JP2003130984A - Monitor for watching performance of core of reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adopt an appropriate plan of a pattern of control rods to improve the versatility and economy in the operation of a reactor without any excessive margins even during a long-term operation by monitoring the output of the control rods during operation and verifying a margin to an output historical design curve. SOLUTION: This monitor is characterized in that it has an output distribution calculation means 11 which calculates the output distribution of a core by inputting a process quantity such as the temperature of pressure reactor water in a reactor and the nuclear property data and output distribution calculated values of fuel assemblies, a fuel rod data memory means 16 which stores the output distribution data and burnup distribution data of fuel rods in the fuel assemblies and a fuel rod output calculation means 17 which calculates the output and burnup of the fuel rods by inputting the output distribution calculated value of the data of the fuel rods.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a reactor core performance monitoring device capable of calculating power density and burnup of a fuel rod online and confirming a margin with a design output history.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIGS.

FIG. 5 shows a schematic diagram of a boiling water reactor. A core 2 composed of several hundred fuel assemblies is arranged in a pressure vessel 1, and a pump 3 circulates cooling water in the core 2 to generate steam. A plurality of cross-shaped control rods 4 are arranged in the core 2, as shown in the schematic sectional view of FIG. The control rods 4 are designed to be inserted into the core from the lower part of the core 2, and the power output of the nuclear reactor is adjusted by inserting / pulling out the control rods 4. Further, a plurality of neutron flux measuring instruments 5 are arranged at about four locations in the axial direction, and the neutron flux at each of the radial and axial positions of the core 2 is measured. The upper left of FIG. 6 shows a situation in which the fuel assemblies 6 are loaded, and four fuel assemblies 6 are arranged around the control rod 4.

FIG. 7 is a schematic sectional view of the fuel assembly 6.
A typical fuel assembly 6 is composed of two water rods 7 at the center and 74 fuel rods 8 arranged on a 9 × 9 grid. The fuel rods 8 indicate the order of enrichment of each fuel rod. Since the thermal load is smaller when the output distribution of each fuel rod is averaged, the enrichment of each fuel rod is adjusted so that the output distribution is flattened.

FIG. 8 shows a control rod pattern during the rated output operation. The squares in FIG. 8 indicate the locations where the control rods are arranged, and the numerical values indicate the pull-out amounts of the control rods. The pulling-out amount indicates that the pulling-out amount is 12/48, for example, when the total pulling-out state is 48. The control rods with blank squares indicate that the control rods are 48, that is, all pulled out. In FIG. 8, 13 control rods are partially inserted, and the other control rods are all fully pulled out.

During operation, the linear power density, which is the output per unit length of the fuel rods, is limited to 44 kW / m or less so that the fuel rods 8 are not overheated. When the reactor is operating, the linear power density of each fuel assembly in the core is calculated by the core performance monitoring device, and the limit value 4
It has been confirmed that it is 4 kW / m or less.

FIG. 9 is a block diagram of this core performance monitoring device. In FIG. 9, the process data 9 such as the cooling water temperature and pressure of the nuclear reactor and the neutron flux measurement value 10 measured by the neutron flux measuring instrument 5 are input to the output distribution calculating means 11.
Further, the nuclear characteristic data storage means 12 of the fuel assembly stores the nuclear characteristic data which is previously obtained by the nuclear calculation and input as an amount depending on the burnup, the void ratio, etc., and the data is output distribution. It is used for the calculation of the calculation means 11. The power distribution calculation means 11 has a core simulation calculation code as its core, and inputs the above data to calculate the power distribution of each fuel assembly in the core. The output distribution is calculated in units of one fuel assembly in the radial direction, and is also calculated in each of the axially divided segments of about 24. This power distribution calculation is usually performed automatically at a time interval of about once an hour, and when the power output or power distribution of the reactor changes due to power adjustment or control rod operation, It is executed according to the operator's request. The outputs of the respective segments are integrated in consideration of the change over time to calculate the burnup, and are stored in the integrated data storage means 13. Since the nuclear characteristic data depends on the burnup of the fuel, the integrated data in the integrated data storage means is also input to the output distribution calculation means 11.

