JP3183978B2 - Reactor operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a boiling water reactor.

[0002]

2. Description of the Related Art In a recent boiling water reactor, a method of operating a reactor by forming a control cell in a reactor core and inserting a control rod in the control cell exclusively during a normal power operation is known. Implemented or planned. The control cell is formed by arranging a fuel assembly having a reactivity lower than the average value of the core around a control rod arranged at a predetermined position.

A conventional example is disclosed in, for example, JP-A-55-70792. The purpose of the control cell is as follows. In general, as the burnup progresses due to long-term use of the fuel assembly, the reactivity of the fuel assembly decreases and the furnace output decreases.

[0004] Therefore, in order to maintain the rated output by compensating for the decreased reactivity, it is necessary to pull out the control rod to increase the furnace output.

[0005] However, if the control rod is simply pulled out from the core, the furnace power at the portion where the control rod is pulled out suddenly rises due to the pulling out, which may have an undesirable effect on the integrity of the fuel assembly.

[0006] Therefore, the above-mentioned furnace output due to the control rod withdrawal is a so-called PCIOMR (Preconditioning).
Interium Operation Management Recommendation; Normally, when the linear output density is 8 kw / ft or more, the linear output output time increase rate is limited and the run-in operation is performed.) Lower the output level below the allowable threshold and then pull out the control rod. There is a need to do.

[0007] However, as described above, the furnace power is controlled by PCIOMR.
Once reduced to a furnace power level below the threshold of
Until the rated power is restored thereafter, the furnace power must be gradually increased by the break-in operation specified in PCIOMR, and the operating rate will decrease.

[0008] The decrease in the operating rate due to the running-in operation leads to a decrease in the operating rate in the reactor operation cycle, which accounts for a considerable portion. Therefore, a control cell was devised for the purpose of improving the operation rate.

In this control cell, a low reactivity fuel is used around a control rod operated during operation. Generally, a fuel having a reactivity always lower than the reactivity of the core is used.

FIGS. 6A to 6C schematically show examples of the relationship between the infinite multiplication factor of the fuel used in the control cell and the infinite multiplication factor of the core. , (C)
Shows examples in the case of a 4-batch, 5-batch, and 6-batch replacement core, respectively. In each case, the infinite multiplication factor of the fuel used for the control cell is lower than that of the core.

In the control cell, since the control rod is operated in the inserted state for a long time, a phenomenon called a control rod hysteresis occurs. This is because the more the combustion progresses with the control rod inserted, the more the combustion of the fuel proceeds asymmetrically, and the local output of the fuel rod on the control rod side of the fuel assembly adjacent to the control rod when the control rod is pulled out Is a phenomenon that may have an adverse effect on fuel integrity due to an increase in

As a countermeasure against this phenomenon, for example,
No. 60-13285. In Japanese Patent Application Laid-Open No. 60-13285, the control rod hysteresis effect has a characteristic that is proportional to a period in which a control rod is inserted and burned, so that a combustion period in a state where only a specific control rod is inserted is not prolonged. In addition, the control cells are divided into groups, and only the control rods of a specific group are used and the other control rods are not used in each of the divided operation cycle periods.

[0013]

As described above, the control rod hysteresis effect increases in proportion to the period during which control rods are continuously inserted. A conventional example in which the total number of control cells used as a countermeasure is increased to reduce the insertion period per control rod is disclosed in, for example, JP-A-60-13285.

However, in this conventional example, a large number of fuels with low reactivity must be arranged in the control cell. Therefore, there is a possibility that economical loss and restrictions on fuel arrangement may occur from the following viewpoints.

(1) In order to equalize the output of the low-reactivity fuel so as not to cause a large peaking in the output distribution of each fuel, it is necessary to place the low-reactivity fuel as close as possible to another high-reactivity fuel so that the linear power density or the like can be improved. This is advantageous for fuel thermal integrity, such as critical power. Therefore, if the low-reactivity fuel is insufficient, a fuel arrangement having excellent thermal characteristics cannot be provided.

(2) Since the low-reactivity fuel is insufficient and the high-reactivity fuel gathers too much, the margin for stopping the furnace is reduced.

(3) The normal fuel is a low-leakage core having a low-reactivity fuel disposed on the outermost periphery. However, if the low-reactivity fuel is insufficient, the low-reactivity fuel cannot be disposed sufficiently on the outermost periphery, resulting in a reaction of the core. The degree is reduced, resulting in an economic loss.

