JPS6013285A - Method of operating boiling water 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] The present invention relates to a method of operating a boiling water nuclear reactor, and particularly to a control cell in which the reactivity of a fuel assembly is lower than the average value in the reactor core. The present invention relates to a method of operating a boiling water nuclear reactor having a boiling water reactor.

[Technical background of Akira Nozuru and its problems]

Recent 1i% boiling water reactors have a method of operating the reactor by forming a control cell in the reactor core and inserting the control rods in this control cell exclusively during normal output operation. It's planned. This control cell is located at a predetermined location 11/i,
Either a fuel assembly with a reactivity smaller than that of the core's 1st diameter fuel assembly is arranged around the 71J rod, and the reactivity is lower than that of the reactor core.
Alternatively, in the case of a replacement core, there are methods such as increasing the burnup above the average sensitivity.

Generally, when the combustion IW of a fuel assembly progresses due to long-term use of the fuel assembly, the reaction rate of the fuel assembly decreases due to its deterioration, etc., and the reactor output decreases. Therefore, in order to compensate for this decreased reactivity and maintain the rated output, it is necessary to withdraw the control rods and increase the reactor output. However, if the control rods are simply withdrawn from the reactor core, as shown by the solid line in Figure 1, the reactor output from the portions of the control rods removed from the side shields increases rapidly, which is not good for the health of the fuel assembly. There is a risk that it will have an adverse effect. Therefore, the above-mentioned reactor output due to control rod withdrawal is so-called P
It is necessary to withdraw the control rods after lowering the output level to below the threshold value allowed by CIOMR. This threshold is typically set at 8 kW/ft.

However, once the reactor power is reduced to a reactor power level below the PCIOMR threshold in this way, the reactor power must be gradually increased through break-in operation until the rated power is restored, which reduces the operating rate. . The decrease in availability due to this accounts for a considerable portion of the decrease in availability in the reactor operation cycle, and a nuclear reactor operating method using control cells was devised with the main purpose of improving this decrease in availability.

In this control cell, the reactivity of the fuel is suppressed to a small level in advance, so when the control cell is operated with the control rods, the increase in the reactor output when the control rods are withdrawn increases as shown by the solid line in Figure 2. This is significantly suppressed compared to when cells are not used. As a result, the integrity of the fuel frame is maintained, and the reactor output paper-F that is performed at 5% of J and 5% of the riill slight withdrawal for 1 hour is also relatively small, so that the upper Jt and reactor movement rate are can be improved. The broken line in FIG. 1 shows the position of the control rod 841 and the furnace output before being pulled out, and the broken line in FIG. 2 shows the furnace output when the control cell is not used.

However, when the control rod is inserted in the 1.1 assembly, the so-called mesoton spectrum hardens, and this causes the 1.1 assembly to harden.
'1' A phenomenon called 'f'-It month 1.r: effect occurs.The former hardening of the neutron spectrum is caused by the proximity of the control fI rod 2 to the fuel 11-combination 1, as shown in Figure 3. In this case, the heated i atoms are absorbed by the neutron absorption effect of the control rods 2, so that the neutron energy distribution within the fuel assembly 1 is distorted to +71 energy 11.

When the control rod 2 is further interposed between these fuel assemblies 1, the light water as a neutron moderator is reduced by the inserted volume, so that the neutron spectrum is further hardened. As a result, IL! 4 U23 occupies most of the uranium dioxide in the fuel rod 3
The singleton capture in 8 increased, this fuel assembly book 10 control $
Geltonium Pu is accumulated in the fuel rods 3 that are 2 K close to each other. The accumulated amount is the fuel assembly I K ftf
It increases corresponding to the length of the period in which the lJ rod 2 is close to each other. Therefore, when the operation is performed in the inserted state with the control rod 2 for a certain period, and then moves to the withdrawn state without the control rod 2, the output distribution of the four units 1 surrounding the control rod 2 will change. n also reaches its maximum at the corner rod 3A of the fuel rod indicated by the black circle in FIG. This corner rod 3A is located at the corner of the fuel assembly 1 close to the cross-shaped intersection of the control rods 2, and in the inserted state with control a2, the output of this corner rod 3A is usually the minimum. be.

Therefore, the output of this corner rod 3A will fluctuate drastically due to the withdrawal of the control rod. The range of fluctuation increases as the period of time that the inserted state with the control rod 2 is maintained increases, and this is directly related to the control rod history effect. FIG. 4 shows the control rod history effect of the corner rod 3A. In Fig. 4, the horizontal axis indicates the combustion period with the control rod inserted;
The slave axis is the increase in the local peaking coefficient of the corner rod 3A, in other words, the control riil 2t? + shows the difference between the case where the player receives a U-resistance attack and the case where he does not receive a hit and the case where he is involved in a corner rond exit cubby king). This FIG. 4 shows the control rod insertion state i1. 1 for j3?・1 for the current period (C ratio f311.Corner rod 3A ii:ll
A scream? This indicates that the +1m history effect becomes larger.

