JP4064775B2 - Core monitoring method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  According to the present invention, the maximum linear power density and the minimum critical power ratio (hereinafter, these two values are referred to as thermal characteristics) that change from time to time during reactor core flow operation or control rod operation are periodically or Calculate the thermal characteristics at the time when the power distribution calculation is not performed from the power distribution calculation results and the in-core nuclear instrumentation measurement values performed at the operator's request, and the thermal characteristics exceed the allowable value or the operation limit value. The core monitoring method is configured to issue an alarm and stop the core flow rate operation or control rod operation whenTo the lawRelated.
[0002]
[Prior art]
At the start of the boiling water reactor or when adjusting the control rod pattern for adjusting the reactivity of the core, the core flow rate is increased / decreased and the control rod is withdrawn / inserted. In these operations, the thermal characteristics of the reactor change from time to time, and it is confirmed that the thermal characteristics satisfy the operating limit values by calculating the power distribution performed at regular intervals or at the operator's request. It is necessary to operate while.
[0003]
FIG. 14 shows a general start-up and control rod pattern adjustment procedure.
That is, control rod operation core flow rate operation, operation stop, output distribution calculation, and thermal characteristic confirmation are repeated as necessary from the start of operation, and collated with the target output.
[0004]
In the power distribution calculation, nuclear instrumentation is used to measure the neutron flux in the reactor core using a three-dimensional simulator that combines the nuclear calculation to calculate the neutron behavior and the thermal hydraulic calculation to calculate the flow rate distribution and void fraction distribution in the core. The thermal characteristics of each fuel assembly constituting the core are calculated from the measured plant data such as system and reactor pressure, control rod pattern, core flow rate, and the like. For this reason, it takes time to calculate the power distribution, and it is necessary to check the thermal characteristics while interrupting the operation as appropriate during the core flow rate operation and the control rod operation.
[0005]
In addition, the thermal characteristics of 16 fuel assemblies surrounded by four strings in which a local power range monitor (hereinafter referred to as LPRM) that measures the local neutron flux level in the reactor exists, Conventionally, a method of predicting from the LPRM indication values of the detector aggregate included in the four strings has been used. Hereinafter, the position of the detector assembly is referred to as a string.
[0006]
A conventional method for calculating the thermal characteristic from the LPRM indicated value will be described with reference to FIG.
In this method, from the average rate of increase in the LPRM indicated value of the detector assemblies B1 to B4 belonging to the four strings, the strictest limit power ratio among the 16 fuel assemblies A1 to A16 surrounded by the four strings For each LPRM height, the strictest linear power density among the 16 fuel assemblies A1 to A16 is calculated by proportional calculation.
[0007]
[Problems to be solved by the invention]
In the conventional core monitoring method, when the fuel assembly having the most severe thermal characteristics is a fuel assembly excluding the fuel assemblies A1, A4, A13, and A16 adjacent to the string, the detector assembly B1 The LPRM detector of ~ B4 is in a state separated from the fuel assembly having severe thermal characteristics. Further, when the fuel assembly having the most severe thermal characteristics in the 16 bodies is any one of the fuel assemblies A1, A4, A13, and A16, the thermal characteristics are the most severe in the calculation of the thermal characteristics. The indicator value of the LPRM of the detector assembly located away from the fuel assembly is also used. That is, when the fuel assembly A1 has the most severe thermal characteristics, since the detector assemblies B2 to B4 are separated, the correlation between the thermal characteristics and the LPRM indicated value is weak, and the thermal characteristics can be calculated accurately. Have difficulty.
[0008]
As described above, in order to monitor the thermal characteristics during the core flow rate operation of the boiling water reactor or the control rod operation with the conventional core monitoring method, it takes time to calculate (as shown in FIG. 14). The operation must be stopped). Further, when the thermal characteristics are easily evaluated from the local output region monitor instruction value, there is a problem that the thermal characteristics cannot be accurately evaluated and a large margin is taken.
[0009]
The present invention has been made to solve the above problems, and based on the indication value of the local power region monitor and the power distribution calculation result performed immediately before, the heat of the reactor at the time of core flow operation and control rod operation It is an object of the present invention to provide a core monitoring method and a core monitoring system that can continuously monitor the mechanical characteristics more quickly and accurately, maintain the soundness of the fuel, and reduce the time required for startup and pattern adjustment.
[0010]
[Means for Solving the Problems]
  According to a first aspect of the present invention, there is provided a local power region monitor arranged at four positions at approximately equal intervals in the axial direction in the core monitoring method in the power increase process in which the core flow rate operation or the control rod operation of the reactor is automatically performed. Among the four fuel assemblies adjacent to the stringAt the stationOutput area monitor height, nodes adjacent to the local output area monitor, or every 1/4 of the fuel active lengthBiggestBased on the output distribution calculation result and the rate of change of the indicated value of the local output area monitor(1) Formula and (2 In the formulaWhen at least one of the calculated maximum value of the linear power density and the calculated minimum value of the limit power ratio of the plurality of fuel assemblies around the entire string deviates from the operation limit valueIn addition,At least one of an automatic operation stop signal, a control rod operation inhibition signal for the control rod operation system, and a flow rate operation inhibition signal for the flow rate control system is generated.
MFLPDAT (K, ISTR) = MFLPDIN (K, ISTR)
    × (1+ (1 / FK (K)) × (LPRMAT (K, ISTR) / LPRMIN (K, ISTR) -1)) ... (1) formula
  here,
  MFLPDAT (K, ISTR) : String position ISTR , Height position K Ratio of maximum linear power density and operating limit value in four fuel assemblies around string
  LPRMAT (K, ISTR) : String position ISTR , Height position K LPRM indication value at
  MFLPDIN (K, ISTR) : String position ISTR , Height position K Ratio of maximum line power density and operation limit value by calculation of power distribution in four fuel assemblies around string
  LPRMIN (K, ISTR) : String position ISTR , Height position K LPRM indicated value when calculating output distribution at
  FK (K) : Height position K Factor for calculating linear power density at
MFLCPAT (ISTR) = MFLCPIN (ISTR)
    × (1 + (1 / FC) × (LPAVAT (ISTR) / LPAVIN (ISTR) -1)) ... (2) formula
  here
  MFLCPAT (ISTR) : Limit output ratio limit value and string position ISTR Ratio of the minimum critical power ratio in four fuel assemblies around
  MFLCPIN (ISTR) : Operation limit value of limit output ratio by output distribution calculation and string position ISTR Ratio of the minimum critical power ratio in four fuel assemblies around
  LPAVAT (ISTR) : String position ISTR Weighted average value of indicated values of four LPRM-A to D belonging to
  LPAVIN (ISTR) : String position when calculating output distribution ISTR Weighted average value of indicated values of four LPRM-A to D belonging to
  FC : Safety factor for calculating the limit output ratio
[0011]
  According to a second aspect of the present invention, there is provided a local power region monitor disposed at four substantially equal intervals in the axial direction in the core monitoring method in the power increase process in which the core flow rate operation or the control rod operation of the reactor is automatically performed. Among the four fuel assemblies adjacent to the string and the fuel assemblies loaded in positions symmetrical to the four fuel assembliesAt the stationThe output area monitor height, or the node adjacent to the local output area monitor, or every 1/4 of the active fuel lengthBiggestBased on the output distribution calculation result and the rate of change of the indicated value of the local output area monitor(1) Formula and (2) By formulaCalculated, and at least one of the maximum value of the calculated linear power density and the minimum value of the calculated limit power ratio of the plurality of fuel assemblies around the entire string and the fuel assemblies at the symmetrical positions deviates from the operation limit value. CaseIn addition,At least one of an automatic operation stop signal, a control rod operation inhibition signal for the control rod operation system, and a flow rate operation inhibition signal for the flow rate control system is generated.
MFLPDAT (K, ISTR) = MFLPDIN (K, ISTR)
    × (1+ (1 / FK (K)) × (LPRMAT (K, ISTR) / LPRMIN (K, ISTR) -1)) ... (1) formula
  here,
  MFLPDAT (K, ISTR) : String position ISTR , Height position K Ratio of maximum linear power density and operating limit value in four fuel assemblies around string
  LPRMAT (K, ISTR) : String position ISTR , Height position K LPRM indication value at
  MFLPDIN (K, ISTR) : String position ISTR , Height position K Ratio of maximum line power density and operation limit value by calculation of power distribution in four fuel assemblies around string
  LPRMIN (K, ISTR) : String position ISTR , Height position K LPRM indicated value when calculating output distribution at
  FK (K) : Height position K Factor for calculating linear power density at
MFLCPAT (ISTR) = MFLCPIN (ISTR)
    × (1 + (1 / FC) × (LPAVAT (ISTR) / LPAVIN (ISTR) -1)) ... (2) formula
  here
  MFLCPAT (ISTR) : Limit output ratio limit value and string position ISTR Ratio of the minimum critical power ratio in four fuel assemblies around
  MFLCPIN (ISTR) : Operation limit value of limit output ratio by output distribution calculation and string position ISTR Ratio of the minimum critical power ratio in four fuel assemblies around
  LPAVAT (ISTR) : String position ISTR Weighted average value of indicated values of four LPRM-A to D belonging to
  LPAVIN (ISTR) : String position when calculating output distribution ISTR Weighted average value of indicated values of four LPRM-A to D belonging to
  FC : Safety factor for calculating the limit output ratio
[0012]
According to a third aspect of the present invention, in the calculation of the critical power ratio according to the first or second aspect, the relationship between the core flow at the time of calculating the power distribution and the core flow at the time of calculating the critical power ratio is expressed by a polynomial expression as a function of the core power. Approximate and use the approximate polynomial to correct the limit output ratio when calculating the minimum limit output ratio.
[0013]
According to a fourth aspect of the present invention, in the calculation of the linear power density according to the first or second aspect, the rate of change of the linear power density based on the position of the control rod at the time of calculating the power distribution and when calculating the power distribution is calculated by The linear power density is calculated as a function of the indicated value change rate and the control rod position.
[0014]
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, when calculating the linear output density of the four fuel assemblies adjacent to the string or the fuel assemblies including their symmetrical positions, the local output is calculated. The line output density at a height where no area monitor exists is calculated from the output distribution calculation result and the interpolated value of the change rate of the indicated value of the local output area monitor above and below the target height.
[0015]
A sixth aspect of the present invention is that, in any one of the first to fifth aspects, when the local output area monitor is in a failure or bypass state, the indicated value change of the local output area monitor existing at the same height at a symmetrical position The rate is substituted as the indicated value change rate of the local output region monitor in the failure or bypass state.
[0016]
According to the seventh aspect of the present invention, when the local output area monitor is in a fault or bypass state, the local output area monitor in the fault or bypass state is obtained when all the strings in which the local output area monitor exists are developed in rotational symmetry. If the local output area monitor of the same height as the fault or bypass local output area monitor of a plurality of strings adjacent to the string containing The rate of increase in the indicated value of the local output area monitor at the same height of the local output area monitor of the fault or bypass state of one string adjacent to the string including the local output area monitor of the state is determined as the local value of the fault or bypass state. It is characterized in that it is substituted as the indicated value change rate of the output area monitor.
[0018]
The core of a nuclear reactor is usually configured to have 1/4 symmetry, and further 1/8 symmetry, and it becomes asymmetric even when symmetry cannot be maintained depending on the type and number of fuel assemblies that make up the core. The fuel loading pattern is determined so that there are few parts.
[0019]
Further, the control rod operation is also performed so that the control rod pattern is also symmetric by performing one or a plurality of symmetrical position control rods simultaneously. This is because by providing symmetry, the radial peaking of the core is reduced and the thermal characteristics are improved, and the combustion history of a plurality of fuel assemblies at the symmetric position and the neutron of the control rod at the symmetric position. Since the irradiation history becomes the same, the management of the fuel and the control rod becomes easy.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a core monitoring method according to the present invention will be described with reference to FIGS.
FIG. 1 is a plan view schematically showing an example of the core arrangement of a 1300 MWe class boiling water reactor. In the core, as shown in FIG. 2 (b), a local power region for measuring the neutron flux level in the reactor is shown. There is a string in which detector assemblies 1 in which monitor detectors (LPRM detectors) 4 are arranged at four positions at almost equal intervals in the axial direction are provided.