In view of the above, simply increasing the number of control cells by the conventional control cell method narrows the range of fuel loading pattern selection, which has a thermal and economical undesirable effect. Could happen. As a specific example, a case where the number of control cells is almost doubled from 13 to 25 will be described.

FIG. 7 shows 764 fuel bodies, 165 replacement bodies,
An example of a fuel loading pattern when 13 control cells are employed in a core of 185 control rods is shown. In the figure, reference numeral 101 denotes a control rod.

The fuel belonging to the control cell is C
_i (meaning of Control), shows a fuel which does not belong to the control cell N _i (meaning of Non-Control), the fuel located in the core outermost at P _i (meaning of Perirpheral), i is the furnace staying cycles Is shown.

The core shows only 1/4 of the second quadrant. The entire core is developed with this quarter core as rotationally symmetric. The fuel arrangement in this control cell core was determined as a typical procedure as follows.

(1) In order to construct a low-leakage core, the P ₅ fuel having the lowest reactivity is preferentially arranged at the outermost periphery of the core. As a result, P ₅ fuel is placed in all core outermost.

(2) The fuel of the fourth cycle is preferentially arranged in the thirteen control cells. As a result, 52 of the 168 fuels in the fourth cycle (13 × 4) are used for the control cell.

(3) The four fuels (non-control cells) around the control rods other than the control cells have N ₁ , N ₂ , N ₃ , N ₄ , N ₄ , which have a low average infinite multiplication factor and a good reactivity balance. N
₄ Arrange them around the control rod so that each one is a combination (balance cell). This is determined by the number of remaining N ₄ fuels (16-52 = 116), and
Of the cells (185−13 = 172), 116 become balance cells.

(4) The remaining fuel is 52 bodies of N ₁ , N ₂ , and N _3, each having a total of 156.
A cell having a slightly poorer reactivity balance (non-balanced cell) in which four bodies are selected from N ₁ , N ₂ , and N ₃ is thermally disadvantageous compared to the balanced cell.

FIG. 8 shows the same number of fuel bodies as FIG.
The figure shows a core with 764 bodies, 168 replacement bodies, and 185 control rods, with 25 control cells almost doubled. In the figure, reference numeral 111 is a control rod. The fuel is loaded according to the above procedures (1) to (4). In this case, the fuel belonging to the unbalanced cell increases to 300,
It is disadvantageous in terms of thermal characteristics and furnace stop margin as compared with the core of FIG.

Further, in the case of a system in which control cells are divided into groups as disclosed in Japanese Patent Application Laid-Open No. 60-13285, the number of control rods that can be used simultaneously is reduced due to the limitation of the number of fuels that can be arranged in the control cells (1 / group). However, there arises a problem that control rods cannot be used at the same time so that the excess reactivity can be sufficiently suppressed.

The present invention has been made in order to solve the above-mentioned problem, and it is possible to control a sufficient number of low-reactivity fuels even when the number of control cells is significantly increased.
It is an object of the present invention to provide a method of operating a nuclear reactor which can be used for other than a cell and can improve thermal characteristics and economy.

[0029]

According to the present invention, there is provided a fuel cell system in which some of the control cells have an infinite multiplication factor of four fuel assemblies whose infinite multiplication factor is one in an operation cycle and includes an infinite increase in core average in a combustion section before the start of the operation cycle. A high-reactivity fuel assembly that is larger than the multiplication factor and becomes smaller than the infinite multiplication factor of the core average in the subsequent combustion section, and a low-reactivity fuel assembly whose infinite multiplication factor is smaller than the infinite multiplication factor of the core average throughout one operation cycle. The control rod of this control cell is used only as an inserted state after the infinite multiplication factor of the high-reactivity fuel assembly becomes smaller than the infinite multiplication factor of the core average. It is characterized in that the entire bar is pulled out.

Some of the control cells have infinite multiplication factors of the four fuel assemblies that are larger than the infinite multiplication factor of the core average in the combustion section before the start of the operation cycle in one operation cycle. In the combustion section, a high reactivity fuel assembly that is larger than the infinite multiplication factor of the core average,
The control rods of this control cell have an infinite multiplication factor of less than the infinite multiplication factor of the core average throughout one operation cycle. The furnace power control is performed by operating only in the combustion section before the infinite multiplication factor becomes larger than the control rod, and in the subsequent combustion section, all the control rods are withdrawn.

[0031]

The magnitude of the output history effect of the control rod in the control cell is basically determined by the following two factors.

