Device for selecting control rod pattern and withdrawal sequence, and automatic power regulator including the same

Abstract

To provide a device for selecting a control rod pattern and a pull-out sequence capable of reducing the sum of power generation loss and the lowering amount of fuel efficiency caused by the change of the control rod pattern during output operation.SOLUTION: The selection device 1 according to the present invention includes a target pattern and withdrawal sequence input device 2 for inputting a plurality of target control rod patterns and withdrawal sequences, a power increase limitation rule storage device 3 for storing a power increase limitation rule, a power loss calculation device 4 for calculating a power loss when the control rod pattern is changed to the target control rod pattern according to the withdrawal sequence, a fuel efficiency decrease calculation device 6 for calculating a decrease amount of the fuel efficiency when the control rod pattern is changed to the target control rod pattern according to the withdrawal sequence, and a device 5 for obtaining the sum of the power loss and the decrease amount of the fuel efficiency. The power generation loss calculator 4 calculates the power generation loss by using the difference between the rated power of the reactor and the reactor power Pi obtained when the control rod pattern is changed to the target control rod pattern and the power increase limitation rule is followed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device for selecting a control rod pattern and withdrawal sequence for adjusting power in a nuclear power plant, and an automatic power adjustment system including this device. [Background technology]

[0002] In a nuclear reactor, particularly one operating at rated power, the control rod pattern is changed according to a withdrawal sequence in order to adjust the reactivity which changes as the fuel burns.

[0003] An example of control rod pattern change in a conventional reactor power control device is described in Patent Document 1. Patent Document 1 discloses a reactor power control device that automatically operates control rods and adjusts core flow rate when changing the control rod pattern, and that calculates a control rod pattern for achieving a target reactor power when the core flow rate reaches a lower or upper limit value in order to safely achieve a predetermined reactor power and core flow rate operating state, and that includes: a target control rod pattern calculation unit that calculates a control rod pattern for achieving a target reactor power when the core flow rate reaches a lower or upper limit value; an operating procedure creation unit that creates a control rod operating procedure from the current control rod pattern to the target control rod pattern; a core state prediction unit that predicts the core state at each stage during operation and after the operation when the control rods are operated according to the created operating procedure; a determination unit that determines whether the predicted core state is sound; and a control unit that outputs control signals for the control rods and the core flow rate when the determination unit determines that the core state is sound. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 144293 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0005] When the control rod pattern is changed, the power generation loss, which is the difference between the core power output and the rated power output, may increase in order to ensure the integrity of the fuel. On the other hand, if the control rod pattern is changed from that planned at the time of design in an attempt to avoid this increase in power generation loss, fuel efficiency may decrease. In other words, there is a trade-off between the power generation loss when the control rod pattern is changed and the subsequent decrease in fuel efficiency. Therefore, when evaluating the overall economic viability of the changed control rod pattern, it is necessary to also consider the decrease in fuel efficiency.

[0006] An object of the present invention is to provide a control rod pattern and withdrawal sequence selection device that can reduce the sum of the power generation loss and the reduction in fuel efficiency that accompany changing the control rod pattern during power operation, and an automatic power adjustment device equipped with this selection device. [Means for solving the problem]

[0007] A control rod pattern and withdrawal sequence selection device according to the present invention comprises a target pattern and withdrawal sequence input device that inputs a plurality of pre-created target control rod patterns and withdrawal sequences for changing to the target control rod patterns, a power increase limit rule storage device that stores power increase limit rules defined for run-in operation for each linear power density of fuel rods, a power generation loss calculation device that calculates a power generation loss when the control rod pattern is changed to the target control rod pattern in accordance with the withdrawal sequence, a fuel efficiency degradation calculation device that calculates a reduction in fuel efficiency when the control rod pattern is changed to the target control rod pattern in accordance with the withdrawal sequence, and a device that calculates the sum of the power generation loss and the reduction in fuel efficiency. The power generation loss calculation device calculates the power generation loss using the difference between the rated power output of the reactor and the reactor power obtained when the control rod pattern is changed to the target control rod pattern and in accordance with the power increase limit rule.

[0008] The automatic power adjustment device according to the present invention comprises a control rod pattern and withdrawal sequence selector according to the present invention, and a power control circuit connected to the selector to control the power output of the reactor, wherein the power generation loss calculation device sends to the power control circuit a set value of the core flow rate at each time that is set to observe the power increase limit rule, and the target pattern selector sends the target control rod pattern and withdrawal sequence that minimize the sum to a control rod drive controller that controls the drive of the control rods, via the target pattern and withdrawal sequence input device, thereby controlling the power output of the reactor based on the set values ​​of the target control rod pattern, the withdrawal sequence, and the core flow rate. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a control rod pattern and withdrawal sequence selector that can reduce the sum of the power generation loss and the reduction in fuel efficiency that accompanies a control rod pattern change during power operation, and an automatic power adjustment device equipped with this selector. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of the overall configuration of a control rod pattern and withdrawal sequence selection device according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a diagram showing an example of an operation flow of the selection device according to the first embodiment. [Figure 3] FIG. 4 is a diagram showing an example of an operation flow of the power generation loss calculation device. [Figure 4] FIG. 4 is a diagram showing an example of an output increase limit rule. [Figure 5] FIG. 2 is a diagram showing an example of the configuration of a fuel efficiency degradation calculation device. [Figure 6] FIG. 10 is a diagram showing an example of the overall configuration of a control rod pattern and withdrawal sequence selection device according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing an example of the overall configuration of a control rod pattern and withdrawal sequence selection device according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing an example of the overall configuration of an automatic output adjusting device according to a fourth embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing an example of the change in core power over time when the control rod pattern is changed. DETAILED DESCRIPTION OF THE INVENTION

[0011] First, the background to the invention will be described.