[0021]
As shown in FIGS. 1 and 2 (a), one cross-shaped control rod 3 is inserted into the center of four fuel assemblies 2 from the lower part of the core (not shown). The detector assembly 1 including four detectors 4 is installed at equal intervals in the core radial direction at a ratio of 16 fuel assemblies 2 and one control rod 3 per four.
[0022]
FIG. 2 (a) shows the positions of the fuel assembly 2, the control rod 3, and the detector assembly 1 in which a part of the core in FIG. 1 is enlarged, and FIG. 2 (b) shows the detection in FIG. 2 (a). An axial configuration in the vessel assembly 1 is shown. In the detector assembly 1, as shown in FIG. 2B, LPRM detectors 4 are arranged at approximately equal intervals in the axial direction from the bottom to LPRM-A, LPRM-B, LPRM-C, LPRM-D 4. Pieces are arranged.
[0023]
In addition, the calibration of the LPRM detector 4 and the TIP calibration in which a mobile in-core instrumentation neutron detector (hereinafter referred to as TIP) for continuously measuring the axial neutron flux distribution moves inside. Consists of a working conduit 5.
[0024]
The effective fuel length filled with the nuclear fuel material in the fuel assembly 2 is divided into 24 (or 25), and this length is called a node. In the detector assembly 1 illustrated in FIG. 2 (b), the LPRM detector 4 includes the LPRM detector A at a height substantially at the center between the third node and the fourth node from the lower end of the effective fuel length. The LPRM detector B is at approximately the center height of the node and the 10th node, and the LPRM detector C is approximately at the center height of the 15th and 16th nodes. Next, the LPRM detector D is located.
[0025]
The LPRM detector measures the neutron flux level at that location, so the power per unit rod length at the height of the LPRM detector at the fuel assembly adjacent to it, i.e. a line The power density is approximately proportional to the increase rate of the indicated value of the LPRM detector, and the output of the adjacent fuel assembly is approximately proportional to the average increase rate of the indicated values of the four LPRM detectors belonging to the string.
[0026]
By using this correlation, the thermal characteristics of the fuel assembly around the string can be expressed as the indicated value of the LPRM detector based on the power distribution calculation result obtained from the core three-dimensional simulator, LPRM detector, and measured plant data. It can be easily calculated from the rate of increase.
That is, the line power density around the string and the limit power ratio can be expressed by the following equations.
[0027]
(Linear power density)
MFLPDAT (K, ISTR) = MFLPDIN (K, ISTR) × (1+ (1 / FK (K)) × (LPRMAT (K, ISTR) / LPRMIN (K, ISTR) -1)) (1)
here,
MFLPDAT (K, ISTR): Ratio of maximum linear power density and operating limit value in four fuel assemblies around string at string position ISTR and height position K
LPRMAT (K, ISTR): LPRM indication value at string position ISTR and height position K
MFLPDIN (K, ISTR): Ratio of maximum line power density and operation limit value by calculation of power distribution in four fuel assemblies around string at string position ISTR and height position K
LPRMIN (K, ISTR): LPRM indication value when calculating output distribution at string position ISTR and height position K
FK (K): Safety factor for calculating the linear power density at the height position K.
[0028]
(Limit output ratio)
MFLCPAT (ISTR) = MFLCPIN (ISTR) × (1+ (1 / FC) × (LPAVAT (ISTR) / LPAVIN (ISTR) -1)) (2)
here
MFLCPAT (ISTR): Ratio of the limit power ratio operation limit value and the minimum limit power ratio in the four fuel assemblies around the string position ISTR
MFLCPIN (ISTR): The ratio between the operation limit value of the limit power ratio and the minimum limit power ratio in the four fuel assemblies around the string position ISTR by the power distribution calculation
LPAVAT (ISTR): Weighted average value of indicated values of four LPRM-A to D belonging to the string position ISTR
LPAVIN (ISTR): Weighted average value of the indicated values of four LPRM-A to D belonging to the string position ISTR at the time of output distribution calculation
FC: Safety factor for calculating the limit output ratio.
[0029]
In the core monitoring method according to the present invention, by using Equations (1) and (2), MFLPDIN (K, ISTR), LPRMIN (K, ISTR), MFLCPN (ISTR), LPAVIN (ISTR) Can be used to calculate the thermal characteristics at the time when the power distribution calculation during the control rod operation and the core flow rate operation is not performed. This method is shown in FIG. 3 in contrast to the conventional case shown in FIG. As shown in FIG. 3, in this method, in each cycle, the result of the output distribution calculation calculated before and the indicated value of the LPRM detector are used without using the time-consuming output distribution calculation, and the expression (1), ( 2) By calculating instantaneously using the formula, it is not necessary to stop the operation of the control rod and the core flow rate every time the thermal characteristics are calculated. That is, the cycle of calculating the thermal characteristics by the simple calculation based on the LPRM instruction value at the time of the control rod operation or the core flow rate operation when the power distribution calculation is not performed, which is indicated by the solid line C1 in FIG. On the other hand, the cycle of calculating the thermal characteristics by the output distribution calculation indicated by the broken line C2 in FIG. 3 is performed at a frequency of every fixed time or upon request.
[0030]
Here, in equations (1) and (2), the most severe thermal characteristics of the four fuel assemblies around each string are calculated. This is the fuel loading pattern, control rod described above. This is because, due to the symmetry of the pattern, the thermal characteristics of the fuel assemblies at the symmetrical positions are equal to each other, so it is sufficient to monitor severe ones among the four bodies around the string.
[0031]
That is, in FIG. 1, 52 detector assemblies represented by reference numeral 1 are numbered from 1 to 52. However, taking the detector assembly of number 1 in the figure as an example, XY Taking a detector assembly displayed in a coordinate system as an example, the thermal characteristics of four fuel assemblies located at fuel assembly coordinates 27-04, 29-04, 27-06, 29-06 are: In the case of rotational symmetry with the symmetry axes aa ′ and bb ′, the four fuel assembly coordinates 03-42, 03-40, 05-42, and 05-40, 41-66, 39-66, and 41- It is equal to the thermal characteristics of four fuel assemblies 64, 39-64, and four fuel assemblies 65-28, 65-30, 63-28, 63-30.
[0032]
Considering such symmetry, the thermal characteristics of all the fuel assemblies in the core except for a part of the fuel assemblies located at the outermost radial direction of the core by only the detector assembly shown in FIG. Can be calculated. Further, the fuel assembly output at the outermost periphery is low due to neutron leakage, and the thermal characteristics are not severe.
