JPS61117481A - Method of exchanging fuel for boiling water type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] 4 The present invention relates to a method for replacing fuel assemblies in a boiling water nuclear reactor.

[Technical background of the invention and its problems]

A conventional fuel exchange method for a boiling water reactor will be described below with reference to FIGS. 7 and 8. FIG. 7 shows a configuration diagram of a conventional boiling water reactor core.

In FIG. 7 1c, fuel assemblies 12 are loaded in an orderly manner in the core 11 of a boiling water reactor.
A control rod 13 is arranged in one out of every four bodies. The arrangement relationship between the fuel assembly 12 and the control rods 13 is shown in Figure 1. Here, FIG. 8 is a detailed view of section A in FIG. 7. 8th
In the figure, fuel rods 14 loaded with fuel pellets (not shown) are arranged in a square array, for example, 8×8, in a fuel assembly 12, and a rectangular cylindrical channel box 15 is arranged around the outer periphery of the squarely arranged fuel rods 14. is located. This 4
A control rod 13 having a cross-shaped cross section is arranged in a gap having a cross-shaped cross section formed by the fuel assembly 12 of the body.

In the above configuration, the coolant (cooling water) is supplied to the fuel assembly 1
2 and between the fuel assemblies 12 from bottom to top. In addition, in FIG. 9, fuel assembly 1
The numbers in 2 indicate the number of cycles, ml is the unburned new fuel assembly, ta is the fuel assembly that has been burned for one cycle, (
2) shows a fuel assembly that has been burned for 2 cycles, and (3) shows a fuel assembly that has been burned for 3 cycles.

In addition, from the start of operation of a nuclear reactor during one cycle, the fuel in the reactor core burns and is consumed, resulting in no longer producing the specified output.
This refers to the period until the end of nuclear reactor operation.

In the above configuration, when a one-cycle nuclear reactor is operated, the fuel assembly 12 that has been burned for three cycles before the start of operation becomes the fuel assembly 12 that has been burned for four cycles.

When borrowing the core in the next cycle, 4? The fuel assembly 12 that has been burned for four cycles is taken out of the furnace, and an unburned I7r fuel assembly is loaded as a substitute for the fuel assembly 12 that has been burned for four cycles. As a result, 11 cores can be operated at a predetermined output.

Conventionally, the replacement period for the fuel assembly 12 was approximately 20 days, and at the same time periodic inspections of the reactor packing equipment were carried out, and these periodic inspections usually took about three months.

Currently, in nuclear power generation, it is desired to greatly improve the operating rate. Operation rate F#i in this reactor
When the core shutdown period is To + the core operating period is T1, the equation 1 is obtained.

F: 'r, /(T, +T, ')
(1) The conventional operation rate FFi was 0.75 because the operating period per cycle was about 9 months.

Furthermore, currently, fuel assemblies removed from reactors are either permanently stored or chemically treated to permanently store only non-fissile radioactive materials, so it is desirable to reduce the amount of this permanent storage. It was rare.

[Purpose of the invention]

The purpose of the present invention is to appropriately arrange the fuel assemblies in the reactor core, thereby shortening the time required to replace the fuel assemblies, and making it possible to remove the fuel assemblies with a high burn-up temperature and economical. An object of the present invention is to provide a method for exchanging fuel in a boiling water reactor, which is effective and can achieve leveling of the output within the reactor core.

[Summary of the invention]

In the present invention, the control rods arranged in the core of a boiling water reactor are divided into two groups, and the four fuel assemblies adjacent to each control rod of the first group combine unburned fuel pF!%.

Consists of a second cycle combustion fuel assembly, a fifth cycle combustion fuel assembly, a seventh cycle twisted and fired fuel assembly, and a second cycle combustion fuel assembly.
The four fuel assemblies adjacent to each control T1 keyaki in the group are a first cycle combustion fuel assembly, a shoulder three-cycle combustion fuel assembly,
Consisting of a 4th cycle combustion fuel assembly and a 6th cycle combustion fuel assembly, after the completion of 1 cycle operation, take out the fuel assembly that has been burned for 8 cycles, and then remove the loaded fuel assembly that has burned for 8 cycles. Boiling water 1! is characterized in that a fuel assembly that has been burned for 4 cycles is loaded into a fuel assembly that has been burned for 4 cycles, and an unburned fuel assembly is loaded at the position where the fuel assembly that has been burned for 4 cycles was loaded. ! Refueling method for nuclear reactor 1cI.