[0012] Nuclear power plants are equipped with a large number of control rods to adjust or stop the nuclear fission reaction in the reactor. For example, in the case of a large boiling water reactor, approximately 200 control rods are inserted into the core when the reactor is shut down. To start up the nuclear power plant, the inserted control rods must be gradually withdrawn out of the core to increase the nuclear fission reaction caused by neutrons. At this time, the control rods must be withdrawn so that the reactivity is uniform across the radial direction of the core, so that excessive reactivity is not introduced into the core by the control rods in operation.

[0013] To comply with these operations, a withdrawal sequence is used, which determines the order in which the control rods are operated. In conventional boiling water reactors, control rods are withdrawn one by one. In the latest advanced boiling water reactors, multiple control rods form a group, and gang operation is also used, in which multiple control rods within a group are operated simultaneously. The order in which the control rods are operated is determined in the withdrawal sequence: one by one in conventional boiling water reactors, and by group in advanced boiling water reactors.

[0014] In a nuclear reactor operating at rated power, reactivity changes as fuel is burned over a continuous operating period (hereafter referred to as a "cycle"), which is usually about one year. In a boiling water reactor, the core flow rate is adjusted to compensate for this and maintain the rated power. For example, in the early stages of the cycle, the neutron absorber loaded in the fuel decreases, causing reactivity to increase over time. To offset this increase in reactivity, the core flow rate is reduced. Also, in the later stages of the cycle, the fissile material in the fuel gradually decreases as it is burned, causing reactivity to decrease over time. To offset the decrease in reactivity, the core flow rate is increased.

[0015] However, once the change in reactivity exceeds a certain value, it becomes difficult to adjust it with the core flow rate. Therefore, the number and position of the control rods inserted in the core are changed several times during the cycle to adjust the reactivity. The number and position of the control rods inserted in the core are called the control rod pattern. In other words, the reactivity of the reactor is adjusted by changing the control rod pattern.

[0016] The number and positions of the inserted control rods must be balanced to prevent fuel adjacent to the control rods from remaining unburned. Control rod operation is performed according to a withdrawal sequence created from the control rod pattern before the change to the control rod pattern after the change.

[0017] When changing the control rod pattern (hereafter referred to as "control rod pattern change"), it is common to operate the control rods after reducing the core power to approximately 60% to 90% of the rated power. This is because there are "run-in" rules when increasing the heat output per unit length of the fuel rods (hereafter referred to as "linear power density") above a predetermined threshold. The run-in rules limit operation to prevent damage to the fuel rods due to mechanical interference between the fuel pellets and the fuel cladding. A typical example of this rule is called the Pre-Conditioning Interim Operating Management Recommendation (PCIOMR), which specifies the threshold value for linear power density based on the fuel type and burnup.

[0018] When the linear power density is below the threshold, both power increase by core flow rate and power increase by control rods are possible. When the linear power density exceeds the threshold, power increase by control rods is not possible, and power increase by core flow rate is only possible, with the rate of increase limited to a few tenths of a percent per hour. However, even if the linear power density exceeds the threshold, if the linear power density is maintained above the threshold for a certain period of time, it is considered that an envelope preconditioned up to this linear power density has been formed, and for linear power densities below the envelope, operations similar to those for linear power densities below the threshold are possible.

[0019] Due to run-in rules, the control rod pattern change operation must be completed with the linear power density below the threshold or envelope. After the control rod pattern change is complete, the core flow rate is increased to restore rated power. If the linear power density reaches the threshold or envelope during the return to rated power, the rate of increase of the linear power density thereafter must be below the value limited by the run-in rules.

[0020] Some recent fuels have high run-in thresholds or have eliminated run-in rules. For these fuels, control rod pattern changes may be completed without being subject to the run-in power increase restrictions.

[0021] Currently, the cycle of boiling water reactors in Japan is about one year, but overseas, there are cases where cores with long cycles of 18 or 24 months are used to improve availability. In such cores, the number of fuel cells replaced at the end of the cycle increases, and the proportion of new fuel in the core increases. In conventional cores, low-power fuel that has been in the core for several years is placed around the control rods inserted during operation, which can suppress the increase in linear power density even when the control rods are withdrawn. On the other hand, in long-cycle cores, the proportion of new fuel increases, and new fuel is also placed around the control rods inserted during operation, which may cause the linear power density to exceed the threshold or envelope during break-in. If the linear power density exceeds the threshold or envelope, it takes a long time to increase the power.

[0022] Figure 9 shows an example of the change in core power over time when the control rod pattern is changed. For example, as shown in Figure 9, if the power is 85% of the rated power and the linear power density exceeds the threshold, it may take approximately 17 hours to increase the power to 100% if there are restrictions on the power increase operation during run-in. On the other hand, if there are no restrictions on the power increase operation during run-in, the power can be increased to 100% in approximately one hour. In this example, when there are restrictions due to run-in rules, the power generation loss, which is the difference between the core power and the rated power, is slightly more than twice as much as when there are no restrictions due to run-in rules.

