JP2008096366A - Quota control rod arrangement bwr reactor core with adjunct - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce costs by reducing the number of control rods and by facilitating regular inspections. <P>SOLUTION: Control rods left by removing every other control rods from a conventional control rod arrangement serve as quota control rods 101. Instead of the control rods thus removed, unburned cruciform flammable poison rods 201, one-cycle burned cruciform flammable poison rods 202, and two-cycle burned cruciform flammable poison rods 203 are loaded. Furthermore, MOX dense nuclear fuel assemblies are loaded. The number of control rods and the number of control rod driving devices are reduced by combining the MOX dense nuclear fuel assemblies and the cruciform flammable poison rods. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a boiling water reactor (BWR) core.

FIG. 1 is a structural diagram of the core of a boiling water reactor (Non-Patent Document 1). The lower end of the nuclear fuel assembly (30) containing the nuclear fuel material is supported by a detachable nuclear fuel support fitting (2) attached to the core support plate (1), and the upper end via a channel box (35). It leans against the upper grid plate (3). At the center of the four nuclear fuel assemblies (30) between the lattices of the upper lattice plate (3), there is a control rod (100) that can be operated up and down to control the nuclear reactor. A control rod drive (Non-Patent Document 2) is shown in FIG. The control rod drive is below the bottom of the reactor pressure vessel.
FIG. 3 is a plan view of the core immediately before the start of operation in which a conventional nuclear fuel assembly (30) at the center of the core height is arranged. Unburned conventional nuclear fuel assembly (11) at the 1 mark position, 1 cycle burning conventional nuclear fuel assembly (12) at the 2 mark position, and 2-cycle burning conventional nuclear fuel fuel at the 3 mark position The assembly (13) is marked with a three-cycle combustion conventional nuclear fuel assembly (14). The cross-dotted line indicates the arrangement of the conventional control rod (100). Usually, most of the control rods (100) are pulled out under the core during the operation of the reactor.
FIG. 4 shows an enlarged plan view of the core in which the conventional nuclear fuel assembly (30) and the control rod (100) are arranged. In the nuclear reactor, the nuclear fuel assemblies (30) are arranged in a lattice pattern with the control rod side leakage water passage (51) and the leakage water passage (52) opposite to the control rod interposed therebetween. A cooling water passage (49) is provided between the nuclear fuel rods (31). Several of the nuclear fuel rods (31) are combustible poison-added nuclear fuel rods (32) to which an oxide of gadolinium (Gd) is added as a combustible poison. In some cases, a water rod (36) is arranged instead of several nuclear fuel rods (31).
: Nuclear Safety Research Association (ed.), 1998 “Light Water Reactor Fuel Behavior”. : Nuclear Safety Research Association (ed.), 1992 "Summary of light water reactor power plant".

In recent years, there has been a demand for a reduction in power charges. As part of this, reduction of power generation cost by BWR is required.
FIG. 5 is a core layout diagram of a pressurized water reactor (PWR) (Non-patent Document 3). Of the fuel assemblies (equivalent to the nuclear fuel assemblies (30) of the BWR), only the fuel assemblies in the staggered grid position absorb the neutrons in the same manner as the control rods (100) of the BWR. Control) can be inserted. The PWR reactivity control is achieved by mixing boric acid water in the coolant in addition to the control rod cluster. Even at the end of the operation, boric acid water is contained in the cooling water.
On the other hand, in BWR, as shown in Fig. 3, two sides of each nuclear fuel assembly face the control rod (100). BWR control rods are thought to be overloaded compared to PWR control rods. The construction cost will increase accordingly.
: Corona, 1975, author Toko “Atomic Power”.

The natural Gd added to the flammable poison-added nuclear fuel rod (32) loaded in the current BWR nuclear fuel assembly (30) includes the isotopes Gadori 155 (Gd155) and Gadori 157 (Gd157 ) And isotopes Gadori 156 (Gd156) and Gadori 158 (Gd158) having a small neutron absorption action. Infinite combustion multiplication factor (k∞) can be reduced if Gd is added even in the early stage of combustion, which contains a lot of fissile material, so that more fissile material can be contained while satisfying the reactor shutdown margin. Can be burned for a long time. When Gd155 or Gd157 absorbs neutrons, it becomes Gd156 or Gd158, which has a small neutron absorption action, so it does not suppress k∞ even at the end of operation when combustion progresses and the amount of fissile material decreases.
If the flammable poison is used well, the number of control rods (100) installed can be reduced to about 1/4 of the current number.

  Costs can be reduced by reducing the number of rods (100) to about 1/4 of the current number while reducing the number of control rod drive units and making periodic inspections easier while satisfying the reactor shutdown margin. .

