JPS5838890A - Reactor stabilizing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a nuclear reactor stabilization device.

Currently, stability evaluation of the reactor core is performed at several points on the natural flow rate curve and the flow rate control curve using a stability analysis code during core design, and the attenuation ratio is determined as shown in Figure 2. In this design analysis, we selected parameter values that took into account safety factors in order to evaluate the safety side, and analyzed the conditions under which the stability margin becomes the smallest regarding the aging of the reactor. There is. These analysis results are
It is used to determine the allowable operating range of a nuclear reactor, and the reactor is to be operated avoiding the condition points that exceed the safe design criteria shown in Figure 1.

On the other hand, in order to reduce the stability margin in the reactor core, it is considered to avoid operating points where the stability margin decreases.

Note that the above stability includes core stability and channel stability.

Core stability refers to core reactivity stability, that is, the stability of neutron flux fluctuations when some reactivity disturbance is applied to the core in a steady state. If the reactivity fluctuates due to some reason, the void ratio will fluctuate through fluctuations in the coolant flow rate in the core, engineering/talvy, etc., and the loop that feeds back to the output via the reactivity coefficient will become a positive feed bank. There is a word. As a result, depending on the operating state, the neutron flux within the core may begin to oscillate, the amplitude may grow, and it may diverge. Core stability is what prevents such unstable neutron flux phenomena from occurring. Core stability is the stability of the reactor itself, which is not dependent on the control system, and operating conditions that cause unstable phenomena are not allowed.

In addition, channel stability refers to the stability of the flow rate of coolant in the channel against pressure loss disturbances in the fuel assembly channel box arranged in the reactor core. In other words, when a change in pressure loss occurs at the channel entrance, the channel flow rate changes. The amount of voids inside also changes. Since the void amount change has a time delay relative to the flow rate change, a phase lag occurs between the flow rate change and the void amount change, and the flow rate may begin to oscillate, and its amplitude may grow and diverge. Channel stability is what prevents such flow rate instability from occurring. Channel stability is essential to the safety of a nuclear reactor, since the above-mentioned flow instability phenomenon has a serious impact on the safety of a nuclear reactor.

Therefore, the above-described width reduction ratio DR used as an index for measuring stability is defined as XI. Incidentally, % XIT

However, in an operating nuclear reactor, the average neutron detector only monitors the presence or absence of neutron flux oscillations, and it is difficult to predict the stability in the current operating state or the stability change after changing the operating point. etc. have not been carried out. Therefore, it is not always guaranteed whether the stability margins of the core and channels are maintained within the standard values.

The present invention was made based on the above-mentioned circumstances, and an object of the present invention is to obtain a nuclear reactor stabilization device that can sufficiently ensure core stability and channel stability during operation and when changing operating conditions.

The invention will now be described in detail with reference to the drawings. In FIG. 2, process signals a such as flow rate, pressure, and neutron flux inside the nuclear reactor 1 are collected by a data collection device 2. Note that an operating point change signal inputted from the operator input device 3 is also input to the data collection device 2 . The process signal a collected by the data collection device 2 is transmitted to the core performance calculation device 4.
The output is then sent to the core state prediction device 5, which receives the input. The output of the core state prediction device 5, that is, the signal C regarding the core state, is input to the stability calculation device 6, and the output of the stability calculation device 6, that is, the core stability signal d, is sent to the stability condition comparison device 7. As a result of the comparison, set pressure change signals e and g are sent to the reactor inlet condition calculation device 8 and the set pressure control device 9.

The reactor inlet condition calculation device 8 provides the reactor inlet condition signal f to the stability calculation device 6. The setting ff1f force control device 9 is
A control signal for changing the set pressure is applied to the pressure control system pressure set point 10.

The apparatus of the present invention described above operates as follows. First, in the device of the present invention having the above configuration, device 2.4.5.6 and k
ka has a reactor stability prediction function, and equipment 5.6.7.
8 and 9 have a reactor stabilization function.