[Embodiments of the invention]

The first embodiment of the present invention will be described below with reference to FIGS. 1 to 3.
I will explain. Here, Fig. fs1 shows a configuration diagram of the core of the first embodiment of the present invention. In FIG. 1, fuel assemblies 17 are loaded in an orderly manner in a core 16 of a boiling water reactor.
Control rods 18 are arranged for each fuel assembly 1704 (rC). The control rods 18 are divided into two groups, and the control rods 18 of the first group are chained, and as shown by IIB, the four adjacent fuel assemblies 17 are divided into unburned fuel assemblies and second cycle burnt fuel assemblies. .

It consists of a 5th cycle combustion fuel assembly, &r7 cycle combustion fuel assembly, and the 12 control rods of the second group are Vr as shown by the dashed line O, and the 4 adjacent fuel assemblies 17 are used as the 1st cycle combustion fuel assembly. Assembly, 3rd cycle combustion fuel vessel combination, 4th
It consists of a cycle combustion bunker fuel assembly and a cylinder six-cycle combustion fuel assembly. The numbers shown on the fuel assemblies 17 in Fig. 1 indicate the number of cycles, 4 indicates the unburned fuel assemblies, and [7] from the river indicates the 7-cycle fuel from the fuel assemblies that have been burned for 1 cycle. The figure shows a four-piece combustion assembly. Dimensions ■■ and ■9 indicate fuel assemblies for adjustment to match the numbers of the first and second groups.

Core 161'C configured as above: t=-, 1
After the completion of the cycle, the fuel assembly that has been burned for 8 cycles is taken out of the core, and the fuel assembly that has been burned for 4 cycles is loaded at the place where it was taken out. Unburned fuel assemblies are loaded in the positions where the assemblies were loaded, and the reactor core is set up for the next cycle.

Here, Table 1 shows how the operation of the nuclear reactor will change as the cause recycling is updated.

(Left below) As shown in Table 1, fuel assemblies whose fissile material has been sufficiently consumed after 8 cycles of combustion due to current cycle operation are removed from the core when forming the core for the next cycle. A fuel assembly that has been burned for four cycles is loaded at υ, and a new unburned fuel assembly is loaded at the position where the fuel assembly that has been burned for four cycles was loaded. This keeps the work required to replace the fuel assembly low, so that the time required for this work is approximately % months. moreover,
In the current cycle, the second group of fuel assemblies consists of the combinations of (3) l III 1 (6), and in the next cycle, the fuel assemblies of the second group consist of the combinations of (2), (5), and (2).
This will be the I1 group fuel assembly.

In this way, the cycle is accelerated while the core configuration is circulated, so that the core configuration hardly changes in each operating cycle of the reactor, and stable performance can be obtained.

Further, the fuel assemblies adjacent to the new fuel assemblies are fuel assemblies whose fissile material has been consumed due to undergoing a new operating cycle. Therefore, excess neutrons generated from the new fuel assembly: Fick's law of diffusion (the net flow of neutrons is directed away from areas with high neutron density,
The magnitude of the flow is proportional to the rate of greatest change.

) is absorbed into the fuel assembly where combustion is progressing.

Therefore, nuclear fission in the new fuel assembly is not excessively promoted, and an excessive increase in output is suppressed.

On the other hand, fuel assemblies that have absorbed surplus neutrons and are well-burned have accelerated fission, resulting in higher output.

This relatively reduces the output sharing ratio of the new fuel assembly, which tends to have the effect of suppressing the output of the new fuel assembly from becoming excessively high.

1+ In the present invention, fuel assembly f'i is taken out from the core, and is a fuel assembly that has been loaded in the core for eight cycles. By increasing this operation cycle, the discharge burnup can be increased. This will be discussed in detail below.

The fission chain reaction is maintained by the fissile material in the fuel assembly and the neutron moderating effect of the surrounding water;
Infinite multiplication coefficient K is one measure of the degree of reaction.
Garalu. This infinite multiplication coefficient is a coefficient that decreases as the combustion of the fuel assembly progresses and the fissile material is consumed, and is approximated by the second equation.