[0033]
From this, if the core monitoring method according to the present invention calculates the thermal characteristics of the fuel assembly around the string, take the most severe of them, and confirm that it does not deviate from the operating limit value It is not necessary to stop the control rod operation and the core flow rate operation.
[0034]
Next, the system configuration of the core monitoring system for carrying out the core monitoring method according to the present invention will be described with reference to FIG.
In FIG. 4, a shroud 9 that wraps the core and forms a coolant flow path is installed in a reactor pressure vessel denoted by reference numeral 6. The core is composed of a fuel assembly 2, a detector assembly 1, and a control rod 3 inserted from the bottom of the core. On the shroud 9 are installed a steam / water separator 8 for separating steam generated in the core and reactor water, and a steam dryer 7 for drying the steam.
[0035]
An internal pump 11 is installed below the reactor pressure vessel 6, and the internal pump 11 adjusts the flow rate of coolant flowing through the core, that is, the core flow rate, according to the rotational speed. A plurality of control rod drive mechanisms 10 that pass through the lower part of the reactor pressure vessel 6 and adjust the position of the control rod 3 downward are provided. The control rod operating system 14 is a device that adjusts the position of the control rod 3 via the control rod drive mechanism 10. The recirculation flow rate control system 13 is a device that adjusts the core flow rate by changing the rotational speed of the internal pump 11.
[0036]
At the time of output increase and control rod pattern adjustment, the core monitoring device 16 transmits an operation prohibition command signal to the recirculation flow rate control system 13 and the control rod operation system 14 when the thermal characteristics of the core deviate from the operation limit value. As a result, the core flow rate operation and the control rod operation are stopped. The plant data 18 is a data group of sensor values such as a reactor core flow rate, a control rod pattern, a core pressure, a main steam flow rate, and a feed water temperature, and these are updated every moment.
[0037]
The in-core instrumentation system 12 averages the signals of a plurality of LPRM detectors that are in-core neutron flux instrumentation, and processes the signal of the average power range monitor (APRM) calibrated to the thermal output equivalent. Based on the signal from the in-core instrumentation system 12, the power distribution calculation is calculated by the process computer 15 and the thermal characteristics are calculated by the core monitoring device 16. The in-core instrumentation system 12 also has a function of transmitting a signal for stopping the plant by an alarm and rapid insertion of all control rods when the neutron flux level in the furnace shows an abnormal value.
[0038]
The process computer 15 receives the plant data 18 and the measured value data from the in-core instrumentation system 12 and performs an output distribution calculation by a built-in core three-dimensional simulator to determine the thermal characteristics and voids of each fuel assembly. Calculate the rate distribution. This output distribution calculation is performed at regular time intervals or at the request of the operator.
[0039]
The automatic output adjustment system 17 is preloaded with core flow rate operation and control rod operation procedures at startup, control rod pattern adjustment, and shutdown, and according to this procedure, the recirculation flow rate control system 13 or the control rod operation system 14 The core flow rate operation and the control rod operation command signal are automatically transmitted to the control unit, respectively, and the core flow rate and the control rod are automatically adjusted according to the procedure.
[0040]
The core monitoring device 16 receives from the process computer 15 the power distribution calculation result by the process computer 15, the plant data at the time of the power distribution calculation and the indication value of the LPRM detector, and the plant data 18 being updated from time to time. The indication value of the LPRM detector from the system 12 is continuously received, and the thermal characteristics of the fuel assembly around the string are continuously calculated by the equations (1) and (2).
[0041]
When the calculated thermal characteristics deviate from the operation limit value, an alarm is sent to the operator, the automatic operation stop signal is sent to the automatic output adjustment system 17 and the prohibition commands for the core flow rate operation and control rod operation are reapplied. This is transmitted to the circulation flow rate control system 13 and the control rod operation system 14 to stop the adjustment of the core flow rate and the control rod operation. In fact, such adjustment / operation has the effect of increasing the output, and is suspended until the situation where the thermal characteristics deviate from the operation limit value can be avoided.
[0042]
Next, specific examples of the core monitoring method according to the present invention will be described.
Example 1
In the core monitoring system shown in the system configuration diagram of FIG. 4, Embodiment 1 of the present invention is based on the power distribution calculation result performed by the process computer 15 at regular time intervals or at the request of the operator. Calculate the maximum flow power density and the minimum critical power ratio during the core flow operation and control rod operation at the time when the power distribution calculation is not performed according to the formulas (1) and (2). When the thermal characteristics deviate from the operation limit value, an alarm is issued and the core flow rate and control rod operation are stopped.
[0043]
Here, the line power density around the strings when calculating the power distribution received by the core monitoring device 16 from the process computer 15 is divided into effective fuel lengths of 24 according to the height of the LPRM detector of each string from the bottom, 3rd and 4th nodes for LPRM-A, 9th and 10th nodes for LPRM-B, 15th and 16th nodes for LPRM-C, 21st and 22nd nodes for LPRM-D It is installed at the height of and receives the line power density at each height.
[0044]
Alternatively, the value of the node having the higher line power density of the adjacent nodes above and below, that is, the higher line power density of the third node and the fourth node is received by LPRM-A, or fuel is supplied to each LPRM detector. It is also possible to receive the maximum within 6 nodes by associating each of the areas obtained by dividing the effective part into 4 nodes by 6 nodes. The core monitoring device 16 calculates the line power density from the indicated value change rate of the LPRM detector with reference to the received line power density.
[0045]
(Example 2)
In the second embodiment of the present invention, in the first embodiment, when the thermal characteristics based on the output distribution calculation as a reference are received from the process computer 15, four fuel assemblies adjacent to each string, and these fuel assemblies Among the fuel assemblies loaded at symmetrical positions, the thermal power is calculated by receiving the most severe limit power ratio and the linear power density corresponding to the height of each LPRM detector.
[0046]
In the case where the fuel loading pattern of the core cannot ensure complete symmetry, the thermal characteristics differ depending on the fuel at the symmetrical position. However, in the second embodiment, the control rod operation, the core is controlled due to the symmetry of the control rod operation. The rate of change of the thermal characteristics due to the flow rate operation utilizes the property of being substantially equal at the symmetrical position.