Now, when changing the operating point from operating point A for the coolant flow rate QAS reactor output to operating point B for the flow rate Qa output P1, the trajectory from operating point A to operating point B and the stability margin at operating point B are Calculated using the furnace stability prediction function. If the stability margin decreases and falls below the standard value, the reactor stability stabilization function performs operations to ensure a certain stability margin.

Those steps will be explained below. First, the operator inputs data b1 regarding the operating point change, that is, the operating point after the change, the operating point sampled from the trajectory at the time of the operation change, etc., using the operator input device 3. The core performance calculation device 4 and the core state prediction device 5 predict the core state at each input point based on the data a about the current operating point collected by the data collection device 2.

The stability calculation device 6 calculates the reactor stability based on each of the calculated data signals C. The obtained core stability signal is compared with a predetermined reference value in a stability condition comparison device 7. If the stability is below the reference value, a set pressure change signal e is sent to the reactor inlet condition calculation device 8. The inlet condition calculation device 8 calculates the increase in furnace output and the decrease in inlet enthalpy when the pressure set point is raised, and the stability calculation device 6 calculates the stability margin when the set point increases based on the calculation results. , when the stability condition comparison device 7 confirms that a predetermined stability margin is secured based on the results,
The set pressure change signal g is sent to the set pressure control device 9, and the control device 9 sends the control signal g to the pressure control system pressure set point 10, raising the set point of the turbine inlet pressure control system and increasing the stability margin. let

In the present invention, as described above, the system pressure is changed to ensure a stability margin, and the system pressure and stability have the relationship shown in FIG. 3.

Figure 3 shows an example of channel stability, and the effect of increasing pressure on channel stability is that when pressure is increased, the specific heat of water increases when compared with the time-heat output at low pressure. This is brought about by the fact that the subcool region length becomes a dog and the void ratio α with respect to the exit quality Xe decreases, so that the two-phase attribute loss becomes smaller.

From Figure 3, it can be seen that the width reduction ratio decreases significantly due to the effect of pressure.
It is clear that the stability is improved.

Therefore, by increasing the set pressure, the stability margin of the reactor can be increased with little change in operating conditions.

Figure 4 shows that as a result of the reduction ratio being lowered by the device of the present invention, the constant reduction ratio operating curve shown by the dashed line in the figure is on the higher output side than the conventional constant reduction ratio operation curve shown by the broken line in the figure. This shows that the stability margin in the operating range will continue to increase.

As is clear from the above, according to the present invention, stability evaluation corresponding to the actual operating state of the plant is performed.
It is possible to secure an operating range that is wider than the allowable operating range determined by design analysis, and when a decrease in the reactor stability margin due to changes in the reactor core condition is detected, it is possible to take measures to prevent the reactor from operating almost immediately. A certain stability margin can be secured without changing the pruritus. Therefore, it is possible to operate even in a region where the operating range is determined by the stability limit while maintaining the planned output.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing channel stability, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram showing the effect of system pressure on stability, and FIG. 4 is a diagram showing the effect of system pressure on stability. Conventional well 3...operator input device, 4...core performance calculation device,
5... Core state prediction device, 6... Stability calculation device,
7... Stability condition comparison device, 8... Reactor inlet condition calculation device, 9... Set pressure control device, lO... Pressure control system pressure set point. Application agent Patent attorney Kikuchi Five departments l Figure 0 20 40 60 60
100 Reactor power (γ) 2nd @ Year 3 Fig. μ-light amount (DA)

Claims (1)

[Claims] A data collection device that collects various process signals of the reactor, a core performance calculation device that calculates core performance from the collected data, a core state prediction device that predicts the power distribution and core performance after changes in operating conditions, and A core stability calculation device that evaluates the stability of the reactor core based on the prediction results of the device;
A stability condition comparison device that compares changes in the stability margin based on the calculation results of this device, and a device that issues a change to the set pressure of the pressure control system when the stability margin is found to be below a reference value as a result of this device comparison. A nuclear reactor stabilization device comprising: