JPS5914199B2 - Fuel loading method in boiling water reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for loading fuel in a boiling water nuclear reactor.

Generally speaking, in a nuclear reactor, the power distribution within the core is not even, so fuel burns out quickly in the center of the core and slows down in the periphery.

Therefore, the inside of the reactor core is divided into several regions, and fuel is moved to different regions for each cycle.

The fuel loading method for conventional boiling water reactors is as follows:
A distributed patch force method is used in which new fuel is loaded once every four cycles into the loading position of the fuel that is to be released after combustion.

In addition, the control rods in this case are operated by dividing the control rods into two groups, and once every two months, the control rods inserted during reactor operation are pulled out and exchanged with each other. The aim is to burn the fuel evenly.

However, in this fuel loading method and control rod operation, the fuel at the position facing the outer periphery of the core is not completely melted in 4 cycles, so it is not efficient to release it after 4 cycles of incineration. However, even if new fuel is loaded at a position facing the outer periphery of the reactor core, its contribution to output is small and it is troublesome to replace the control rods.

In view of the above, the present invention provides fuel for a boiling water reactor in which the fuel is completely burnt out and then released, the power distribution of the reactor core is even, and the control rods are relatively easy to operate. The purpose is to provide a loading method for

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 1, the reactor core The fuel compartments are symmetrical about the vertical axis, the horizontal axis, and the diagonal axis bisecting the vertical and horizontal axes with the control rod as the center, and a set of fuel compartments selected every other section is located in the second area B (in the figure). The outermost fuel compartments facing the reflector of the reactor core are set in the third area C (the part with English lowercase letters in the figure).
The set of fuel compartments selected adjacent to and spaced from each other in the third region C1 is the fourth region D ([F] ■ in the figure).
part).

Next, the fuel loading order for each region will be explained with reference to Table 1 in addition to FIG.

At the beginning of n cycles (BOC) t in the first region A, new fuel 1, 1st cycle, 2nd cycle and 3rd cycle in the first region A.
The cycle burnt fuels 2, 3 and 4 are combined with the 1, 2 and 3 cycle burnt fuels 2, 3 and 4 at the end of the cycle (EOC) and the fuel discharged or loaded into the third zone. d, and at the beginning of the n + 1 cycle, new fuel 1 is loaded in place of the extracted fuel d, and at the end of the cycle, this new fuel 1 is combined with fuel 2 burned for one cycle. Become.

Furthermore, fuels 2, 3, and 4 at the beginning of the cycle become fuels 3.4 and d at the end of the cycle, and this fuel d is either discharged or loaded into the third region.

In this way, one fuel assembly in the first zone A is fired for four cycles and then discharged, or the third
It is loaded in area C.

That is, since new fuel is loaded in a distributed batch manner every four cycles, the replacement work is simple and clear.

In this region, the number of control rods inserted during operation is less than or equal to A during the current cycle period.

At the beginning of the cycle in the n cycles of the second region B, the fuel G burned for one cycle in the fourth region and the second
Fuels H, I, and J that have been fired in the furnace for one cycle, two cycles, and three cycles are loaded, and at the end of the cycle, fuels G, H, and I become fuels HI and J, and fuel J is discharged.

At the beginning of the n + 1 cycle, instead of the released fuel J, the fuel G that has been burned for one cycle in the fourth region is loaded, and the fuels H, I, G at the beginning of the n + 1 cycle are loaded.
are fuels I and J, respectively, at the end of the cycle.

H, and the fuel J that is present at the beginning of the cycle is released at the end of the cycle.

At the beginning of the nth cycle of the third region C,
Fuel g burned for 1 cycle in the fourth region, fuel li, i, j burned for 1 cycle, 2 cycles, 3 cycles, and 4 cycles in the third region, and fuel d burned for 4 cycles in the first region A. is loaded and at the end of its cycle, the fuels g, h, i, jk and d are respectively i, j, k,
At the beginning of the n + 1 cycle, fuels g and d are loaded instead of the released fuel, and at the end of the cycle, 2g and d are loaded into each fuel i, j, and d at the beginning of the cycle. are fuel i, jk, released fuel, h, and released fuel.

In addition, new fuel is always loaded into the fourth zone at the beginning of the cycle, and after this new fuel is burned for one cycle, the fuel [F] is burned for one cycle in the second zone, and the fuel [F] is burned for one cycle in the third zone. The fuel (■) to be combusted consists of the initial LCF charge of the next cycle as fuel G, and the fuel (■) is
It is loaded into the third region as fuel g.

In addition, in the second region, a control rod was inserted during operation, the fuel was burned, the control rod was gradually withdrawn, and the part in contact with this control rod was burned for one cycle. Later fuel is loaded.

In this region, reactor operation is easy because the control rods to be inserted during operation are fixed.

