JPH0631777B2 - Output control device for natural circulation furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a nuclear reactor plant, particularly a natural circulation reactor,
The present invention relates to an output control device capable of reducing the heat generation amount of a nuclear reactor when a control rod cannot be inserted in a transient event.

[Conventional technology]

With reference to FIG. 5, a change in the control rod insertion impossible event of the BWR plant will be described.

In the BWR plant, when the control rod cannot be inserted, the recirculation pump is tripped by the scrum signal to reduce the core flow rate.

As a result, the amount of core voids increases and a negative reactivity is added, so that the neutron flux is suppressed and the reactor power decreases.

[Problems to be solved by the invention]

Since there is no recirculation pump in the natural circulation reactor, the reactor output reduction method by the recirculation pump trip when the control rod cannot be inserted, which is used in the BWR plant, cannot be adopted. Must be included.

An object of the present invention is to provide an output control device for a natural circulation reactor that can reduce the reactor output even when the control rod cannot be inserted when the main steam isolation valve is closed or the feed water flow rate is lost.

[Means for solving problems]

The above-mentioned object is a reactor vessel containing a reactor core, a tubular body installed in the reactor vessel and surrounding the reactor core, formed between the tubular body and the reactor vessel, and A natural circulation flow path that guides the coolant discharged from the upper part to the lower part of the core, a steam pipe that discharges the steam generated in the reactor vessel, a pressure reducing valve provided in the steam pipe, and discharge from this pressure reducing valve. A device for controlling the output of a natural circulation reactor having an exhaust pipe for guiding the generated steam to a cooling water pool, a liquid poison tank is connected to the reactor vessel via an injection valve, and a water level detector for detecting the reactor water level , A pressure detector for detecting the reactor pressure, and a plurality of neutron detectors provided in the core, the average output region monitor to input and average the output of these neutron detectors, the reactor pressure is Is it over the pressure setting value? When the output of the average power range monitor is equal to or higher than the first output set value for a certain period of time, or when the reactor water level is lower than the water level set value lower than the scrum water level, and the average power range monitor is Control device for opening the pressure reducing valve and the injection valve, respectively, when the output of the above is greater than or equal to a second output set value different from the first output set value. Can be achieved by

[Action]

When the reactor pressure exceeds the pressure set value and the output of the average power range monitor remains above the first output set value for a certain period of time, or when the reactor water level is lower than the scrum water level When the output of the average power range monitor becomes equal to or more than the second output setting value different from the first output setting value, the pressure reducing valve and the injection valve are opened, so that even in the natural circulation reactor, Even if the control rod cannot be inserted when the steam isolation valve is closed or the feedwater flow rate is lost, the reactor power can be reduced.

FIG. 3 is a conceptual diagram of the present invention, and shows the behavior in the reactor in each event and the corresponding change in the reactor pressure.

The event (I) in FIG. 3 is a 100% rated output operation state,
Steam generated on the reactor side is supplied to the turbine side through the main steam pipe.

Event (II) is due to some cause (MSI) during rated output operation.
This is a state where the control rod could not be inserted and the scrum did not occur when the reactor pressure increased due to V fully closed, etc.). As the reactor pressure rises, the voids in the core collapse and disappear, so a positive reactivity is input and the power rises by about 1.5 times.

In the event (III), a void is generated in the reactor by lowering the pressure by operating the automatic pressure reducing valve when the reactor power is high. Due to the generation of voids, the output decreases and the steam generated in the core decreases, but the amount of steam flowing out from the automatic pressure reducing valve is almost constant, so the pressure drop is promoted. Due to this synergistic effect, the reactor power decreases sharply.

Further, it is designed to inject SLC in the process of depressurization to keep the core reactivity negative after the depressurization is completed.

〔Example〕

FIG. 1 shows an output control device for a natural circulation reactor, which is an embodiment of the present invention. The natural circulation reactor is provided with a reactor core 35 in the reactor pressure vessel 1, and has a cylindrical shroud 36 surrounding the reactor core 35. The shroud 36 and the reactor pressure vessel 1 are provided.
And a natural circulation passage for guiding the cooling water discharged from the upper end of the core 35 to the lower end of the core. Although not shown,
It has a control rod (inserted in the core 35) for adjusting the reactor power. 40 is a reactor containment vessel.

During normal operation of the reactor, the steam generated in the reactor pressure vessel 1 is sent to the turbine 4 through the MSIV 3A and the main steam pipe 2 provided with the steam control valve 3. Turbine 4
The steam that has driven is condensed and liquefied by the ascites device 5. This condensed water is pressurized by the water supply pump 6 as the water supply, heated by the water supply heater 7 and returned to the reactor pressure vessel 1.