[0047]
In the second embodiment, among the fuel assemblies adjacent to the string and the fuel assemblies loaded in the symmetrical position, the most severe limit output ratio and linear output density are calculated from the LPRM indicated value increase rate. If this is performed for all strings, the strictest limit power ratio and line power density are required for all fuel assemblies excluding a part of the outermost periphery of the core.
[0048]
(Example 3)
The third embodiment of the present invention corrects the limit power ratio in consideration of the change in the limit power caused by the change in the core flow rate in the limit power ratio calculation process in the first or second embodiment.
[0049]
The critical power ratio is defined as the ratio of the critical power causing the boiling transition to the fuel assembly power. As the coolant flow rate in the fuel assembly increases, the cooling capacity increases and the marginal power increases. FIG. 5 shows the relationship between the flow rate in the fuel assembly and the limit output. Here, 1.0 in the fuel assembly flow rate corresponds to the flow rate in the fuel assembly per fuel assembly at the rated core flow rate.
[0050]
As can be seen from the relationship shown in FIG. 5, when the effect of increasing the limit power as the coolant flow rate is not taken into account, the limit power ratio calculated by the equation (2) is larger than the actual power when the core flow rate is increased. Overestimate and underestimate when the core flow rate decreases.
[0051]
Therefore, in the third embodiment, at the time of calculating the power distribution performed at regular intervals or at the request of the operator, and at the time when the core monitoring device 16 calculates the thermal characteristics, that is, at the time of calculating the limit power ratio. Based on the core flow rate (flow rate in the fuel assembly), the correlation between the core flow rate and the limit output is approximated by a polynomial or a function. That is, a critical power corresponding to the core flow rate is obtained, and from this relationship, a polynomial or function approximating a curve or a plot broken line as shown in FIG. 4 is obtained.
[0052]
Next, using this approximate polynomial or approximate function, the ratio between the critical power corresponding to the core flow at the time of calculating the power distribution and the critical power corresponding to the core flow at the time of calculating the minimum critical power ratio is obtained, and this ratio is calculated as By multiplying the right side of equation (2) to calculate the limit power ratio, it is possible to correct the limit power ratio and obtain a limit power ratio reflecting the change in the limit power due to the change in the core flow rate.
[0053]
Example 4
In the fourth embodiment of the present invention, in the linear power density calculation process in the first or second embodiment, each increase rate (change) of the linear power density and the indicated value of the LPRM detector caused by the change in the position of the control rod is calculated. The linear output density is corrected in consideration of the change in the relationship of the rate.
[0054]
As described above, the linear output density in the vicinity of the LPRM detector is substantially proportional to the indicated value increase rate (change rate) of the LPRM detector, but the linear output density and the indicated value of the LPRM detector depend on the position of the control rod. The relationship of change rate changes slightly. FIG. 5 shows four fuel assemblies adjacent to the string when one control rod adjacent to the string is pulled out from the fully inserted state (control rod position 0) to the fully extracted state (control rod position 200). The relationship between the control rod position and the ratio of the increase rate (change rate) of the maximum linear power density at the height position of LPRM-A and the indicated value increase rate (change rate) of LPRM-A is shown.
[0055]
As is apparent from FIG. 5, the ratio of the linear power density increase rate to the LPRM indicated value increase rate is approximately 1.0 from the control rod full insertion position (0) to the control rod position (150) pulled out to about 3/4. It can be seen that this ratio drops slightly between the control rod position of 150 and the full extraction position of 200. That is, the rate of increase of the linear power density becomes smaller than the rate of increase of the indicated value of the LPRM detector.
[0056]
The linear output density increase rate at the height position of each LPRM detector thus determined is determined as a function of the LPRM indicated value increase rate and the control rod position by a graph as shown in FIG. In the case of LPRM-A shown in FIG. 5, when the control rod position is in the range of 0 to 150, the LPRM instruction value increase rate is substantially equal to the linear output density.
[0057]
In the fourth embodiment, when obtaining the maximum linear power density at the height position of each LPRM detector of the four fuel assemblies adjacent to the string in the first or second embodiment, the operator is operated at regular intervals or at an operator's time. The position of the control rod adjacent to the string at the time of the power distribution calculation performed at the request of the power supply and the time when the core monitoring device 16 calculates the thermal power following the power distribution calculation, that is, the maximum linear power density calculation Is obtained as a function of the increase rate (change rate) of the indicated value of the LPRM detector and the control rod position. That is, for example, as shown in FIG. 5, a linear output density is approximated by a curve or a plot line indicating the relationship between the control rod position, the ratio of the increase rate of the linear output density and the increase rate of the LPRM detector indicated value. Is calculated using two parameters: the increase rate of the indicated value of the LPRM detector and the increase rate of the control rod density.
[0058]
Using the function thus obtained, the line output density calculated by the above equation (1) is corrected. For example, the actual linear power density increase rate is calculated from the control rod position and the LPRM detector indicated value increase rate for the two time points described above using the above function, and this increase rate is calculated on the right side of equation (1). The line power density is calculated by multiplying by, so that the maximum line power density can be corrected, and the maximum line power density reflecting the change in the LPRM detector instruction value caused by the change in the control rod insertion position can be obtained.
[0059]
FIG. 5 shows the relationship between the ratio of the linear power density increase rate and the LPRM indicated value increase rate at the height position of LPRM-A and the control rod position. LPRM-B, C, By obtaining the relationship corresponding to this figure with respect to the height position of D, a line output density subjected to more appropriate correction can be obtained.
[0060]
(Example 5)
The fifth embodiment of the present invention uses the fact that the linear power density is continuous in the axial direction when calculating the linear power density at the node position not adjacent to the height of the LPRM detector in the first or second embodiment. Thus, the line output density at the target node position is calculated using a value obtained by interpolating the indicated value increase rate of the LPRM detector located above and below the target node by the height of the target node.
[0061]
As the detector assembly shown in FIG. 2B, LPRM-A is the third and fourth nodes from the bottom of the effective fuel length, LPRM-B is the ninth and tenth nodes, and LPRM-C is the fifteenth node. And 16 nodes, LPRM-D is installed at almost the middle height of 21 nodes and 22 nodes.
