JPS5811036B2 - Output control device for pressure tube reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a power control device for a pressure tube nuclear reactor.

Conventional reactor output distribution and output level control devices perform output control by averaging the signals from output detectors uniformly placed within the reactor and feeding this signal back to the control rods. was.

In Figure 1 showing the conventional reactor core tank 1
A large number of pressure pipes 2 are provided inside, and a coolant for cooling the fuel circulates within the pressure pipes 2, and a part of the coolant turns into steam and reaches the steam drum 3.

In addition, inside the reactor core tank 1, there is a power detector 4 that detects the local power of the reactor, a control rod 5 that controls the power of the reactor, and high-energy neutrons generated by the fuel and decelerates thermal energy. There is a moderator 6.

FIG. 2 shows a cross-sectional view of the nuclear reactor, and the signals from the pressure detectors 4, which are uniformly arranged in the moderator 6 shown in FIG. The circuit 8 periodically calibrates the thermal output of each of the reactor cooling system loops 13n determined by a heat balance meter or the like.

This signal is compared in the sampling regulator 9 with the reactor power setting signal A requested by the reactor operator.

For example, if the former signal is a negative signal and the latter is a positive signal, if the difference is positive, the SCR circuit 1
At 0, a control rod withdrawal signal is generated, and the control rod 5 is withdrawn from the core by the control rod drive source 12 and control rod drive motor 11 until the signal becomes zero.

Conversely, if the difference between the plus signal and the minus signal is negative, the control rod 5 is inserted and the nuclear power output level is set to a predetermined level.

13 is a reactor cooling system loop, and 14 is a recirculation pump.

In the conventional reactor power control device described above, the power detector 4
used a fission ionization chamber made of uranium dioxide (UO2) fuel, which is sensitive to neutron flux, so that it could respond immediately to changes in reactor power.

However, since the output detector 4 has good sensitivity, the output response characteristics are very good, but on the other hand, the sensitivity is severely degraded.

According to actual measurement data obtained by irradiating the output detector 4 with neutrons in a material testing reactor, as shown in sensitivity deterioration curve B in Figure 3, when the neutron irradiation amount is 50% of the detector lifetime irradiation amount, the sensitivity decreases to 35%. As a result, the response characteristics of the output also deteriorate accordingly.

Furthermore, as shown in FIGS. 1 and 4, since the output detector 4 is inserted into the moderator 6 with the highest neutron flux, the amount of neutron irradiation received by the output detector 4 is large, and the output detector 4 4
The lifespan of the output detector 4 becomes very short, and it becomes necessary to frequently replace the expensive output detector 4.

In FIG. 4, C is the position of the output detector 4, D is the moderator area, and E is the fuel area.

Figure 5 quantitatively explains the above phenomenon, with the horizontal axis representing the reactor core power density (KW/l) and the vertical axis representing the pressure detector 4.
This figure shows the amount of detector replacement that occurs every two years due to the lifetime of the reactor, and the rate of deterioration in output sensitivity (%) per two cycles of reactor operation.

Curve F shows the relationship between the biennial replacement amount and core power density, and curve G shows the relationship between the detector sensitivity deterioration rate and core power density.

From Figure 5, in a prototype reactor class reactor (capacity up to 12KW/l), the detector must be replaced every year, and the deterioration in sensitivity reaches 55% per two weeks. It is necessary to calibrate the output detector 4 to the heat output determined from a heat balance meter or the like every two weeks.

On the other hand, when a nuclear reactor becomes a large-scale reactor such as a demonstration reactor or a commercial reactor, the power density of the reactor increases increasingly to 20 KW/l or more in order to improve the economic efficiency of the reactor.

In this case, as shown in Fig. 5, it becomes necessary to replace the output detector 4 every six months, and not only do the expensive pressure detectors have to be replaced every six months, but also the reactor has to be shut down when replacing it. The operating rate of the reactor will decrease.

In addition, the sensitivity deterioration of the pressure detectors 4 reaches 8% every two weeks, so it becomes necessary to calibrate all the pressure detectors 4 in the core to thermal output once a week. This method has the drawbacks of increasing the required amount of equipment and placing a heavy burden on the operator.

SUMMARY OF THE INVENTION An object of the present invention is to provide an output control device for a pressure tube nuclear reactor in which the output detector does not cause deterioration in sensitivity and has improved operability.

The present invention combines a thermal output signal in the reactor core tank, which is compared with a nuclear reactor output setting signal and controls the reactor output based on the difference, with a main steam flow rate signal or a self-power detector signal and a neutron flux signal. The differential signal of a pressure detector with high sensitivity characteristics, such as a nuclear fission ionization chamber, installed at a low position is added to the differential signal of the pressure detector.

That is, the main steam flow rate for each steam drum in the cooling loop is fed back to the reactor control material as a reactor power detector.

In this case, the value of the main steam flow rate itself represents the thermal output of each cooling system loop, so there is no need to calibrate the pressure detector to the thermal output as in a fission ionization chamber, and there is no problem of sensitivity deterioration. .

On the other hand, the main steam flow rate has poor response characteristics to changes in reactor thermal output, and a time delay of about 10 degrees occurs.

To solve this problem, an output detector with good response characteristics, such as a nuclear fission ionization chamber, is installed at a location near the reactor core where the neutron flux is low, and its differential signal is fed back to the control material in the same way as the main steam flow rate. This controls the reactor output.