An exhaust pipe 8 having an automatic pressure reducing valve 7 is connected to the main steam pipe 2 in order to discharge surplus steam in a transient event such as a pressure increase. The lower end of the exhaust pipe 8 opens into the cooling water in the pressure suppression chamber 9. The pressure suppression chamber 9 surrounds the reactor pressure vessel 1 and has a vent passage 31 inside thereof.
2 is provided outside. The vent passage 31 also opens into the cooling water in the pressure suppression chamber 9.

Further, a boric acid water injection system storage tank 10 that constantly stores a sodium borate solution as a neutron absorber is provided in the reactor building. A pipe 33 equipped with a boric acid water injection valve 11 connects the boric acid water injection system storage tank 10 and the reactor pressure vessel 1.

The detector for detecting the behavior in the reactor includes a neutron flux detector provided in the core, a pressure detector 13 for detecting the pressure in the reactor pressure vessel 1, and water in the reactor pressure vessel 1. There is a water level detector 14 for detecting.

Outputs of a large number of neutron flux detectors 12 arranged in the core.
That is, a local power range monitor (LPRM) 15 for continuously measuring the local power of the core and an average power range monitor (APRM) 12A equipped with a device for averaging the output signals from the amplifiers 16 of the LPRM 15 are measured. The pressure detector 13 is connected to the gas phase part of the reactor pressure vessel 1 and continuously measures the pressure of this gas phase part.

The water level detector 14 draws out the reference pipe 17 connected to the reactor pressure vessel 1 to the outside of the reactor containment vessel 40, and the water head difference from the water level in the reactor pressure vessel 1 which is the measurement target of the water level of the reference level gauge 17A. To measure.

The controller 34 includes the APRM 12A and the pressure detector 13.
Also, the output signals of the water level detector 14 are input, and the automatic pressure reducing valve 7 and the injection valve 11 are controlled based on these signals. The function of the controller 34 is shown in FIG.

Next, the function of the apparatus of the present invention will be described with reference to FIGS. 1, 2, and 4 by taking the case where the control rod cannot be inserted during a transition as an example.

In FIG. 1, the solid line shows the flow of steam and the coolant, and the dotted line shows the flow of signals.

FIG. 4 shows a case where the control rod cannot be inserted together with the transient change when the main steam isolation valve is closed.

When the reactor pressure rises above a predetermined value when the main steam isolation valve 3A is closed, the controller that receives the measurement signal of the pressure detector 13 generates a "reactor pressure high" signal. At this time, if the control rods are not inserted into the core for some reason, the increase in pressure in the reactor pressure vessel 1 collapses the voids in the core and a positive reactivity is injected. For this reason, the reactor power also sharply increases. The controller 34, which receives the output of the APRM 12A, detects that the output of the APRM 12A continues to be equal to or higher than the set position a, and generates an "APRM upscale" signal. A of controller 34
The ND circuit 19 outputs a valve operation signal by inputting these two signals. The automatic pressure reducing valve 7 and the boric acid water injection valve 11 are opened by the valve operation signal.

When the automatic pressure reducing valve 7 is opened, the steam generated in the reactor pressure vessel 1 is discharged into the cooling water in the pressure suppression chamber 9 through the exhaust pipe 8 and then condensed. In this way, the reactor pressure is reduced, the core void amount is increased, and the neutron flux in the core is suppressed, so that the reactor power is reduced.

Further, by opening the boric acid water injection valve 11, the sodium borate solution in the boric acid water injection system storage tank 10 is injected into the atomic test pressure container 1. The boric acid in the sodium borate solution absorbs neutrons in the reactor core and reduces the reactor power for a long time.

On the other hand, if the control rod cannot be inserted together with the transient change when the feed water flow rate is lost, the reactor water level will drop due to the feed water flow loss. At this time, the controller 34 which inputs the measured value of the water level detector 14 generates a "reactor water level low" signal. At this time, by the time the low water level signal is generated, the APRM12A
The level of the output signal is almost reduced. However, the controller 3 that inputs the output of the APRM 12A
When the output of the APRM 12A input to is equal to or more than the set value b, the "APRM output signal present" signal is generated. AN
The D circuit 20 outputs a valve operation when the "reactor water level low" signal and the "APRM output signal present" signal are input. The operation valve signal opens the automatic pressure reducing system 7 and the injection valve 11. 21
Is an OR circuit.

