JP2008145286A - Boiling-water reactor core and boiling-water reactor core construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boiling-water reactor core achieving elongation of the operation period and higher enrichment of fuel, by appropriately implementing operations of a boiling water reactor power plant, using a reduced number of control cells. <P>SOLUTION: The boiling water reactor core is constituted to include a step of classifying control-cell constituting fuels into a first candidate fuel to a third candidate fuel, according to the reactivity, with the loading position in the core and the residence time in the core; a step of making the deciding on whether the control cell can be constituted of the first candidate fuel, a step of making decision on whether the insertion time of a control rod is not shorter than a specified period and the step of constituting the control cell by using the first candidate fuel to the third candidate fuel, according to an excess reactivity pattern, when the constitution of the control cell is decided as being in a step of making the decision on whether the control cell can be constituted of the first candidate fuel, or when the control rod insertion time is decided as being not shorter than the specified period, in a step of making the decision on whether the control rod insertion time is shorter than the specified period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a boiling water reactor core and a configuration method thereof, and more particularly to a boiling water reactor core and a configuration method thereof that can cope with a high enrichment of fuel and a prolonged operation period.

  In the boiling water nuclear power plant, the reactivity is controlled by operating the control rod insertion ratio and adjusting the core flow rate. Here, the control rod insertion ratio is adjusted step by step with respect to the change in reactivity, and while the control rod is inserted at a certain control rod insertion ratio, it is operated while maintaining a constant reactivity by adjusting the core flow rate. The

  The change in the reactivity with respect to the operation period in a state where the thermal power of the core and the flow rate are rated and the control rod is pulled out is referred to as excess reactivity, which is determined by the fuel loaded in the reactor. About a quarter of the fuel loaded in the reactor is replaced after about one year of operation, but flammability (over time) neutron absorber is added to the new fuel that has been replaced. Therefore, after the start of use, the reactivity tends to increase as the combustible neutron absorber burns, and the reactivity decreases in the absence of the combustible neutron absorber. On the other hand, there is no combustible neutron absorbing material except for new fuel, and the reactivity will decrease. By combining these fuels, it is possible to flatten the excess reactivity during the operation period, but the excess reactivity starts to decrease after the second half of the operation for about one year. Furthermore, as the enrichment of uranium 235 in the fuel increases, the absolute value of this excess reactivity also increases.

  In addition, if a control rod at the same position is inserted for a long period (about 3 months or more) in a boiling water nuclear power plant, the fuel rods on the control rod side of the unit cell consisting of four fuels around the control rod will remain unburned. Since neutrons are less likely to be decelerated and plutonium is likely to accumulate, the output tends to increase locally when the control rod is pulled out (control rod history effect). Once the output of the reactor was reduced, it was necessary to gradually increase the output, causing a loss of power generation.

  For this reason, in the prior art, the operation of changing the insertion position of the control rod, that is, the control rod insertion ratio, is performed about once every three months.

  In addition, in the conventional technology, fuel that has been loaded in the core and advanced in the 3rd to 4th cycles is placed in a unit cell (control cell) where control rods that are mainly operated and inserted during operation are placed. is doing. Therefore, even if the output increases locally due to the operation of the control rod, the reactivity of the fuel in the control cell is low. Therefore, the absolute value of the maximum output (line output per fuel rod per fuel length) Density) is suppressed.

  In this way, the reactor core is designed to minimize the amount of decrease in reactor power during control rod operation. By this method, operation efficiency is improved by using a control rod at a control cell position for an operation of a cycle of about one year. In addition, a cycle means the period after a boiling water nuclear power plant complete | finishes a periodic inspection and starts an operation | movement until it stops operation in order to enter the next periodic inspection.

  Furthermore, as the fuel constituting the control cell, since the material of the fuel deteriorates when the fuel stays in the furnace for a long time, the output is at a relatively high position in the previous operation, and the stay in the furnace is When the control rod is pulled out in the cycle, the fuel needs to be within a specified number of months, and in addition, the fuel needs to have a reduced reactivity.