Further, the data of the nuclear characteristic data storage means 12 includes the data of the output peaking of the maximum output fuel rod in the fuel assembly, and each fuel assembly is obtained from the output peaking data and the output distribution calculation value. The maximum line power density of is calculated by the power distribution calculation means 11. The calculation result of the power distribution and the maximum line power density is output to the output means 14 such as a printer or a CRT so that the core performance can be confirmed.

On the other hand, in the thermomechanical design of fuel rods, it is assumed that an output history that envelops the change in output experienced by an actual fuel rod is set as the design output history, and the fuel rod burns at the design output history. , The stress of the fuel cladding is analyzed and evaluated, and the soundness of the fuel rod is evaluated. FIG. 10 shows an example of the fuel rod output history. A large number of data points plotted in FIG. 10 indicate the value at the position where the linear power density becomes maximum in the axial direction and the burnup at that position for each fuel rod of each fuel assembly in the core at the design stage. It is the point with the highest linear power density for each burnup. Core 2
In addition to the newly loaded fuel assemblies, the burned fuel assemblies that have been continuously used for about 2 to 5 cycles are also loaded therein. Further, since the burnup of the fuel assembly and the fuel rods forming the assembly increases from the beginning to the end of the cycle, plotting the data of each of these time points and each fuel assembly shows the plot points as shown in FIG. The range extends to the range of maximum burnup in the core. The polygonal line A is a design output history set so as to envelop these data. Generally, the output of individual fuel rods is not constant because it varies depending on the control rod pattern and power distribution during operation, but it is not constant in burned fuel rods because the fissionable material is depleted. There is. Reflecting this, the design output history A matches the operating limit value of 44 kW / m at low burnup, and is set to decrease when the burnup exceeds 30 GWd / t from 25 GWd / t. I am doing it. In actual reactor operation, conventionally, it has been confirmed by the core performance monitoring device that the maximum linear power density of the fuel assembly in the core satisfies the operation limit value. Even in the case of fuel rods with high power, the line power density had a margin with respect to the design output history.

[0010]

SUMMARY OF THE INVENTION The present invention monitors the output of a fuel rod during operation and confirms a margin with respect to an output history design curve, so that it is suitable even during long-term operation without taking an excessive margin. Adopting various control rod pattern plans,
The purpose is to improve the flexibility and economic efficiency of reactor operation.

In recent years, it has been studied to prolong the operating period to improve the operating rate of the nuclear reactor. However, when the long-term cycle operation is performed, the axial output is a factor related to the thermal load of the fuel rods. The peaking of the distribution is increased and the control rod hysteresis effect is increased. These will be described below.

FIG. 11 shows an example of the axial average output distribution at the beginning of the cycle and at the end of the cycle. In boiling water reactors, the axial power distribution tends to be distorted to the lower peak due to the occurrence of voids.On the other hand, at the end of the cycle when combustion progresses, the combustion in the lower part of the core progresses more than in the upper part, and In the region with a high void fraction in the upper part, the fast neutron flux is higher than in the lower part, and relatively large amount of plutonium is accumulated,
The output distribution tends to be around the upper peak. In the case of long-term operation, the tendency is to have a lower peak at the beginning of the cycle and an upper peak at the end of the cycle.

The control rod history effect is an effect that occurs when the inserted control rod is pulled out. When the control rod 4 adjacent to the fuel assembly 6 of FIG. 7 is inserted, the output of the fuel rod on the side closer to the control rod in the cross section of the fuel assembly 6 is greatly suppressed. Therefore, when the control rod is pulled out, the output of the fuel rod on the side close to the control rod in which the loss of the fissile material is suppressed tends to be higher than usual. Since the control rod is withdrawn downwards, this effect occurs in the axially upper position after the control rod is withdrawn. The amount of increase in output is
The longer the control rod is inserted, the larger it becomes.
When the operating period is prolonged, the period during which the control rod is inserted becomes longer, and when the control rod is pulled out at the end of the cycle, the output of the fuel rod due to the control rod hysteresis effect tends to increase more than before.