[0062]
When the LPRM detector has such an arrangement, as a simple example, it is assumed that the line power density varies locally at a constant rate in the axial direction, and the line power density change rate is applied to the interpolation operation. Consider the case. When the line output density change rates at the respective node positions of LPRM-A and LPRM-B are calculated as a and b, respectively, the midpoint between 6 nodes and 7 nodes which are the midpoints of the node positions of these two LPRMs The linear power density change rate at the vertical position is
a + (b−a) / 2 = (a + b) / 2
Is calculated. Similarly, the linear power density change rate at the middle height between 7 and 8 nodes is
a + 2 (b−a) / 3 = (a + 2b) / 3
Is calculated.
[0063]
The first node, the second node, and the upper 23rd node and the 24th node do not have LPRM in the lower and upper parts, but these nodes have low output due to neutron leakage from the lower and upper cores. Monitoring is unnecessary because the line power density does not reach the maximum in the core at the height of these nodes.
[0064]
Thus, the four LPRM detectors can accurately obtain the line output density at the focused height position without performing detection directly by the LPRM detector at the focused node position.
[0065]
(Example 6)
The LPRM detector may be in a bypass state in which the signal is intentionally cut off due to a failure or inspection due to leakage of ionized gas or disconnection during operation. In such a case, the core monitoring device 16 cannot receive an appropriate indication value of the LPRM in the fault or bypass state from the in-core instrumentation system 12, and the thermal characteristics of the fuel assembly adjacent to the string including the LPRM are determined. It cannot be calculated.
[0066]
As shown in FIG. 1, since the strings exist with cc ′ as the axis of symmetry, the LPRM included in the strings excluding the string on the axis of symmetry cc ′ always has the same height position when the LPRM is in a failure or bypass state. There will be one symmetric LPRM.
[0067]
The sixth embodiment of the present invention uses the symmetry of LPRM in any of the first to fifth embodiments, and uses other LPRMs at the same height and symmetrical position of the LPRM in a fault or bypass state. The rate of increase of the indicated value is used as a substitute to calculate the thermal characteristics around the string in a fault or bypass state. This embodiment utilizes the fact that the LPRM instruction value increase rate at the symmetrical position is substantially equal due to the symmetry of the fuel loading pattern and the control rod pattern.
[0068]
In the sixth embodiment, when the LPRM-A of the first string is in a failure or bypass state, the indicated value of the LPRM-A of the 17th string that is symmetric with respect to this and cc ′ is the furnace It is received by the core monitoring device 16 via the internal instrumentation system 12, and the core monitoring device 16 treats this indicated value as a substitute value for the indicated value of LPRM-A of the first string and performs calculation.
[0069]
Thereby, even when the LPRM detectors of some strings are in a failure or bypass state, the thermal characteristics of the fuel assembly adjacent to the strings including the LPRMs can be calculated with high accuracy.
[0070]
(Example 7)
In the above-described sixth embodiment, the LPRM of the string on the symmetry axis cc ′ does not have the LPRM at the symmetry position. Therefore, when the LPRM of the string on the symmetry axis is in a failure or bypass state, the substitute value is set. I can't ask for it. Further, when a plurality of LPRMs at symmetrical positions are simultaneously in a failure or bypass state, a substitute value cannot be obtained.
[0071]
The seventh embodiment of the present invention can cope with such a case in the sixth embodiment. First, the string position is developed in a rotationally symmetrical manner with respect to the symmetry axes aa ′ and bb ′ of FIG. To do. FIG. 7 shows a plan view of the core in which the strings are developed. In FIG. 7, the square grids represent control rods and four fuel assemblies adjacent to the control rods, that is, control rod cells. In FIG. 7, each number is a string number in the upper left corner of the square mesh. The strings with the marks (numbers 1 to 52) indicate the strings (actual strings) in which the detector assembly 1 exists. Other than that, the real string number is shown when the real string is expanded in rotational symmetry.
[0072]
From FIG. 7, for example, the expanded strings adjacent to the string of the string number 6A are the strings 23A, 34A, 26A, and 24A. That is, the string number 6A is surrounded by the strings 23A, 34A, 26A, and 24A, and they are the closest strings. For this reason, when the LPRM of the string number 6 is in a failure or bypass state, the average of the indicated value increase rate of the LPRM of the same height of one to four strings adjacent to each other when they are symmetrically deployed is substituted. . That is, the indicated value change rate of the LPRM detector of the strings 26B and 34B adjacent to the string 6B at the symmetrical position with the string number 6A and the LPRM detection of the strings 23C and 24C adjacent to the string 6C at the symmetrical position of the string number 6A An average with the indicated value change rate of the detector is obtained and used as a substitute for the indicated value change rate of the LPRM detector of the string 6A.
[0073]
Further, as a modification of the present embodiment, when the symmetry of the nuclear reactor is used and the detector assembly is arranged at a string position symmetrical to the string position where a certain detector assembly exists, When the LPRM detector of either one of the detector assemblies is in a failure or bypass state, the thermal characteristics are determined based on the indicated value of the LPRM detector at the same height and symmetrical position as this LPRM detector. It is also assumed that the calculation of
In the seven embodiments described above, a plurality of embodiments can be applied in combination as appropriate.
[0074]
Next, as the operation of the core monitoring method according to the present invention, the results of obtaining the response of the core monitoring method according to the present invention using an off-line core three-dimensional simulator will be described.
[0075]
FIGS. 8A to 8I show the core states 1 to 9 in the middle of increasing the output. Since the control rod pattern is 1/4 symmetric, each figure shows the 1/4 region of the core, and the power and flow rate are shown as rated thermal power and rated core flow rate as 100%.
[0076]
The power distribution calculation is performed in the core state 1 shown in FIG. 8A, and the core state 2 shown in FIG. 8B to FIG. The thermal characteristics calculated by the core monitoring method in ~ 6 and the power distribution calculation results by the off-line core three-dimensional simulator corresponding to each core state are compared.
[0077]
Similarly, assuming that the power distribution calculation was performed in the core state 6 shown in FIG. 8 (f), the thermal characteristics by the core monitoring method in the core states 7-9 shown in FIGS. 7 (g) to (i). The calculated value and the power distribution calculation result by the off-line core 3D simulator corresponding to each core state are compared.
