JP2667856B2 - Boiling water reactor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nuclear reactor, and more particularly to a nuclear reactor suitable for a boiling water reactor without a channel box.

[Conventional technology]

Currently, a high conversion burner reactor is being developed as a next-generation light water reactor aiming at high burnup and significant reduction of fuel cycle cost by effective use of plutonium (Japanese Patent Application No. 59-
In the high conversion burner reactor, the conversion ratio is increased in the high conversion region in the first half of the fuel life compared to the current light water reactor, and the thermal neutron utilization rate is improved in the burner region in the latter half to efficiently burn fissionable materials.

Examples of fuel assemblies in the high conversion region and the burner region are shown by A and B in FIG. 4, respectively. FIG. 5 is a longitudinal sectional view of a fuel assembly used in a high conversion burner furnace. The fuel assembly is mainly composed of an upper tie plate 4, spacers 13, a plurality of fuel rods 3, a water rod 12, a lower tie plate 5, and a channel box 11 for containing them. The fuel rods 3 have a close-packed structure in a triangular arrangement in order to increase the H / U ratio. Therefore, the horizontal cross section of the fuel assembly has a hexagonal shape. Upper and lower tie plate 5
Are fixed at both ends of a plurality of fuel rods 3. Spacer 13
Are provided in the channel box 11 at intervals in the axial direction, and a plurality of fuel rods are aligned and supported to form a fuel bundle. Channel box surrounding the fuel bundle
11 has a hexagonal cylindrical horizontal section. FIG. 6 is a horizontal sectional view of three adjacent fuel assemblies. In each fuel assembly, a cluster-type control rod 10 is inserted into a control rod guide tube 7 in a fuel rod arrangement. Between adjacent assemblies, there is a gap separated by a channel box, and a small amount of non-boiling cooling water flows.

The channel box provided in the fuel assembly has the following functions.

(1) By forming an isolated coolant flow path for each fuel assembly, output mismatches between the assemblies and cross flow of the coolant due to the difference in void ratio are stopped.
Furthermore, the flow rate of the coolant flowing through the fuel assembly is ensured, and the coolant flows evenly.

(2) Increase the rigidity of the fuel assembly and make it easier to handle.

During the reactor interior loading period of the fuel assembly, a pressure difference occurs between the inner and outer surfaces of the channel box 11 due to the pressure loss of the coolant flowing in the fuel assembly. Therefore, channel box
In No. 11, irradiation creep deformation occurs with an increase in the neutron irradiation amount, and expands outward as shown in FIG. Such deformation of the channel box gives rise to the possibility of deteriorating the function of the channel box. Furthermore, if the deformation is significant, the gap between the channel boxes closes,
The fuel assemblies may not be able to be taken out of the furnace.

In a high conversion burner furnace aiming for a significantly higher burnup (burnup of about 100 GWd / tU), the interior loading period of the fuel assembly will be extended to 11 to 12 years. In the high conversion region, the pressure difference between the inside and outside of the channel box is 1.5 to 2 times that of the current BWR.
Furthermore, in the high conversion region, the fast neutron flux is several times that of the conventional BWR, and the amount of swelling deformation of the channel box is
It can be expected to increase even more than in the case of conventional BWR. In the conventional fuel assembly, the channel box thickness is 1.5 mm and the inter-assembly gear box width is 1.5 mm in order to enhance neutron economy, and the BWR channel box thickness is 2.5 mm and the inter-assembly gear group width is 15.8 mm. The structure is relatively small and severe against radial bulging of the channel box.

Also, in the high conversion burner reactor, the gap width between the fuel assemblies is small, so the conventional BWR
The upper lattice plate used in cannot be used. Therefore, as shown in FIG. 8, a structure is adopted in which a fuel assembly support ring plate is installed at the outermost periphery of the core. In such a structure, the bending of the integral fuel assembly affects the assembly configuration of the entire core. Therefore, it is necessary to suppress the bending of the fuel assembly more than the conventional BWR. On the other hand, in the high conversion burner furnace,
As described above, since the irradiation period is extended and the fast neutron flux is also increased, it is predicted that the bending that occurs in the currently designed fuel assembly will be more than that of the conventional BWR.