  On the other hand, recently, in order to improve the economic efficiency of boiling water nuclear power plants, the uranium 235 enrichment of fuel has been increased to reduce the number of new fuels (number of batches) used in one fuel change, or The direction of extending the operation period and increasing the equipment utilization rate has become prominent.

  However, if the operation period is the same, increasing the uranium 235 enrichment of the fuel will reduce the number of batch bodies, increase the excess reactivity, and increase the number of control rods used in the operation. It becomes a situation where there is not enough fuel required.

  Further, if the current operation period of about one year is extended from about one and a half years to two years, the amount of increase in the linear output density due to the control rod history effect increases, resulting in a loss of fuel soundness.

Patent Document 1 as a prior art document shows a nuclear reactor core in which a low-reactivity fuel assembly is arranged in a control cell in a boiling water reactor. It cannot be applied to a core that employs
JP-A-7-209460

  As described above, in recent years, there has been a demand for higher fuel enrichment and longer operation period in order to improve operation efficiency. However, in a conventional boiling water reactor core configuration, it is arranged in a control cell. Because it is difficult to operate the fuel and it is difficult to cope with the local output improvement due to the control rod history effect, it has not been possible to cope with the high enrichment of fuel and the prolonged operation period.

  The present invention has been made in view of the above circumstances, and a boiling water reactor core that can cope with higher fuel concentration and longer operating period by appropriately operating the fuel disposed in the control cell. It is an object of the present invention to provide a configuration method thereof.

  Another object of the present invention is to provide a boiling water reactor core and a method for configuring the same, in which a control cell configuration method is mechanically determined in accordance with the operating conditions of the boiling water nuclear power plant and the type of fuel constituting the core. To do. .

  Another object of the present invention is to provide a boiling water reactor core using a control cell according to a surplus reactivity pattern, which is a basic reactivity of a boiling water nuclear power plant, and a method of configuring the same. is there.

  Another object of the present invention is to provide a boiling water reactor core and a method for constructing the same, in which fuel that has been loaded at a relatively low output in the previous operation can also be used as a control cell.

  In order to solve the above-described problems, the method for configuring a boiling water reactor core according to the present invention classifies the control cell constituent fuels as candidate 1 fuel to candidate 3 fuel according to the reactivity, the load position inside the reactor, and the residence time in the reactor. Determining whether the control cell can be configured with the candidate 1 fuel, determining whether the control rod insertion period is equal to or longer than a predetermined period, and configuring the control cell with the candidate 1 fuel. When it is determined that it is impossible in the step of determining whether it is possible or when it is determined that the control rod insertion period is longer than a certain period in the step of determining whether the control rod insertion period is longer than a certain period, according to the surplus reactivity pattern And a step of configuring a control cell from the candidate 1 fuel to the candidate 3 fuel.

  The present invention provides a boiling water reactor core capable of efficient operation even with high enrichment of fuel uranium 235 and prolonged operation period, and a method of operating the same, with the above-described characteristic configuration. It becomes possible.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a top view of fuel arranged in a reactor core of a boiling water nuclear power plant as a symbol for each loading cycle. A combination of four fuels centering on the control rod is called a unit cell (hereinafter simply referred to as “cell”), and a plurality of cells are arranged in the core. In particular, a cell having a control rod inserted into a nuclear reactor during rated power operation is called a control cell.

  When the control rod is inserted, the fuel rod on the control rod side of the fuel assembly remains unburned, so that the linear output density increases when the control rod is pulled out. In order to suppress this, the fuel loaded into the control cell, that is, the control cell fuel uses a fuel with a lowered reactivity, but due to the fuel material, the number of months spent in the furnace at the time of pulling out the control rod is about 4 months. There is a limit of less than a year. The fuel outside the circumferential broken line in FIG. 1 is loaded at a position where the output is relatively low, but the fuel loaded at the position where the output is low during the previous cycle is used as the control cell fuel. Then, since the fuel does not experience high output, it is not suitable as a control cell fuel.

  Based on the above consideration, the configuration procedure of the control cell corresponding to the high enrichment of fuel and the prolonged operation period in the future boiling water nuclear power plant will be described with reference to FIG.

