JP7267189B2 - Analysis method of output limit value, safety evaluation method, reactor core design method and analysis device - Google Patents

Description

The present disclosure relates to a power limit value analysis method, a safety evaluation method, a reactor core design method, and an analysis apparatus.

Conventionally, the occurrence of accidental transient power changes in a nuclear reactor is simulated to identify the presence or absence of fuel rod cladding failure, and to prevent fuel rod cladding failure, the operability of the reactor is determined. A method for determining the value of a parameter representing is known (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2011-506920

However, in Patent Document 1, when the reactor becomes difficult to operate during a transient change in reactor power, there is a possibility of physical damage to the cladding of the fuel rods. Also, in the event of a loss of coolant accident (LOCA), it is difficult to prevent physical damage to the cladding due to reactor operation. By the way, when the fuel pellets stored inside the fuel rod have a high burnup, during LOCA, the fuel pellets become finer and the fuel pellets leak out due to physical damage to the cladding tube. A so-called FFRD (Fuel Fragmentation, Relocation and Dispersal) phenomenon is known. In order to suppress the occurrence of the FFRD phenomenon, it is required to suppress the occurrence of physical damage to the fuel rod cladding during LOCA.

Therefore, an object of the present disclosure is to provide a power limit value analysis method, a safety evaluation method, a reactor core design method, and an analysis apparatus that can suppress the occurrence of physical damage to the fuel rod cladding even in the event of a LOCA. and

The power limit value analysis method of the present disclosure is a power limit value analysis method for deriving a power limit value for limiting the local power of a fuel rod by executing an analysis process, wherein the power limit value is provided in the core The fuel rod has a fuel pellet and a cladding tube that coats the fuel pellet, and the input parameters input to the analysis process are the internal pressure of the fuel rod and the fuel assembly consisting of the fuel rods. analyzing the behavior of the fuel rods at a given burnup based on the input parameters, including the average power, the average power of the fuel rods, and the axial power distribution of the core; a first step of analyzing the physical damage of the fuel rod, and repeating the first step while changing the burnup to obtain a local power of the fuel rod at which the physical damage of the cladding occurs; a second step of deriving the burnup corresponding to the local power; and based on the derived local power and the burnup, physical failure of the cladding corresponding to each burnup occurs. and a third step of deriving said power limit below said local power.

The safety evaluation method of the present disclosure evaluates the local power of the fuel rod designed in core design based on the power limit value derived by the power limit value analysis method described above. It is determined whether or not physical damage will occur.

In the core design method of the present disclosure, the core is designed so that the power limit is equal to or less than the power limit value derived by the power limit value analysis method described above.

The analysis device of the present disclosure is an analysis device having a calculation unit that derives a power limit value for limiting the local power of a fuel rod by executing analysis processing, wherein the fuel rods provided in the core are: A fuel pellet and a cladding tube that coats the fuel pellet. The calculation unit analyzes the behavior of the fuel rods at a predetermined burnup based on the input parameters, including the average power of the fuel rods and the power distribution in the axial direction of the core, and analyzes the behavior of the fuel rods at the time of LOCA. a first step of analyzing physical tube failure; repeating said first step while varying said burnup to determine the local power of said fuel rod at which physical failure of said cladding occurs; a second step of deriving a burnup corresponding to the local power, and based on the derived local power and the burnup, physical failure of the cladding corresponding to each burnup occurs. and a third step of deriving said power limit below said local power.

According to the present disclosure, it is possible to suppress the occurrence of physical damage to the fuel rod cladding even during a LOCA.

FIG. 1 is a block diagram schematically showing an analysis apparatus according to this embodiment. FIG. 2 is a configuration diagram schematically showing a fuel rod analysis model used in the method for analyzing the output limit value according to the present embodiment. FIG. 3 is a flowchart relating to an output limit value analysis method according to this embodiment. FIG. 4 is a flowchart relating to analysis processing in the output limit value analysis method according to the present embodiment. FIG. 5 is an explanatory diagram of the power distribution in the axial direction of the core. FIG. 6 is a diagram relating data relating the average power of the fuel rods to the average power of the fuel assemblies. FIG. 7 is a graph showing the relationship between local power and local burnup for fuel rods with power limits set. FIG. 8 is a flowchart relating to the core design method according to this embodiment. FIG. 9 is a flowchart relating to the safety evaluation method according to this embodiment. FIG. 10 is an explanatory diagram relating to the safety evaluation method according to this embodiment.

