JPS5950395A - Reactor water level lowering control 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 [Technical Field of the Invention] The present invention relates to a reactor water level drop suppression device when abnormal transient changes occur during plant operation in a boiling water nuclear reactor.

[Technical background of the invention and its problems] FIG. 1 is a vertical cross-sectional view showing the schematic configuration of a general boiling water nuclear reactor,
Inside the reactor pressure vessel, a cylindrical shroud is disposed concentrically with the body of the reactor pressure vessel, and a reactor core J is installed within this shroud. Above shroud
A steam/water separator 3 is provided above the shroud head formed at the top of the shroud, and a steam dryer 6 is further provided above the steam/water separator S. On the other hand, a plurality of jet pumps 7 are disposed within the annular gap formed by the inner peripheral surface of the reactor pressure vessel/ and the shroud λ, and each of the jet pumps 7 is connected to the reactor pressure vessel. The reactor water pumped up from the current gap by a recirculation pump g provided outside the reactor is supplied as driving water. In addition, the code 7 in the figure is a water supply pipe, 1
0 is the main steam pipe, // is the recirculation pump drive motor.

Thus, when the coolant is supplied into the reactor pressure vessel/from the water supply pipe D and the recirculation pump g is driven by the recirculation pump drive motor/l, the five recirculation pumps g are used to cool the reactor pressure vessel/. Reactor water within the current gap formed by the inner circumferential wall and the shroud 2 is supplied to each jet pump as driving water. Therefore, the reactor water in the reactor pressure vessel/ is forcibly sent to the lower part of the reactor pressure vessel/, and is further supplied and circulated to the reactor core 3.

The reactor water supplied to the reactor core 3 section is heated as it passes through the reactor core 3 and becomes a two-phase flow of water and steam, which passes through the shroud header and is sent to the steam separator 5 where steam and water flow. The steam separated from water is removed from moisture in a steam dryer 6 and then sent to a turbine (not shown) via a main steam pipe IO.
supplied to

By the way, in the above-mentioned boiling water nuclear reactor, the water level in the reactor pressure vessel l is controlled to be constant during normal operation of the plant. In other words, when the reactor water level rises, the moisture in the main steam led to the turbine increases, while when the reactor water level falls, the cooling phase flow 1: decreases, and if the reactor water level falls extremely, There is a danger that the fuel will become exposed and cannot be cooled, leading to overheating and melting of the fuel. Therefore, in order to prevent such a situation from occurring, the reactor water level instrumentation system is designed to activate various devices and perform protective operations when the reactor water level reaches a preset water level. It's Nishide.

In other words, when the water level of one nuclear reactor rises, if the water level rises by a certain amount above the normal operating water level, a Takagi level warning will be issued, and if it rises further and reaches a predetermined water level, the turbine will be tripped and the moisture will be removed. This prevents a large amount of steam from flowing into the turbine.

On the other hand, when the reactor water level falls by a predetermined amount below the normal operating water level, a low water level alarm is issued, and when the water level drops substantially, the output is reduced by reactor scram, and the main steam isolation valve By completely closing the reactor, the reactor was isolated and the emergency core cooling system was activated to ensure cooling.

However, various transient changes can occur during reactor operation. In particular, in transient changes accompanied by a drop in reactor water level,
It is necessary to suppress the amount of decrease. In other words, when the reactor water level rises, the turbine is stopped and the reactor is scrammed to secure the coolant, but when the reactor water level falls, the reactor is not only scrammed, but also the reactor is scrammed. After a reactor scram occurs, it is necessary to replenish coolant to compensate for the steam that flows out due to heat.

By the way, reactor scram is one of the transient changes accompanied by a transient drop in reactor water level. FIGS. 2 and 3 are transient diagrams when a reactor scram occurs. When the reactor scrams, the neutron flux decreases due to the negative reactivity due to the control rods being fully inserted. As a result, the amount of voids inside the reactor decreased, and as shown in Figure 3, the reactor water level temporarily fell, and then the D7 sub-reactor water level recovered due to the action of the reactor feed water flow rate control system. However, if the transient water level drop is rapid, the reactor feed water control system may be unable to keep up with it.
Furthermore, errors in the reactor water level instrumentation system are also taken into consideration.
This may result in unnecessary activation of the emergency core cooling system, etc., and furthermore, if the emergency core cooling system is activated at a high temperature of 61 degrees, thermal stress may be applied to the reactor itself. There are other problems, such as the fact that it gives rise to problems such as the impact on the design life of the emergency core cooling system.