  As a result, the construction cost was low, and as a result, a BWR core with low power generation cost could be provided.

FIG. 6 is a cross-sectional view of an unburned MOX dense nuclear fuel assembly (130). By closely arranging MOX nuclear fuel rods (231) using MOX, which is a mixed oxide of uranium (U) and plutonium (Pu), as a nuclear fuel, the neutron moderating action by water is suppressed and Pu is burned efficiently. In the nuclear fuel assembly in which the MOX nuclear fuel rods (231) are densely arranged, Pu is burned efficiently even if the combustion progresses, and the decrease in k∞ is slow. In low-speed reactors, MOX dense nuclear fuel assemblies have been considered taking advantage of this feature (Non-patent Document 4). Furthermore, even if the operation is stopped from low density with high-temperature water during operation and the density changes with low-temperature water, the amount of change in water is small and the amount of change in neutron moderating action is small. The fluctuation range of k∞ is also small. Therefore, the degree of control degree adjustment of the control rod is small. There is a high possibility that the number of control rods can be reduced.
FIG. 7 is a schematic view of the BWR core with the auxiliary quota control rod arrangement of the present invention immediately before the start of operation. A quarter control rod (101) is left out from the conventional control rod (100) in the center of the core, leaving the other control rod (100) and the drive unit attached to it as a substitute. A poison rod (201), a one-cycle combustion cross-shaped flammable poison rod (202), and a two-cycle combustion cross-shaped flammable poison rod (203) are loaded.
Four unburned MOX dense nuclear fuel assemblies (130) are loaded at the position of the N mark around the quota control rod (101). The unburned MOX dense nuclear fuel assembly (130) burned for one cycle at the position of N and replaced with the one-cycle combustion MOX dense nuclear fuel assembly (131) at the position of E mark. A new unburned cross-shaped flammable poison rod (201) is loaded. A one-cycle combustion MOX dense nuclear fuel assembly (131) at the position of E and an unburned cross-shaped flammable poison rod (201) in the center burns for one cycle and a two-cycle combustion MOX dense nuclear fuel assembly (132) and The one that becomes a one-cycle burning cross-shaped flammable poison rod (202) is rearranged to the position of the F mark and the center thereof. Two-cycle combustion MOX dense nuclear fuel assembly (132) at the position of F and one-cycle combustion cross-shaped flammable poison rod (202) at the center burns one cycle and three-cycle combustion MOX dense nuclear fuel assembly (133) And the two-cycle burning cross-shaped flammable poison rod (203) is rearranged to the position of the G mark and the center. The three-cycle combustion MOX dense nuclear fuel assembly (133) burned by one cycle at the position of G and changed to the four-cycle combustion MOX dense nuclear fuel assembly (134) is relocated to the position of the Z mark on the outer periphery of the core. Most of the three-cycle combustion MOX dense nuclear fuel assembly (134), the cross-shaped combustible poison rod (203), and the four-cycle combustion MOX dense nuclear fuel assembly (135) burned for one cycle are taken out of the core. The auxiliary quarter control rod arrangement BWR core of the present invention is characterized by the above core configuration and operation plan. The 3-cycle combustion MOX dense nuclear fuel assembly (133) has considerably less U235, so the 2-cycle combustion cross-shaped flammable poison rod (203) can be dispensed with. In addition, at the position of the F mark or G mark and in the center, after the two-cycle combustion MOX dense nuclear fuel assembly (132) and the one-cycle combustion cross-shaped flammable poison rod (202) burn for one cycle, do not rearrange them. A three-cycle combustion MOX dense nuclear fuel assembly (133) and a two-cycle combustion cross-shaped flammable poison rod (203) can also be used.
Depending on the core configuration and operation plan, the number of control rods and drive units will be about 1/4. Unburnt cross-shaped flammable poison rod (201) is cadmium (Cd) or boron (B) or erbium (Er) or dysprosium (Dy) flammable poison or cadmium oxide (CdO) or erbium oxide (Er2O3) Alternatively, it is a cross-shaped plate made of a zirconium alloy to which a compound such as dysprosium oxide (Dy2O3), boron carbide (B4C) or zirconium boride (B12Zr) is added. A large amount of the flammable poison is added to the unburned cross-shaped flammable poison rod 201 so that it remains unburned even at the end of the operation. The flammable poison is left on the one-cycle combustion cross-shaped flammable poison rod (202) to be slightly burned even at the end of operation. Cd and B have a thermal neutron absorption cross section that is not as large as Gd, so the consumption rate is slow and they remain burned even at the end of operation.
FIG. 8 shows the operation of the core of the present invention. The density of the cooling water during operation of the reactor is low due to its high temperature. Therefore, the action of slowing down fast neutrons is small. As a result, the thermal neutron flux during operation is small. On the other hand, combustible poisons have a large thermal neutron absorption cross section, but a fast neutron absorption cross section is very small. Therefore, the reactivity suppression effect that is substantially proportional to the product of the neutron absorption cross section and the neutron flux is small during operation and large during stoppage. Even if flammable poisons remain during operation, the effect on reducing the output is small because the effect of suppressing reactivity is small. On the other hand, if flammable poisons remain at the time of stoppage, the reactivity suppression effect is great, so the increase in reactivity due to the disappearance of xenon, the disappearance of vapor voids, and the decrease in fuel temperature is offset.
Figure 9 shows an unburned MOX dense nuclear fuel assembly (130) to 3-cycle combustion MOX dense nuclear fuel assembly (133), a quota control rod (101), an unburned cruciform flammable poison rod (201) to a 2-cycle combustion cruciform It is the figure which expanded the plane arrangement | positioning relationship of the combustible poison stick | rod (203). Four unburned MOX dense nuclear fuel assemblies (130) are loaded around the upper left quarter control rod (101). An unburned cross-shaped flammable poison rod (201) is loaded at the lower right, and four 1-cycle combustion MOX dense nuclear fuel assemblies (131) are loaded around it. A 1-cycle combustion cross-shaped flammable poison rod (202) is loaded on the upper right, and four 2-cycle combustion MOX dense nuclear fuel assemblies (132) are loaded around it. A two-cycle combustion cross-shaped flammable poison rod (203) is loaded in the lower left, and four three-cycle combustion MOX dense nuclear fuel assemblies (133) are loaded around it.
Furthermore, in order to increase the shutdown margin when the reactor is shut down for a long period of time such as periodic inspections, boric acid water that has been proven in PWR can be injected into the cooling water. In PWR, the reactor operation is expected to continue to some extent even if the steam generator tube is damaged. Meanwhile, water containing boric acid goes to the turbine. Therefore, even if boric acid water is mixed in the cooling water of the BWR, operation is possible with little adverse effect on the reactor and turbine. In order to reduce the concentration of boric acid water, the boric acid water is transferred to the spent fuel storage, and pure water is injected into the reactor core instead. The stop margin can also be increased by injecting an aqueous solution of sodium pentaborate into the cooling water.
Since the number of control rods can be significantly reduced, the control rod drive can be laid on the reactor pressure vessel. As a result, the control rod drive device can be easily inspected, and the power generation cost can be reduced through inspection time and cost.
: Journal of the Atomic Energy Society of Japan, 2006, Vol48, Tsutomu Okubo et al.

