JPH02201291A - Operating method of reactor - Google Patents

Abstract

PURPOSE:To execute reuse safely by setting the direction of the face of a fuel assembly so that a bend of a channel box toward the reactor control rod side may not exceed a prescribed value when the channel box wherein the combustion of fuel is ended is reused. CONSTITUTION:A plurality units are formed by surrounding a reactor control rod 14 by channel boxes 15 each of which contains four fuel assemblies 13. The units in a plurality are sorted into a peripheral part region 11 and a central part region 12. While the central part 12 is subjected to substantially the same irradiations of fast neutrons from all quarters and deformation hardly occurs therein, large deformation takes place in the peripheral part 11 due to a difference between the irradiations of the fast neutrons. Surfaces 3 and 4 containing a channel fastener 15 out of the surfaces of numbers 1 to 4 of the box 15 of each of units A to D on the outermost periphery and (a), (b), (e) to (h) in the second array are given numeric values being proportional to a time of reuse in such a manner that for instance, + or -1 is given to those on the outermost periphery and + or -0.5 to those in the second array, and the channel boxes are disposed so that the total of these values do not exceed 2. According to this constitution, the channel boxes are reused safely.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a method of operating a nuclear reactor, and particularly to a method of operating a nuclear reactor in which a channel box of a fuel assembly can be reused. Regarding driving methods.

(Prior Art) A large number of fuel assemblies 1 are regularly arranged and loaded in the core of a boiling water reactor as shown in FIG. (Furthermore, in Fig. 11, the fuel assembly 1 is shown in the fourth row from the top of the drawing, but the parts below it are omitted. ). In this way, the combination of four fuel assemblies 1 and one reactor control rod 2 is called a cell, and the core fuel consists of fuel assemblies in cells and a single fuel assembly in a part of the outermost periphery of the core. It is made up of.

As shown in FIG. 12, the fuel assembly 1 has a large number of fuel rods 3 arranged regularly, the upper and lower ends of which are connected by an upper tie plate 4 and a lower tie plate 5, respectively, and a spacer 6 in the middle. , and these are surrounded by a channel box 7.

The fuel assembly 1 loaded in the reactor core is used for 3 to 4 years and after reaching the end of its life, it is taken out as spent fuel. The fuel assembly 1 taken out from the reactor core is cooled in water in a fuel pool until the heat generated by the atomic decay of the fission products is reduced to a certain level, and then the channel box 7 is removed and sent to a reprocessing process.

(Problem to be Solved by the Invention) By the way, the removed channel box 7 is currently being disposed of as waste, but a huge amount of the channel box 7 is discarded due to the operation of a nuclear reactor. Moreover, the cost required for disposal is also enormous.

Therefore, if the channel box 7 that has been used once as the fuel assembly 1 can be reused by attaching it to a new fuel bundle, it can significantly contribute to the reduction of waste and the cost of nuclear power generation.

However, the channel box 7 is made of a zirconium alloy, and is subjected to a large amount of neutron irradiation during use, resulting in the following deformation. That is, a bulge occurs in the cross-sectional direction of the channel box 7 due to creep deformation due to the pressure difference inside and outside the channel box 7, and elongation occurs in the longitudinal direction. Furthermore, if the two opposing surfaces of the channel box 7 have different amounts of elongation, the channel box 7 will bend and deform.

If the channel box 7 is reused, it is easily predicted that the amount of bending deformation will increase, which is considered to be an important problem in terms of nuclear reactor safety.

The present invention has been made in consideration of the above circumstances, and addresses the problem of bending and deformation of the channel box that is expected when the channel box is reused. The purpose is to provide driving instructions.

[Structure of the invention]

(Means for Solving the Problems) A method for operating a nuclear reactor according to the first invention is a method for operating a nuclear reactor in which a channel box of a fuel assembly is reused after combustion of the fuel is finished and the fuel assembly is dismantled. In the operating method, the placement positions of fuel assemblies in the reactor core are divided into a peripheral area and a central area, and reactor control of channel boxes that occurs when fuel assemblies are loaded in the placement positions of each area. A value corresponding to the amount of bending toward the rod side is given to the target surface of the channel box, and the fuel assembly is arranged and operated so that the total value over the period of use of the channel box does not exceed a separately determined allowable value. It is.

A method of operating a nuclear reactor according to the second invention of the present invention is a method of operating a nuclear reactor in which a channel box of a fuel assembly is used after combustion of the fuel is finished and the fuel assembly is dismantled.
In a unit cell consisting of four fuel assemblies and a reactor control rod, each fuel assembly is arranged and operated so that the fuel assemblies equipped with reusable channel boxes are not placed next to each other. It is something to do.

(Operation) The first invention of this case is a channel box nuclear reactor II.
A value corresponding to the amount of bending toward the III rod side is given to the target surface of the channel box, and the fuel assembly is arranged so that the total value over the period of use of each channel box does not exceed the separately determined allowable value. , the amount of bending deformation of the channel box can be suppressed within a safe range for nuclear reactor operation, and even when the channel box is reused, it can be used safely.

