JPH07117598B2 - Reactor operation support device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a reactor operation support device in a boiling water nuclear power plant, and particularly to a plant operator when a drywell inspection is performed at the time of initial startup of the reactor. The present invention relates to a reactor operation support device that supports reactor operation.

[Technical background of the invention and its problems]

Generally, when the reactor is first started up, the operation of the reactor during temperature rising and boosting operation is suspended to confirm the soundness of the reactor, and a worker enters the dry well of the containment vessel for inspection and inspection. There is a need.

When carrying out this drywell inspection work, it is necessary to make the reactor subcritical and to sufficiently reduce the reactor power in order to minimize the radiation exposure of workers.

Next, based on FIG. 5, a conventional reactor operating method at the time of inspecting the inside of the dry well will be described.

As shown in FIG. 5, the dry well 2 of the reactor containment vessel 1
A boiling water reactor 3 is housed in the reactor 3. The reactor 3 has an in-core neutron detector 5 installed in a core 4 inside thereof, and a control rod 6 is provided so as to be insertable and removable. The reactor power is adjusted by controlling the core reactivity.

The control rod 6 is driven by the control rod drive mechanism 7, and the core 4
Inserted in or pulled out.

In FIG. 5, reference numeral 8 is a turbine, 9 is a condenser, and 10 is a water supply pump.

During the inspection work inside the dry well 2, the reactor power is reduced to be subcritical in order to safely perform this inspection work, but the reactor water temperature decreases as the reactor output decreases. In a boiling water type light water reactor that uses water as a neutron moderator, when the reactor water temperature decreases, the density of water increases, the neutron moderating effect increases, and a positive reactivity is added to the reactor 3. For this reason, the reactor 3 that has once been made subcritical may become supercritical. The reactor power continues to decrease while the reactor 3 is subcritical, but once the reactor 3 becomes supercritical, the reactor power starts increasing, and if this state is left unattended, the reactor power further increases. Then, the amount of radiation exposure to the worker in the dry well 2 increases, which is extremely dangerous.

Therefore, conventionally, a plant operator constantly monitors the fluctuation of the reactor power during the inspection work in the dry well, and immediately when the reactor power starts to rise, the control rod 6 is immediately additionally inserted into the core 4 and the reactor power is output. Was in control. This is because it was difficult to grasp the subcritical state of the reactor 3 because there was no means for calculating and monitoring the reactivity, and during the drywell inspection, a particularly skilled reactor operation operation was performed by the plant operator. This was required, and the burden on the plant operator was heavy.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to simply post a subcritical state of a reactor to a plant operator and to assist the plant operator in determining a control rod operation. It is intended to provide a reactor operation support device that reduces the load on the operation of the plant and prevents erroneous judgments and erroneous operations by the plant operator before it is performed to improve work safety during inspection in the drywell.

[Outline of Invention]

The present invention, the reactivity calculation mechanism for calculating the reactivity of the reactor based on the detection output from the in-reactor neutron detector that detects the neutron flux in the reactor, and the reaction calculated by this reactivity calculation mechanism And the reactivity monitoring mechanism that outputs the deviation between the two and the control rod operation that converts the deviation from this reactivity monitoring mechanism into the control rod operation amount and indicates the control rod to be operated. It is characterized by having an indicating mechanism, a control rod to be operated, and an indicator for displaying the reactivity from the reactivity calculating mechanism.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. In the figure, parts common to those in FIG. 5 are designated by the same reference numerals.

A reactivity calculation mechanism 20 is connected to an in-core neutron detector 5 which is installed in the core 4 of the nuclear reactor 3 and detects neutrons in the nuclear reactor 3. The reactivity calculation mechanism 20 calculates the core reactivity based on the output signal S5 from the in-core neutron detector 5, and the reactivity signal S20 indicating the reactivity calculated here is sent to the reactivity monitoring mechanism 21. Given and compared to the reactivity setpoint 22. The reactivity set value 22 is set to, for example, the reactivity that makes the reactor 3 subcritical, and the reactivity signal S20 indicates the reactivity set value 2
When it exceeds 2, the reactivity monitoring mechanism 21 gives the deviation to the control rod operation instructing mechanism 23 as a reactivity reduction request signal S21.

