 is arranged to connect the collection space 15 to the outlet opening 9. The cleaned water is thus passed out of the container 5 via the outlet conduit 16 and the outlet opening 9.

When the capacity of the filtering member to clean water has been reduced to a predetermined level, or when the cleaning process is to be terminated, the hose means 10 is detached from the outlet opening 9 whereupon the outlet opening 9 is sealed.

Before sealing of the inlet opening 8 is carried out, drainage of the container 5 with respect to water and moisture must be carried out.

The hose means 10 connected to the inlet opening 8 is arranged with the suction nozzle-like member 11 to a compressed air-generating device (not shown) . The supplied compressed air is preferably heated to a temperature, preferably in the interval of 20-80°C. Heating of the compressed air permits a faster drainage. The compressed air is passed through the cleaning device 4, whereby water remaining in the container 5 is pressed into a filter unit 12 in the upper container part 13a, whereupon it is pressed out into the space 18 between the filter units 12. Thereafter, the water is pressed into one of the filter units 12 in the lower container part 13b and down into the collection space 15. A drainage channel 19 is arranged to 'connect the collection space 15 to a draining opening 20 arranged in the top part 7. The water and the moisture are thus drained by means of the compressed air out of the container 5 via the drainage channel 19.

When the interior of the container 5 has been dried to the desired extent, the hose means 10 is removed from the inlet opening 8, whereupon this opening as well as the drainage opening 20 are sealed.

The drained container 5 is then transported by means of the handling machine M from the pool 2 or 3 to a space where a transport container, intended for the nuclear reactor plant in question, for spent nuclear fuel is placed. Thereafter, the drained container is transported in the transport container, for example to an ultimate waste disposal storage.

An example of a material which may be used in the filtering member is glass fibre which is arranged in the form of a wire in a plurality of turns around a core, preferably of stainless steel. This filter has a limitation in that it allows ion-formed radioactivity to pass therethrough. In this case, the cleaning device, when the radioactive activity level is high, needs to be supplemented by a separate ion exchanger for capturing the radioactive ions, which is preferably inorganic. This ion exchanger is, for example, made of zeolite or a metal-oxide ceramic. In an alternative embodiment, the filtering member comprises a mechanical filter member. This filter member takes care of both radioactive particles and radioactive ions . Such a mechanical filter member comprises, for example, a ceramic filter made of zeolite or some metal oxide.

Figure 4 shows a cleaning plant 21 for cl'eaning of water comprising a plurality of cleaning devices 4 of the embodiment described above. The cleaning plant 21 comprises a first and a second cleaning device 4 arranged in series in such a way that water which is to be cleaned passes only through the first or first through the first and then through the second or only through the second cleaning device 4. The first and second cleaning devices 4 are, in one embodiment of the invention, arranged in parallel with a third cleaning device 4a, through which the water to be cleaned passes. This third cleaning device 4a may either be placed before or after the serially arranged cleaning devices 4.

Figure 4 shows an example of a cleaning plant 21 which more specifically comprises five cleaning devices 4 according to the invention. Four of the cleaning devices 4, that is, a first, a second, a third and a fourth cleaning device 4, are connected in series with one another. The four series- connected cleaning devices 4 are in their turn connected in parallel with the fifth (cf. the third above) cleaning device 4a. The series-connected cleaning devices 4 are connected according as the upstream cleaning devices 4 are filled with contaminants. The fifth cleaning device 4a comprises a filter, a so-called fine filter, which has the ability to capture particles which, from the size point of view, are relatively smaller than the particles which are captured by the series-connected cleaning devices 4. All water which is conducted into the cleaning plant 21 thus has the possibility to pass through this fine filter. In an alternative embodiment, the fine filter is in the form of an ion exchange filter. In still another embodiment of the invention, an ion exchange filter 30 is arranged downstream of the fifth cleaning device 4a.

The cleaning devices 4 are interconnected via a conduit system comprising a supply conduit 22 for conducting contaminated water to the cleaning plant '21 and a discharge conduit 23 for conducting cleaned water from the cleaning plant 21 back to the pool 2 or 3 in which they are placed.

Downstream of an opening to the supply conduit 22 and upstream of an opening to the discharge conduit 23, a valve member VI is arranged for opening and closing, respectively, of the supply and discharge flows, respectively.

A pressure-measuring device 25 is connected between the supply conduit 22 and the discharge conduit 23 for continuously measuring the pressure difference in these conduits. In dependence on the pressure difference, connection and closing, respectively, of the individual cleaning devices 4 are controlled. Further, valve members V2 are arranged for connection and disconnection of the respective cleaning device 4, 4a.

