JPH01262496A - Automatic start-up device for nuclear reactor - Google Patents

Abstract

PURPOSE:To efficiently and safely attain the critical state at a specified change rate of neutron flux by executing the automatic operation of control rods in proportion to the deviation between an estimated reactivity and target reactivity. CONSTITUTION:The neutron flux of a reactor core 1 is measured by a neutron flux detector 2 disposed in the core and is inputted as a neutron flux detector reading by a nuclear instrumentation device 3 to a reactivity estimating device 4. The estimating device 4 calculates the estimated reactivity of the core 1 by using a physical model from the neutron flux reactor reading. The estimated reactivity is inputted to a control rod manipulated variable deciding device 5. The deciding device 5 determines the manipulated variable of the reactivity in proportion to the estimated reactivity and the target reactivity inputted from a reactivity setting device 6 and outputs the control rod operation signal as to whether the control rods are withdrawn or inserted at what notches to a control rod drive control device 8. The control device 8 drives the selected control rods 11 automatically by a control rod drive device 9. The increase of the neutron flux is thus executed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic nuclear reactor startup device that safely and efficiently achieves criticality and increases neutron flux in a nuclear power plant. .

(Prior Art) In general, in nuclear power plants, such as boiling water nuclear power plants, operators have conventionally operated control rods manually while monitoring the readings of neutron flux detectors and the reactor period, which is the logarithmic rate of change. Extraction criticality has been achieved.

Control operations up to criticality are predicted by offline calculation; AI
Using the J criticality pattern as a guide, the control rods are pulled out one by one according to the withdrawal sequence, and the timing of withdrawal is determined by looking at the response of the neutron flux during and after the withdrawal.

At the beginning of control rod withdrawal in a deep subcritical state, the neutron flux immediately rises and stabilizes as the control rod is withdrawn.

Furthermore, at this time, the neutron flux level is lower than the predicted value at the critical time, and the difference between the predicted pattern and the current pattern is large, so the control rods can be continuously withdrawn in this region.

As criticality approaches, the neutron flux increases and the time required to stabilize after the control rod is withdrawn increases.

In response to this, the operator reduces the amount of control rod withdrawal and carefully withdraws the control rod, and in the vicinity of criticality, the operation is performed in units of notches.

When a nuclear reactor reaches a state of physical criticality, that is, the reactivity is greater than zero, the neutron flux increases at a constant positive reactor period, that is, the reciprocal of the logarithmic rate of change of the neutron flux; The control rods are withdrawn to ensure a positive value, and the reactor cycle is measured to confirm that the reactor has reached a critical state.

To achieve this criticality, 20 to 40% of all control rods will be used during cold startup when the normal reactor water temperature is around 70℃, and in areas where the reactor water temperature is high such as during restart from scram. Pull out about 50% of the control rods.

(Problems to be Solved by the Invention) In the above-mentioned operation, the workload is large because the control rods are manually pulled out by the operator, and in a state approaching criticality, over-criticality due to excessive withdrawal of the control rods may occur. Careful operation is required to prevent alarms and reactor trips due to a sudden increase in neutron flux, which places a heavy mental burden on operators.

Therefore, it is being considered to automate control rod operations to reduce the burden on operators and prevent plant trips due to erroneous operations.

A method for automating control rod operation is to directly automate the monitoring operation described above. In other words, the reactor period is determined from the neutron flux detector reading, and if this is greater than a set value, the control rod is pulled out. A possible method is to determine that the condition is critical if the condition continues to exceed a set value.

However, with this method, the reactor period can only be measured after control rod operation, and therefore the behavior of the neutron flux cannot be monitored during control rod operation and period measurements. This poses a problem in terms of driving safety.

In particular, if a disturbance enters the water supply control system and the water supply increases rapidly, the reactivity applied by the cold water will cause the neutron flux to rise rapidly, potentially reaching an alarm level or causing a reactor trip. be.

The present invention has been made in response to such conventional circumstances, and aims to provide an automatic nuclear reactor startup device that can safely and efficiently achieve criticality of a nuclear reactor.