The control rod operation instruction mechanism 23 converts the reactivity reduction request signal S21 into a control rod operation amount, and a control rod operation sequence database
From the control rod operation sequence data S24 stored in 24 and the signal indicating the control rod position from the control rod position detector 25,
The control rod 6 to be operated next is determined, and the reactivity reduction request signal is issued.
When S21 (deviation) is received, select operation control rod instruction S23 is CR
Output to the display 26 such as T. The display 26 is a reactivity calculation mechanism 2
It always receives the reactivity signal S20 from 0 and presents it to the plant operator in plain notation.

The plant operator operates the control rod manipulator 27 based on the selected operation control rod instruction S23 and the reactivity S20 to insert the control rod 6 into the core 4 by the control rod drive mechanism 7.

Therefore, when the reactivity set value 22 is set to a predetermined negative value at the time of inspecting the inside of the dry well, the control rod operation for making the reactor 3 subcritical is performed by the plant operator who monitors the display 26. If presented and the operator operates the control rod manipulator 27 accordingly, a predetermined control rod 6 is inserted into the core 4 and the reactor 3 can reach subcritical.

By the way, the relationship between the reactivity and the neutron density is expressed by the following one-point reactor approximate dynamic characteristic equation.

Where N (t) is the neutron density at time t S is the external neutron source ρ is the reactivity β is the total production rate of delayed neutrons βi is the production rate of delayed neutrons in the i-th group (i = 1,6) l is the neutron lifetime Ci (t) is the delayed neutron precursor nucleus density of the i-th group at time t. λi is the decay constant of the delayed neutron precursor nucleus of the i-th group.

In this equation (1) and (2), the reactor 3
Since it is determined by the properties of the fuel (not shown) forming the core 4, it can be calculated and set in advance. Further, N (t), Ci (t), and S are arbitrary units, and if any one of these is determined, the others are determined in relation to it. Here, the output signal S5 from the in-core neutron detector 5 is used as it is as N (t).

Then, when the reactor 3 enters a sub-critical state, the reactor output decreases and reaches a certain output level according to the external neutron source S. At that time, the relationship between the reactivity ρ and the external neutron source S is as described above. The following equation is established from the equation (1).

The reactivity ρ is the defined control rod pattern of the reactor subcritical,
For example, it can be obtained by calculating the core eigenvalue when the control rod is fully inserted at the start of reactor startup. If the core eigenvalue obtained by this core calculation is Keff, the reactivity ρ is Becomes

The external neutron source S can be obtained from the neutron density N corresponding to the output signal of the in-core detector 5 from the equations (4) and (3). You only have to do the core calculation once.
Since the reactivity changes but the external neutron source S does not change,
The reactivity ρ can be calculated from the neutron density obtained using this and the equations (1) and (2). Delayed Neutron Leading Nuclear Density Ci
(T) can be calculated using time-series data of neutron density N (t) if equilibrium is assumed at the start of calculation. Therefore, the reactivity calculation mechanism 20 calculates the reactivity according to the procedure shown in the flowchart of FIG. In addition,
In FIG. 2, reference numerals P1 to P7 indicate respective steps of the flowchart.

That is, the output signal S5 from the in-core neutron detector 5 is sampled at a predetermined cycle, and is online stored as time series data of the neutron density signal at P1.

Next, in P2, the time series data of this neutron density signal is fitted with a function to remove the noise of the signal, or if the data is continuously input, digital processing cannot be performed, so the noise is removed by a filter. Then, the most probable value of the current neutron density N (t) is calculated.

At P3, it is judged whether or not the external neutron source S is already set based on the neutron density N (t), and if not set at P4
To P5, if already set, go to P5.

In P5, the delayed neutron preceding nuclear density Ci (t) is calculated by the equation (2), and in P6, the reactivity ρ is calculated.

The reactivity ρ is calculated by using the following equations obtained from the equations (1) and (2),
It is calculated from the delayed neutron preceding nuclear density Ci (t).

The reactivity ρ is calculated periodically corresponding to the reactivity ρ that changes with the passage of time.