[0023] To avoid this increase in power generation loss, it is possible to change the control rod pattern planned during core design to a control rod pattern that is less affected by the restrictions imposed by the run-in rules. Such a change in control rod pattern can minimize power generation loss, reducing it to just under half of the amount that would be expected with run-in restrictions. This control rod pattern can be realized, for example, by slightly withdrawing control rods from the pre-change control rod pattern to compensate for the decrease in reactivity associated with fuel burnup. In other words, if the control rod pattern is returned to the pre-change control rod pattern, the linear power density of each fuel returns to near its original value. However, a preconditioning envelope has already been formed for this linear power density, and power can be increased substantially without restrictions up to this linear power density.

[0024] However, if the control rod pattern is returned to the one before the change, the fuel adjacent to the control rods will continue to be adjacent to the control rods after the change in the control rod pattern, resulting in a decrease in fuel efficiency compared to the control rod pattern set at the time of core design.

[0025] Thus, there is a trade-off between the power generation loss caused by changing the control rod pattern and the subsequent decrease in fuel efficiency. Therefore, when evaluating the overall economic viability of a changed control rod pattern, it is necessary to take into account the decrease in fuel efficiency.

[0026] The present invention has been made to solve the above-mentioned problems. The present invention can reduce the sum of the power generation loss and the decrease in fuel efficiency that occurs when the position and number of control rods (control rod pattern) are changed in a nuclear power plant, particularly during power operation. Generally, attempts to reduce the power generation loss caused by extending the power rise time result in a significant decrease in fuel efficiency. On the other hand, reducing the decrease in fuel efficiency increases the power generation loss. The present invention takes into account both the power generation loss and the decrease in fuel efficiency, thereby improving the efficiency of the entire plant.

[0027] Hereinafter, a control rod pattern and withdrawal sequence selection device and an automatic power adjustment device according to an embodiment of the present invention will be described with reference to the drawings. In the drawings referred to in this specification, the same or corresponding components are designated by the same reference numerals, and repeated description of these components may be omitted. [Example]

[0028] A control rod pattern and withdrawal sequence selection device according to a first embodiment of the present invention will be described.

[0029] FIG. 1 is a diagram showing an example of the overall configuration of a control rod pattern and withdrawal sequence selection device according to this embodiment.

[0030] The control rod pattern and withdrawal sequence selection device 1 includes a target pattern and withdrawal sequence input device 2, a power increase limit rule storage device 3, a power generation loss calculation device 4, a target pattern selection device 5, a fuel efficiency degradation calculation device 6, and an output device 7, and is connected to the core performance monitoring device 30. Hereinafter, the control rod pattern and withdrawal sequence selection device 1 will also be referred to as the selection device 1.

[0031] The target pattern and withdrawal sequence input device 2 inputs and stores a plurality of pre-created target control rod patterns and withdrawal sequences. The stored target control rod patterns are control rod patterns created in advance as candidates for achieving the target reactor power. The stored withdrawal sequences are withdrawal sequences for changing to each target control rod pattern, and are created in advance. Hereinafter, the target control rod patterns will also be referred to as target patterns.

[0032] The power increase limit rule storage device 3 stores power increase limit rules determined for run-in operation with respect to the linear power density of the fuel rods. The power increase limit rules include threshold values ​​for the linear power density during run-in operation.

[0033] The power generation loss calculation device 4 calculates the power generation loss when the control rod pattern is changed. The power generation loss is the difference between the core power output and the rated power output.

[0034] The target pattern selection device 5 selects the optimum target pattern and extraction sequence.

[0035] The fuel efficiency reduction calculation device 6 calculates the amount of reduction in fuel efficiency. The fuel efficiency reduction calculation device 6 will be described later with reference to FIG.

[0036] The output device 7 displays the calculation results of the selection device 1 on a monitor provided in the selection device 1.

[0037] The reactor core performance monitoring device 30 has the same configuration as existing reactor core performance monitoring devices, has a known reactor core performance prediction calculation function, and is capable of executing reactor core performance prediction calculations.

[0038] The operation of the selection device 1 will be described with reference to FIG.

[0039] FIG. 2 is a diagram showing an example of the operation flow of the selection device 1 according to this embodiment.

[0040] In S1, the power generation loss calculation device 4 reads a plurality of target patterns and withdrawal sequences stored in the target pattern and withdrawal sequence input device 2. Furthermore, the power generation loss calculation device 4 reads the output increase limit rule stored in the output increase limit rule storage device 3.

[0041] In S2, the power generation loss calculation device 4 assigns numbers to the read target patterns and extraction sequences. Then, the power generation loss calculation device 4 selects the target pattern and extraction sequence with number 1 as the evaluation target. After S5, the power generation loss calculation device 4 selects the next target pattern and extraction sequence in numerical order.

[0042] In S3, the power generation loss calculation device 4 changes the control rod pattern to the target pattern to be evaluated in accordance with the withdrawal sequence from the point when the core flow rate is reduced and the power starts to decrease from the rated power, and then calculates the power generation loss when the control rod pattern is changed from the core power at every moment when the power is increased in the shortest time within the power increase limit rule until the power reaches the rated power due to an increase in the core flow rate.The power generation loss calculation device 4 then sends the calculated power generation loss to the target pattern selection device 5.