Furthermore, since new fuel is not loaded in this area, there is no unburnt residue even if the control rod is inserted for a long period of time, and the output is reduced, so there is little thermal shock due to movement of the control rod.

In the third region 1, fuel that has been burned for more than one cycle is loaded, and no new fuel is loaded here.

This is the outermost fuel facing the reflector, so it will not explode.
In addition, since the fuel is burnt for 5 cycles in this region, there is no remaining fuel left after the 5 cycles, and the fuel is discharged outside the furnace after 5 cycles.

Note that the fuel shortage in this area is compensated for by the fuel d released from the first area.

The fuel fired for one cycle in the fourth zone is loaded into the second and third zones instead of new fuel, so it must not burn too much.

This region is therefore located adjacent to the inside of the fuel facing the reflector.

Next, another embodiment will be explained.

In Fig. 2, the arrangement of the fuel assemblies is rotationally symmetrical with respect to the control rod at the center of the reactor, and the position shown in Fig.
The arrangement of the fuel assemblies remains unchanged even after rotation.

That is, the fuel arrangement on the vertical axis passing through the control rod at the center of the reactor and the horizontal axis are the same.

The first head area is A', and the second area is the part B' surrounded by a large frame.
In Fig.
Here, V4 of the core is shown, with other parts being rotationally symmetrical.

In the figure, each code 1, 2, 3t4tg, htmlJ+
, H2I, J, [F]■ have the same meaning as each symbol in Table 1.

In addition, code A indicates new fuel loaded in the fourth area, code entry indicates fuel burned for one cycle in the fourth area, code C indicates fuel burned for two cycles in the fourth area, and code 2 indicates fuel burned for three cycles in the fourth area.
Shows cycle-burned fuel.

In the fourth region D' of this embodiment, in addition to the fuel [F] (2), two ports of the solvents (A), (C) and (2) are loaded, and the fuel (2) is loaded around the reactor center control rod r.

Therefore, even if the control rod r is operated frequently and rapidly to adjust the output, no problem will arise in terms of the health of the fuel since the output of the fuel around it is small.

In addition, in this embodiment, since the fuel arrangement is rotationally symmetrical, the status of the entire core can be monitored just by looking at the 14 parts of the core, which is convenient for core management, and because of the symmetry, the power distribution is even. become.

When the reactor is operated with a different cycle length than planned, the core reactivity is adjusted by the number of new fuels loaded.

For example, if the previous cycle was longer than expected,
Since the core reactivity is lower than planned, the number of new fuel loading bodies increases, but the fuel may be loaded in the same manner as in the above-described embodiment.

However, if the previous cycle is shorter than planned, the burn-up of the new fuel will be low and the core surplus reactivity will be high, so the number of fuel bodies loaded in the next cycle must be reduced. However, the above-mentioned loading method may be undesirable from the standpoint of reactor shutdown margin.

Therefore, if the previous cycle is shorter than planned, the following fuel loading method can be considered.

That is, the core is divided into regions as shown in FIG. 1, and the fuel loading method is performed as shown in Table 2 below.

In this loading method, the burn-up of the new fuel is low and the core surplus reactivity is high, so the number of fuel bodies to be loaded in the next cycle is reduced.

Therefore, it is not desirable to load the fuel from the fourth area where the furnace combustion does not progress much into the second area B where the control rods are inserted, and instead load the fuel G' that has been burned for one cycle in the first area A. At the same time, fuel g' that has been burned for one cycle in the first region A is loaded in the third region (J).

Further, since there is little new fuel, only the new fuel [F]', which is fired for one cycle, is loaded in the fourth area D/I to be loaded into the first area A.

Since the present invention is configured as described above, the power distribution of the core is even and the fuel is completely burned before being released, making it efficient.The fuel loading procedure is also clear, which reduces exposure to radiation. The period is shortened, and there is no need for polishing to change the position of the control rod inserted during operation as in the past, so the operation of the control rod becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a fuel arrangement diagram showing the fuel arrangement in a reactor core according to the present invention, and FIG. 2 is a fuel arrangement diagram showing another fuel arrangement. A, A'...First area, B, B'......
Second area, c, c'...Third area, D, D'・
...Fourth area, X...Reactor core.

Claims (1)

[Claims] 1. A reactor core including a first region, which is a major region of the core excluding the surrounding area, and a first region excluding a part of the core, and a fuel region selected at symmetrical intervals within the major region. A second region consisting of a set of The first area is loaded with new fuel in a batch manner every four cycles, and the second area is loaded with fuel that has been burned for one or more cycles in other areas, and then released after being burned for four cycles. The third region is loaded with fuel that has been burned for one or more cycles in another region, and is discharged after being fired for five cycles;
The lack of fuel in this region is filled with the fuel released in the first region, and the fourth region is loaded with new fuel for loading into other regions, and is burned for only one cycle. A fuel loading method for a boiling water reactor.