FIG. 12 is a diagram showing an example of changes in the control rod pattern near the end of the cycle. Near the end of the cycle,
The control rod withdrawal is adjusted at certain intervals, and during that period, the rated power operation is continued by adjusting the core flow rate. In FIG. 12, after the pull-out adjustment of the control rods is performed once, all the control rods are finally pulled out completely. However, the control rod pattern in the center of FIG. 12 (9 pull-out positions 18) is a state in which the control rods are pulled out by about 40% downward, and the output below the core is suppressed and the output distribution of the upper peak is more It tends to be encouraged. Furthermore, the control rod pattern a in FIG.
When the control rod is pulled out from the control rod to the control rod pattern b, the output of the fuel rod also becomes high due to the control rod history effect. In general, fuel assemblies with advanced combustion are arranged around the control rods used during operation, so if the output of fuel rods with relatively high burnup in these fuel assemblies becomes high, the design output The margin for history may be reduced. When operating for a long period of time, these effects are greater than in the past.

FIG. 13 shows an example in which the control rod pattern is changed in order to secure a sufficient margin with respect to the design output history. The pull-out adjustment of the control rod pattern is increased once, and some of the control rods are pulled out earlier than in FIG. 12 to alleviate the control rod history effect and the influence of the control rod on the output distribution. In the control rod pattern plan of FIG. 13, the margin for the design output history improves, but the number of control rod adjustments increases,
Not only is the load on the operation increased, but because the reactor output must be temporarily reduced when adjusting the control rods, increasing the number of control rod adjustments will also reduce the load factor.

According to the present invention, by monitoring the output of the fuel rod during operation and confirming the margin with respect to the output history design curve, even during long-term operation without taking an excessive margin,
The purpose is to improve the flexibility and economic efficiency of reactor operation by adopting an appropriate control rod pattern plan.

[0017]

The invention according to claim 1 is
Power distribution calculation means for calculating the core power distribution by inputting process quantities such as reactor pressure and reactor water temperature, and nuclear characteristic data of the fuel assembly, and power distribution data of fuel rods in the fuel assembly And fuel rod data storage means for storing burnup distribution data, and fuel rod output calculation means for calculating fuel rod output and burnup by inputting fuel rod data and output distribution calculation values.

According to a second aspect of the present invention, in the first aspect of the invention, there is provided output means for comparing the fuel rod output calculated by the fuel rod output calculating means with a previously input design output history. Characterize.

The invention according to claim 3 is the invention according to claim 1 or 2.
The invention according to (1) is characterized by further comprising fuel rod output storage means for storing the data of the fuel rod output and burnup calculated at a specific time interval or when the output or output distribution changes.

The invention according to claim 4 is the invention according to claim 1 or 2.
In the invention according to (1), there is provided a fuel assembly output storage means for storing the data of the output and burnup of the fuel assembly calculated at a specific time interval or when the output or the output distribution changes.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the stored output history is input to perform thermomechanical analysis of the fuel rod, and the calculation result is transmitted to the output means. It is characterized by having a fuel rod analysis means.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, a thermo-mechanical analysis of the fuel rod is performed by inputting the fuel rod output and burnup calculated by the fuel rod output calculating means, It is characterized by including fuel rod analysis means for transmitting the calculation result to the output means, and fuel irradiation characteristic data storage means for storing the fuel irradiation characteristic data calculated by the fuel rod analysis means.

The invention according to claim 7 is characterized in that, in the invention according to any one of claims 1 to 6, the power distribution calculating means has a predictive calculation function for performing predictive calculation of future core performance.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a block diagram showing a core performance monitoring device of the present invention. Reference numerals 9 to 14 are common to FIG. 9 showing a block diagram of a conventional core performance monitoring device.