On the other hand, in P4, first calculate the initial value of the delayed neutron nuclear density Ci, then calculate the external neutron source S in P7, and return to P2,
The most probable value of the current neutron density N (t) is calculated, and thereafter, these calculations are repeated to periodically calculate the constantly changing reactivity.

The reactivity ρ thus calculated is displayed by the display 26 and provided to the plant operator who monitors it.

Further, since the selected control rod operation instruction S23 is displayed on the display unit 26, if the plant operator operates the control rod operation unit 27 according to this instruction S23, the reactivity ρ of the reactor 3 is set to the reactivity set value 22. Can be controlled.

Therefore, if the reactivity set value 22 is set to a reactivity at which the reactor 3 becomes subcritical, the reactor 3 can be maintained extremely easily in the subcritical state, and it is extremely easy to perform the inspection in the dry well. Can be kept subcritical. As a result, it is possible to reduce the burden on the plant operator, prevent erroneous judgments and erroneous operations by the operator, and improve the safety of the inspection work inside the dry well.

In the present invention, the reactivity set value 22 may be programmed in advance or may be configured to be adjustable by an operator's adjustment operation.For example, the reactivity set value 22 may be set to a positive value to set the reactivity. The selection control rod operation instruction S23 may be displayed on the display unit 26 so as to increase.

Further, not only the selection control rod operation instruction S23 is displayed on the display device 26, but the control rod operation device 27 may be automatically operated by the selection control rod operation instruction S23.

FIG. 3 and FIG. 4 show another embodiment of the present invention. The main difference of this embodiment from the above embodiment is that it changes within a predetermined time, for example, the inspection work time in the dry well. It is because a reactivity prediction system that calculates the reactivity change amount that is predicted and calculates this reactivity change amount in advance in the reactivity setting value is provided, and the part shown by the double frame in the figure is added. is doing.

In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals.

The present embodiment is configured as shown in FIG. 3, and its reactivity prediction system has a reactor state change recording mechanism 30, a plant data time series database 31, a temperature prediction calculation mechanism 32, and a reactivity prediction calculation mechanism 33. Have and.

The reactor state change recording mechanism 30 outputs the detection output from the in-reactor neutron detector 5 together with plant data such as pressure and temperature of reactor water in the reactor 3, main steam flow rate, feed water flow rate and reactor cleaning system flow rate. It is received and stored in the plant data time series database 31 as these plant data time series data S31.

The temperature prediction calculation mechanism 32 calculates the relationship between the reactor output and the reactor water temperature change based on the time series data S31, and the predicted value when the reactor output becomes zero during the drywell inspection work time 34. A certain predicted temperature decrease S32 is calculated and given to the reactivity prediction calculation mechanism 33.

From the predicted temperature decrease S32 and the set reactivity coefficient 35, the reactivity prediction calculation mechanism 33 calculates the reactivity set value 22 by the following equation.

Here, ρset is the set reactivity ΔT is the predicted temperature decrease δρ / δT (<0) is the set reactivity temperature coefficient ρ ₀ is the maximum value of the set reactivity.

However, when ΔT <0, ρset = ρ ₀ .

The reactivity monitoring mechanism 21 outputs the reactivity reduction request signal S21 until the reactivity is expected to increase the reactivity due to the decrease in reactor water temperature during the inspection work in the dry well. As a result, the control rod operation instruction mechanism 23 determines the control rod 6 to be inserted from the control rod position signals from the control rod operation sequence database 24 and the control rod position detector 25, and displays the selected control rod operation instruction S22. Output to the container 26. The plant operator operates the control rod operating device 27 based on the selected control rod operating instruction S23 and the reactivity S20, and the control rod driving mechanism 7 inserts the control rod 6 into the core 4.

Therefore, at the start of the inspection in the dry well, the control rod operation that incorporates the increase in the reactivity accompanying the decrease in the reactor water temperature is performed, so that the control rod operation thereafter can be reduced.

FIG. 4 shows a calculation procedure for calculating the predicted value of the reactor water temperature decrease in the temperature prediction calculation mechanism 32. The pressure and temperature changes of the reactor water temperature in the plant data time series data S31 and the atomic The amount of reactor water held in the reactor 3 is calculated to obtain the change in the enthalpy of reactor holding.