EMBODIMENT OF THE INVENTION Below, embodiment which concerns on this invention is described in detail based on drawing. In addition, this invention is not limited by this embodiment. In addition, components in the following embodiments include components that can be easily replaced by those skilled in the art, or components that are substantially the same. Furthermore, the components described below can be combined as appropriate, and when there are multiple embodiments, each embodiment can be combined.

[Embodiment]
The power limit value analysis method according to the present embodiment is a method of analyzing the behavior of the fuel rods 5 in the fuel assemblies loaded in the core and deriving the power limit value that limits the local power of the fuel rods 5. ing. The output limit value analysis method derives the output limit value for suppressing physical damage to the cladding tube during LOCA, and in particular, derives the output limit value for suppressing the occurrence of the FFRD phenomenon. . In addition, in the analysis method of the output limit value of the present embodiment, under the condition that the fuel rod 5 in which the FFRD phenomenon occurs has a burnup in the middle of the cycle (MOC: Middle of Cycle) or the end of the cycle (EOC: End of Cycle), That is, the analysis process is executed under the condition that the combustion of the fuel is advanced.

FIG. 1 is a block diagram schematically showing an analysis apparatus according to this embodiment. FIG. 2 is a configuration diagram schematically showing a fuel rod analysis model used in the method for analyzing the output limit value according to the present embodiment.

(fuel rod)
First, the fuel rod 5 to be analyzed will be described with reference to FIG. As shown in FIG. 2 , the fuel rod 5 includes a plurality of fuel pellets 6 arranged axially and a cladding tube 7 covering the plurality of fuel pellets 6 . The fuel pellet 6 is formed in a cylindrical shape centered on the axial direction, and is formed by sintering nuclear fuel. The cladding tube 7 is formed in a cylindrical shape centered on the axial direction, and is formed using a metal material. In the fuel rod 5, a plurality of fuel pellets 6 are arranged in the cladding tube 7 in the axial direction, and a gap G is formed between the cladding tube 7 and the fuel pellets 6 in the radial direction. A plurality of fuel rods 5 are bundled to form a fuel assembly, and the formed fuel assembly is loaded into the core.

(Analysis device)
Next, the analysis device 1 will be described with reference to FIG. The analysis device 1 analyzes the physical damage of the fuel rods 5 at the time of LOCA, and simulates the behavior of the fuel rods 5 at the time of LOCA. Specifically, the analysis device 1 executes a LOCA analysis of the core.

The analysis device 1 has an arithmetic unit 11 , a storage unit 12 , a display unit 13 and an input unit 14 .

The calculation unit 11 includes an integrated circuit such as a CPU (Central Processing Unit), for example. The calculation unit 11 executes analysis processing and the like related to LOCA analysis based on input information. The memory unit 12 is an arbitrary memory device such as a semiconductor memory device and a magnetic memory device. The storage unit 12 stores various programs for executing various processes and various data used for the processes. Examples of various data include input information (input parameters) D1 input to the LOCA analysis, output information D2 output as analysis results, and the like. The display unit 13 is, for example, a display device such as a liquid crystal display. The input unit 14 is, for example, an input device such as a keyboard and mouse. Note that the display unit 13 and the input unit 14 may be integrated as an input display device such as a touch panel capable of input operation.

(Analysis method of output limit line)
Next, with reference to FIGS. 3 to 7, the output limit value analysis method executed by the analysis device 1 will be described. FIG. 3 is a flowchart relating to an output limit value analysis method according to this embodiment. FIG. 4 is a flowchart relating to analysis processing in the output limit value analysis method according to the present embodiment. FIG. 5 is an explanatory diagram of the power distribution in the axial direction of the core. FIG. 6 is a diagram relating data relating the average power of the fuel rods to the average power of the fuel assemblies. FIG. 7 is a graph showing the relationship between local power and local burnup for fuel rods with power limits set.

In the output limit value analysis method, the calculation unit 11 of the analysis device 1 performs LOCA analysis and derives the output limit line L1 from the analysis result of the LOCA analysis. At this time, the input parameters input as input conditions for the LOCA analysis are the internal pressure of the fuel rods 5, the average power F _ASS'Y of the fuel assemblies, the average power F _ΔH ^N of the fuel rods 5, the axial power of the core It contains the distribution _FZ . The F _ASS'Y , F _ΔH ^N , and F _Z are relative values to the average power of the core. In addition, in the LOCA analysis, by analyzing the behavior of fuel rods with a predetermined burnup during LOCA, the physical damage of the cladding tube 7 of the fuel rod during LOCA is analyzed.