[Structure of the Invention] (Means for Solving the Problems) In other words, the present invention is an automatic reactor startup device that injects reactivity through control rod operation, achieves a critical state in the reactor core, and increases neutron flux. a reactivity estimating means for calculating an estimated reactivity of the nuclear reactor core based on information from a neutron flux detector arranged in the reactor core; and the estimated reactivity calculated by the reactivity estimating means. It is characterized by comprising a control rod operating means that determines the reactivity input amount in proportion to the deviation from a preset target reactivity, and controls the operation of the control rod according to this reactivity input amount. .

(Function) In the automatic reactor startup system of the present invention having the above configuration, the neutron flux of the reactor core is monitored based on the estimated reactivity estimated from nuclear instrumentation data placed in the reactor, and the estimated reactivity is monitored. By determining the input reactivity in proportion to the deviation from the target reactivity, it is possible to maintain the target reactivity by keeping the logarithmic rate of change in the neutron flux constant.

(Example) Hereinafter, an example in which the present invention is applied to a boiling water reactor will be described with reference to the drawings.

FIG. 1 shows the configuration of an automatic nuclear reactor startup system according to an embodiment of the present invention, in which the neutron flux of a nuclear reactor core 1 is measured as an electrical signal by a neutron flux detector 2 disposed within the reactor core.
The nuclear instrumentation device 3 inputs it to the reactivity estimation device 4 as a neutron flux detector reading.

The reactivity estimating device 4 calculates the estimated reactivity of the core from the neutron flux detector readings using a physical model. This estimated reactivity is input to the control rod manipulated variable determining device 5, and the control rod manipulated variable determining device 5 uses the estimated reactivity and the reactivity setting device 6.
The reactivity input amount is determined in proportion to the deviation from the target reactivity input from the control rod sequencer 7, and the control rod 11 is withdrawn or inserted by how many notches based on this reactivity input amount and information from the control rod sequence device 7. A control rod operation signal, which is the control rod operation amount and the coordinates of the control rod 11 to be operated, is output to the control rod drive control device 8.

In this control rod drive control device 8, the selected control rod 11
is automatically driven by the control rod drive device 9 to increase the neutron flux. Further, the selected control rod, control rod operation amount, and estimated reactivity are displayed on the display device 10.

After these operations are completed, the reactivity estimation calculation is performed again to determine the next control rod operation, which is similarly executed one after another.

In the reactor automatic startup system of this embodiment with the above configuration, the reactivity input amount ρ'a per unit time is determined by the reactivity estimation device 1
Estimated reactivity ρ and target reactivity ρt (≧0
) is determined in proportion to the difference between

That is, ρ゛a−Kl(ρt−ρ) ・・・・・・■
shall be. Here, 1 is a control gain that determines the input reactivity, and is a constant having a unit of (time)-1.

If the reactivity input amount is determined as in the above equation
Also, if there is no error in estimating the reactivity, then ρa-ρ, so ρ'a-Kl(-ρa) ・・・・・・■
Then,! The relationship between the neutron flux n and the reactivity ρ in a deep subcritical state is expressed by the following equation, where is the neutron lifetime and S is the fixed neutron source in the reactor core. dt n , and the logarithmic rate of change of the neutron flux becomes equal to Kl, that is, it becomes possible to increase the neutron flux up to criticality at a constant period.

Therefore, by setting Kl below the alarm level of the neutron flux change rate, near-critical operation can be performed efficiently without generating an alarm.

The actual control rod operation amount ΔN is calculated by correcting the control rod value to the input reactivity ρ゛a, and is calculated as ΔN-W(x・y,z) ρ゛a
Find it as...■. Here, W is the conversion coefficient of reactivity to control rod operation amount, and W is the in-core position (x, y
, z). The control rod value can be determined by off-line three-dimensional neutron flux distribution calculation.

In other words, ΔN is the control rod operation amount that changes the reactivity change of ρ°a per unit time.

Furthermore, according to this method, the time tc required to reach criticality is tc - (-1/K I
) In[(ρc-pt) HapO-pt)]...
...■ It is possible to know the time of criticality achievement in advance,
This enables automatic control rod operation that is easy for operators to understand. However, here, ρ0 is the reactivity at the start of control rod withdrawal.

If control rod operation is held when criticality is achieved, the reactivity when criticality is achieved will be ρC, but in the supercritical state, the stable reactor period and reactivity are as shown in the graph in Figure 2. There is a one-to-one relationship and is consistent with conventional operating methods.