[0043] In S4, the target pattern selection device 5 calculates an integrated loss (the sum of the power generation loss and the amount of reduction in fuel efficiency) for the target pattern and extraction sequence to be evaluated by adding the amount of reduction in fuel efficiency calculated by the fuel efficiency reduction calculation device 6 to the power generation loss calculated by the power generation loss calculation device 4. The method by which the fuel efficiency reduction calculation device 6 calculates the amount of reduction in fuel efficiency will be described later.

[0044] In S5, the selection device 1 determines whether the processes of S3 and S4 have been performed on all of the target patterns and extraction sequences read in S1. If the processes of S3 and S4 have been performed on all of the target patterns and extraction sequences, the selection device 1 performs the process of S6. If the processes of S3 and S4 have not been performed on all of the target patterns and extraction sequences, the selection device 1 performs the process of S2.

[0045] In S6, the target pattern selection device 5 selects the target pattern and extraction sequence that minimizes the sum of the power generation loss and the reduction in fuel efficiency (the above-mentioned integrated loss) as the optimal target pattern and extraction sequence. The target pattern selection device 5 outputs the selected optimal target pattern and extraction sequence to the output device 7. The output device 7 displays the optimal target pattern and extraction sequence selected by the target pattern selection device 5 on a monitor.

[0046] 3 is a diagram showing an example of the operation flow of the power generation loss calculation device 4. As described above, the power generation loss calculation device 4 calculates the power generation loss when the control rod pattern is changed.

[0047] In S11, the power generation loss calculation device 4 reads a plurality of target patterns, withdrawal sequences, and power increase limit rules (S1 in FIG. 2). At this time, the power generation loss calculation device 4 reads the minimum core flow rate Fs during control rod operation together with the target pattern and withdrawal sequence.

[0048] In S12, the power generation loss calculation device 4 selects the target patterns and extraction sequences in numerical order as targets for evaluation (S2 in FIG. 2).

[0049] In S13, the power generation loss calculation device 4 sets the control rod position in the selected target pattern as the target control rod position Rt to be evaluated, and obtains the maximum linear power density Ws and reactor power Ps before the power increase at the target control rod position Rt. The power generation loss calculation device 4 can obtain the maximum linear power density Ws and reactor power Ps from the core performance monitoring device 30 (FIG. 1). The core performance monitoring device 30 calculates the maximum linear power density Ws and reactor power Ps by executing a core performance prediction calculation function. Note that before the power increase, the core flow rate is the minimum core flow rate Fs.

[0050] In S14, the power generation loss calculation device 4 compares the obtained maximum linear power density Ws with the threshold value and envelope in the power increase limit rule read in S11, and checks whether the maximum linear power density Ws is equal to or less than the threshold value or the envelope in all fuel regions.

[0051] S15 is a process performed when there is a maximum linear power density Ws that exceeds the threshold value and the envelope. In this case, since it is not possible to change to the target pattern by operating the control rods, the power generation loss calculation device 4 determines that the target pattern and withdrawal sequence to be evaluated selected in S12 are not applicable. Then, the power generation loss calculation device 4 returns to the process of S12 and selects the next-numbered target pattern and withdrawal sequence to be evaluated.

[0052] S16 is a process performed when there is no maximum linear power density Ws that exceeds the threshold value and the envelope (when the maximum linear power density Ws is equal to or less than the threshold value or the envelope). In S16, the power generation loss calculation device 4 sets the core flow rate Fi when time is advanced by a predetermined time step Δt (for example, 10 minutes) so that the rate of change of power becomes the target rate of change of power. The target rate of change of power is a preset target value for the rate of change of core power. Then, the power generation loss calculation device 4 obtains the maximum linear power density Wi and reactor power Pi when the core flow rate is Fi from the core performance monitoring device 30. The core performance monitoring device 30 calculates the maximum linear power density Wi and reactor power Pi by executing a core performance prediction calculation function. Note that the subscript i indicates the value at a time advanced by (Δt × i).

[0053] At this time, if the reactor power Pi obtained by the set core flow rate Fi does not match the reactor power P(t) that realizes the target power change rate, the power generation loss calculation device 4 corrects the core flow rate Fi. For example, the power generation loss calculation device 4 corrects the core flow rate Fi as shown in formula (1) using the difference (Pi-Ps) between the reactor power Pi and the reactor power Ps before the time step Δt, and the difference (Fi-Fs) between the set core flow rate Fi and the minimum core flow rate Fs. Corrected core flow rate Fi' = (Fi - Fs) / (Pi - Ps) × (P(t) - Ps) + Fi (1) The power generation loss calculation device 4 can thus determine the corrected core flow rate Fi' and set the corrected core flow rate Fi' as the set core flow rate Fi.

[0054] In this way, the power generation loss calculation device 4 obtains the maximum linear power density Wi and the reactor power Pi (=P(t)) from the core flow rate Fi that can obtain the reactor power P(t) that realizes the target power ramp rate.

[0055] In S17, the power generation loss calculation device 4 checks whether the acquired maximum linear power density Wi is equal to or less than the threshold value or the envelope in all fuel regions.