As shown in FIG. 3, in the output limit line analysis method, first, the calculation unit 11 of the analysis device 1 acquires the input parameters stored in the storage unit 12, and performs analysis including LOCA analysis based on the acquired input parameters. Processing is executed (step S11: first step). In step S11, the analysis process is repeatedly executed while changing the burnup.

Specifically, as shown in FIG. 4, in step S11, the analysis device 1 receives the internal pressure of the fuel rods 5 as input parameters, the average power F _ASS'Y of the fuel assemblies, the average power F _ΔH ^N of the fuel rods 5, and , the power distribution _FZ in the axial direction of the core is input. In step S11, the internal pressure of the fuel rods 5, the average power F _ASS'Y of the fuel assembly, and the power distribution F _Z in the axial direction of the core are set as fixed values, and the average power F _ΔH ^N of the fuel rods 5 is set as a variable value. there is

The calculation unit 11 calculates the temperature of the coolant, the flow velocity of the coolant, etc. based on the input average power F _ASS'Y of the fuel assemblies and the average power F _ΔH ^N of the fuel rods 5 (step S21). . Further, the calculation unit 11 calculates the distribution of the local power in the axial direction of the fuel rods 5 based on the inputted average power F _ΔH ^N of the fuel rods 5 and the power distribution F _Z in the axial direction of the core (step S22). In step S22, the distribution of local power in the axial direction of the fuel rods 5 is calculated by multiplying the average power F _ΔH ^N of the fuel rods 5 by the power distribution F _Z in the axial direction of the core. Then, the calculation unit 11 calculates the temperature of the coolant and the flow velocity of the coolant calculated in step S21, and the distribution of the local power in the axial direction of the fuel rod 5 calculated in step S22. A temperature distribution in the axial direction is calculated (step S23). Thereafter, the calculation unit 11 sets the burnup of the fuel rods 5 to a predetermined burnup, and based on the internal pressure of the fuel rods 5 and the temperature distribution in the axial direction of the cladding tube 7, A LOCA analysis based on the analysis model is performed to analyze the behavior of the cladding tube 7 up to physical damage (step S24).

After executing step S11, the calculation unit 11 corresponds to the local output of the fuel rod 5 where physical damage to the cladding tube 7 occurs and the local output based on the analysis results obtained by repeatedly executing step S11. The burnup to be applied is derived (step S12: second step). Specifically, in step S12, the local power of the fuel rod 5 at which physical damage to the cladding tube 7 occurs at a predetermined burnup is obtained. Then, in step S12, a plurality of local powers are obtained by obtaining the local power of the fuel rod 5 where physical damage to the cladding tube 7 occurs over the varying burnup. As a result, for example, it is possible to acquire a plurality of plots of “◯ (white circles) and Δ (white triangles)” as shown in FIG. FIG. 7 is a graph of fuel rod 5 local power as a function of fuel rod 5 local burnup. In FIG. 7, the horizontal axis is the local burnup, and the vertical axis is the local power. The burnup of the fuel rods 5 and the local power of the fuel rods 5 are the local power of the fuel rods 5 calculated in step S22 and the burnup of the fuel rods 5 set when performing the LOCA analysis.

After step S12 is executed, the calculation unit 11 outputs a value lower than the local output at which physical damage occurs in the cladding tube 7 based on the derived minimum value of the local output at which physical damage occurs and the burnup. It is derived as the limit value L1 (step S13: third step). In step S13, the output limit value L1 is set to the line connecting the plots so that it falls below the minimum value of the local outputs such as the plots of a plurality of "○ (white circles)" as shown in FIG. 7 derived in step S12. (hereinafter also referred to as output limit line L1).

After executing step S13, the computing unit 11 sets the power limit line L1 (first power limit value) derived in step S13 in the power limit map shown in FIG. step S14: fourth step). Although the output limit line L1 is linear, it may be curved and is not particularly limited. Here, in the power limit map shown in FIG. 7, a power limit line L2 (second power limit value) that can maintain a core coolable shape is set. The output restriction line L2 is a line on the side where the output restriction is relaxed with respect to the output restriction line L1. In other words, the output restriction line L1 is a line with a stricter output restriction than the output restriction line L2. Further, the output limit line L1 is set at a predetermined burnup or more, and the predetermined burnup is the burnup in the middle of the cycle or the end of the cycle. Specifically, the predetermined burnup is in the range of 60 GWd/t or more and 75 GWd/t or less, and preferably the output limit line L1 is set at 60 GWd/t or more. Therefore, in step S14, the output limit line L2 is set when the burnup is less than the predetermined burnup, and the output limit line L1 is set when the burnup is greater than or equal to the predetermined burnup.