In the core monitoring device of the present invention, the output of the fuel assembly calculated by the power distribution calculating means 11 and the output of each fuel rod stored in the fuel rod data storing means 16 are different from those of the conventional monitoring device. It has a fuel rod output calculation means 17 for calculating the linear power density and burnup of the fuel rods by inputting the distribution data and the burnup distribution data.

The output distribution data of each fuel rod and the burnup distribution data of each fuel rod constituting the fuel assembly are calculated in advance by nuclear calculation, and are input to and stored in the fuel rod data storage means 16. The fuel rod output calculation means 17 calculates the linear output density and burnup of the fuel rod from the output of each part of the fuel assembly calculated by the output distribution calculation means 11 and the data of the fuel rod data storage means 16. For a certain fuel assembly, the linear power density Prod (I, J, at a certain axial position (K) of the fuel rods (I, J) arranged in a grid pattern.
K) and burnup Erod (I, J, K) are calculated as follows.

Prod (I, J, K) = P (K) × LPFrod (I, J) Erod (I, J, K) = E (K) × LEFrod (I, J) where P (K) , E (K) are the segment average power and the segment average burnup at the axial position K of the fuel assembly, respectively, and P (K) is the power distribution calculation means 1.
1 and E (K) is the integrated data storage means 1
It is stored in 3. In addition, LPFrod (I, J), L
EFrod (I, J) are output peaking and burnup peaking, which are expressed by normalizing the output and burnup of the fuel rod (I, J) in the cross section of the fuel assembly to the average value in the cross section. LPFrod (I, J), LEFrod (I, J)
Is calculated from the fuel rod data stored in the fuel rod data storage means 16 depending on the burnup and the void ratio.

With such a structure, it can be confirmed that the actual fuel rod output has a margin with respect to the design output history A.

FIG. 2 shows a second embodiment of the present invention. The embodiment of FIG. 2 has a fuel rod output storage means 18 for storing the data of the fuel rod output and burnup calculated by the fuel rod output calculation means 17, as compared with FIG. 1, and is further stored. It is characterized by having a fuel rod analysis means 19 for inputting fuel rod output data and performing a fuel rod analysis.

The fuel rod data storage means 18 stores the fuel rod output calculation result calculated by the fuel rod output calculation means 17 for each burnup. Further, by outputting it to the output means 14, the margin for the design output history can be confirmed.

The fuel rod analysis means 19 inputs the combustion history of the output of each fuel rod from the fuel rod output storage means 18, performs mechanical analysis such as stress calculation of the cladding of the fuel rod, and outputs the calculation result. It outputs to 14. The actual fuel rod output is not always high, and there is a margin compared with the design output history A. With such a configuration, mechanical characteristic analysis based on the actual results of the fuel rod output history can be carried out, and it is an envelope. Design output history A
It is possible to confirm how much mechanical property margin each fuel rod actually has, as compared with the analysis based on.

Recent core monitoring devices have a core state predictive calculation function for studying future control rod pattern plans and operation plans as well as core performance monitoring. In such a case, the future power distribution and burnup distribution are calculated by inputting the future power distribution and burnup distribution predicted and calculated by the power distribution calculation means 11 into the fuel rod power calculation means 17. be able to. Further, the fuel rod analysis means 19 can input the predicted fuel rod output in addition to the actual data of the fuel rod output, and analyze the mechanical characteristics of the fuel rod in the predicted core state.

1 and 2, since the nuclear characteristic data storage means 12 and the fuel rod data storage means 16 are data relating to the nuclear characteristics of the fuel assembly, the same storage device collectively constitutes the storage means. Alternatively, the integrated data storage means 13 and the fuel rod output storage means 18 in FIG.
Alternatively, the history data may have the same configuration.