Further, in the fuel assembly of the high conversion burner furnace, the arrangement of the fuel rods is a dense lattice, so that the flow passage cross-sectional area is reduced and the pressure loss between the assemblies is increased.

Further, in the high conversion burner furnace, since the fuel assemblies are reassembled during the irradiation period, an assembly structure that is easy to disassemble and assemble is required.

[Problems to be solved by the invention]

An object of the present invention is to provide a boiling water nuclear reactor that is structurally stable with little deformation caused by irradiation, can improve thermal neutron economic efficiency, and has little pressure loss.

[Means for solving the problem]

The above-mentioned object is a boiling water reactor equipped with a plurality of fuel rods, a control rod guide tube, a water rod, an upper tie plate, a lower tie plate, and a fuel bundle consisting of a plurality of spacers provided in the axial direction of the reactor core. A partition plate for separating mutual cooling water flow paths of the fuel bundle in a region from a position where voids are generated in the fuel bundle to a position where the void ratio of the cooling water reaches the void ratio of the outlet of the fuel assembly, This is achieved by providing them in between.

Further, in a boiling water reactor including a fuel bundle including a plurality of fuel rods, a control rod guide tube, a water rod, an upper tie plate, a lower tie plate, and a plurality of spacers provided in the axial direction of the core, a fuel assembly is provided. Providing a partition plate between the fuel bundles that separates the mutual cooling water flow paths of the fuel bundles in a region from the core support plate to a position where the void ratio of the cooling water reaches the void ratio at the outlet of the fuel assembly. Is achieved by

Here, the region from the position where voids occur in the fuel bundle to the position where the void ratio of the cooling water reaches the void ratio of the outlet of the fuel assembly, and the void ratio of the cooling water from the core support plate of the fuel assembly is The region up to the position where the void rate at the outlet of the fuel assembly is reached is a region where the cross flow of cooling water is likely to occur due to the difference in void rate between fuel bundles and mismatch.

[Action]

According to the present invention, the partition plate provided between the fuel bundles can prevent the cross flow of the cooling water without the channel box. In addition, since there is no channel box, radial bulging due to a pressure difference between the inside and outside of the channel box is eliminated. At the same time, the bending of the entire assembly due to the irradiation growth of the channel box is also eliminated, and the core structure is constructed by using the support ring plate of the assembly at the outermost periphery of the core without using the upper lattice plate. The structure can be sufficiently stabilized.

Further, since the amount of the structural material corresponding to the channel box is reduced to half or less, the amount of thermal neutrons absorbed by the structural material can be reduced and the thermal neutron economic efficiency can be improved. At the same time, the amount of waste is reduced to less than half, which can contribute to a reduction in the entire power generation cost.

In addition, the partition plate, in the core height direction or core diameter direction,
By providing the cooling water in a region (specific portion) where crossflow is likely to occur, it is possible to suppress the pressure loss generated between the upper and lower sides of the fuel assembly.

Particularly, in the high conversion burner furnace, the high conversion region and the burner region are divided in the core radial direction, and the thermal-hydraulic characteristics, that is, the axial power distribution is greatly different in the two regions. Therefore, by providing the partition plate only at a specific portion between the fuel assemblies, it is possible to match the axial power distributions of the high conversion region and the burner region, and the effect of the present invention is limited to the maximum.

At the same time, by providing the partition plate only in the portion where the cross flow of the cooling water is likely to occur in the core height direction, the length of the partition plate itself is shortened, and the cooling water flow velocity at the upper portion of the partition plate becomes relatively slow. There is no reduction in strength due to vibration fatigue due to vibration of the upper part of the partition plate. Moreover, since the surface area of the partition plate is reduced by providing the partition plate only at a specific portion in the core height direction, it is possible to suppress irradiation deformation of the entire partition plate.

Furthermore, in the high conversion burner furnace, since it is necessary to reassemble the fuel assembly during the irradiation period, the reassembly process can be greatly simplified by eliminating the channel box as in the present invention.