[Object of the Invention] In view of these points, the present invention suppresses the amount of decrease in the reactor water level to a small extent when a transient change in which a drop in the reactor water level is expected to occur, and eliminates the need for an emergency core cooling system. An object of the present invention is to provide a reactor water level drop suppression device that prevents startup.

[Summary of the invention]

The present invention is '? To Ii8? In a water expansion reactor, a reactor water level drop suppression signal generation position that generates a reactor water level low 1 suppression signal based on a transient change occurrence signal that indicates a drop in reactor water level is expected, and an upper SL reactor water level drop suppression signal generation position. It has a recirculation flow rate control 'f11 device which adds a recirculation flow rate control device to the recirculation pump drive ηjII motor.
7.It is characterized by reducing the number of flow cups to prevent an extreme drop in the water level.

[Embodiments of the invention]

Figure 7 shows a system diagram showing one embodiment of the reactor water level drop suppression of the present invention, which causes a reactor scram, which is one of the transient changes expected to result in a reactor water level drop. Then,
The scram signal is applied to the reactor water level drop suppressor ↑11b to the signal generator 15. When the scram signal is applied to the reactor water level drop suppression signal generation device 15 in this way,
61. This reactor water level drop suppression signal generator ff3/! r
A reactor water level drop suppression signal is outputted from the recirculation flow rate controller 1A, and the signal is applied to the recirculation flow rate controller lA, and the recirculation flow rate control signal from the recirculation flow rate controller 1q, /A drives the recirculation pump. The stuttering is transmitted to the moke //, and the r'' rotational speed of the circulation ear pump is reduced or its rotation is stopped by -1J.

However, when the reactor scrams, the four neutral bundles decrease due to the negative reactivity due to the control rods being fully inserted, which increases heat generation in the reactor core and causes voids in the reactor. reactor water level is low]. However, as mentioned above, the speed of the water circulation pump is controlled by the reactor signal via the reactor water level low 1 suppression (No. 6j generation crystal i3 and the circulation flow rate control device 47B). 1.F'J' The VM ring core flow rate decreases, the void n in the reactor increases transiently, and the reactor water level shows a rising tendency.Therefore, this rising tendency of the reactor water level causes the Furnace.

The drop in water level due to crumbs is alleviated, and a large drop in the reactor water level is prevented.

In the above embodiment, the reactor water level drop suppression device is activated by the reactor scram signal, but other transient change signals 1 that are expected to cause the reactor water level to drop, such as a main steam isolation valve closing signal, The speed of the recirculation pump may also be controlled by a stop signal of the reactor feed water pump or the reactor condensate pump to suppress a transient drop in the reactor water level.

[Effects of the Invention] As explained above, in the present invention, a reactor water level drop suppression signal is generated based on a transient change signal indicating that a water level drop in the reactor is expected, and a reactor water level drop suppression signal is generated. We have installed a recirculation flow rate control device that applies the recirculation flow rate side 601 (No. The speed of the circulation pump is reduced or stopped, and the drop in the water level is mitigated and suppressed.Therefore, it is possible to reliably prevent the emergency core cooling system from being activated frequently due to the transient change. Qin effect.

[Brief explanation of the drawing]

The first @ is a vertical cross-sectional view showing the schematic configuration of a boiling water reactor,
The wealth lambda diagram is a diagram showing changes in feed water flow rate, steam flow rate, and neutron flux during reactor scram, Figure 3 is a diagram showing changes in reactor water level during reactor scram, and Section 4 shows the atom of the present invention. FIG. 2 is a block diagram of a reactor water level drop suppression device. l...Reactor pressure vessel, Co...Shroud, 3...Reactor core 1g...An circulation pump, /C...Recirculation pump drive motor, l! ...Reactor water level drop suppression signal generator, /6...Recirculation flow rate control device. Applicant's agent Kiyoshi Inomata 81st issue 2nd issue 83rd paper 40

Claims (1)

[Scope of Claims] 1. A reactor water level drop suppression signal generating device that generates a reactor water level drop suppression signal based on a transient change occurrence signal that indicates a predicted water level drop in the reactor, and the above-mentioned reactor water level drop suppression tl)1
1 < A reactor water level drop suppression device in a boiling water nuclear reactor, characterized by having a recirculation flow rate control device that adds a recirculation flow rate control device to a recirculation pump drive motor by No. M. (h) The reactor water level drop suppression device according to claim (h), wherein the transient change occurrence signal is a closing signal of a main steam isolation valve. 3. The reactor water level drop suppression device according to claim 1, wherein the transient change occurrence signal is a reactor scram signal. 2. The reactor water level drop suppression device according to claim 1, wherein the transient change occurrence signal is a stop signal of a reactor feed water pump or a reactor condensate pump.