[0056] S18 is a process performed when there is no maximum linear power density Wi that exceeds the threshold value and the envelope in S17 (when the maximum linear power density Wi is equal to or less than the threshold value or the envelope). In S18, the power generation loss calculation device 4 determines whether or not the reactor power Pi has reached the rated power. If the reactor power Pi has not reached the rated power, the process returns to S16. If the reactor power Pi has reached the rated power, the process of S19 is performed.

[0057] In S19, the power generation loss calculation device 4 calculates the power generation loss L due to the target pattern and extraction sequence selected as the evaluation target in S12 using equation (2). Power generation loss L = Σi (rated output - Pi) × Δt (2) In equation (2), the power generation loss L is calculated using the difference between the rated power output of the reactor and the reactor power Pi obtained when the control rod pattern is changed to the target pattern and the power increase limit rule is followed. Note that in equation (2), Σi (rated power - Pi) is the sum for all times at which the reactor power Pi is calculated (times determined by (time step Δt × i)).

[0058] If it is determined in S17 that there is a maximum linear power density Wi that exceeds the threshold value and the envelope, the power generation loss calculation device 4 executes the process of S20.

[0059] In S20, the power generation loss calculation device 4 determines whether the reactor power Pi has reached the rated power. If the reactor power Pi has not reached the rated power, the process of S21 is carried out. If the reactor power Pi has reached the rated power, the process of S19 is carried out.

[0060] In S21, the power generation loss calculation device 4 sets the core flow rate Fi when time is advanced by a predetermined time step Δt (e.g., 10 minutes) (i.e., at the same time as S16) so that the rate of change of the maximum linear power density is equal to or less than the rate of change of the maximum linear power density determined by the power increase limit rule. Then, the power generation loss calculation device 4 obtains the maximum linear power density Wi and the reactor power Pi when the core flow rate is Fi from the core performance monitoring device 30. The core performance monitoring device 30 calculates the maximum linear power density Wi and the reactor power Pi by executing a core performance prediction calculation function.

[0061] At this time, if the set core flow rate Fi results in a maximum linear power density Wi that does not match the maximum linear power density W(t) allowed by the power increase limit rule, the power generation loss calculation device 4 corrects the core flow rate Fi. For example, the power generation loss calculation device 4 corrects the core flow rate Fi as shown in equation (3) using the difference (Wi-Ws) between the maximum linear power density Wi and the maximum linear power density Ws before the time step Δt, and the difference (Fi-Fs) between the set core flow rate Fi and the minimum core flow rate Fs. Corrected core flow rate Fi' = (Fi - Fs) / (Wi - Ws) × (W(t) - Ws) + Fi (3) The power generation loss calculation device 4 can thus determine the corrected core flow rate Fi' and set the corrected core flow rate Fi' as the set core flow rate Fi.

[0062] In this way, the power generation loss calculation device 4 obtains the maximum linear power density Wi (= W(t)) and the reactor power Pi from the core flow rate Fi that can obtain the maximum linear power density W(t) that is equal to or less than the rate of change of the maximum linear power density defined by the power increase limit rule.

[0063] Thereafter, the power generation loss calculation device 4 performs the process of S17 to check whether or not the maximum linear power density Wi is equal to or less than the threshold value or the envelope in all fuel regions.

[0064] The power generation loss calculation device 4 performs the processes from S12 to S21 for all of the target patterns and extraction sequences read in S11 (S5 in FIG. 2).

[0065] 4 is a diagram showing an example of the output increase limiting rule. The output increase limiting rule is determined in advance and stored in the output increase limiting rule storage device 3.

[0066] In the power rise limit rule shown in Figure 4, the threshold for the maximum linear power density is 10 kW / ft, and when the linear power density is below this threshold, there are no restrictions on the operation of control rods or core flow rate. When the linear power density exceeds the threshold, an envelope is formed by preconditioning (for example, preconditioning to maintain the current linear power density for 12 hours or more). When the linear power density exceeds the threshold but is below the envelope, there are no restrictions on the operation of control rods or core flow rate. When the linear power density exceeds the threshold and exceeds the envelope, restrictions are imposed on the operation of control rods and core flow rate, as shown in Figure 4.

[0067] Next, a method for calculating the amount of fuel efficiency reduction by the fuel efficiency reduction calculation device 6 will be described.

[0068] 5 is a diagram showing an example of the configuration of the fuel efficiency degradation calculation device 6. The fuel efficiency degradation calculation device 6 includes a control rod pattern plan input device 9, a removed fuel input device 10, an arithmetic and control device 8, and a core burnup calculation device 11.

[0069] The control rod pattern plan input device 9 stores a control rod pattern plan that determines what control rod pattern to use for operation at each burnup point during an operation cycle. This control rod pattern plan is set during core design and stored in the control rod pattern plan input device 9.

[0070] The fuel to be taken out at the end of the driving cycle is determined in advance and stored in the fuel to be taken out input device 10. Data defining the fuel to be taken out at the end of the driving cycle is stored in the fuel to be taken out input device 10.

[0071] First, the arithmetic and control device 8 reads the control rod pattern plan from the control rod pattern plan input device 9. By reading the control rod pattern plan, the arithmetic and control device 8 determines what control rod pattern to use for operation at each burnup point during the operation cycle.