〔Example〕

The present invention will be described in detail based on examples. FIG. 1,
FIG. 2, FIG. 3, FIG. 9, FIG. 10, FIG. 12, FIG. 13 and FIG. 13 show various partition plates and fuel assemblies that constitute the core of the present invention.

As a first embodiment, the partition plate 1 is shown in FIG. 1 in the core height direction except the region where the void ratio is constant above the core.
The example in which was provided. FIG. 2 shows AA 'in FIG.
FIG. 3 shows a perspective view of only the partition plate 1 of FIG. In this embodiment, a partition plate 1 is provided for each fuel bundle 2 so as to separate a cooling water flow path. In the high conversion burner furnace, since the fuel bundle 2 has a hexagonal shape, the partition plate 1 provided in the core also has a hexagonal shape in one cell as shown in FIG. The partition plate 1 is integrated as a whole in the furnace as shown in the perspective view in FIG. 3, and becomes one honeycomb type structure as a whole. Further, in the present embodiment, the partition plate 1 does not exist in the core height direction up to the uppermost part of the fuel bundle, but is provided from the lower core support part 6 to a height at which the void fraction in the upper part of the core becomes constant. By installing the partition plate 1 only in a specific region in the core height direction as in the present embodiment, the partition plate 1 is installed when the channel box is used or over the entire region in the core height direction. The pressure drop between the top and bottom of the fuel assembly is reduced by 12% compared to the case.

Further, in the present embodiment, the length of the partition plate 1 is shorter than the case where the partition plate 1 is installed over the entire region in the core height direction, so that the deformation amount (irradiation growth strain) accompanying the irradiation of zircaloy is reduced. Less.

The partition plate 1 is a lower tie plate 5 of the fuel bundle 2.
Is coupled to the lower core support plate 6 without being coupled. The partition plate 1 is made of Zircaloy, and is installed in the furnace before the fuel bundle 2 is loaded.

The fuel bundle 2 has the same structure as that of the conventional fuel assembly shown in FIG. 5, except that the channel box 11 is omitted. The channel box has a role of securing the rigidity of the fuel assembly and facilitating handling. In the fuel bundle 2 loaded in the core of the present invention, the channel box 11 does not exist, but there are twelve control rod guide tubes 7 in the integral fuel bundle 2, which secure the rigidity of the fuel assembly. When handling the fuel bundle 2 loaded in the core of the present invention, the control rod guide pipe 7
Is 32.9kg / piece. This value is the load applied to the control rod guide tube of the current PWR (44.
It is smaller than 0 kg / piece), and it can be seen that the fuel bundle 2 can secure the rigidity of the fuel assembly even without the channel box 11.

Next, a second embodiment is shown in FIG. In this embodiment, the partition plate 14 is formed in a region where the cooling water is in a single phase, that is, from the lower core support plate 6 to the point where voids start to be generated.
However, the shape is such that the central part of the plate is missing and only the pillars at the corners are present. Further, the partition plate 14 does not exist in the height direction of the core up to the uppermost portion of the fuel bundle, but is provided up to a height at which the void ratio in the upper portion of the core becomes constant. FIG. 10 is a perspective view of the second embodiment.

As a third embodiment, FIG. 11 shows an example in which partition plates 15 and 15 'having different lengths in the core height direction are used in the high conversion region and the burner region, respectively. As shown in FIG. 12, the void ratio distribution in the core height direction is significantly different between the high conversion region and the burner region. In the high conversion region, the point of void generation is low, and the void ratio at the exit is reached at a low position. on the other hand,
In the burner region, the point where voids are generated is high, and the void ratio at the exit reaches a high position. For this reason, in the present embodiment, the height of the partition plate in the high conversion region is set lower than the height of the partition plate in the burner region. Further, since a cross flow is likely to occur at the boundary between the high conversion area and the burner area, the partition plate 15 ″ is installed up to the top of the assembly only in this boundary area.