[0078]
FIG. 9 to FIG. 12 show the calculation results of the line output density at each LPRM height position calculated from the LPRM indicated value increase rate located at the detector assembly number 26 in FIG. 9 to 12 show the ratio of the line power density and the operation limit value having the same meaning instead of the line power density, and the horizontal axis core states 1 to 9 show the above-described FIG. 8 (a). Respectively correspond to (i). Here, the solid line shows the ratio obtained from the response by the core monitoring method of the present invention, and the dotted line shows the ratio obtained from the actual line power density by the core three-dimensional simulator.
[0079]
FIG. 9 corresponds to the height of LPRM-A, and the line power density indicates the maximum of the line power density of the third node and the fourth node of the four fuel assemblies around the string. Similarly, FIG. 10 corresponds to the height of LPRM-B, the line power density is the maximum of the line power density of the ninth node and the tenth node of the four fuel assemblies around the string, and FIG. C corresponds to the height of C, the line power density is the maximum of the line power density of the 15th and 16th nodes of the four fuel assemblies around the string, FIG. 12 corresponds to the height of LPRM-D, The line power density indicates the maximum of the line power density of the 21st node and the 22nd node of the four fuel assemblies around the string, respectively.
[0080]
The calculation of the line power density by the core monitoring method according to the present invention shown in FIGS. 9 to 12 does not include the correction based on the control rod position described in the fourth embodiment according to the equation (1). From FIG. 9 to FIG. 12, it can be seen that in the core states 1 to 9, the core monitoring obtains the line power density more accurately than the indicated value increase rate of LPRM. Note that, at the height position of LPRM-A shown in FIG. 9, the line power density calculated by the core monitoring method in the core states 3 to 6 is slightly overestimated. The accuracy can be further improved by correcting the relationship.
[0081]
FIG. 13 similarly shows the transition of the minimum limit power ratio among the four fuel assemblies adjacent to the detector assembly number 23 of FIG. In FIG. 12, instead of the limit output ratio, the ratio of the limit output ratio operation limit value to the limit output ratio is shown. Here, the solid line is a ratio obtained from the limit power ratio calculated by the core monitoring method of the present invention, and the dotted line is an actual power distribution calculation result by the core three-dimensional simulator.
[0082]
Here, the calculation of the limit power ratio by the core monitoring method of the present invention is carried out by the equation (2), and the weighted average of the LPRM indicated values is the same weight (weight) for all LPRM-A to D, The change in the limit output due to the change in the core flow rate is corrected using the relationship shown in FIG. From FIG. 13, it can be seen that, according to the core monitoring method of the present invention, the limit power ratio is accurately calculated according to the core state.
[0083]
【The invention's effect】
According to the present invention, the thermal characteristics of the core at the time when the power distribution calculation is not performed at the time of control rod operation and core flow rate operation can be obtained instantaneously and easily, and the power distribution calculation result performed immediately before The thermal characteristics can be continuously monitored with high accuracy from the constantly updated plant data and the LPRM detector indicated value.
[0084]
In addition, when the thermal characteristics deviate from the operation limit value, automatic control rod and core flow rate operation is prohibited, fuel integrity can be maintained, and thermal characteristics can be confirmed during startup and control rod pattern adjustment. Since it is not necessary to stop the operation and perform the output distribution calculation, the time required for starting and pattern adjustment can be shortened.
[Brief description of the drawings]
FIG. 1 is a plan view schematically showing a core showing positions of a fuel assembly, a control rod, and a detector assembly of a 1300 MWe class boiling water reactor for explaining the present invention.
2A is an enlarged plan view showing the main part of the core in FIG. 1, and FIG. 2B is an elevation view schematically showing the axial direction of the detector assembly in FIG.
FIG. 3 is a system diagram showing a procedure of start-up and control rod pattern adjustment in the embodiment of the core monitoring method according to the present invention.
FIG. 4 is a system configuration diagram for explaining an embodiment of a core monitoring method according to the present invention.
FIG. 5 is also a characteristic diagram showing the relationship between the flow rate in the fuel assembly and the limit output.
FIG. 6 is also a characteristic diagram showing the ratio of the position of the control rod adjacent to the string at the LPRM-A height position, the linear output density increase rate, and the LPRM-A indicated value increase rate.
7 is a core plan view when the detector assembly position of FIG. 1 is developed in a rotational symmetry with aa ′ and bb ′. FIG.
FIGS. 8A to 8I are diagrams for explaining core states during startup in the embodiment of the core monitoring method according to the present invention, wherein FIGS. 8A to 8I are quarter core plan views in the respective core states; FIGS.
FIG. 9 is a first characteristic diagram in the embodiment of the core monitoring method according to the present invention.
FIG. 10 is a second characteristic diagram in the embodiment of the core monitoring method according to the present invention.
FIG. 11 is a third characteristic diagram in the embodiment of the core monitoring method according to the present invention.
FIG. 12 is a fourth characteristic diagram in the embodiment of the core monitoring method according to the present invention.
FIG. 13 is a fifth characteristic diagram in the embodiment of the core monitoring method according to the present invention.
FIG. 14 is a system diagram showing a general start-up and control rod pattern adjustment procedure.
FIG. 15 is a plan view partially showing a core for calculating thermal characteristics from a conventional LPRM indicated value.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Detector assembly, 2 ... Fuel assembly, 3 ... Control rod, 4 ... LPRM detector, 5 ... TIP calibration conduit, 6 ... Reactor pressure vessel, 7 ... Steam dryer, 8 ... Steam-water separator , 9 ... Shroud, 10 ... Control rod drive mechanism, 11 ... Internal pump, 12 ... Nuclear instrumentation system, 13 ... Recirculation flow rate control system, 14 ... Control rod operation system, 15 ... Process computer, 16 ... Core monitoring device, 17 ... Automatic output adjustment system, 18 ... Plant data.

Claims (7)

In the core monitoring method of the power increase process in which the core flow rate operation or the control rod operation of the nuclear reactor is automatically performed, the four units adjacent to the strings where the local power region monitors are arranged at four positions at almost equal intervals in the axial direction. station plant power range monitors among the fuel assembly height, or the node adjacent to the local power range monitor, or the fuel effective length maximum linear power density and minimum critical power ratio for each quarter of the output more calculated distribution calculation result and from the rate of change of the indicated value of the local power range monitors (1) and (2), the maximum value and the linear power density calculated in a plurality of fuel assemblies of all strings around If at least one of the calculated minimum values of the limit output ratio deviates from the operation limit value, at least one of an automatic operation stop signal, a control rod operation prohibition signal for the control rod operation system, and a flow operation prohibition signal for the flow control system 1 Core monitoring method characterized by emitting.