  In step (1), prior to the start of operation, a replacement core design for determining the fuel arrangement as shown in FIG. 1 is started. This design determines the control cell fuel composition.

  In step (2), the fuel that can constitute the control cell is selected and the candidates are divided into three.

  Candidate 1 fuel is a fuel that has a low reactivity and the stay in the furnace is less than the specified number of months when the control rod is pulled out in this cycle, and is loaded at the high power position in the previous cycle, that is, inside the broken line shown in FIG. Yes, it is the best fuel for the control cell.

  Candidate 2 fuel has low reactivity and the number of months staying in the furnace when the control rod is withdrawn in the current cycle is within the specified number of months, but was loaded in the low power position in the previous cycle, that is, outside the broken line shown in FIG. It is a fuel that has not experienced high output.

  Candidate 3 fuels are new fuels in the previous cycle, and the reactivity is high in the first half of the operation in the current cycle, but the reactivity decreases in the second half of the operation. Is the fuel.

  By classifying the fuel in this way, it becomes possible to select the control cell fuel according to the purpose when setting the control cell later.

  In step (3), the number of control rods inserted from the start of operation to the end of operation is confirmed and set. As a result, the number of control cells required is grasped in advance.

  If the control cell at the control rod insertion position can be configured with the candidate 1 fuel in step (4) and the operation ends in about one year (hereinafter referred to as “normal operation”) in step (5), the conventional technology Thus, the control cell can be configured, and the present invention is not applicable.

  If the control cell fuel cannot be configured with candidate 1 fuel in step (4), the control cell fuel configuration procedure corresponding to the excess reactivity in step (6) is applied.

  This is the basic reactivity of the reactor. When the core thermal power and the core flow rate are set to the rated values without inserting the control rod, the pattern of the change in the excess reactivity, which is the change with the operating period of the reactivity at the time. This is a procedure for determining the structure of the control cell fuel according to the above.

  FIG. 3 shows the change pattern of the excess reactivity. As shown by the solid line, the surplus reactivity pattern 1 is a pattern in which the reactivity increases from the beginning of operation to the middle and decreases toward the end.

  The surplus reactivity pattern 2 is a pattern in which the reactivity decreases monotonously from the beginning to the end of the operation as indicated by the broken line.

The surplus reactivity pattern 3 is a pattern in which the reactivity is substantially constant from the initial stage of operation to the middle period and the reactivity decreases from the latter stage to the latter stage, as indicated by a one-dot chain line. This surplus reactivity pattern changes depending on the type of fuel constituting the core and the staying period of the fuel. FIG. 4 is a control cell configuration diagram when the surplus reactivity is pattern 1 during normal operation, and FIG. ) Is six control rod pattern diagrams (CR-1 to CR-6) represented by a 1/4 core, FIG. 4 (b) is an operation pattern diagram showing the insertion period of each control rod pattern, and FIG. c) is a core configuration diagram to which the numbers of candidate fuels constituting the control cell are attached. In FIGS. 5 to 9 described below, since (a) to (c) are the same as those in FIG. 4, detailed description thereof will be omitted.

  As shown in FIG. 4, in the case of the surplus reactivity pattern 1, the control cell at the control rod position to be inserted from the initial stage to the end stage of the operation is constituted by the fuel of the candidate 1, and the surplus reactivity increases and is additionally inserted. The position of the control rod is composed of candidate 2 fuel. As a result, the candidate 2 fuel experiences high output because it experiences operation with the control rods pulled out before the control rods are inserted. It can be optimized as a cell component fuel.

  In the case of the surplus reactivity pattern 2, as shown in FIG. 5, the control cell at the control rod position to be inserted from the beginning to the end of the operation is composed of the candidate 1 fuel, and the control rod position to be inserted within the initial three months of the cycle. The candidate 2 fuel is used for the control cell. When the control rod insertion period is within 3 months, the control rod history effect is small, and even if the fuel does not experience a high output in the previous operation, the soundness of the fuel is ensured.