The cleaning plant 21 shown in the embodiment is designed in a very flexible way. As the pressure drop across one or more cleaning devices 4 increases, additional cleaning devices 4 are connected. Preferably, the already used cleaning devices 4 are not disconnected until they have been filled to a pre- determined degree. The advantage of this is that each cleaning device 4 is allowed to be filled to a maximum before it is sealed and is brought further to ultimate waste disposal. This, in turn, reduces the consumption of cleaning devices 4, 4a, which otherwise have to be discarded before their capacity has been utilized in full/ This also con- siderably reduces the cost of ultimate waste disposal of the cleaning devices 4.

By arranging the cleaning devices 4, 4a according to the invention according to Figure 4, filling of a minimum number of cleaning devices 4, 4a is made possible. This implies that cleaning devices 4, 4a which are only haϊf-filled do not occupy unnecessary space in, for example, fuel stands in the pools or in an ultimate storage.

A cleaning device 4, 4a according to the present invention may, of course, comprise an arbitrary number of filter units 12 for achieving cleaning of water passed therethrough. The cleaning device 4 according to the invention may either be used as a separate unit for cleaning of contaminated water or be used as part of a system including cleaning of water.

Claims

1. A cleaning device (4) for a nuclear power plant for cleaning of water contaminated with radioactive particles and/or radioactive ions, wherein the cleaning device comprises a filtering member arranged in a container (5) , wherein a pump means is arranged connected to the cleaning device for circulation of water therethrough, characterized in that the container (5) is made as a substantially straight cylinder with a first end which is sealed by a bottom part (6) and a second end which is sealed by a top part (7) forming a unit which exhibits an outer geometry which corresponds to the outer shape of a fuel assembly intended for the nuclear power plant in question, whereby an inlet opening is arranged for inlet of the water which is to be cleaned and an outlet opening is arranged for outlet of the cleaned water.

2. A cleaning device (4) according to claim 1, characterized in that the inlet opening (8) and/or the outlet opening (9) are arranged in the top part (7) of the container (5) .

3. A cleaning device (4) according to claim 1, characterized in that it comprises a first and a second filter unit (12) arranged one after the other in such a way that the water which is to be cleaned first passes through the first filter unit (12) and then through the second filter unit (12) .

4. A cleaning device (4) according to claim 1, characterized in that the container (5) is divided into a first and a second part (13a, 13b) for cleaning of water in two stages, whereof the first part (13a) comprises a filter unit (12) for filtering relatively larger particles whereas the second part (13b) comprises a filter unit (12) for filtering relatively smaller particles.

5. A cleaning device (4) according to claim 4, characterized in that the container (5) comprises a third part (15) arranged adjacent to the downstream end of at least one filter unit (12) and to an outlet conduit (16) which opens out into an outlet conduit (9) at the outside of the container (5) .

6. A cleaning device (4) according to claim 4, characterized in that the container (5) comprises a third part (15) arranged adjacent to the downstream end of at least one filter unit (12) and to a drainage channel (19) which opens out in the form of a drainage opening (20) at the outside of the container (5) .

7. A cleaning device (4) according to claim 6, characterized in that the drainage opening (20) is arranged at the top part (7) of the container (5).

8. A cleaning device (4) according to any of the preceding claims, characterized in that a handle (7a) is arranged connected to the second end of the container (5) such that the container (5) may be handled as a fuel assembly intended for the nuclear power plant in question.

9. A cleaning plant (21), characterized in that it comprises a plurality of cleaning devices (4) according to any of claims 1-8, wherein the cleaning devices (4) are interconnected by means of a supply conduit (22) and a discharge conduit (23 ) .

10. A cleaning plant (21) according to claim 9, characterized in that it comprises a first and a second cleaning device (4) arranged in series in such a way that water which is to be cleaned passes through only the first or first through the first and then through the second or only through the second cleaning device (4) .

11. A cleaning plant (21) according to claim 10, characterized in that the first and second cleaning devices (4) are arranged in parallel with a third cleaning device (4a) through which the water to be cleaned passes.

12. A cleaning plant (21) according to claim 11, characterized in that the third cleaning 'device (4a) is arranged downstream of the first and second cleaning devices

(4) and comprises a fine filter or an ion exchange filter for cleaning of the water to a higher degree than the cleaning which is achieved by means of the first and second cleaning devices (4) .

13. A cleaning plant (21) according to claim 11, characterized in that an ion exchange filter (30) is arranged downstream of the third cleaning device (4a) .