If such a method is adopted, the output detector for detecting neutrons is installed in a place with low neutron flux, so the amount of neutron irradiation is low, and therefore the lifespan is long and there is no need to replace the pressure detector.

Since the differential value signal is fed back to the control material, even if the sensitivity of the output detector deteriorates, there is no need to calibrate the output detector to the thermal output.

Furthermore, instead of the main steam flow rate, a self-powered detector with low sensitivity and slow response characteristics may be used.

It is something. An embodiment of the present invention will be described below with reference to the drawings.

Parts that are the same as before are shown with the same symbols.

In FIG. 6, the reactor core tank 1 is divided into several regions in units of reactor cooling system loops 13.

A part of the coolant circulated in the reactor cooling system loop 13 by the recirculation pump 14 becomes steam during the reactor cooling process, and the steam is separated from the coolant in the steam drum 3,
It is guided to the reactor main steam system 17.

The main steam flow rate W for each reactor cooling system loop 13 is detected by the main steam flow rate detector 15 provided in the main steam system 17 .

This signal passes through a signal n from an output detector 4 such as a nuclear fission ionization chamber installed around the reactor core, and then enters a sampling regulator 9 together with a reactor output setting signal requested by the operator.

For example, the addition value of the reactor output, the main steam flow rate for measuring the output change, and the differential output change signal is set as a minus signal, and the reactor output setting signal is set as a plus signal.

The sampling regulator 9 calculates the difference, and if the difference is positive, a signal for withdrawing the control rod 5 is generated in the SCR circuit 10, and the control rod 5 is moved by the control rod drive power source 12 and the control rod drive motor 11. , are withdrawn from the core until the difference signal at the sampling regulator 9 becomes zero.

Conversely, in the sampling regulator 9, if the difference signal is negative, the control rod is inserted, and the reactor power level and the power distribution among the reactor cooling system loops 13 are controlled to predetermined values.

FIG. 7 shows another embodiment of the present invention, which differs from the embodiment in FIG. 6 in that instead of the main steam flow rate, a reactor power detector is used as a reactor power detector with less sensitivity loss and slower response characteristics. This uses a 4A output detector (self-powered detector).

Since the sensitivity of the self-power detector 4A deteriorates by about 5% during the reactor life, there is no need to replace the self-power detector 4A, and self-power is detected only when the power distribution within the reactor changes significantly due to the movement of the control rods 5. The detector 4A may be calibrated to the heat output determined by a heat balance meter or the like.

In this embodiment, further, from the reading of the self-output detector 4A,
It has the advantage of being able to determine the power distribution within the reactor.

In addition, as a control material to control the reactor power level and power distribution, chemical shims such as heavy water level control, which is a moderator, and liquid poison B10 dissolved in the moderator are used, or the speed of the recirculation pump. It may also be possible to control the flow rate by changing the flow rate.

The reactor output (integral output) detector may measure the temperature, pressure, steam flow rate, etc. of the reactor cooling system.

As described above, the present invention serves as a reactor power (integral power) detector and feeds back the main steam flow rate of each reactor cooling system loop to the control material, eliminating the problem of deterioration in sensitivity of the conventional power detector. ,Therefore, there is no need to replace the detector and the economic efficiency of the reactor is improved.

Furthermore, since the integrated reactor output is directly measured, there is no need to calibrate the output detector to the thermal output, making operation easier and improving operability.

In response to sudden fluctuations in reactor power, the differential value of the measured value of the neutron output detector installed in the vicinity of the reactor core where neutron flux is low is fed back to the control material, so the response characteristics of reactor power are extremely good. It is.

Furthermore, since this output detector is installed at a location where the neutron flux is low, the sensitivity deterioration rate of the detector itself is small.

Furthermore, even if the sensitivity deteriorates, the differential value is fed back to the control material, so the deterioration in sensitivity has no effect on the reactor control system.

The present invention is as described above, and has the effect of improving operability without causing deterioration of the pressure detector.

[Brief explanation of drawings]

Figure 1 is a schematic sectional view of a pressure tube reactor, Figure 2 is a schematic diagram of a conventional pressure tube reactor output control device, and Figure 3 is a sensitivity deterioration curve of the output detector of the device shown in Figure 2. , Fig. 4 is a neutral distribution diagram within a unit fuel assembly, Fig. 5 is a graph showing the detector sensitivity deterioration rate characteristic for reactor core power density, year of detector replacement and reactor operation two weeks, and Fig. 6 is FIG. 7 is a schematic diagram showing an embodiment of the present invention, and shows a power control device for a pressure tube reactor according to the present invention. Seventh is a schematic diagram showing another embodiment of the power control device for a pressure tube reactor according to the present invention. . Explanation of symbols: 1...Reactor core tank, 4...Output detector, 4A...Self output detector, A...Nuclear power output setting signal.

Claims (1)

[Claims] 1. In a system in which the thermal output signal in the reactor core tank and the reactor output setting signal are compared and the output is controlled based on the difference, the thermal output signal is the main steam flow rate signal or 1. An output control device for a pressure tube nuclear reactor, characterized in that it is configured to add a signal from an output detector and a differential signal from an output detector with high sensitivity characteristics provided at a location with low neutron flux.