MFLPDAT (K, ISTR) = MFLPDIN (K, ISTR)
× (1+ (1 / FK ( K)) × (LPRMAT (K, ISTR) / LPRMIN (K, ISTR) -1)) ... (1) Equation
here,
MFLPDAT (K, ISTR) : Ratio of the maximum linear power density in the four fuel assemblies around the string at the string position ISTR and the height position K to the operation limit value
LPRMAT (K, ISTR) : LPRM indication value at string position ISTR and height position K
MFLPDIN (K, ISTR) : Ratio of maximum line power density and operation limit value by calculation of power distribution in four fuel assemblies around string at string position ISTR and height position K
LPRMIN (K, ISTR) : LPRM indication value when calculating output distribution at string position ISTR and height position K
FK (K) : Safety factor for calculating linear power density at height position K
MFLCPAT (ISTR) = MFLCPIN (ISTR)
× (1 + (1 / FC) × (LPAVAT (ISTR) / LPAVIN (ISTR) -1)) … (2) Formula
here
MFLCPAT (ISTR) : The ratio between the operation limit value of the limit power ratio and the minimum limit power ratio in the four fuel assemblies around the string position ISTR
MFLCPIN (ISTR) : Ratio of the limit power ratio operation limit value by power distribution calculation and the minimum limit power ratio in the four fuel assemblies around the string position ISTR
LPAVAT (ISTR) : Weighted average value of indicated values of four LPRM-A to D belonging to the string position ISTR
LPAVIN (ISTR) : Weighted average value of the indicated values of four LPRM-A to D belonging to the string position ISTR at the time of output distribution calculation
FC : Safety factor for calculating the limit output ratio In the core monitoring method of the power increase process in which the core flow rate operation or the control rod operation of the nuclear reactor is automatically performed, the four units adjacent to the strings where the local power region monitors are arranged at four positions at almost equal intervals in the axial direction. fuel assemblies, and this 4-body fuel assemblies symmetrical station plants among the fuel assembly loaded in position power range monitors in height, or the node adjacent to the local power range monitor or fuel effective, the maximum linear power density and minimum critical power ratio for each quarter of the length, power distribution calculation result and from the rate of change of the indicated value of the local power range monitors (1) and (2) calculated by formula, When at least one of the maximum value of the calculated linear power density and the minimum value of the calculated limit power ratio of the plurality of fuel assemblies around the entire string and the fuel assemblies at symmetrical positions thereof deviates from the operation limit value , Automatic operation stop signal, control A core monitoring method characterized by generating at least one of a control rod operation prohibition signal for a bar operation system and a flow operation prohibition signal for a flow control system.
MFLPDAT (K, ISTR) = MFLPDIN (K, ISTR)
× (1 + (1 / FK (K)) × (LPRMAT (K, ISTR) / LPRMIN (K, ISTR) -1)) ... (1) Equation
here,
MFLPDAT (K, ISTR) : Ratio of the maximum linear power density in the four fuel assemblies around the string at the string position ISTR and the height position K to the operation limit value
LPRMAT (K, ISTR) : LPRM indication value at string position ISTR and height position K
MFLPDIN (K, ISTR) : Ratio of maximum line power density and operation limit value by calculation of power distribution in four fuel assemblies around string at string position ISTR and height position K
LPRMIN (K, ISTR) : LPRM indication value when calculating output distribution at string position ISTR and height position K
FK (K) : Safety factor for calculating linear power density at height position K
MFLCPAT (ISTR) = MFLCPIN (ISTR)
× (1+ (1 / FC) × (LPAVAT (ISTR) / LPAVIN (ISTR) -1)) … (2) Formula
here
MFLCPAT (ISTR) : The ratio between the operation limit value of the limit power ratio and the minimum limit power ratio in the four fuel assemblies around the string position ISTR
MFLCPIN (ISTR) : Ratio of the limit power ratio operation limit value by power distribution calculation and the minimum limit power ratio in the four fuel assemblies around the string position ISTR
LPAVAT (ISTR) : Weighted average value of indicated values of four LPRM-A to D belonging to the string position ISTR
LPAVIN (ISTR) : Weighted average value of the indicated values of four LPRM-A to D belonging to the string position ISTR at the time of output distribution calculation
FC : Safety factor for calculating the limit output ratio   When calculating the limit power ratio, the core flow dependence at the time of power distribution calculation and the core flow at the time of limit power ratio calculation are approximated by a polynomial flow, and the relationship between the critical power and the core flow rate is approximated by a polynomial. 3. The core monitoring method according to claim 1, wherein the limit power ratio is sometimes corrected.   When calculating the line output density, the line output density change rate based on the control rod position at the time of output distribution calculation and line output density calculation is used as a function of the indicated value change rate of the local output area monitor and the control rod position. The core monitoring method according to claim 1, wherein the density is calculated.   When calculating the linear power density of four fuel assemblies adjacent to the string or the fuel assemblies including their symmetrical positions, the line power density at a height where no local power region monitor exists is calculated as the output distribution calculation result. The core monitoring method according to any one of claims 1 to 4, wherein the core monitoring method is calculated based on an interpolated value of the rate of change of the indicated value of the local output region monitor above and below the height of interest.   When the local output area monitor is in a failure or bypass state, the indicated value change rate of the local output area monitor existing at the same height at the symmetrical position is used as the indicated value change rate of the local output area monitor in the failure or bypass state. The core monitoring method according to claim 1, wherein the core monitoring method is used instead.   When the local output area monitor is in a fault or bypass state, when all the strings in which the local output area monitor exists are expanded in rotation symmetry, the local output area monitor is close to a string including the local output area monitor in the fault or bypass state. When the local output area monitor of the same height as the local output area monitor in the fault or bypass state of a plurality of strings is expanded in a rotationally symmetrical manner or the local output area monitor in the fault or bypass state The indication value increase rate of the local output area monitor at the same height of the local output area monitor in the fault or bypass state of one string adjacent to the string including 6. The core monitoring method according to claim 1, wherein the rate of change is substituted.

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