K = '-m-E ... (2) Here, 0 indicates the infinite multiplication coefficient at a burnup of 0, and m is the infinite multiplication coefficient aK due to the consumption of fissile material due to combustion. shows a decreasing slope, indicating the Bid burnup.

Generally, in a nuclear reactor, some of the neutrons generated in the core escape to the outside of the core, and if the correction coefficient representing this effect is L, then the burnup Kd of the fuel assembly taken out of the core and the number of operating cycles N are The relationship is shown in the third equation (%).Furthermore, the burnup increment ED per one operating cycle of the reactor is shown in the fourth equation.

ED=2・((g)0・L−t), leak・Ltα+l)
ml...(47Here, the concentration of Ura 7-235 is 3
Taking the case of Q as an example, K' = 1.21, m = 0.01 ('/io
"M~vD/T), T=0.98, and by substituting this value into the third and fourth equations, the fifth and sixth equations are obtained.

Ed=38・(1-(N+t)-')
・totgD=3s・(N+1)−”
(6) Based on Equations 5 and 6, the burnup of the fuel assembly taken out of core 1 is plotted on the vertical axis and the number of operating cycles is plotted on the horizontal axis in Figure 2. A characteristic diagram of the fuel assembly is shown in FIG. 3, in which the vertical axis represents the burnup per one operating cycle of the reactor and 9 represents the number of operating cycles, and the horizontal axis represents the number of operating cycles. As shown in Figure 2, when the number of operating cycles is 4, the burnup of the four fuel assemblies taken out from the core is 3. OX 10'(MW
D/T) However, as the number of operating cycles increases, the burn-up increases, and when the number of operating cycles is 8, the burn-up of the fuel assembly taken out from the core is 3.3.
X 10' (MWD/T).

- As shown in Figure 3, the burnup increment per one operating cycle of a nuclear reactor increases from 4 to 8 (7 x
10" (MWD/T) to 4 x 10' (L
TtV'D/T). This burn-up increment increases the daily burn-up by approximately 25 degrees (MWD/
T), the number of operating days per vehicle that rotates 15 times is 9.
This will decrease from 3 months to 5.3 months, and along with this, the operating rate will also be lower than before. However, in the reactor core according to the present invention, the number of loaded fr fuel assemblies can be reduced as the number of operating cycles increases, and in general, the movement of fuel assemblies is small, so the fuel exchange work can be shortened, and the reactor Since the operation cycle period of the machine 2τ is approximately 34 minutes, by performing inspection work on the machine 2τ every other time, it is possible to obtain the same operating rate as in the past.

As an example, if the number of fuel change days is 0.7 months, the number of EIIs in one operation cycle is 5.3 months, and the number of regular inspection days is 3 months, the operating rate is 0.74 from equation 1, which is about the same as before. Become.

Next, a second embodiment of the present invention will be described with reference to FIG.

Here, Fig. 4 shows a configuration diagram of a reactor core according to a second embodiment of the present invention. In FIG. 4, fuel assemblies 21 are arranged in an orderly manner in a core 20 of a boiling water reactor, and a control rod 22 is arranged in one out of every four fuel assemblies 21. ing. The 22 control rods in the first embodiment are divided into two groups, and the four adjacent fuel assemblies 21 are assembled into unburned fuel as shown by the dashed line. body, first
Consisting of a cycle combustion fuel assembly, a sixth cycle combustion fuel assembly, and a seventh cycle combustion fuel assembly, the second group of control rods 22 connects the four adjacent fuel assemblies 21 as shown by the dashed line E. 2nd cycle combustion fuel assembly, 3rd cycle combustion fuel assembly, 4th cycle combustion fuel assembly.

It consists of a fifth cycle combustion fuel assembly.

Here, Table 2 shows how the cycle changes depending on the operation of the nuclear reactor.