  In the case of the surplus reactivity pattern 3, as shown in FIG. 6, the control cell at the control rod position to be inserted from the initial stage to the final stage of the operation is composed of the candidate 1 fuel, and if the control cell is still insufficient, the second half of the operation The control cell in the position where it is withdrawn early is composed of candidate 2 fuel, but the control cell in this position does not insert the control rod for the first month of operation and the control rod is in a position where the output is relatively low except for the control cell. Insert. By allowing candidate 2 fuel to experience high output without control rods for about one month, candidate 2 fuel can be used under the same conditions as candidate 1 fuel, so one month after the start of operation, other than the control cell The control rod is pulled out and inserted into the control cell position of the candidate 2 fuel position to operate. If there are not enough control rods even if the candidate 2 fuel is used, the control rods with low output are also inserted while being replaced at intervals of 3 months, so that the fuel is sound and efficient. Driving is possible.

  From the above, if the operation is performed during the normal operation period, an efficient operation can be performed by the control cell setting procedure according to the above-described change in the excess reactivity.

The above procedure is summarized as follows.
First, a fuel that has a low reactivity that can be used as a control cell fuel at the core configuration design stage of a boiling water nuclear power plant, and that satisfies the number of months in the reactor when the control rod is pulled out is selected. Among them, the fuel loaded in the position where the output was relatively high in the previous cycle is the first candidate, the fuel in the position where the output is low is the second candidate, the reactivity is high at the initial stage of operation, but the reactivity after the middle period is high By classifying the decreasing fuel as the third candidate, the next stage control cell configuration is prepared.

  Next, the number of control rods required for operation is confirmed at the design stage. If the operation period is the normal operation period and the control cell fuel candidate 1 can be configured, the control cell configuration is completed at that stage. To do.

  If the control cell cannot be constructed, the procedure of the present invention is used to first check the excess reactivity and perform pattern classification. There are three patterns: pattern 1 in which reactivity increases at the beginning of operation and decreases at the end, pattern 2 in which reactivity decreases from the beginning of operation to the end, and pattern 3 in which reactivity is substantially constant from the beginning of operation to the middle and decreases toward the end. The control cell configuration method is mechanically switched from the classified pattern.

  Next, using the fuel of the control cell candidate 1, a control cell having a high output and a position where the control rod is inserted for about one year from the beginning to the end of the operation is configured.

  Next, according to the surplus reactivity pattern confirmed in advance, the control cells for the shortage using the candidate 2 fuel are configured under conditions that can ensure the soundness of the fuel by setting the control rod insertion conditions.

  Further, if the number of control cells is insufficient, control the prospect insertion period 3 months good relatively outputs low position without reducing the power of the reactor during the control rod operation in cells other than the control cell bars Insert.

On the other hand, in step (5) of FIG. 2, when the operation period is long, for example, one and a half years to two years (hereinafter referred to as “long-term operation”), the control rod insertion period is It is necessary to configure the control cell fuel in consideration of being limited to about one year. In this case, the control cell fuel configuration procedure when the operation period is the long-term operation period in step (7) is applied.
Also in this case, the setting procedure is changed according to the surplus reactivity change pattern of FIG.

  In the case of the surplus reactivity pattern 1, as shown in FIG. 7, the control cell at the control rod position to be inserted for one year after the period of (cycle-1 year) / 2 from the beginning of the cycle is configured with candidate 1 fuel. The control cell at the position of the control rod to be inserted after this period is composed of candidate 2 or candidate 3, or a combination of candidates 2 and 3. For the period from the beginning of the cycle (operation period-1 year) / 2, control rods other than the control cell are replaced every three months. The candidate 3 fuel is originally the fuel that becomes the candidate 1 in the next operation, but since it is used in the next period when the surplus reactivity in the latter half has decreased, the number of fuels can be reduced, and at the same time, the same control cell can be inserted. Satisfaction is achieved, and the operation efficiency becomes possible with only a slight loss at the beginning of the cycle.