First, by burning the control rod in the inserted state, the side opposite to the control rod burns more, and the output of the highly reactive fuel rod on the control rod side, on which the combustion has not progressed when the control rod is withdrawn, is reduced. Local peaking caused by the increase. Since this magnitude depends on the magnitude of the asymmetry of combustion, it becomes almost proportional to the period during which the control rod is inserted.

The second is the output of the aggregate. Since the output of the fuel rod is proportional to the product of the local peaking coefficient and the output of the assembly, the output of the fuel rod when the control rod is pulled out of the assembly in the control rod history is proportional to the output of the assembly at the time of extraction. I do.

Therefore, in order to suppress the output rise due to the output history of the control rod in the control cell within a certain range, the length of the control rod insertion period and the output of the aggregate at the time of control rod withdrawal are fixed. It will be good if it is a range.

In the conventional control cell, the length of the control rod insertion period is not restricted, and the output of the aggregate is controlled so that the output history effect is not excessively increased even when the control rod is pulled out at an arbitrary time at an arbitrary time. It was assumed that only low-reactivity fuels were used at all times so as to be sufficiently low, which limited the number of fuel assemblies that could be applied to the control cell.

However, as described above, the output history effect of the control rod can be suppressed by limiting the reactivity during the operation when the control rod is in the inserted state and at the time when the control rod is fully pulled out.

From this fact, the infinite multiplication factor is larger than the core average in a certain section of one operation cycle, which is a fuel not used in the conventional control cell, but is infinitely increased in another section than the core average. As for control cell fuel, by limiting the control rod insertion period and limiting the time of full withdrawal to the period in which the infinite multiplication factor of the fuel is smaller than the core average, the fuel with a lower multiplication factor is also limited. It can be used.

One of such fuels is a new fuel. For example, in the case of a core having a small fuel exchange ratio, the initial reactivity of the burnable poison of the new fuel needs to be increased, and the infinite multiplication factor may be smaller than the core average in the first half of combustion. Another example is one in which the infinite multiplication factor at the beginning of the operation cycle is greater than the average infinite multiplication factor of the core and the infinite multiplication factor is less than or equal to the core average during the operation cycle.

If the fuel (high-reactivity fuel) is arranged adjacently in the control cell, the heat output of the high-reactivity fuel becomes too large in the high-reactivity section. (Reactivity fuel). Therefore, in order to keep the high-reactivity fuels from being adjacent to each other, it is necessary to arrange them at diagonal positions when two high-reactivity fuels are used. It is not desirable to arrange three or more fuels.

When these fuels are arranged in the control cell, the control rod insertion period is limited to a range where the infinite multiplication factor of the fuel is equal to or less than the core average, thereby reducing the power rise due to the control rod hysteresis effect. Is possible.

[0041]

【Example】

(First Embodiment) A first embodiment will be described with reference to FIGS. Figure 1 shows 764 fuel bodies and 136 replacement bodies.
Control rods in 185 cores
An example of a fuel loading pattern of a core employing 25 reactors is shown.

The fuel belonging to the control cell is C
_i (meaning of Control), shows a fuel which does not belong to the control cell N _i (meaning of Non-Control), the fuel located in the core outermost at P _i (meaning of Perirpheral), i is the furnace staying cycles Is shown.

The core shows only the second quadrant of 1/4 of the whole, and the whole core is developed with this 1/4 core being rotationally symmetric. These control cells are divided into groups 1 to 7, and the same group of control cells are provided with a combination of fuels having the same residence time in the furnace.

[0044] Place 4 body of the C ₅ fuel for group 1, C ₄ 2 body in the group 2, C ₅ 2 bodies are arranged, C ₄ 2 body is disposed at diagonal positions. Group 3 and Group 7
Has _one C ₁ body and three C ₅ bodies, and group 5 has C
₁ two bodies, C ₅ two bodies are arranged. C ₁ 2 body is disposed at diagonal positions, C ₄ 4 body to Group 4 and Group 6,
C ₅ 1-body is arranged.

The number of fuel exchange units per cycle is 136. 136 units are loaded in the furnace from 1 cycle stay fuel to 5 cycle stay fuel, and 84 units are 6 cycle stay fuel. Becomes Fuel disposed on other than the control cell N ₁ and N ₁ and N ₂ and N ₂ are arranged so as not directly adjacent to each other. The fuel surrounding the control rods 8 at positions other than the control cells is arranged so that the average core residence time of the four fuel rods is 2.75 or more.