[0072] The arithmetic and control device 8 specifies the control rod positions in accordance with the read control rod pattern plan and starts the core burnup calculation device 11. The core burnup calculation device 11 calculates the predicted value of the burnup of each fuel region until the end of the operation cycle in accordance with this control rod pattern plan using a known method.

[0073] The arithmetic and control device 8 reads which fuel will be removed at the end of the operation cycle from the removed fuel input device 10. Then, the arithmetic and control device 8 reads from the core burnup calculation device 11 the predicted value of the burnup (GWd / t) of the fuel to be removed at the end of the operation cycle.

[0074] Next, the arithmetic and control device 8 reads the control rod pattern plan corresponding to the target pattern and withdrawal sequence selected as the evaluation target in S2 of Fig. 2 (or S12 of Fig. 3) from the control rod pattern plan input device 9, and starts the core burnup calculation device 11. The core burnup calculation device 11 calculates the predicted value of the burnup of each fuel region up to the end of the operation cycle in accordance with this control rod pattern plan.

[0075] The arithmetic and control device 8 reads from the core burnup calculation device 11 the predicted value of the burnup (GWd / t) of the fuel to be removed at the end of the operation cycle in the control rod pattern plan corresponding to the target pattern to be evaluated and the withdrawal sequence.

[0076] Next, the arithmetic and control device 8 calculates, for each fuel to be removed, the difference between the predicted value of the burnup (GWd / t) of the fuel to be removed when the control rod pattern plan corresponding to the target pattern and withdrawal sequence to be evaluated is followed and the predicted value of the burnup (GWd / t) of the fuel to be removed when the control rod pattern plan set at the time of core design that was read in earlier.The arithmetic and control device 8 then obtains a value by multiplying the calculated difference by the fuel loading amount (t), calculates the sum of these values ​​for all the fuel to be removed, and regards the obtained sum as the amount of reduction in fuel efficiency.

[0077] The reduction in fuel efficiency calculated in this way has the unit of power generation (GWd) and represents the amount of power generation lost due to the reduction in burnup of the removed fuel.

[0078] In this way, the fuel efficiency degradation calculation device 6 calculates the amount of fuel efficiency degradation for all target patterns and extraction sequences that have been evaluated, and sends the calculated amount of fuel efficiency degradation to the target pattern selection device 5.

[0079] The target pattern selection device 5 calculates the sum of the power generation loss and the reduction in fuel efficiency by adding the power generation loss calculated by the power generation loss calculation device 4 to the reduction in fuel efficiency calculated by the fuel efficiency reduction calculation device 6 for each target pattern and extraction sequence to be evaluated (S4 in FIG. 2).The target pattern selection device 5 then selects the target pattern and extraction sequence that minimizes the sum of the power generation loss and the reduction in fuel efficiency as the optimal target pattern and extraction sequence (S6 in FIG. 2).

[0080] The output device 7 displays the optimum target pattern and extraction sequence selected by the target pattern selection device 5 on a monitor.

[0081] As explained above, the control rod pattern and withdrawal sequence selection device 1 according to this embodiment can select an optimal target control rod pattern and withdrawal sequence in consideration of both the power generation loss and the amount of decrease in fuel efficiency when the rules for run-in are applied when changing the control rod pattern during rated power operation. Therefore, the selection device 1 according to this embodiment can reduce the sum of the power generation loss and the amount of decrease in fuel efficiency that accompanies a control rod pattern change during power operation. [Example]

[0082] A control rod pattern and withdrawal sequence selection device according to a second embodiment of the present invention will be described. The following mainly describes the differences between the selection device according to this embodiment and the selection device according to the first embodiment. The selection device according to this embodiment can determine the date and time for changing the control rod pattern from among multiple candidates so that the sum of the power generation loss and the reduction in fuel efficiency is minimized.

[0083] FIG. 6 is a diagram showing an example of the overall configuration of the control rod pattern and withdrawal sequence selection device 1 according to this embodiment.

[0084] The selection device 1 according to this embodiment does not include the target pattern selection device 5 that the selection device according to embodiment 1 (FIG. 1) includes, but instead includes an implementation timing determination device 12. Furthermore, the selection device 1 according to this embodiment includes an input device 13 connected to the power generation loss calculation device 4. The selection device 1 according to this embodiment may also include the target pattern selection device 5.

[0085] A plurality of candidate dates and times for implementing a control rod pattern change are input in advance to the power generation loss calculation device 4 by the input device 13. Note that the power generation loss and the amount of reduction in fuel efficiency can vary depending on the date and time for implementing a control rod pattern change, since the state of the fuel changes over time as the fuel is burned.

[0086] In S1 of Fig. 2, the power generation loss calculation device 4 reads the target pattern and withdrawal sequence stored in the target pattern and withdrawal sequence input device 2, and the output increase limit rule stored in the output increase limit rule storage device 3. Below, an example will be described in which the power generation loss calculation device 4 reads one target pattern and withdrawal sequence, but the power generation loss calculation device 4 may also read multiple target patterns and withdrawal sequences.

[0087] Next, the power generation loss calculation device 4 calculates the power generation loss for each of the multiple candidate dates and times for implementing the control rod pattern change, which are input via the input device 13, in accordance with the procedure shown in FIG. 3 .