The second invention of the present invention operates by arranging each fuel assembly in a unit cell so that the fuel assemblies equipped with channel boxes to be reused are not placed next to each other, so that the channel box bends and deforms. Even if this occurs, interference between the channel box and the reactor II Ill rod can be prevented, and even when the channel box is reused, it can be used safely.

(Example) An example of the method for operating a nuclear reactor according to the first invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the arrangement positions of fuel assemblies in the core. In this figure, the core is indicated by diagonal lines in the peripheral region 11.
and a central region 12, reference numeral 13 indicates a fuel assembly, and reference numeral 14 indicates a nuclear reactor 1111all rod.

By the way, in the outer periphery of a nuclear reactor core, the fast neutron flux is larger on the core center side than on the outer periphery side of the core. That is, there is a gradient in the fast neutron flux at the core end face. Therefore, a channel box placed on such an end face produces a difference in fast neutrons 1) on both sides.

Furthermore, the elongation of the zirconium alloy, which is the material of the channel box, due to irradiation shows dependence on the amount of fast neutron irradiation as shown in FIG. Therefore, in the channel box at the outer periphery of the core, the amount of longitudinal elongation differs between the channel surfaces, as shown in Figures 3 (A> and (B).
), the high dose of fast neutron irradiation causes a bending deformation in which the surface with greater elongation becomes convex. This bending deformation increases as the difference in fast neutron irradiation amount increases.

FIG. 4 is a diagram showing the relationship between the position in the core periphery and the amount of fast neutron irradiation. As shown in this figure, in the periphery of the reactor, up to about the third row from the outermost periphery, fast neutrons between the surface of the channel box facing the core and the surface facing the outermost periphery The difference in irradiation amount is large, and at loading positions further toward the center, there is almost no such difference. Therefore, a large bend occurs in the first row of the outermost periphery, a bend of approximately 1/2 of that bend occurs in the second row, and almost no bend occurs in the center. Therefore, in this embodiment, the peripheral area 11 is defined as the range of fuel assembly loading positions from the outermost periphery to the second row, and the other positions are defined as the central area [12].

Further, the direction in which the bending deformation occurs differs depending on the arrangement position, and the bending deformation occurs in the direction indicated by the arrow in FIG. Therefore, as shown in FIG. 6, among the fuel assembly arrangement positions in the peripheral region 11, A, B, C, D,
, a in the second row from the outermost circumference.

b, e, f, g, and h, number each side of the channel box 15 as shown in FIG.
Quantify as shown in the figure.

In this case, the channel box 15 is arranged so that the two surfaces (the third surface and the fourth surface) sandwiching the channel fastener 16 always face the reactor control rod 14 side, and the third surface and the M4 surface are quantified. will be carried out.

Then, using such arrangement positions and numerical values, numerical values are added to each of the third and fourth surfaces of the channel box 15 throughout the period of use, and the channel box 15 is used so that the total does not exceed +2. This +2 is an allowable value, and the channel box 15
This numerical value represents the upper limit of the amount of bending deformation that may cause contact between the reactor control rod 14 and the reactor control rod 14 to interfere with the direction of the reactor control rod. Therefore, by keeping the total value below +2, channel box 15 and reactor control rod 1
Interference with 4 can be prevented.

For example, when it is attached to the first fuel assembly 13, if it moves from center → e-+A → C, the third surface will be +1
．． 5. The fourth surface is +1, so when reusing it, if you arrange it so that the third surface does not exceed +0.5 and the fourth surface does not exceed +1, the amount of bending deformation will be reduced between the channel box 15 and the reactor control rod. There is no possibility that interference will occur to the extent that there will be interference with 14.

In this way, according to the above embodiment, even after the fuel life of the fuel assembly 13 has ended and the fuel has been dismantled and removed, the channel box 15 is reinstalled with new fuel and reused.
Channel box 15 can be used safely.

In the above embodiment, the peripheral region 11 of the core was set to the second row from the outermost side, but it may be set to the first row depending on the size of the core, that is, the total number of fuel assemblies. Double-headed area 11.
All you have to do is decide on a range of 12. Furthermore, the numerical values and allowable numerical values for each arrangement position are not limited to those in the above embodiments, and may be appropriately determined in consideration of the amount of fast neutron irradiation.

Next, an embodiment of the method for operating a nuclear reactor according to the second invention will be described with reference to the accompanying drawings.

The life of the channel box 15 depends on the reactor I due to deformation.
Since it is determined by interference with the I m rod 14, it cannot be reused if there is a possibility that it will interfere with the reactor control rod 14 during reuse. As shown in FIG. 9, this interference occurs between one of the reactor control rods 1214a and the two channel boxes 1 facing each other with it in between.
This can be determined using a 5-plane deformer. Now 114
Focusing on a and the left and right channel boxes 15 that sandwich it, even if one channel box 15 is deformed, if the other channel box 15 is not deformed, there will be no hindrance to the insertion of the reactor control rods 14. I can see that there isn't. That is, the modification of the channel box 15 is as follows:
Since it is proportional to the total burnup of the fuel assembly 13 in which it was installed, the channel box 15 being reused is placed on one side of the l114a of the reactor control rod 14, and the channel box 15 before reuse is placed on the other side. By arranging the box 15, m1 of the channel box 15 and the reactor control rod 14 is
Interference with 4a can be prevented.