FIG. 2 shows the infinite multiplication factor change of the fuel loaded in the core, and the fuel is burned in the furnace for a period up to the sixth cycle. In the usable section A indicated by the arrow, the fuel in the first cycle is smaller than the infinite multiplication factor (about 1.05) of the core average. In the usable section B indicated by the arrow, the fuel in the fourth cycle is the infinite multiplication factor of the core average (about 1.0%).
5) It is smaller.

FIG. 3 shows the periods during which the control rods surrounded by the control cells of groups 1 to 7 are used. During operation of the control rod, only the control rod belonging to the control cell is
The control rods of the cell groups 3, 5, and 7 are used during the operation period corresponding to the section A, and the control rods are pulled out otherwise. The control rods of groups 2, 4, and 6 are used in the latter half of the operation period, and the control rods are fully withdrawn only in the operation period corresponding to section B.

Next, the operation and effect of the first embodiment will be described. Since the infinite multiplication factor of the fuel in section A is lower than the infinite multiplication factor of the core average for the fuel having the in-reactor cycle period of one cycle, the C ₁ fuel arranged in the control cell groups 3, 5, and 7 is used. The infinite multiplication factor becomes lower than the core average in the first half of the operation cycle.

In the case of the fuel whose in-furnace cycle period is 4 cycles, the infinite multiplication factor of the fuel in section B is lower than the infinite multiplication factor of the core average, and the control cell group 2,
The infinite multiplication factors of the C ₄ fuels arranged at 4, 6 are lower than the core average in the latter half of the operation cycle.

Therefore, by limiting the control rod insertion period to only this period, it is possible to suppress an increase in output when the control rod is pulled out. Further, in any of the control cells, the high-reactivity fuels of the first cycle fuel and the fourth cycle fuel are not arranged adjacent to each other, and the output does not become excessively large in any operation period.
In groups 2 and 5 in which two first-cycle fuels or fourth-cycle fuels are arranged, the two high-reactivity fuels are arranged diagonally, and the output does not become excessively large.

The P ₆ fuel disposed at the outermost periphery of the core is the most burned fuel and has the smallest infinite multiplication factor. By disposing the P ₆ fuel in the core periphery, the relative core center to place the high reactive fuel, a so-called low leakage core. As a result, the same heat output can be generated with a fuel with a lower enrichment than when the low-leakage core is not used, and the fuel economy is improved.

The fuel assemblies belonging to the control rod cells (non-control cells) surrounding the control rods other than the control cells are not controlled so that the infinite multiplication factor of the non-control cell average does not become significantly larger than the infinite multiplication factor of the core average. The cells are arranged so that the average number of in-furnace cycles in the furnace exceeds 2.5. For this reason, the reactivity does not specifically increase when the control rod is pulled out when the furnace is stopped.

Since it is considered that two or more fuels of the first cycle fuel or the same fuel of the second cycle are not arranged in the same uncontrolled cell, the output of the assembly does not become excessive during the output operation.

(Second Embodiment) A second embodiment will be described with reference to FIGS. In this embodiment, the number of fuel bodies is 764.
This shows an example of a fuel loading pattern of a core employing 25 control cells in a core having 168 bodies and 185 replacement rods and 185 control rods, and the symbols have the same meaning as in the first embodiment.

The control cells are divided into groups 21 to 27, and the same group of control cells is provided with a combination of fuels having the same period of stay in the furnace. The group 21,23,24,27 arranged 4 body to C ₄ fuel, C ₃ 2 body in the group 22, 25, 26, C ₃ 2 body C ₄ 2 bodies are disposed are arranged in diagonal positions You.

The number of exchanged fuels per cycle is 168. 168 fuels are loaded in the furnace from 1 cycle staying fuel to 4 cycle staying fuel, and 92 fuels are spent in 5 cycle staying fuel. Becomes P ₅ fuel is the least reactive fuel are arranged at the outermost periphery of the core, a so-called low leakage core. In the figure, reference numeral 28 is a control rod.

FIG. 5 shows an infinite multiplication factor change of the fuel loaded in the core, and the fuel is burned in the furnace for a maximum period of up to the fifth cycle. In the usable section C indicated by the arrow, the fuel in the third cycle is smaller than the infinite multiplication factor (about 1.05) of the core average.

In operation of the control rod during operation, only the control rod belonging to the control cell is used exclusively in the inserted state. The control rods of the control cell groups 22, 25, and 26 are operated only in the second half of the cycle, which is the period corresponding to the section C, and are completely removed in other periods. The control rods of the other groups 21, 23, 24, and 27 are used without limitation of the use period.

