JPH0567000B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention is directed to a boiling water nuclear power plant,
Reactor cooling systems that have water pumps that supply coolant into the reactor, and that are highly reliable and economically viable and can operate both during normal operation and during plant abnormalities. It is. [Background of the Invention] Figure 2a is a schematic diagram of a reactor cooling system of a boiling water reactor (BWR). The steam generated in the reactor 1 is transferred to four main steam pipes 2.
The steam passes through the main steam stop valve and steam control valve, respectively, and enters the high pressure turbine 3. The exhaust gas of the high pressure turbine enters the low pressure turbine 4 via a moisture separator and a combination intermediate valve and is condensed in a condenser 5. Thereafter, the pressure is increased by the condensate pump 6, the water is heated by the low-pressure feedwater heater, and after the pressure is increased by the feedwater pump 7, it is further heated by the high-pressure feedwater heater and supplied to the reactor 1. FIG. 2b is a detailed view of section A in FIG. 2a, showing details of the water supply pump 7. During normal operation, water is supplied to the reactor by two 50% capacity turbine-driven pumps 8 and 9, and when one steam turbine-driven pump fails, a 25% capacity electric motor-driven pump 1 is used as a standby system.
It is designed to operate two units, 0 and 11, and maintain 100% rated operation. [Object of the Invention] The object of the present invention is to obtain a nuclear reactor cooling system that can easily perform high-temperature standby operation of a plant and is highly economical. [Summary of the Invention] A feature of the present invention is that, in the reactor water supply system that supplies coolant into the reactor, the reactor water supply pump is used in parallel with the steam turbine-driven water supply pump used during normal operation, and is used during plant abnormalities or accidents. The point is that an auxiliary water supply pump is provided with a capacity sufficient to compensate for the amount of water that evaporates due to decay heat after scram. [Embodiments of the Invention] The present invention aims to obtain the following effects by installing an auxiliary water pump driven by an electric motor and having a capacity to compensate for the evaporation of the reactor due to post-scram decay heat. It is. The electric motor-driven water supply pump can reduce equipment costs by significantly reducing the capacity of one of the two 25% capacity conventional pumps. In the event of a loss of coolant accident, it can be switched to diesel generator drive as an emergency system, and by being incorporated as part of the emergency core cooling system (ECCS), it is possible to eliminate one of the conventional ECCS systems. During high-temperature standby operation, it is possible to supply water to compensate for the release of steam generated inside the reactor to the outside of the system. capacity)
By injecting water, it is possible to supplement the evaporated content, making it easier to control the reactor water level and water supply control operation. Hereinafter, specific embodiments of the present invention will be described using the drawings. Figure 1 is a schematic diagram of the reactor cooling system of the present invention.
In the figure, parts given the same reference numerals as in FIG. 2 are the same parts. Further, FIG. 1b is a detailed view of section B in FIG. 1a. In the present invention, the following water supply device is installed in the basic configuration of the BWR shown in FIG. 2. Two 50% capacity turbine-driven water supply pumps 12 and 13 are installed as a regular system, and one 25% capacity electric water supply pump 14 is installed as a standby system, with a capacity that can compensate for the amount evaporated by decay heat after scram ( Approximately 1-2
%) is installed. Large capacity auxiliary water supply pump 14 in the backup system
The small-capacity water supply pump 15 is powered by the in-house power source 16, and the small-capacity water pump 15 is powered by the emergency diesel generator 1 so that it can operate even when an external power source is lost in addition to the in-house power source 16.
7 can also be used as a power source. In addition, the small capacity auxiliary water supply pump 15 is connected to the condenser 5.
After pumping out the water from the condenser 5, the water source is automatically switched to the condensate storage tank 18 so that the water source can be continuously supplied to the reactor core. The water supplied from the pump is discharged into the water supply pipe to the reactor, and is guided into the reactor pressure vessel through a spargeer installed in the reactor pressure vessel. Conventionally, during normal operation, two turbine-driven water pumps supply water at 100% of the rated flow rate to the reactor, but even if one of these pumps breaks down for some reason, two motor-driven water pumps can supply water at 100% of the rated flow rate to the reactor.