Here, in step S11, in order to rationalize the LOCA analysis, rationalization of the power distribution _FZ in the axial direction of the core and rationalization of the average power F _ASS'Y of the fuel assemblies, which are input as input parameters, are attempted. may

Rationalization of the power distribution _FZ in the axial direction of the core will be described with reference to FIG. As shown in the graph on the left side of FIG. 5, the output distribution _FZ has a cosine distribution (inclusive distribution) of values on the safe side in the LOCA analysis. In the graph on the left side of FIG. 5, the vertical axis represents the height of the core, and the horizontal axis represents the power in the axial direction of the core. In the power distribution _FZ , which is a cosine distribution, the core power is estimated to be high at the central portion in the axial direction of the core. On the other hand, since the output limit line L1 is a line for suppressing the occurrence of the FFRD phenomenon, it is possible to adopt the output distribution _FZ in the middle of the cycle (MOC) or the end of the cycle (EOC). Be realistic. The power distribution _FZ at the middle of the cycle or the end of the cycle has a lower core power than the cosine distribution at the central portion in the axial direction of the core. In other words, the power distribution _FZ , which is a cosine distribution, sets the core power excessively on the safe side (strict side), while the power distribution _FZ in the middle of the cycle or at the end of the cycle assumes that the core power is realistic. is set.

Here, the power limiting line L1 derived when the cosine distribution, the mid-cycle power distribution, and the end-cycle power distribution _FZ are adopted as the power distribution _FZ in the axial direction of the core as an input parameter will be described. . In the graph on the right side of FIG. 5, the vertical axis represents the local power of the fuel rods, and the horizontal axis represents the power in the axial direction of the core. In the graph on the right side of FIG. 5, the power limit line L1a is the power limit line L1 derived when the power distribution _FZ in the axial direction of the core, which is a cosine distribution, is adopted. The power limit line L1b is the power limit line L1 derived when the power distribution _FZ in the axial direction of the core in the middle of the cycle is adopted. The power limit line L1c is the power limit line L1 derived when the power distribution _FZ in the axial direction of the core at the end of the cycle is adopted. Comparing the output limit lines L1a, L1b, and L1c, the output limit line L1a is the line on the safest side, and the output limit line L1b is a line that is relaxed more than the output limit line L1a. L1c is a line that is more relaxed than the output restriction line L1b. In this way, in step S11 in FIG. 4, by using the axial power distribution of the core in the middle of the cycle or the end of the cycle as the axial power distribution _FZ of the core, the axial power distribution of the core becomes a cosine distribution. Compared to the case of using _FZ , the output limit line L1 can be pulled up to the relaxing side.

Next, rationalization of the average power F _ASS'Y of the fuel assembly will be described with reference to FIG. 6, the vertical axis represents the average power F _ASS'Y of the fuel assembly, and the horizontal axis represents the average power F _ΔH ^N of the fuel rods 5. In FIG. As shown in the graph of FIG. 6, the average power F _ASS'Y varies with changes in the average power F _ΔH ^N of the fuel rods 5 . Further, the graph shown in FIG. 6 is data associated with the average power F _ΔH ^N of the fuel rods 5 and the average power F _ASS'Y of the fuel assembly, and is one of the data included in the input information D1. is stored in the storage unit 12 as. The graph shown in FIG. 6 is a graph of a linear function in which the average power F _ASS'Y of the fuel assembly increases as the average power F _ΔH ^N of the fuel rods 5 increases. When the variable average power F _ΔH ^N of the fuel rods 5 is input as an input parameter, the calculator 11 responds to the input average power F _ΔH ^N of the fuel rods 5 based on the data in FIG. Obtain the average power F _ASS'Y of the fuel assembly. Then, the calculation unit 11 inputs the acquired average output F _ASS'Y of the fuel assembly as an input parameter. As described above, in step S11 in FIG. 4, compared to the case where a constant value is used as the average power F _ASS'Y of the fuel assembly, the variable power F _ΔH ^N of the fuel rods 5 based on the data of FIG. By using the value, the output limit line L1 can be raised to the relaxed side.