The total number of fuel rods in the core is, for example, 764 (the number of fuel assemblies) × 74 (the number of fuel rods in one fuel assembly) = 565 in a typical reactor having an electric output of 1.1 million kW.
There are 36 (pieces), and in the case of storing the data of changes in the output and burnup with time at each axial position, it is necessary to store a huge amount of data in the fuel rod output storage means 18. On the other hand, regarding the burnup of each fuel rod in the fuel assembly, the burnup of fuel rods with generally high output tends to be high. For this reason, the fuel rod data storage means 16 stores the highest output peaking Prod and the highest burnup peaking Erod, and the fuel rod output calculation means 17 calculates the output and burnup only for the fuel rod with the maximum peaking. However, the amount of data to be stored can be reduced by storing it in the fuel rod output storage means 18. Although the fuel rod output and burnup calculated by such a configuration are somewhat more severe than the detailed evaluation, the calculation amount and the stored data amount can be reduced without significantly degrading the evaluation accuracy. .

Further, the fuel rod analysis means 19 can shorten the calculation time by preparing a plurality of analysis devices and performing parallel processing.

FIG. 3 shows a third embodiment of the present invention.
In the embodiment of FIG. 3, instead of the fuel rod output storage means 18 of the embodiment of FIG. 2, a fuel assembly output storage means 20 is provided.
Shall have. In the present embodiment, instead of storing the changes over time in the output and burnup of each fuel rod, the changes over time in burnup, output, etc. at each axial position of each fuel assembly calculated by the output distribution calculation means 11 are stored. Is stored, and the amount of data to be stored is reduced compared to the case where output history data of all fuel rods is stored. The fuel rod output calculation means 17 inputs the output history data of the fuel assembly output storage means 20 and the fuel rod data of the fuel rod data storage means 16, calculates the output history of each fuel rod, and outputs it to the output means 14. To do. Further, it is transmitted to the fuel rod analysis means 19 to perform mechanical analysis of the fuel rods.

Although the embodiments shown in FIGS. 1 to 3 show an online core performance monitor installed in a nuclear power plant or the like, the process data 9 is not an actual measurement value but an external input, By adopting a configuration in which the input of the neutron flux measurement value 10 is excluded, the present apparatus can also be used as a single core performance calculation apparatus separated from the reactor.

FIG. 4 shows a fourth embodiment of the present invention. The present embodiment is characterized in that it has a fuel rod analysis means 19 as compared with FIG. 1, and further has a fuel irradiation characteristic data storage means 21 for storing the fuel irradiation characteristic data analyzed by the fuel rod analysis means 19. I am trying. The fuel rod analysis means 19 inputs the output and burnup of the fuel rod calculated by the fuel rod analysis means 17, performs a fuel rod mechanical characteristic analysis at specific time intervals, and outputs the calculation result to the output means 14.
Further, the fuel irradiation characteristic data such as the burnup, the amount of fission products generated, the fuel rod internal pressure, and the fuel temperature, which are obtained by the mechanical characteristics reflecting the combustion history of the fuel rod, are transmitted to the fuel irradiation characteristic data storage means 21, The fuel irradiation characteristic data storage means 21 stores this data. When a specific time interval elapses and the burnup progresses, the fuel irradiation characteristic data reflecting the past irradiation history and the fuel output at that time are input, and the fuel rod mechanical characteristics of the fuel rod advanced by the fuel rod analysis means 19 are input. The analysis is performed and the fuel irradiation characteristic data is updated to the latest one. With such a configuration, mechanical characteristics analysis can be performed at specific time intervals as combustion progresses, stress of the fuel rod cladding tube at each time can be evaluated, and a margin of mechanical characteristics with respect to a design value can be confirmed. Moreover, since the latest fuel irradiation characteristic data may be stored instead of the fuel combustion history data, the amount of data to be stored can be reduced.

[0040]

As described above, according to the core performance monitoring device of the present invention, it is possible to confirm the margin between the output of the fuel rod and the design output history. Therefore, even if the operation cycle is prolonged in the future, The rational control rod pattern can be used, and the flexibility of reactor operation is improved. Further, the operating rate of the nuclear reactor can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a core performance monitoring device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a core performance monitoring device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a core performance monitoring device according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a core performance monitoring device according to a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram of a boiling water reactor.