(Leaving space below) Table 2 As shown in Table 2, the twisted assemblies whose fissile material has been sufficiently consumed through 8 cycles of combustion due to the current cycle operation are removed from the core when forming the core for the next cycle. A fuel assembly that has been taken out and burned for 6 cycles is then loaded. Then, due to the current cycle operation, a fuel assembly that has been burned for 2 cycles is loaded in the position where the fuel assembly that has been burned for 6 cycles was loaded, and the fuel assembly that has been burned for 2 cycles is loaded at the location where the fuel assembly that was burned for 2 cycles was loaded. A new fuel assembly is loaded into the tank. As a result, the same effects as in the first embodiment of the present invention can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 5 shows a block diagram of a reactor core according to a third embodiment of the present invention. In FIG. 5, fuel assemblies 24 are loaded in an orderly manner in a core 23 of a boiling water reactor, and control rods 25 are arranged for every 2404 fuel assemblies vC1. This control rod 25 is divided into two groups as in the first embodiment, and the control rods 25 of the first group control the four adjacent fuel assemblies 24 as shown by the dashed line F, the unburned fuel assemblies and the third group. Cycle combustion fuel Hayabusa combination, 4th cycle combustion fuel assembly, 7th
Consists of cycle combustion fuel assembly, second group control n25
is the four fuel assemblies 24 that are in contact with each other as shown by the dotted line G.
a first cycle combustion fuel assembly, a second cycle combustion fuel assembly, and a fifth cycle combustion fuel assembly.

It consists of a 6th cycle combustion fuel assembly.

Here, Table 3 shows how the cycle changes depending on the operation of the nuclear reactor.

As shown in Table 3, fuel assemblies that have been burnt for 8 cycles during the current cycle operation and have had enough fissile material consumed are taken out of the core and replaced with 6 Cycle combustion fuel assemblies are loaded. Then, due to the current cycle operation, a fuel assembly that has burned for 4 cycles is loaded in the position where the fuel assembly that has burned for 6 cycles was loaded, and a fuel assembly that has burned for 4 cycles is loaded in the position where the fuel assembly that has burned for 4 cycles was loaded. The cycle-burned fuel assembly is loaded, and a new fuel assembly is loaded in the position where the two-cycle burnt fuel assembly was loaded.

As a result, the same effects as in the first embodiment of the present invention can be obtained.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

Here, FIG. 6 shows a block diagram of a reactor core according to a fourth embodiment of the present invention. In FIG. 6, fuel assemblies 27 are loaded in an orderly manner in a core 26 of a boiling water reactor, and a control rod 28 is arranged for every four fuel assemblies 27. .

The control rods 28ij are divided into three groups, and the first group of control rods 2
8 indicates four adjacent fuel assemblies 2 as shown by dotted lines H.
7 is an unburned fuel assembly, a second cycle combustion fuel assembly,
The 5th cycle combustion fuel assembly is formed by the 7th cycle combustion fuel assembly, and the control rods 28 of the 2nd group are formed by the 4 adjacent fuel assemblies 27 as shown by the dashed line J in the 1st cycle. Combustion fuel assembly, third cycle combustion fuel assembly.

It consists of a fourth cycle combustion fuel assembly and a sixth cycle combustion fuel assembly.

The first group of control rods and the second group of control rods are arranged in the central region of the reactor core 26. Further, as shown in FIG. 6, adjusting fuel assemblies indicated by ω] to ■ are loaded in the vicinity of the central region.By means of these adjusting fuel assemblies, the number of fuel assemblies for each cycle number is the same. The control rods 28 of the tIK3 group are arranged in the outer peripheral region of the reactor core, and in addition to the regulating fuel assemblies, the portions indicated by the opening and the portion indicated by the sections include fuel assemblies that have been burned for 8 cycles to fuel assemblies that have been burned for 11 cycles. is loaded. The fuel assemblies shown in the middle section of FIG. 8 are adjustment fuel assemblies in the outer peripheral region of the core where no control rods are adjacent.

Here, Table 4 shows how the cycle changes depending on the operation of the nuclear reactor. As shown in Table 4, when one cycle of operation is completed, the fuel assemblies that have undergone 12 operation cycles and are loaded in the outer peripheral area are taken out of the core and loaded in their place in the central area. A fuel assembly that has undergone a driving cycle is loaded. In addition, fuel assemblies that have experienced 4 operation cycles are loaded in the position of the fuel assemblies that have experienced 8 operation cycles that were loaded in this central area, and the positions of the fuel assemblies that have experienced 4 operation cycles are loaded. The next cycle core is constructed by loading a new fuel assembly into r.