Therefore, for the first army of control cells mentioned in zl
Even if s t is high, the control frame effect-prefecture will occur, so 1il
If it is held for l (lu:'+B・11 people dog 4 long JIJ), i in the control cell;': ,+t'l set 1 corner rod sin 1 lsl violation history ゛guri will increase , the output Be Kinder coefficient increases, and the output) J change I 1
becomes K-sounding. When this control rod history effect becomes large, it cancels out the control cell bundle output by setting the reactivity lower than the core average (v' If it cannot be realized, there will always be Wf.

[Purpose of Shomei]

Thurs. J6 Ming was made in consideration of the circumstances mentioned above, and the fire (
-1 It is possible to minimize the control rod hysteresis effect that occurs in the Toai sea lion and maximize the effectiveness of the control cell, thereby reducing the operating rate loss caused by break-in operation based on PCIOMR. The present invention aims to provide a method for operating a 111b water reactor.

[Summary of the invention]

In order to achieve the above-mentioned object, a method for operating a boiling water reactor according to the present invention is configured as follows.

Divide one fuel operation cycle into a plurality of combustion periods, classify them into control cellular multiple darugs, and make each of these groups correspond to each of the above combustion periods,
Moreover, the groups corresponding to adjacent combustion periods are made to be different from each other, and for one combustion period, only the control rods belonging to one group are operated to control the reactor output, and when transitioning to the next combustion period, the control rods belonging to one group are controlled. It is configured to perform a pattern exchange in which the control rods inserted during the previous combustion period are fully withdrawn.

[Embodiments of the invention]

An embodiment of the method for operating a boiling water reactor according to the present invention will be described below with reference to the drawings.

r:, 1'g 51QI is a schematic horizontal cross-sectional view of a core for showing an example of the arrangement of control cells formed in the core of a 1.1 million kW 6 class boiling water reactor. The reference numeral 10 in FIG. 5 is the reactor core, and the core 0 has a large number of lattices, and within each lattice there are four fuel assemblies 1, and between these fuel assemblies 1, as shown in FIG. It houses control rods 12 with 1.11 people arranged in a cross shape. Inside these grids are control rods accommodating control rods [2] indicated by X in Figure 5.
There are many things formed in cell L1. The fuel assembly 1 housed in this control cell 11 is heated at tV so that its reactivity is lower than the average value of the core.
For example, one control cell 11 is formed for every four grids. A plurality of these control cells 11, for example, FIG. 6(4), (
As shown in B), it is classified into two groups, A group and B group.

For example, both groups A and B can be used both vertically and horizontally.
A, A% A, B, B, B are arranged so that there are no identical groups, and groups that are always next to each other, such as A, B, A, B, etc., are classified so that they belong to different groups. φ is done. As shown in Figure 6 (A) and (B), both groups A and B are distributed evenly in the core [0], and the core [0
Efforts are being made to level out the overall reactor power distribution.

On the other hand, the burnup period E is divided into a plurality of periods, for example, into 2)lJJ of El and E2 as shown in FIG.

The burnup cycle E is divided into two periods, the first half E1 and the second half E2, with the transition time EC, which is approximately 1/3 a degree advanced from the start of the burnup cycle E, as a boundary. In the first half of the cycle E1, the reactor output is controlled by withdrawing the control rods in the control cells 1 at appropriate locations belonging to group A shown in FIG. 6. However, in the first half of this cycle E1, in order to fine-tune the reactivity, control and
It is possible to insert or withdraw control rods within the cell 11. At the end of the first half of this cycle E1 and the transition to the second half of the next cycle E2, the control cell 1 of the A group inserted in the first half of the cycle El
After that, all the control rods in control cell 1 in control cell 1 in group B are pulled out, and after that, a so-called pattern exchange is performed in which control rod 11 in control cell 1 in group B (1 lll J cape is performed with only 1 demolition. However, the reaction occurs in E2 in the second half of the cycle. In order to adjust the degree, control cell of B group [f!II in
ii) Insertion or withdrawal of the swipe may be performed.