Note that either one of the rationalization of the core axial power distribution _FZ and the rationalization of the fuel assembly average power F _ASS'Y may be applied, or both may be applied. You don't have to apply both. By rationalizing the power distribution _FZ in the axial direction of the core and by rationalizing the average power F _ASS'Y of the fuel assemblies, excessive restriction of the local power of the fuel rods 5 is suppressed. be able to.

(Reactor core design method)
Next, referring to FIG. 8, a core design method for designing the core using the power limitation map shown in FIG. 7 will be described. FIG. 8 is a flowchart relating to the core design method according to this embodiment. The core is designed so that the local power of the fuel rods 5 is below the power limit line L1. The core design method shown in FIG. 8 is executed by an analysis device similar to the analysis device 1 shown in FIG.

First, the calculation unit 11 acquires input parameters as input conditions for core design (step S31). After that, when the arrangement of the fuel assemblies to be loaded into the core is created, the calculation unit 11 acquires the created arrangement of the fuel assemblies in the core (step S32). Subsequently, the calculation unit 11 performs core calculation based on the input parameters and the arrangement of the fuel assemblies to calculate and evaluate the core characteristics (step S33). After that, the calculation unit 11 evaluates whether or not the evaluated core characteristics match the design requirements, thereby judging the feasibility of the arrangement of the fuel assemblies (step S34). In step S34, the design requirements include a requirement that the local power of the fuel rods 5 included in the core be equal to or lower than the power limit lines L1 and L2. If so (step S34: No), the arrangement of the fuel assemblies is reviewed again (step S35). After executing step S35, the calculation unit 11 executes steps S32 and S33 again. On the other hand, if the calculation unit 11 determines in step S34 that the design requirements are satisfied and established (step S34: Yes), it determines that the arrangement of the fuel assemblies in the core has been completed (step S36). As a result, the core designed according to the core design shown in FIG. 8 can suppress the local power of the fuel rods 5 from exceeding the power limit lines L1 and L2 even during LOCA.

(Safety evaluation method)
Next, referring to FIGS. 9 and 10, using the output limit line L1 derived by the output limit line analysis method, it is determined whether physical damage to the cladding tube 7, particularly the FFRD phenomenon, occurs. The safety evaluation method will be explained. FIG. 9 is a flowchart relating to the safety evaluation method according to this embodiment. FIG. 10 is an explanatory diagram relating to the safety evaluation method according to this embodiment. The safety evaluation method shown in FIG. 9 is executed by an analysis device similar to the analysis device 1 shown in FIG. Moreover, this safety evaluation method is a method for determining whether or not the FFRD phenomenon occurs in an existing reactor core.

First, the calculation unit 11 obtains the output limit line L1 derived by the output limit line analysis method (step S41). The calculation unit 11 determines whether or not the local power of the fuel rods 5 obtained by core calculation for the existing core is below the power limit line L1 (step S42). Here, for example, there is a graph shown in FIG. 10 as a local output that changes according to the burnup of the fuel rods 5. Δ (white triangle) in FIG. 10 is an example of the local output of the fuel rod 5 (pattern 1), and ● (black circle) in FIG. 10 is another example of the local output of the fuel rod 5 (pattern 2). be. When the calculation unit 11 determines that the local power of the fuel rod is below the power limit line L1 (step S42: Yes), it determines that the fuel is safe (step S43). In FIG. 10, the local power output of the fuel rod 5, which is pattern 2, is determined as good. On the other hand, if the calculation unit 11 determines that the local power of the fuel rod is greater than the power limit line L1 (step S42: No), it determines that it is not safe (step S44). In FIG. 10, the local power output of the fuel rod 5, which is pattern 1, is negative.

As described above, the power limit value analysis method, the safety evaluation method, the core design method, and the analysis apparatus 1 described in the present embodiment are understood as follows, for example.