FIG. 10 is a schematic view of a BWR core having a quota control rod arrangement with auxiliary arrangement unnecessary for reorganization according to the present invention immediately before the start of operation. Unburned MOX dense nuclear fuel assembly (130) at the position of N around the quota control rod (101), 1 cycle combustion MOX dense nuclear fuel assembly (131) at the position of E, 2 cycles at the position of F mark It is assumed that the combustion MOX dense fuel assembly (132) is a three-cycle combustion MOX dense nuclear fuel assembly (133) at the position indicated by G. The quota control rods (101) are arranged in a staggered pattern centered on the control rod (100) in the center of the core, the other control rods (100) are excluded, and the associated control rod drive is also excluded. Was loaded with an unburned cross-shaped flammable poison rod (201). Around the unburned cross-shaped flammable poison rod (201), unburned MOX dense nuclear fuel assembly (130), 1 cycle burning MOX dense nuclear fuel assembly (131), 2 cycle burning MOX dense nuclear fuel assembly (132), 3 Cycle combustion MOX dense nuclear fuel assembly (133) is loaded.
When the operation for one cycle is completed, the three-cycle combustion MOX dense nuclear fuel assembly (133) burns four cycles, so it is taken out from the core as a spent nuclear fuel assembly. Instead, a new unburned MOX dense nuclear fuel assembly ( 130) can be loaded at this position, so no recombination of nuclear fuel assemblies is required, the time required for core configuration is shortened, the operating rate of the nuclear power plant is improved, and power generation costs are reduced.
In addition, the unburned MOX dense nuclear fuel assembly (130) loaded around the unburned cross-shaped flammable poison rod (201) was shut down by adding a flammable poison separately or reducing the plutonium ratio. The margin can be increased.

  In recent years, nuclear power has begun to attract attention as a measure to prevent global warming caused by carbon dioxide gas and oil prices. Among them, since a BWR composed of a nuclear fuel assembly in which MOX nuclear fuel rods are densely arranged can be a high conversion reactor, the core of the BWR of the present invention is immediately back-fitted to the current core.