J soot 1 from the first half of the cycle E1 to the second half of the cycle E2
If the pattern of control I1 is not exchanged from the FJCKA group to the B group, the control rod jfI history effect is accumulated in one aggregate as shown in Fig. 8 (A),
Reactor output decreases significantly when withdrawing control rods to adjust reactivity. As the reactor output decreases, the operating rate loss due to the break-in operation based on pc_orast increases. On the other hand, once the control ill+salary pattern is exchanged at the transition EC of the cycle burnup period E, the furnace output decrease increases by -1,i when the pattern is exchanged, as shown in Fig. 8(i()). , the subsequent control for reaction adjustment (1r pull 1 person 1) The decrease in furnace output during operation was caused by the pattern not being replaced (see Figure 8).
It remains significantly smaller than that shown in 4). This is because the control rod history effect of the control cell 11 of group B starts from zero at transition time EC and 1-. As a result, the total availability loss through the burnup cycle E is significantly lower when the pattern is replaced than when it is not, and the availability can be significantly improved. Figure 9 shows the relationship between EC at the time of transition when control rod patterns are exchanged and the availability loss due to break-in operation based on PCIOMR. This shows that the operating rate loss is almost at its lowest during the combustion period. In addition, in Fig. 9, the burnup cycle E is a certain period of time, for example, E
) 6000i14Wd/Tf indicates that when the transition period EC is the beginning O or the end IIJIE, the control rod pattern will not be exchanged even once during the cycle, and p
Based on cIoMR, the operating rate loss due to break-in is the maximum, and both have the same value. This j motive power loss is a function of the fuel design and the length of the burnup cycle E, so it cannot be generalized, but as mentioned above, the It can be determined that it is optimal.

In addition, in the case of water supply, the burnup cycle E' was set to 2 minutes and 1 minute.
．． I mentioned the case of operating a nuclear reactor, but...
The invention is not limited to this, and various modifications can be made without changing the gist of the invention.

For example, the burnup cycle E may be divided into three parts of appropriate length. The cycle IC divided into three parts may be operated by sequentially intersecting control cells with, for example, A group, B group, rlH, and A group. Also,
The control cell 11 may be a tertiary term instead of a dichotomous Ifi, and is not limited to the number of classifications. Burnup cycle E
The number of divisions and the number of classifications of control cells 11 may be any appropriate number, and a combination of the two may be selected as appropriate. Of course, at the transition time EC of the burnup cycle E, control rod patterns are exchanged.

[・、Effect of gauze]]

As described above, the present invention changes the fuel operation cycle from i to il.
In addition to dividing the control cells into multiple groups, each divided group is assigned to each divided combustion period, and the control cells are assigned to the required group during the required combustion period. Only the rods are operated by 4+11 people, and at the time of transition to the next combustion period, all the control rods of the previous group that have been inserted so far are pulled out, and from then on, only the control rods of the next group can be inserted. For this purpose, PCIOMf
1.1 to minimize the operating rate loss due to break-in operation based on t.
This has the effect of significantly improving the operating rate.

[Brief explanation of drawings]

,'g1 Figure is a reactor power distribution diagram showing the reactor power output in the control rod axial direction before and after control rod withdrawal, and 70 distribution fluctuations, and Figure 42 is the reactor power distribution fluctuation in the control rod axial direction depending on the presence or absence of control cells.・Figure 3 is a plan view showing how control rods are inserted between fuel assemblies, Figure 4 is a curve diagram showing the increase in corner rod peaking coefficient, and Figure 5 is a control cell diagram. FIG. 6 is a schematic horizontal cross-sectional view of the core for explaining an example of the arrangement of control cells, and FIG. (B) is a schematic horizontal cross-sectional view of the reactor core showing an example of the arrangement of control cells in Group B, Figure 7 is a conceptual diagram of a burnup cycle divided into two parts, and Figure 8 (
A) is a reactor output level diagram showing a decrease in reactor output level due to control rod pattern exchange not being executed, and (B) is a reactor output level diagram showing a decrease in reactor output level due to pattern exchange being executed. 9 are graphs showing the relationship between the operating rate loss due to break-in operation based on PCIOMR and the transition time when pattern exchange is performed. 1...Fuel assembly, 2...Control rod, 3...Fuel rod,
3A... Corner rod, E... Burnup cycle, E
l...first half of the cycle, E2...second half of the cycle,
EC...At the time of transition. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. It has a control cell in which the reactivity of the fuel assembly is lower than the average value in the core, and during normal reactor power operation, control rods are exclusively connected to the control cell. In the method of operating a boiling water reactor in which the reactor power is being operated by placing the fuel in the inserted state, one fuel operation cycle is divided into multiple combustion periods, and the control cell is The groups are classified into side number groups, and each of these groups is assigned to a combination combustion period, and the groups assigned to adjacent combustion periods are different from each other, and for one combustion period, the controls belonging to one group are It is characterized in that only the rods are operated during reactor power operation, and at the time of transition to the first combustion period, a pattern exchange is performed in which the control rods inserted in the previous combustion period are fully withdrawn. Boiling water reactor operating method. 2. One fuel operation cycle is divided into three combustion periods, and the control cells are classified into two groups, and these groups are sequentially changed for each combustion period. A method for operating a boiling water reactor according to claim 1, characterized in that the reactor output is controlled by inserting and withdrawing the control rods. 3. The control rod pattern exchange is carried out in one step. 2. The method of operating a boiling water nuclear reactor according to claim 1, wherein the boiling water reactor is operated at approximately a ladle period from the beginning of a fuel operation cycle.