A method of analyzing a power limit value according to a first aspect is a method of analyzing a power limit value L1 for deriving a power limit value L1 for limiting the local power of fuel rods provided in a core by executing analysis processing. The fuel rod 5 has a fuel pellet 6 and a cladding tube 7 covering the fuel pellet 6, and the input parameters input to the analysis process are the internal pressure of the fuel rod 5, a plurality of of the fuel assembly consisting of the fuel _rods 5, the average power F _ΔH ^N of the fuel rods 5, the power distribution F _Z in the axial direction of the core, and based on the input parameters, a predetermined A first step (step S11) of analyzing the behavior of the fuel rod 5 at the burnup of , and analyzing the physical damage of the cladding tube 7 at the time of LOCA (step S11), and the first step while changing the burnup a second step (step S12) of deriving the local power of the fuel rod 5 at which physical damage to the cladding tube 7 occurs and the burnup corresponding to the local power by repeating the step of , based on the derived local power and the burnup, the power limit value L1 below the local power at which physical damage to the cladding tube 7 corresponding to the burnup occurs is derived. and a step (step S13).

According to this configuration, it is possible to derive the output limiting line L1 in which the cladding tube 7 is not physically damaged. Therefore, by using the derived power limit line L1, it is possible to suppress the local power of the fuel rods 5, so that physical damage to the cladding tubes 7 of the fuel rods 5 can be suppressed even during a LOCA. can.

As a second aspect, the core design for designing the core further comprises a fourth step (step S14) of setting the derived power limit value L1, wherein the power limit value L1 is set to a predetermined burnup or more. is set in

According to this configuration, the output limit value L1 can be set at a predetermined burnup or higher at which the FFRD phenomenon occurs. Therefore, the occurrence of the FFRD phenomenon can be suppressed, and physical damage to the cladding tube 7 of the fuel rod 5 can be suppressed even during LOCA.

As a third aspect, in the fourth step, if the output limit value set at the predetermined burnup or more is set as a first output limit value L1, the first output limit value is set at less than the predetermined burnup. A second power limit value L2 is set on the side of the power limit line L1 that is relaxed so that the core coolable shape can be maintained.

According to this configuration, it is possible to suppress excessive restriction of the local power of the fuel rods 5 when the burnup is less than the predetermined burnup. Therefore, it is possible to suppress the deterioration of the usage efficiency of the fuel rods 5 .

As a fourth aspect, the predetermined burnup is the burnup at the middle of the cycle or at the end of the cycle.

According to this configuration, the local power of the fuel rods 5 can be suppressed in the middle of the cycle or the end of the cycle when the FFRD phenomenon is likely to occur.

As a fifth aspect, the predetermined burnup is 60 GWd/t or more.

According to this configuration, the local power output of the fuel rods 5 can be suppressed at a burnup of 60 GWd/t or higher where the FFRD phenomenon is likely to occur.

As a sixth mode, in the first step, among the input parameters, the power distribution in the axial direction of the core is that of the middle cycle or the end of the cycle.

According to this configuration, since the power distribution _FZ in the axial direction of the core, which is an input parameter, can be set to a reasonable value, it is possible to prevent the local power of the fuel rods 5 from being excessively restricted.

As a seventh aspect, data associated with the average power F _ΔH ^N of the fuel rods and the average power F _ASS'Y of the fuel assemblies are prepared in advance, and are input as the input parameters in the first step. The fuel bundle average power output is the fuel bundle average power associated with the fuel rod average power entered as the input parameter based on the data.

According to this configuration, the average power F _ASS'Y of the fuel assembly, which is the input parameter, can be set to a reasonable value, so that excessive restriction of the local power of the fuel rods 5 can be suppressed. .

The safety evaluation method according to the eighth aspect evaluates the local power of the fuel rods 5 designed in the core design based on the power limit line L1 derived by the above power limit line analysis method, It is determined whether or not the cladding tube 7 is physically damaged.

According to this configuration, it is possible to determine whether or not physical damage to the cladding tubes 7 occurs in the core fuel rods 5 designed for the core. It is possible to suppress the occurrence of physical damage.

In the core design method according to the ninth aspect, the core is designed so that the local power of the fuel rods is equal to or less than the power limit line L1 derived by the power limit line analysis method described above.

According to this configuration, it is possible to suppress the occurrence of physical damage to the cladding tube 7 of the fuel rod 5 at the time of LOCA.