The infinite multiplication factor of the fuel of this embodiment is lower than the infinite multiplication factor of the core average in the middle of the third cycle. The hysteresis effect of the control rod can be sufficiently suppressed by using the control rod limitedly.

In this embodiment, the third cycle fuel is disposed in the control cells (eight in total) of the groups 22, 25 and 26.
It is not necessary to arrange the third cycle fuel at the cell position. For example, the fuels of the groups 23, 24, and 27 may be exchanged so as not to lose the symmetry.

Although the groups 23, 24, and 27 are all composed of only the fuel in the fourth cycle, the arrangement can be changed so that the fuel in the third cycle is arranged in any of these control cells.

The same type of fuel is usually placed in the 21 control cells at the center of the core in consideration of the 1/4 symmetry, but if the symmetry is ignored, the fuel in the third cycle is placed in this control cell. It is also possible to arrange them within a range of two or less and at diagonal positions.

Although the embodiment of the present invention has been described on the assumption of 1/4 symmetry, it goes without saying that the present invention can be applied regardless of the presence or absence of symmetry. Further, in the embodiment, an example of 25 control cells has been described, but it is needless to say that the present invention can be applied to control cells other than 25 control cells.

Further, for the least reactive fuel,
In the embodiment, an example is shown in which a low-leakage core is disposed at the outermost periphery of the core, but when the low-leakage core is not used, the fuel having the lowest reactivity is also applied to the control cell and the fuel is disposed by the method of the present invention. It goes without saying that you can do it.

[0065]

According to the present invention, even when the number of control cells is greatly increased, a sufficient number of low-reactivity fuels can be used for other than the control cells, and as a result, the thermal characteristics and Economic efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a fuel arrangement diagram of a 1/4 reactor core for explaining a first embodiment of a method for operating a nuclear reactor according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an infinite multiplication factor of fuel and a control cell control rod use period in FIG.

FIG. 3 is an explanatory view showing a control cell control rod use period during one operation cycle in FIG. 1;

FIG. 4 is a fuel arrangement diagram of a 1/4 reactor core for describing a second embodiment of the method for operating a nuclear reactor according to the present invention.

FIG. 5 is a characteristic diagram showing a relationship between the infinite multiplication factor of fuel and a control cell control rod use period in FIG. 4;

6A and 6B are explanatory diagrams showing an infinite multiplication factor of fuel used in a control cell of a conventional example. FIG. 6A is an example of fuel for a 4-batch core, and FIG. 6B is an example of fuel for a 5-batch core. so,
(C) shows an example of fuel for a 6-batch core.

FIG. 7 is a fuel arrangement diagram of a 1/4 reactor core when 13 control cells are used among the control cells of the conventional example.

FIG. 8 is a fuel arrangement diagram of a 1/4 reactor core when 25 control cells are used among the control cells of the conventional example.

[Explanation of symbols]

1 to 7: control cells of the first embodiment, 8: control rods, 21 to 27: control cells of the second embodiment, 28 ...
Control rod, 101… Control rod, 111… Control rod.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 7/08 G21C 7/00 G21C 5/00

Claims (2)

(57) [Claims] 1. A control cell according to claim 1, wherein the infinite multiplication factor of the four fuel assemblies is greater than the infinite multiplication factor of the core average in a combustion section of the one operating cycle before including the beginning of the operating cycle. In the combustion section, it is composed of a high reactivity fuel assembly that is smaller than the infinite multiplication factor of the core average, and a low reactivity fuel assembly whose infinite multiplication factor is smaller than the infinite multiplication factor of the core average throughout one operation cycle.
The control rods of this control cell shall be used exclusively after the infinite multiplication factor of the high reactivity fuel assembly becomes smaller than the infinite multiplication factor of the core average, and the control rods shall be completely withdrawn before the combustion section. A method for operating a nuclear reactor, comprising: 2. A control cell according to claim 1, wherein the infinite multiplication factor of the four fuel assemblies is larger than the infinite multiplication factor of the core average in a combustion section of the one operating cycle before including the beginning of the operating cycle. In the combustion section, it is composed of a high reactivity fuel assembly that is larger than the infinite multiplication factor of the core average and a low reactivity fuel assembly whose infinite multiplication factor is smaller than the infinite multiplication factor of the core average throughout one operation cycle.
The control rod of this control cell operates the furnace only in the combustion section before the infinite multiplication factor of the high reactivity fuel assembly becomes larger than the infinite multiplication factor of the core average, and controls the furnace power.
A method of operating a nuclear reactor, wherein control rods are completely withdrawn in a subsequent combustion section.