FIG. 6 is a sectional view of a core.

FIG. 7 is a sectional view of a fuel assembly.

FIG. 8 is a control rod pattern.

FIG. 9 is a configuration diagram of a conventional core performance monitoring device.

FIG. 10: Fuel rod output history.

FIG. 11 is an example of an axial power distribution.

FIG. 12: Control rod pattern plan.

FIG. 13: Control rod pattern plan after improvement.

[Explanation of symbols]

1 pressure vessel 2 core 3 pumps 4 control rod 5 Neutron flux measuring instrument 6 Fuel assembly 7 Water rod 8 fuel rods 9 Process data 10 Neutron flux measurement 11 Output distribution measuring means 12 Nuclear characteristic data measuring means 13 integrated data storage means 14 Output means 16 Fuel rod data storage means 17 Fuel rod output calculation means 18 Fuel rod output storage means 19 Fuel rod analysis means 20 Fuel Assembly Output Storage Means 21 Fuel Irradiation Characteristic Data Storage Means A design output history

Continued front page    (72) Inventor Manabu Yoshida             Kanagawa Prefecture Yokosuka City 23-13-1 Kawa             Ceremony company Global Nuclear Fue             Within Le Japan (72) Inventor Sadayuki Izutsu             Kanagawa Prefecture Yokosuka City 23-13-1 Kawa             Ceremony company Global Nuclear Fue             Within Le Japan (72) Inventor Yasushi Hirano             Kanagawa Prefecture Yokosuka City 23-13-1 Kawa             Ceremony company Global Nuclear Fue             Within Le Japan (72) Inventor Akira Kikuma             Kanagawa Prefecture Yokosuka City 23-13-1 Kawa             Ceremony company Global Nuclear Fue             Within Le Japan F term (reference) 2G075 CA08 CA40 CA49 DA03 DA04                       FA02 FA04 FA06 FB08 FB09                       FB10 FB16 FB18 FC03 FC06                       GA15 GA18

Claims (7)

[Claims] 1. A power distribution calculation means for calculating a core power distribution by inputting process quantities such as reactor pressure and reactor water temperature and nuclear characteristic data of the fuel assembly, and fuel in the fuel assembly. Fuel rod data storage means for storing rod power distribution data and burnup distribution data, and fuel rod output calculation means for inputting fuel rod data and output distribution calculation values to calculate fuel rod output and burnup A core performance monitoring device for a nuclear reactor. 2. The reactor core performance monitoring system according to claim 1, further comprising output means for comparing the fuel rod output calculated by the fuel rod output calculating means with a previously inputted design output history and outputting the result. apparatus. 3. A fuel rod output storage means for storing the data of the fuel rod output and burnup calculated at a specific time interval or when the output or the output distribution changes, wherein: 2. The reactor core performance monitoring device according to 2. 4. A fuel assembly output storage means for storing the data of the output and burnup of the fuel assembly calculated at a specific time interval or when the output or the output distribution changes. 1. The reactor core performance monitoring device according to 1 or 2. 5. A fuel rod analyzing means for inputting the stored output history, performing thermomechanical analysis of the fuel rod, and transmitting the calculation result to the output means. The reactor core performance monitoring device according to 1. 6. A fuel rod analysis means for performing a thermomechanical analysis of a fuel rod by inputting the fuel rod output and burnup calculated by the fuel rod output calculation means, and transmitting the calculation result to the output means, and a fuel rod analysis means. 6. The reactor core performance monitoring device according to claim 1, further comprising a fuel irradiation characteristic data storage unit that stores the calculated fuel irradiation characteristic data. 7. The reactor core performance monitoring device according to claim 1, wherein the power distribution calculation means has a predictive calculation function for performing a predictive calculation of future core performance.