% rated operation could continue. 25% in this invention
Since the capacity of one of the capacity motor-driven water pumps has been reduced, if one turbine-driven water pump fails, the reactor output will be reduced and operated. However, the occurrence of such an event is extremely rare, and if low-output operation can be continued without scramming, rated output operation can be resumed after the turbine-driven water pump failure is repaired, so it is a comprehensively rational design. It can be said. Rather, during high-temperature standby operation, an electric motor-driven auxiliary feedwater pump with a capacity of 2% of the rated flow rate is used to inject feedwater heated by a feedwater heater from a condenser, thereby preventing steam generated within the reactor from being released outside the system. This has the advantage that supplementary water supply control can be easily performed. Figure 3 shows BWR and new boiling reactor (ABWR)
FIG. 1 is a schematic diagram of a nuclear reactor. Based on Figure 3, the BWR on the left side of the diagram describes the operating characteristics during LOCA.
The plant has large-diameter recirculation piping (PLR) installed below the Bethel, so a guillotine rupture here would be the worst case scenario, and the coolant inside the reactor would flow out through the PLR piping, exposing the reactor core. Resulting in. For this reason, in conventional BWRs, even if water was injected outside the shroud using the auxiliary water supply pump during LOCA, water would flow out of the fracture opening and could not be expected to be very effective in cooling the reactor core. On the other hand, in the ABWR plant on the right side of the diagram,
As a design basis accident is assumed to be a rupture of a small or medium-sized pipe in the upper part of the reactor core, the amount of coolant leaking inside the reactor will be suppressed, and the reactor water level will be maintained high even during LOCA. Therefore, if coolant is injected to the outside of the shroud using the auxiliary water supply pump, it can contribute to flooding of the reactor core and cooling of the reactor core. As described above, the small capacity auxiliary feed water pump of the present invention is particularly effective as a core cooling system during LOCA of an ABWR plant. Figure 4 shows the operating characteristics of the BWR. This figure shows that 100-77% operation can be achieved with just the recirculation flow rate without operating the control rod drive mechanism. As shown at point C in Figure 4, during normal operation, the main steam flow rate and feed water flow rate are balanced and the rated operation is performed at 100%, but with the present invention, the capacity steam turbine is driven at 50% capacity during normal operation. When one water supply pump fails, the water supply flow rate reaches point D.
The reactor thermal output is reduced to 77% of the rated output.
I will be driving. Thereafter, by repairing the failed pump and increasing the water supply flow rate from point D to point C again, rated output operation can be performed. In addition, in the event of a loss of coolant accident (LOCA), it is required to achieve the function without relying on an external power source, and the auxiliary water pump of the present invention has a capacity of about 1 to 2%, so it is necessary to perform the function within the station. In addition to the power supply, it can also be powered by an emergency diesel generator. As a result, when a LOCA occurs, the power supply for the small capacity auxiliary water pump is switched from the on-site power source to the emergency diesel generator, and the coolant from the condenser (approx.
100m ³ ) is supplied to the reactor core. After that, if the capacity of the condenser decreases, the water source will automatically switch to the condensate storage tank, providing long-term core cooling. Next, another embodiment of the present invention will be described with reference to FIGS. 5 and 6. This embodiment has the same function as a small-capacity electric motor-driven auxiliary feed water pump emergency core cooling system (ECCS), omitting one of the current high pressure core spray systems (HPCS), and replacing it with the This involves incorporating an auxiliary water pump (HSP) into the ECCS. FIG. 5 is a diagram showing the ECCS system of the present invention. The emergency core cooling system of this embodiment has an independent structure so that the safety function of the system can be achieved even if a single failure occurs. It is divided into 2 sections, and emergency diesel generators are installed as power sources for each section. The HSP is located in the section and is connected to a diesel generator 22 as a driving source. In addition, in Figure 5, LPFL is a low pressure water injection system,
WDCS is a residual heat removal system, RCIC is a reactor isolation cooling system, MS is a main steam pipe, and ADS is an automatic depressurization system. Table 1 shows how to ensure ECCS functionality assuming a single failure during LOCA. Figure 6 shows the reactor water level changes during LOCA (assuming a single failure). Assuming a HPCS pipe rupture, which is a design basis accident, the solid line shown in the figure is the HS

【table】

[Table] Failure of the diesel generator that supplies power to P (operation
ECCS is RCIC + 2LPFL + 8ADS), the reactor water level is maintained submerged and the core is not exposed. This is the same as the worst-case ECCS combination of the current design, so it can be said that the same core cooling function is ensured. In addition, assuming other diesel generator failures (operating ECCS is RCIC + H.S.P + 2LPFL)
The reactor water level change in the case of +8ADS becomes the dashed line shown in Figure 6, which is HSP1 higher than the worst case case.