Overview of the core structure of a conventional boiling water reactor. Control rod drive. The core top view just before the start of operation which arrange | positions the conventional nuclear fuel assembly (30) of a core height center part. FIG. 3 is a plan view of a core in which a conventional nuclear fuel assembly (30) and a control rod (100) are arranged. Core layout of pressurized water reactor (PWR). Sectional drawing of an unburned MOX dense nuclear fuel assembly (130). FIG. 3 is a schematic view of an auxiliary quarter control rod arrangement BWR core according to the present invention immediately before the start of operation. The figure which shows the effect | action of the core of this invention. Unburned MOX Dense Nuclear Fuel Assembly (130)-3-cycle Combustion MOX Dense Nuclear Fuel Assembly (133), Quarter Control Rod (101), Unburnt Cross Combustible Toxic Bar (201)-2-cycle Combustion Cross Combustible Toxic The figure which expanded the plane arrangement | positioning relationship of the stick | rod (203). FIG. 3 is a schematic view of a BWR core having a quota control rod arrangement with auxiliary arrangement unnecessary according to the present invention immediately before the start of operation.

Explanation of symbols

1 is a core support plate.
2 is a nuclear fuel support bracket.
3 is the upper grid plate.
11 is an unburned conventional nuclear fuel assembly.
12 is a one-cycle combustion conventional nuclear fuel assembly.
13 is a two-cycle combustion conventional nuclear fuel assembly.
14 is a three-cycle combustion conventional nuclear fuel assembly.
30 is a conventional nuclear fuel assembly.
31 is a nuclear fuel rod.
32 is a flammable poison-added nuclear fuel rod.
35 is a channel box.
36 is a water rod.
49 is a cooling water passage.
51 is a control rod side leakage water passage.
52 is the leaking water passage opposite to the control rod.
100 is a control rod.
101 is a quota control rod.
130 is an unburned MOX dense nuclear fuel assembly.
131 is a one-cycle combustion MOX dense nuclear fuel assembly.
132 is a 2-cycle combustion MOX dense nuclear fuel assembly.
133 is a three-cycle combustion MOX dense nuclear fuel assembly.
134 is a 4-cycle combustion MOX dense nuclear fuel assembly.
201 is an unburned cross-shaped flammable poison stick.
202 is a one-cycle burning cross-shaped flammable poison rod.
203 is a two-cycle burning cross-shaped flammable poison rod.
231 is a MOX nuclear fuel rod.

Claims (2)

A quarter control rod (101) is left out from the conventional control rod (100) in the center of the core, leaving the other control rod (100) and the drive unit attached to it as a substitute. A poison rod (201), a one-cycle combustion cross-shaped flammable poison rod (202), and a two-cycle combustion cross-shaped flammable poison rod (203) are loaded.
Four unburned MOX dense nuclear fuel assemblies (130) are loaded at the position of the N mark around the quota control rod (101). The unburned MOX dense nuclear fuel assembly (130) burned for one cycle at the position of N and changed to the one-cycle combustion MOX dense nuclear fuel assembly (131) at the position of E, A new burning cross-shaped flammable poison rod (201) is loaded. A one-cycle combustion MOX dense nuclear fuel assembly (131) at the position of E and an unburned cross-shaped flammable poison rod (201) in the center burns one cycle, and a two-cycle combustion MOX dense nuclear fuel assembly (132) and The one that becomes a one-cycle burning cross-shaped flammable poison rod (202) is rearranged to the position of the F mark and the center thereof. Two-cycle combustion MOX dense nuclear fuel assembly (132) at the position of F and one-cycle combustion cross-shaped flammable poison rod (202) at the center burns one cycle and three-cycle combustion MOX dense nuclear fuel assembly (133) And the two-cycle burning cross-shaped flammable poison rod (203) is rearranged to the position of the G mark and the center. The three-cycle combustion MOX dense nuclear fuel assembly (133) burned by one cycle at the position of G and changed to the four-cycle combustion MOX dense nuclear fuel assembly (134) is relocated to the position of the Z mark on the outer periphery of the core. Most of the three-cycle combustion MOX dense nuclear fuel assembly (134), the cross-shaped flammable poison rod (203) and the four-cycle combustion MOX dense nuclear fuel assembly (135) burned for one cycle are taken out of the core. BWR core with auxiliary quota control rod arrangement characterized by the above core configuration and operation plan. Combustible poisons such as cadmium (Cd) or boron (B) or erbium (Er) or dysprosium (Dy) or cadmium oxide (CdO) or erbium oxide (Er2O3) or dysprosium oxide (Dy2O3) or boron carbide (B4C) ) Or an unburned cross-shaped flammable poison rod (201) comprising a cross-shaped plate made of a zirconium alloy to which a compound such as zirconium boride (B12Zr) is added.

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