As a fourth embodiment, FIG. 13 shows a partition plate 16 having a shape surrounding these fuel bundles in the core height direction so that the cooling water flow paths of a plurality of fuel bundles having the same output are integrated. Indicated. Also in this embodiment, similarly to the first and second embodiments, the partition plate 16 is provided only in a specific region in the core height direction.

The configuration of the core of the present invention is an advanced core of a high conversion boiling water reactor, a Pu multiplication type boiling water reactor, and a fast reactor which is currently being researched and developed as a next generation light water reactor in addition to a high conversion burner reactor. It is also applicable in the future to the fast-reacting fast-reactor. In these reactors, the internal loading period of the fuel assembly is two to three times longer than that of conventional BWRs, and in superfluid life fast reactors, it is more than ten times longer. Under such conditions of use, if one channel box is used for the entire fuel period, the horizontal blistering of the channel box is expected to significantly exceed the design allowable limit.

According to the present invention in which the reactor core is formed by using partition plates without using the channel box, even in these reactors, deformation due to irradiation is small and structurally stable, thermal neutron economic efficiency is improved, and pressure loss is reduced. It is possible to provide a core having a structure which is small and in which reassembly of the fuel assembly is easy.

〔The invention's effect〕

According to the present invention, deformation due to irradiation is small and structurally stable, thermal neutron economic efficiency can be improved, and pressure loss can be suppressed to be small.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a part of an embodiment of the boiling water reactor of the present invention, FIG. 2 is a lateral sectional view of three fuel assemblies using the partition plate according to the present invention, and FIG. FIG. 4 is a perspective view of one embodiment of a partition plate of the invention, FIG. 4 is a cross-sectional view of a conventional high conversion burner core structure and a fuel assembly in each core region, and FIG. 5 is a conventional fuel assembly for a high conversion burner furnace. FIG. 6 is a cross-sectional view of a conventional fuel assembly for a high conversion burner furnace, FIG. 7 is a view showing a horizontal blister caused by a pressure difference between the inside and outside of a channel box, and FIG. FIG. 9 is a partial longitudinal sectional view of one embodiment of a boiling water reactor according to the present invention, and FIG. 10 is a perspective view of one embodiment of a partition plate of the present invention. FIG. 11, FIG. 11 is a partial vertical cross-sectional view of one embodiment of the boiling water reactor of the present invention, and FIG. 12 is a high conversion of the high conversion burner reactor with the current design. Axial power distribution and void fraction distribution diagram of frequency and the burner area, Figure 13 shows a perspective view of an embodiment of a partition plate of the present invention. 1 ... partition plate, 2 ... fuel bundle, 3 ... fuel rod,
4 ... upper tie plate, 5 ... lower tie plate, 6
... core support plate, 7 ... control rod guide tube, 10 ... control rod.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kikuo Umegaki 1168 Moriyama-cho, Hitachi, Hitachi, Ibaraki Prefecture Energy Research Laboratory, Hitachi Ltd. (56) References

Claims (3)

(57) [Claims] 1. A boiling water nuclear reactor comprising a plurality of fuel rods, a control rod guide tube, a water rod, an upper tie plate, a lower tie plate, and a fuel bundle composed of a plurality of spacers provided in the axial direction of the reactor core. A partition plate separating the mutual cooling water flow paths of the fuel bundle in a region from a position where voids are generated in the fuel bundle to a position where the void ratio of the cooling water reaches the void ratio of the outlet of the fuel assembly; A boiling water reactor provided between bundles. 2. A boiling water reactor comprising a plurality of fuel rods, control rod guide tubes, water rods, an upper tie plate, a lower tie plate, and a fuel bundle composed of a plurality of spacers provided in the axial direction of the core. A partition plate for separating the cooling water flow paths of the fuel bundles from each other in a region from the core support plate to a position where the void ratio of the cooling water reaches the void ratio at the outlet of the fuel assembly is provided between the fuel bundles. A boiling water reactor provided in 3. The partition plate according to claim 1, wherein the partition plate surrounds the plurality of fuel bundles in the axial direction so that the cooling water passages of the plurality of fuel bundles having the same output are integrated. And a boiling water reactor.