Since there are more tanks available, changes in water level will be even smaller. The embodiments of the present invention described above have the following effects. (1) During high-temperature standby operation Conventionally, water supply flow rate was controlled by throttling operation using a 25% capacity electric motor-driven water supply pump, but in the present invention, evaporation can be compensated for by rated operation using a small capacity electric motor-driven auxiliary water supply pump. Since water can be supplied, water supply control operation becomes easier. (2) Conventional electric motor-driven water supply pumps had two units with a capacity of 25%, but in the present invention, one of these pumps has a capacity of 2% of the rated flow rate, so the capacity can be significantly reduced and equipment costs can be reduced. It is drastically reduced. Also,
Small-capacity motor-driven water pumps can be operated with emergency diesel generators, so they can be incorporated into the emergency core cooling system.
As a result, the number of existing emergency core cooling systems can be reduced by one, and from this aspect as well, equipment costs can be significantly reduced. [Effects of the Invention] As described above, according to the present invention, it is possible to easily carry out high-temperature standby operation of a plant, and moreover, it is possible to obtain a highly economical reactor cooling system.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a reactor cooling system showing an embodiment of the present invention, Figure 2 is a diagram of a conventional BWR reactor cooling system, and Figure 3 is the structure of a BWR and ABWR reactor. Figure 4 is a schematic cross-sectional view showing a comparison of the
BWR operating characteristic diagram, Figure 5 is a diagram explaining another embodiment of the present invention, and ECCS system division explanatory diagram, Figure 6
The figure is a diagram showing changes in reactor water level during LOCA (assuming a single failure). <Explanation of symbols>, 1...Nuclear reactor, 2...Main steam pipe, 3...High pressure turbine, 4...Low pressure turbine,
5...Condenser, 6...Condensate pump, 7...Water pump, 8, 9...Steam turbine-driven water supply pumps A, B, 10, 11...Electric motor-driven water supply pumps A, B, 12, 13 ... Steam turbine-driven water supply pumps A, B (50% capacity), 14 ... Electric motor-driven water supply pump C (25% capacity), 15 ... Electric motor-driven water supply pump D (approximately 2% capacity), 16 ... In-house power supply , 17...
...Emergency diesel generator, 18... Condensate storage tank, 20, 21, 22... Diesel generator.

Claims (1)

[Scope of Claims] 1. In the reactor water supply system that supplies coolant into the reactor, in parallel with the steam turbine-driven water supply pump used during normal operation, the reactor collapses after scram in the event of a plant abnormality or accident. A nuclear reactor cooling system characterized by being equipped with an auxiliary water supply pump that has enough capacity to compensate for water that evaporates due to heat. 2. A nuclear reactor cooling system according to claim 1, characterized in that the drive source for the auxiliary water supply pump is switchable between an on-site power supply and an emergency diesel generator. 3. A nuclear reactor as set forth in claim 1, characterized in that the water source for the auxiliary feedwater pump can be switched to either the hot well of the main condenser or the coolant from the condensate storage tank. cooling system. 4. Claim 1 is characterized in that an auxiliary feed water pump and an emergency core cooling system (ECCS) are combined, and the auxiliary feed water pump supplies coolant to the reactor in the event of a loss of coolant accident (LOCA). reactor cooling system.