Further, in the automatic reactor startup system of the present invention, since the reactor reactivity is estimated and fed back, the behavior of the reactivity can be known even during control rod operation, and it is possible to quickly respond to disturbances.

The graph in Figure 3 shows an example of changes in control rod withdrawal amount, neutron flux, reactor period, and reactivity when criticality is achieved by automatically operating the control rods using the automatic reactor startup system of this embodiment. ing. In addition, in this example, K l -90J'
(see-'), p t = 0.03%. As shown in this graph, the neutron flux increases smoothly with a rate of change of about 90'(see-') and about 1
After 0 minutes, the critical judgment level ρ-0.0% ΔK is reached.

After criticality is achieved, the neutron flux increases at a reactor period of 250 seconds corresponding to the target reactivity ρt -o, oa%.

The above has explained the case where the reactivity value of the control rod is known, but if the control rod value is not known, the control rod may be operated as follows.

In other words, it is only necessary to operate the control rods so that the condition of equation (2) is satisfied, and from the estimated value of reactivity, ρ゛ and Kl
(ρ equals ρ), and operate the control rod so that these become equal at each step.

For example, the number of control rod operation notches ΔN per l step is ΔN"-" [ρ(1)-ρ(t-Δt)-Kif, tCρt-ρ) dtl+ΔNr, ΔN-1ntΔN' It is given by ΔNr - ΔN' - ΔN. where Δt is the control time step, K′ is the gain for control rod operation, and ΔN′
is the remaining amount of the manipulated variable of one notch or less, and tnt is a function of integer conversion.

Here, if we set K---0,5, Δt-10 seconds,
It is enough. FIG. 4 shows the results when critical proximity was performed using this method. In this case, the control rod value is estimated to be small, so the control rods are operated continuously until 8 minutes after the start of startup, and after that, the control rods are operated in notch units, and the target reactivity is 0203%Δ In other words, it can be seen that criticality is achieved and the neutron flux is increased at the target period of 200 seconds (reciprocal: 0.005 (seconds-1)).

[Effects of the Invention] As explained above, according to the automatic reactor startup system of the present invention, the automatic operation of the control rods is performed in proportion to the deviation between the estimated reactivity and the target reactivity, thereby achieving criticality using neutrons. It can be carried out efficiently and safely with a constant flux change rate, and can respond quickly to reactivity disturbances such as reactor water temperature, improving the safety, stability, and efficiency of operation. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an automatic reactor startup system according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between stable reactor period and reactivity, and FIG. 3 is a reactor reactor shown in FIG. 1. Control rod withdrawal amount, neutron flux, and
A graph showing an example of changes in reactor cycle and reactivity. Figure 4 shows the neutron flux, reactor cycle, and reaction when starting operation is performed using the reactor automatic startup system shown in Figure 1 when the control rod value is not known. It is a graph showing an example of a change in degree. 1・・・・・・・・・・・・・・・Core 2・・・・・・
・・・・・・・・・Neutron flux detector 3・・・・・・・・・
・・・・・・Nuclear instrumentation device 4・・・・・・・・・・・・
・・・Reactivity estimation device 5・・・・・・・・・・・・・・・
・Control rod operation amount determination device 6・・・・・・・・・・・・・・・
・Reactivity setting device 7・・・・・・・・・・・・・・・
Control rod sequence setter 8・・・・・・・・・・・・・・・
・・Control rod drive control device 9・・・・・・・・・・・・・
...Control rod drive device 10...Display device 11...Control rod applicant Japan Atomic Energy Corporation Applicant
Toshiba Corporation Representative Patent Attorney Satoshi Suyama - Figure 1 Figure 3 Σ a 8 4th rgJ

Claims (1)

[Claims] (1) An automatic reactor startup device that increases neutron flux by injecting reactivity through control rod operation to achieve a critical state in the reactor core and increase neutron flux, from a neutron flux detector located in the reactor core. reactivity estimating means for calculating the estimated reactivity of the reactor core based on information on the reactivity; 1. An automatic nuclear reactor start-up device comprising control rod operating means for determining an input amount and controlling the operation of the control rods according to the reactivity input amount.