Next, the enthalpy change to and from the reactor 3 is calculated from the main steam flow rate, the feed water flow rate, the reactor cleaning system flow rate, etc., and the change in the enthalpy of the reactor possession due to causes other than heating by fuel is obtained. From these, it is possible to calculate the change in reactor water temperature at any reactor power, but during the drywell inspection work, the reactor power is considered to be almost zero, so
Predict the decrease in reactor water temperature that will decrease within this drywell inspection time. That is, if the reactor power is reduced due to the inspection work in the dry well, the work continuation time setting is decreased with the lapse of time, and the reactor water temperature decrease until the scheduled dry well work end time is calculated.

As described above, according to the present embodiment, it is possible to surely make the nuclear reactor subcritical when inspecting the inside of the dry well and safely perform the inspection work inside the dry well.

In addition, before the start of the drywell inspection, the predicted amount of reactivity that rises with the decrease in reactor water temperature during the inspection work is woven into the reactivity setting value 22, so the plant during the drywell inspection work The control rod operation by the operator can be reduced, and the burden on the plant operator during inspection can be reduced.

Although the set reactivity temperature coefficient 35 is a constant in the above embodiment, the present invention is not limited to this, and a value that changes corresponding to the reactor water temperature or a value obtained from a change in the reactivity during temperature change is used. You may use.

〔The invention's effect〕

As described above, the present invention displays the reactivity of the reactor and the control rods that need to be operated to control the reactivity to the reactivity set value, so that the plant operator can If the control rod is operated according to the display on the display, the operation for controlling the reactivity of the nuclear reactor to the reactivity set value can be easily performed. As a result, it is possible to reduce the burden on the plant operator and prevent erroneous decisions and erroneous operations.

Therefore, if the reactivity set value is set to the reactor subcritical reactivity required during drywell inspection, it is possible to easily maintain the reactor subcritical, and to operate the plant during drywell inspection. The burden on the worker can be reduced and the work safety of the inspection worker can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of a reactor operation support device according to the present invention, and FIG. 2 is a flowchart showing a reactivity calculation procedure in a reactivity calculation mechanism of the embodiment shown in FIG. FIG. 3 is a block diagram showing the overall configuration of another embodiment of the present invention, and FIG. 4 is a flow chart showing the calculation procedure for calculating the predicted value of the reactor water temperature decrease by the temperature prediction calculation mechanism shown in FIG. FIG. 5 is a configuration diagram showing a general configuration of a boiling water nuclear power plant for explaining a conventional reactor operating method. 3 ... Reactor, 4 ... Core, 5 ... Neutron detector in reactor,
6 ... Control rod, 20 ... Reactivity calculation mechanism, S20 ... Reactivity, 21 ... Reactivity monitoring mechanism, 22 ... Reactivity setting value, 23 ...
… Control rod operation instruction mechanism, 24 …… Control rod operation sequence database, 25 …… Control rod position detector, 26 …… Display unit,
30 …… Reactor state change recording mechanism, 31 …… Plant data time series database, 32 …… Temperature prediction calculation mechanism, 33 ……
Reactivity prediction calculation mechanism.

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number for FI FI technical display location G21C 17/10 GDB G21C 17/00 GDB Y (56) Reference JP-A-55-101084 (JP, A) Special features Kai 55-46131 (JP, A) JP 61-172094 (JP, A) JP 61-110087 (JP, A) JP 61-73092 (JP, A) Actual 60-170799 ( JP, U)

Claims (2)

[Claims] 1. A reactivity calculation mechanism for calculating the reactivity of a reactor based on a detection output from an in-core neutron detector for detecting a neutron flux in the reactor, and a reactivity calculation mechanism for calculating the reactivity. A reactivity monitoring mechanism that compares the reactivity with the reactivity set value and outputs the deviation between the two, and a control rod that indicates the control rod to be operated by converting the deviation from this reactivity monitoring mechanism into a control rod operation amount. A reactor operation support device comprising an operation instruction mechanism, a control rod to be operated, and a display for displaying the reactivity from the reactivity calculation mechanism. 2. The reactivity set value is set to the reactivity for making the reactor subcritical, or the reactivity is expected to increase within the working time during which the dry well inspection is performed. The reactor operation support device according to claim 1, wherein a change amount is included as a reactivity margin.