[0088] In the fuel efficiency degradation calculation device 6 (FIG. 5), the arithmetic and control device 8 reads, from the control rod pattern plan input device 9, control rod pattern plans corresponding to each of a plurality of candidate dates and times for implementing a control rod pattern change, and calculates the amount of degradation in fuel efficiency at each of these candidate dates and times.

[0089] Then, the implementation timing determination device 12 adds the amount of decrease in fuel efficiency calculated by the fuel efficiency decrease calculation device 6 to the power generation loss calculated by the power generation loss calculation device 4 to calculate the sum of the power generation loss and the amount of decrease in fuel efficiency (processing corresponding to S4 in Fig. 2).The implementation timing determination device 12 then determines, from among multiple candidate dates and times, the date and time for implementing the control rod pattern change that minimizes the sum of the power generation loss and the amount of decrease in fuel efficiency.

[0090] As described above, the selection device 1 according to this embodiment can determine the date and time for implementing a control rod pattern change so as to minimize the sum of the power generation loss and the amount of decrease in fuel efficiency. Therefore, the selection device 1 according to this embodiment can determine the optimal timing for implementing a control rod pattern change, taking into consideration both the power generation loss and the amount of decrease in fuel efficiency. [Example]

[0091] A control rod pattern and withdrawal sequence selection device according to a third embodiment of the present invention will be described below. The following mainly describes the differences between the selection device according to this embodiment and the selection device according to the first embodiment. The selection device according to this embodiment can determine the set of fuel to be removed at the end of the reactor operation cycle so as to minimize the sum of the power generation loss and the decrease in fuel efficiency.

[0092] FIG. 7 is a diagram showing an example of the overall configuration of the control rod pattern and withdrawal sequence selection device 1 according to this embodiment.

[0093] The selection device 1 according to this embodiment does not include the target pattern selection device 5 included in the selection device according to embodiment 1 (FIG. 1), but instead includes an extraction fuel determination device 14. Furthermore, the selection device 1 according to this embodiment includes an input device 15 connected to the fuel efficiency reduction calculation device 6. Note that the selection device 1 according to this embodiment may include one or both of the target pattern selection device 5 and the implementation timing determination device 12 (FIG. 6) described in embodiment 2.

[0094] A plurality of candidates for the set of fuel elements to be removed at the end of the operation cycle of the reactor are input in advance to the fuel efficiency degradation calculation device 6 by the input device 15. The number of fuel elements to be removed is usually several hundred.

[0095] In S1 of Fig. 2, the power generation loss calculation device 4 reads the target pattern and withdrawal sequence stored in the target pattern and withdrawal sequence input device 2, and the output increase limit rule stored in the output increase limit rule storage device 3. Below, an example will be described in which the power generation loss calculation device 4 reads one target pattern and withdrawal sequence, but the power generation loss calculation device 4 may also read multiple target patterns and withdrawal sequences.

[0096] Next, the power generation loss calculation device 4 calculates the power generation loss according to the procedure shown in FIG.

[0097] In the fuel efficiency degradation calculation device 6 (FIG. 5), the arithmetic and control device 8 reads the control rod pattern plans corresponding to each of a plurality of candidate sets of fuel to be removed from the control rod pattern plan input device 9, and calculates the amount of fuel efficiency degradation for each of these candidate sets.

[0098] Then, the extraction fuel determination device 14 calculates the sum of the power generation loss and the reduction in fuel efficiency by adding the reduction in fuel efficiency calculated by the fuel efficiency reduction calculation device 6 to the power generation loss calculated by the power generation loss calculation device 4 (processing corresponding to S4 in FIG. 2).The extraction fuel determination device 14 then determines, from among multiple candidate combinations, a combination of fuels to be extracted that minimizes the sum of the power generation loss and the reduction in fuel efficiency.

[0099] As described above, the selection device 1 according to this embodiment can determine the set of fuels to be extracted at the end of an operation cycle so as to minimize the sum of the power generation loss and the amount of decrease in fuel efficiency. Therefore, the selection device 1 according to this embodiment can determine the optimal set of fuels to be extracted at the end of an operation cycle, taking into account both the power generation loss and the amount of decrease in fuel efficiency. [Example]

[0100] An automatic power adjustment device according to an embodiment of the present invention will be described. The automatic power adjustment device according to this embodiment includes a control rod pattern and withdrawal sequence selection device according to any one of embodiments 1 to 3, and controls the power of a nuclear reactor.

[0101] 8 is a diagram showing an example of the overall configuration of the automatic power adjustment device 21 according to this embodiment. The automatic power adjustment device 21 shown in FIG. 8 includes, as an example, the control rod pattern and withdrawal sequence selector 1 according to embodiment 1, and also includes a power control circuit 22.

[0102] The power control circuit 22 is connected to the selection device 1 and is a device that controls the power output of the reactor 23. The power control circuit 22 is connected to a control rod drive controller 26 and a recirculation controller 28 and issues operation commands to them. The control rod drive controller 26 controls the drive of the control rods 25. The control rods 25 are attached in a removable form to a reactor core 24 located inside the reactor 23. The recirculation controller 28 controls the operation of a recirculation pump 27 located inside the reactor 23. A neutron detector 31 is installed inside the reactor core 24. A neutron flux monitor 29 is connected to the neutron detector 31.