Therefore, in this embodiment, as shown in FIG. 10, a channel box 15 is arranged to operate the nuclear reactor. That is, among the fuel assembly placement positions, those marked with an 8 are the placement positions of the fuel assembly 13 with the channel box 15 installed during reuse, and those marked with B are the placement positions of the fuel assembly 13 before reuse. Fuel assembly 13 with channel box installed
This is the placement position.

After the initially installed fuel assembly 13 has completed its fuel life and the fuel has been removed from the channel box 15,
It is attached to a new fuel bundle and reused as the fuel assembly 13, but in this example, as shown in FIG.
A reusable channel box 15 is installed in a unit cell consisting of four fuel assemblies 13 and a reactor control rod 14.
The nuclear reactor is operated by arranging the fuel assemblies 13 such that the fuel assemblies 13 equipped with the fuel assemblies 13 are not adjacent to each other.

In this way, according to the above embodiment, one of the reactor control rods 14
By limiting the channel boxes 15 attached to the left and right fuel assemblies 13 that sandwich the two fuel assemblies 1114a to those that are reused and those that have not yet been reused, reuse on the left and right that may occur if they are placed completely randomly. Cases where channel boxes are placed (when the sum of left and right transformations is large)
After the fuel life of the fuel assembly 13 has ended and the fuel has been dismantled and removed, even if the channel box 15 is reinstalled with new fuel and reused, the channel box 15. can be used safely.

〔Effect of the invention〕

The operating method of the nuclear reactor according to the present invention is such that the arrangement position of the fuel assemblies in the reactor core is divided into a peripheral region and a central region, and the fuel assemblies are loaded in the arrangement positions of each region. A value corresponding to the amount of bending of the channel box toward the reactor control rod side that occurs during the fuel assembly is given to the target surface of the channel box, and the fuel assembly is adjusted so that the total value over the period of use of the channel box does not exceed the separately determined allowable value. In addition, within a unit cell consisting of four fuel assemblies and reactor control rods, the fuel assemblies with channel boxes to be reused are arranged so that they are not placed next to each other. Since the fuel assembly is placed and operated, the channel box can be used safely even if the fuel assembly's fuel life has ended and the fuel has been dismantled and removed, and then the channel box is reinstalled with new fuel and reused. It has the excellent effect of being able to

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the reactor core for explaining one embodiment of the method of operating a nuclear reactor according to the first invention of the present invention, and Fig. 2 is a cross-sectional view of the reactor core for explaining an embodiment of the method of operating a nuclear reactor according to the first invention. Characteristic diagrams showing the relationship between elongation and fast neutron irradiation dose. Figures 3 (A) and (B) are diagrams showing the state of bending of the channel box around the core in the above example, and Figure 4 is a diagram showing the state of bending of the channel box in the core periphery in the above example. A diagram showing the relationship between the position in the core periphery and the amount of fast neutron irradiation, FIG. 5 is a diagram showing the bending direction of the channel box in the core periphery in the above embodiment, and FIG. 6 is a diagram showing the arrangement of fuel assemblies in the above embodiment. Figure 7 is a diagram showing the numbering of each surface of the channel box in the above embodiment, and Figure 8 is a diagram showing the bending deformation that occurs on the target surface of the channel box at each placement position in the above embodiment. A diagram quantifying the direction and amount of bending deformation, and FIG. 9 is an arrangement diagram showing the arrangement of fuel assemblies in the imperial cell for explaining one embodiment of the method of operating a nuclear reactor according to the second invention of the present case. , FIG. 10 is a layout view showing the above embodiment, FIG. 11 is a sectional view showing an example of a conventional core cross section, and FIG. 12 is a perspective view showing a general fuel assembly. 11... Peripheral region, 12... Central region, 13.
...Fuel assembly, 14...Reactor control rod, 14a...
・Wing, 15...Channel box, 16...Channel fastener. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 1 Figure 1O Figure 11

Claims (1)

[Claims] 1. In a method of operating a nuclear reactor in which a channel box of a fuel assembly is reused after fuel combustion is completed and the fuel assembly is dismantled, In addition to dividing the channel box into a central region and a central region, the target surface of the channel box is calculated based on the amount of bending of the channel box toward the reactor control rod side that occurs when fuel assemblies are loaded in the placement position of each region. A method of operating a nuclear reactor, characterized by arranging and operating fuel assemblies so that the total value over the period of use of the channel box does not exceed a separately determined allowable value. 2. In a nuclear reactor operation method in which the channel box of a fuel assembly is used after fuel combustion is finished and the fuel assembly is dismantled, the channel box is placed inside a unit cell consisting of four fuel assemblies and a reactor control rod. A method of operating a nuclear reactor, comprising arranging and operating each fuel assembly so that fuel assemblies equipped with channel boxes to be reused are not arranged next to each other.