  In the case of the surplus reactivity pattern 2, as shown in FIG. 8, the control cell at the control rod position inserted for about one year from the beginning of the cycle is composed of the fuel of candidate 1, and the control cell at the position inserted in the latter half is candidate 2 Or it is comprised with the fuel which combined candidate 3 or candidate 2 and 3. Thereby, the same effect as the excess reactivity pattern 1 is obtained.

  In the case of the surplus reactivity pattern 3, as shown in FIG. 9, the control cell at the position of the control rod inserted for about one year from the beginning of the cycle is configured using the candidate 1 fuel. If the number of control rods is insufficient in the control cell of candidate 1 during this period, control rods with low output other than the control cell are used for one month from the start of operation, and then candidate 2 is used as the control cell position to be used thereafter. The control cell is constructed using the fuel of If the number of inserted control rods is still insufficient, control rods with low output other than the control cells are used while changing the insertion position every three months. The control cell at the position to be used in the subsequent operation is composed of the fuel of candidate 2 or candidate 3 or the combination of candidates 2 and 3, so that the same effect as surplus reactivity pattern 1 can be obtained.

  As described above, by configuring the core in the above control cell configuration procedure, the economic efficiency of the boiling water nuclear power plant can be improved. As a result, the enrichment of fuel uranium 235 is increased, and the operation period is long. It is possible to provide a boiling water reactor core and a method for constructing the same that can be operated efficiently even when the system is operated.

The figure which shows the boiling water reactor core which concerns on this invention. The flowchart which shows the structure method of the boiling water reactor core which concerns on this invention. Surplus reactivity pattern diagram. FIG. 4 is a diagram showing a control cell configuration method of the surplus reactivity pattern 1 when the reactor operation is normal operation. (A) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected. FIG. 5 is a diagram showing a control cell configuration method of surplus reactivity pattern 2 when the reactor operation is normal operation, (a) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected. FIG. 6 is a diagram showing a control cell configuration method of the surplus reactivity pattern 3 when the reactor operation is normal operation. (A) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected. FIG. 7 is a diagram showing a control cell configuration method of surplus reactivity pattern 1 when the reactor operation is long-term operation, (a) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected. FIG. 8 is a diagram showing a control cell configuration method of the surplus reactivity pattern 2 when the reactor operation is long-term operation, where (a) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell diagram. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected. FIG. 9 is a diagram showing a control cell configuration method of surplus reactivity pattern 3 when the reactor operation is long-term operation, (a) is a control rod pattern diagram, (b) is an operation pattern diagram, and (c) is a control cell. The core block diagram to which the number of the candidate fuel to comprise was attached | subjected.

Explanation of symbols

  1 ... Boiling water reactor core, 2 ... Control cell.

Claims (3)

  Classifying the control cell constituent fuel into candidate 1 fuel to candidate 3 fuel according to reactivity, furnace interior loading position and period of stay in the furnace, and determining whether the control cell can be configured with the candidate 1 fuel; When it is determined that the control rod insertion period is not possible in the step of determining whether the control rod insertion period is longer than a predetermined period and the step of determining whether the control cell can be configured with the candidate 1 fuel, or the control rod insertion period is A step of determining whether or not the period is longer than a certain period, and a step of configuring a control cell from the candidate 1 fuel to the candidate 3 fuel according to the surplus reactivity pattern when it is determined that the period is longer than the certain period. How to construct a boiling water reactor core.   The candidate 1 fuel is a fuel having a low reactivity and staying in the furnace within a specified number of months when the control rod is pulled out in the current cycle, and loaded in a high output position during the previous cycle operation. The fuel stays in the furnace within the specified number of months when the control rod of the current cycle is pulled out and is loaded at a low power position during the previous cycle operation, and the candidate 3 fuel is a new fuel at the previous cycle. The fuel having high reactivity at the initial stage of operation of the current cycle but low reactivity after the middle period, and fuel staying in the furnace within a specified number of months when the control rod of the current cycle is withdrawn. A method of configuring a boiling water reactor core according to claim 1.   A boiling water nuclear reactor core, wherein the constituent fuel of the control cell of the boiling water reactor core is constituted by the method for constructing a boiling water nuclear reactor core according to claim 1.

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