[0103] The core performance monitoring device 30 obtains information such as the distribution of neutron flux inside the core 24 from the neutron flux monitoring device 29 and monitors the core 24. As described above, the core performance monitoring device 30 has a core performance prediction calculation function and can execute core performance prediction calculations. The power generation loss calculation device 4 causes the core performance monitoring device 30 to execute core performance prediction calculations.

[0104] In this embodiment, the target pattern selection device 5 sends the optimal target pattern and withdrawal sequence selected in consideration of both the power generation loss and the reduction in fuel efficiency to the target pattern and withdrawal sequence input device 2 instead of outputting them to the output device 7 (FIG. 1). The target pattern and withdrawal sequence input device 2 sends the optimal target pattern and withdrawal sequence selected by the target pattern selection device 5 to the control rod drive controller 26. In other words, the target pattern selection device 5 sends the optimal target pattern and withdrawal sequence to the control rod drive controller 26 via the target pattern and withdrawal sequence input device 2.

[0105] The control rod drive controller 26 operates the control rods 25 by controlling the drive of the control rods 25 using the transmitted optimal target pattern and withdrawal sequence.

[0106] 3 to the power control circuit 22. The power control circuit 22 uses the set value of the core flow rate Fi at each time sent from the power generation loss calculating device 4 to control the recirculation pump 27 by issuing an operation command to the recirculation control device 28.

[0107] As described above, the automatic power adjustment device 21 according to this embodiment can control the power output of the reactor 23 based on the selected target pattern and withdrawal sequence, and the set value of the core flow rate Fi that is set to observe the power increase limit rule.

[0108] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to embodiments including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete part of the configuration of each embodiment, or to add or replace other configurations. [Explanation of symbols]

[0109] 1...control rod pattern and withdrawal sequence selection device, 2...target pattern and withdrawal sequence input device, 3...power increase limit rule storage device, 4...power generation loss calculation device, 5...target pattern selection device, 6...fuel efficiency reduction calculation device, 7...output device, 8...arithmetic and control device, 9...control rod pattern plan input device, 10...removed fuel input device, 11...core burnup calculation device, 12...implementation timing determination device, 13...input device, 14...removed fuel determination device, 15...input device, 21...automatic power adjustment device, 22...power control circuit, 23...reactor, 24...core, 25...control rod, 26...control rod drive control device, 27...recirculation pump, 28...recirculation control device, 29...neutron flux monitoring device, 30...core performance monitoring device, 31...neutron detector.

Claims

1. a target pattern and withdrawal sequence input device for inputting a plurality of target control rod patterns created in advance and withdrawal sequences for changing to the target control rod patterns; a power increase limit rule storage device that stores a power increase limit rule that is determined for the break-in operation with respect to the linear power density of the fuel rod; a power generation loss calculation device that calculates a power generation loss when the control rod pattern is changed to the target control rod pattern in accordance with the withdrawal sequence; a fuel efficiency degradation calculation device that calculates a fuel efficiency degradation amount when the control rod pattern is changed to the target control rod pattern in accordance with the withdrawal sequence; a device for calculating the sum of the power generation loss and the decrease in fuel efficiency; Equipped with the power generation loss calculation device calculates the power generation loss using a difference between the rated power output of the reactor and the reactor power obtained when the control rod pattern is changed to the target control rod pattern and the power increase limit rule is followed; A control rod pattern and withdrawal sequence selection device.

2. The device for calculating the sum is a target pattern selection device that selects the target control rod pattern and the withdrawal sequence that minimize the sum.

2. The control rod pattern and withdrawal sequence selection device according to claim 1.

3. a plurality of candidates for the date and time at which the control rod pattern is changed are input in advance into the power generation loss calculation device; The device for calculating the sum is an implementation time determination device that determines, from the candidates, the date and time for changing the control rod pattern that minimizes the sum.

2. The control rod pattern and withdrawal sequence selection device according to claim 1.

4. a plurality of candidates for a set of fuel to be removed at the end of an operation cycle of the nuclear reactor are input in advance to the fuel efficiency degradation calculation device; the device for calculating the sum is a device for determining fuel to be removed that determines, from the candidates, a set of fuel to be removed at the end of the operation cycle of the reactor, which minimizes the sum; 2. The control rod pattern and withdrawal sequence selection device according to claim 1.

5. the fuel efficiency degradation calculation device calculates the amount of degradation in fuel efficiency using a difference between a predicted value of burnup of fuel to be removed at the end of an operation cycle of the reactor in the target control rod pattern and a predicted value of the burnup in the control rod pattern at the time of core design; 2. The control rod pattern and withdrawal sequence selection device according to claim 1.

6. a control rod pattern and withdrawal sequence selection device according to claim 2; a power control circuit connected to the selection device to control the power output of the nuclear reactor; Equipped with The power generation loss calculation device sends a set value of the core flow rate at each time, which is set so as to observe the power increase limit rule, to the power control circuit; The target pattern selection device sends the target control rod pattern and the withdrawal sequence that minimize the sum to a control rod drive control device that controls the drive of the control rods via the target pattern and withdrawal sequence input device, controlling the reactor power based on the target control rod pattern, the withdrawal sequence, and the set value of the core flow rate; An automatic output adjustment device characterized by:

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