An analysis device 1 according to a tenth aspect is the analysis device 1 having a calculation unit 11 that executes analysis processing and derives an output limit value L1 for limiting the local output of fuel rods provided in the core. The fuel rod 5 has a fuel pellet 6 and a cladding tube 7 covering the fuel pellet 6, and the input parameters input to the analysis process are the internal pressure of the fuel rod 5, the plurality of The input parameters include the average power F _ASS'Y of the fuel assembly consisting of the fuel rods 5, the average power F _ΔH ^N of the fuel rods 5, and the power distribution F _Z in the axial direction of the core. Based on this, a first step (step S11) of analyzing the behavior of the fuel rod 5 at a predetermined burnup to analyze the physical damage of the cladding tube 7 at the time of LOCA (step S11), and changing the burnup While repeating the first step, the second step (step S12), and based on the derived local power and burnup, the power limit value L1 below the local power at which physical damage to the cladding tube 7 corresponding to each burnup occurs is derived. A third step (step S13) is executed.

According to this configuration, it is possible to derive the output limit value L1 that does not cause physical damage to the cladding tube 7 . Therefore, by using the derived power limit value L1, it is possible to suppress the local power of the fuel rods 5, so that physical damage to the cladding tubes 7 of the fuel rods 5 can be suppressed even during a LOCA. can.

1 analysis device 5 fuel rod 6 fuel pellet 7 cladding tube 11 calculation unit 12 storage unit 13 display unit 14 input unit D1 input information D2 output information

Claims (10)

A power limit value analysis method for deriving a power limit value for limiting the local power of fuel rods provided in a core by executing analysis processing, comprising:
The fuel rod has a fuel pellet and a cladding tube that coats the fuel pellet,
The input parameters input to the analysis process include the internal pressure of the fuel rods, the average power of a fuel assembly consisting of a plurality of the fuel rods, the average power of the fuel rods, and the power distribution in the axial direction of the core,
a first step of analyzing the behavior of the fuel rod at a given burnup based on the input parameters to analyze the physical failure of the cladding during a LOCA;
By repeating the first step while changing the burnup, the local power of the fuel rod at which physical damage to the cladding occurs and the burnup corresponding to the local power are derived. 2 steps;
a third step of deriving, based on the derived local power and the burnup, the power limit below the local power at which physical failure of the cladding corresponding to each burnup occurs; A method of parsing power limits comprising In the core design for designing the core, further comprising a fourth step of setting the derived power limit value,
2. The method of analyzing an output limit value according to claim 1, wherein the output limit value is set at a burnup equal to or higher than a predetermined burnup. In the fourth step, if the output limit value set at the predetermined burnup or more is set as a first output limit value, the output limit value is relaxed more than the first output limit value at less than the predetermined burnup. 3. The power limit value analysis method according to claim 2, wherein a second power limit value that can maintain a core coolable shape is set on the side where the core is to be cooled. 4. The output limit value analysis method according to claim 2, wherein the predetermined burnup is a burnup in the middle of the cycle or the end of the cycle. 5. The output limit value analysis method according to claim 4, wherein the predetermined burnup is 60 GWd/t or more. 6. The analysis of the power limit value according to any one of claims 1 to 5, wherein in the first step, among the input parameters, the power distribution in the axial direction of the core is that of the middle cycle or the end of the cycle. Method. Data associated with the average power of the fuel rods and the average power of the fuel assemblies are prepared in advance,
In the first step, the average power of the fuel assembly input as the input parameter is associated with the average power of the fuel rod input as the input parameter based on the data. 7. The method for analyzing the output limit value according to any one of claims 1 to 6, wherein the average output of By evaluating the local power of the fuel rod designed in core design based on the power limit value derived by the power limit value analysis method according to any one of claims 1 to 7, the coating A safety evaluation method for determining whether or not physical damage to pipes will occur. A core design method for designing a core so that the local power of said fuel rods is equal to or less than the power limit value derived by the power limit value analysis method according to any one of claims 1 to 7. An analysis device having a calculation unit that executes analysis processing to derive a power limit value for limiting the local power of a fuel rod provided in a core,
The fuel rod has a fuel pellet and a cladding tube that coats the fuel pellet,
The input parameters input to the analysis process include the internal pressure of the fuel rods, the average power of a fuel assembly consisting of a plurality of the fuel rods, the average power of the fuel rods, and the power distribution in the axial direction of the core,
The calculation unit is
a first step of analyzing the behavior of the fuel rod at a given burnup based on the input parameters to analyze the physical failure of the cladding during a LOCA;
By repeating the first step while changing the burnup, the local power of the fuel rod at which physical damage to the cladding occurs and the burnup corresponding to the local power are derived. a step of
a third step of deriving, based on the derived local power and the burnup, the power limit below the local power at which physical failure of the cladding corresponding to each burnup occurs; An analysis device that performs

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