When setting the logic, it is considered that "it does not operate when there is an abnormal transient change, but it operates only when it is determined that the control rod cannot be inserted."

An example of the reason for selecting each setting value of the controller 34 is shown below. The "reactor pressure high" setting value should be a value with a margin for the rated pressure.

"APRM upscale" is set value a or more,
Current BWR APRM reading upscale 125%
Therefore, the setting value a is set to 125%.

However, there is a possibility that the automatic pressure reducing valve will malfunction if an abnormal transient change that does not result in the inability to insert the control rod occurs and a temporary upscale of the APRM occurs.
In order to prevent this, a CPu that detects that upscaling continues for a certain period of time or longer.
It has the function of (Time Delay Pickup). "Low reactor water level" set value is L2 below scrum water level (L3)
And “With APRM output signal” is set value b or more, and the maximum reactor output level is 215% or less converted to the APRM signal at the present BWR plant start-up time. Considering ease
Allow 20% for 15%.

It is shown below that the automatic depressurization system does not operate during the transient changes shown in FIGS. 6 and 7 by using the logic for reducing the reactor pressure shown in FIG.

(A) Transient change when the main steam isolation valve is closed Fig. 6 shows the behavior of the transient change when the main steam isolation valve is closed.

Although the reactor pressure rises and the reactor pressure high signal is detected by closing the MSIV, although the APRM upscale signal is higher than the neutron flux high scrum set value, the condition is not satisfied from the viewpoint of TPU as a temporary one.

(B) Transient change when the total feed water flow rate is lost Fig. 7 shows the behavior of the transient change when the total feed water flow rate is lost.

Low reactor water level signal is detected due to loss of feedwater flow, but L
By the time the level reaches 2, the APRM level becomes almost zero.

As described above, the automatic pressure reducing valve and the SLC injection valve do not operate due to the reactor pressure reduction logic during the transient change.

〔The invention's effect〕

According to the present invention, even in the natural circulation reactor, the reactor output can be reduced even if the control rod cannot be inserted when the main steam isolation valve is closed or the feed water flow rate is lost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an output control device for a natural circulation reactor which is an embodiment of the present invention. FIG. 2 is a detailed configuration diagram of a first controller, and FIG. 3 is a behavior in a reactor according to an embodiment of the present invention. FIG. 4 is a reactor output change diagram according to an embodiment of the present invention, FIG. 5 is a transient change diagram when the control rod of the conventional BWR cannot be inserted, and FIGS. 6 (A) and 6 (B) are FIGS. 7A and 7B are transient change diagrams when the main steam isolation valve of the conventional BWR is closed, and FIGS. 7A and 7B are transient change diagrams of the conventional BWR when the total feed water flow rate is lost. 1 ... Reactor pressure vessel, 7 ... Automatic pressure reducing valve, 8 ... Exhaust pipe, 9
… Pressure suppression chamber, 10… Boric acid water injection system storage tank, 11
... Boric acid water injection valve, 12 ... Neutron flux detector, 12A ... A
PRM, 13 ... Pressure detector, 14 ... Water level detector, 34 ...
controller.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Masao Hirose 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Yukio Hatakeyama 3--2, Saiwaicho, Hitachi, Ibaraki No. 1 in Hitachi Engineering Co., Ltd. (72) Inventor Toshio Yasushima 3-2-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Engineering Co., Ltd. (56) Reference JP-A-63-75691 (JP, A)

Claims (1)

[Claims] 1. A reactor vessel having a built-in reactor core, a tubular body installed in the reactor vessel and surrounding the reactor core, and a reactor body formed between the tubular body and the reactor vessel. A natural circulation flow path that guides the coolant discharged from the upper part to the lower part of the core, a steam pipe that discharges the steam generated in the reactor vessel, a pressure reducing valve provided in the steam pipe, and discharge from this pressure reducing valve. A device for controlling the output of a natural circulation reactor having an exhaust pipe for guiding the generated steam to a cooling water pool, a liquid poison tank is connected to the reactor vessel via an injection valve, and a water level detector for detecting the reactor water level , A pressure detector for detecting the reactor pressure, and a plurality of neutron detectors provided in the core, the average output region monitor to input and average the output of these neutron detectors, the reactor pressure is The pressure exceeds the set value, and When the output of the average power range monitor is above the first output set value for a certain period of time or when the reactor water level is below the water level set value lower than the scrum water level, and the average power range monitor Control device for opening the pressure reducing valve and the injection valve, respectively, when the output of the above is greater than or equal to a second output set value different from the first output set value. .