(Left below) As described above, according to the method of the M4 embodiment of the present invention, since the fuel assemblies in which combustion has progressed are placed in the outer peripheral region of the core, the first
In addition to the effects of the embodiment, surplus neutrons generated in the central region are absorbed in the outer peripheral region, reducing the number of neutrons leaking out of the core, and furthermore, the absorbed neutrons can increase the output of the outer peripheral region. Therefore, the burnup of the fuel assembly taken out of the core in the fourth embodiment is increased by the excess neutrons generated in the central region, so the relationship between burnup and operation cycle shown in Equation 5 is expressed as follows: It is possible to obtain a higher burnup than the indicated value.

In addition, in the fourth embodiment of the present invention, the arrangement of the four fuel assemblies adjacent to the control rods of the first group and the second group is changed as in the second and third embodiments of the present invention. However, the same effects as in the fourth embodiment can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to shorten the period required to replace a fuel assembly, and moreover, it is possible to increase the discharge burnup of the fuel assembly.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a core of a boiling water reactor showing a first embodiment of the present invention, and FIG. 2 is a diagram of a fuel assembly showing the relationship between the burnup of a fuel assembly taken out from the core and the number of operating cycles. Figure 3 is a characteristic diagram of a fuel assembly showing the relationship between the burnup per operating cycle of a nuclear reactor and the number of operating cycles.
6 to 6 are block diagrams of the core of a boiling water reactor showing the second to fourth embodiments of the present invention, and FIG. 7 is a block diagram of the core of a conventional boiling water reactor. Figure 8 (d Detailed view of part A in Figure 7. 11.16, 20, 23.26...core 12.17,
21.24,27...Fuel assembly 13.18,22,
25.28...Control rod 14...Fuel rod 15...Channel Box agent Patent attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Book 3 Figure 1 Turn-build guy Figure 4 Figure 5

Claims (2)

[Claims] (1) Control rods placed in the core of a boiling water reactor are
The four fuel assemblies adjacent to each control rod in the first group are an unburned fuel assembly, a second cycle combustion fuel assembly, a fifth cycle combustion fuel assembly, and a seventh cycle combustion fuel assembly. 4 adjacent to each control rod of the second group.
The fuel assemblies of the body include a first cycle combustion fuel assembly, a third cycle combustion fuel assembly, a fourth cycle combustion fuel assembly,
It consists of a 6th cycle combustion fuel assembly, and after the completion of 1 cycle operation, the fuel assembly that has been burned for 8 cycles is taken out,
After that, a fuel assembly that has been burned for 4 cycles is loaded in the position where the fuel assembly that has been burned for 8 cycles was loaded,
A method for exchanging fuel for a boiling water reactor, characterized by loading an unburned fuel assembly into the position where the fuel assembly that has been burned for four cycles was loaded. (2) Control rods placed in the core of a boiling water reactor
The four fuel assemblies adjacent to each control rod in the first group are an unburned fuel assembly, a second cycle combustion fuel assembly, a fifth cycle combustion fuel assembly, and a seventh cycle combustion fuel assembly. 4 adjacent to each control rod of the second group.
The fuel assemblies of the body include a first cycle combustion fuel assembly, a third cycle combustion fuel assembly, a fourth cycle combustion fuel assembly,
It consists of a 6th cycle combustion fuel assembly, and the 4 fuel assemblies adjacent to each control rod of the 3rd group are an 8th cycle combustion fuel assembly, a 9th cycle combustion fuel assembly, and a 10th cycle combustion fuel assembly. The control rods of the first group and the second group are arranged in the central region of the reactor core, the control rods of the third group are arranged in the outer peripheral region of the core, and the control rods of the first group and the second group are arranged in the outer peripheral region of the core. After the completion of the combustion, the fuel assembly that has been burned for 12 cycles is taken out, and then the fuel assembly that has been burned for 8 cycles and placed in the central area of the reactor core is loaded in the position where the fuel assembly that has been burned for 12 cycles was loaded. A fuel assembly that has been burned for 4 cycles is loaded in the position where the burned fuel assembly was loaded, and an unburned fuel assembly is loaded in the position where the 4-cycle burned fuel assembly was loaded. How to replace fuel in a boiling water reactor.