JPH083555B2 - Boiling water nuclear power plant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a boiling water nuclear power plant, and more particularly to a system configuration for controlling the dissolved oxygen concentration of the reactor primary coolant.

[Conventional technology]

In a boiling water reactor, a part of water as a reactor primary coolant is irradiated with radiation in the core part and decomposes into oxygen and hydrogen. This oxygen is carried out of the reactor pressure vessel together with steam generated by boiling of the reactor coolant. However, part of the residual oxygen remains in the primary coolant in the reactor pressure vessel (hereinafter referred to as reactor water), and the dissolved oxygen concentration in the reactor water is 100 pp.
b. This residual oxygen may accelerate the corrosion of the primary constituent materials of the reactor, and therefore, for the purpose of reducing this oxygen, conventionally, as described in JP-A-57-1994, the reactor feed water was used. Was being injected with hydrogen.

[Problems to be solved by the invention]

The injected hydrogen moves to the steam side together with hydrogen and oxygen generated by the decomposition of the reactor water in the boiling portion of the core. The hydrogen and oxygen in these vapors are finally recovered and then returned to water in a hydrogen-oxygen recombiner. Therefore,
In order to constantly control the dissolved oxygen in the reactor water to a low level, it was always necessary to inject hydrogen into the feed water from outside the system.

Further, the above-mentioned flow rate relationship between hydrogen and oxygen at the inlet of the recombiner is excessive by the amount of injected hydrogen with respect to the stoichiometric ratio relating to water and composition, that is, the volume flow rate ratio of 2: 1. In order to return this to water, it was necessary to inject oxygen corresponding to the stoichiometric ratio of water into the recombiner inlet side with respect to hydrogen injected into the feed water. The hydrogen and oxygen were discharged outside the system.

Therefore, the hydrogen to be injected into the feed water and the oxygen to be injected into the recombiner have to be constantly supplied, which has a drawback that the cost thereof becomes huge.

An object of the present invention is to provide a boiling water nuclear power plant capable of reducing and increasing the dissolved oxygen concentration of reactor water by injecting hydrogen and oxygen, and capable of arbitrarily adjusting the dissolved oxygen concentration of reactor water. It is to be.

[Means for solving problems]

The present invention, in order to achieve the above object, a condenser for returning steam generated in a reactor pressure vessel and worked in a turbine to water, and feed water heating for heating the returned water and supplying it to the pressure vessel. In a boiling water nuclear power plant having a reactor and a recombiner that recovers oxygen and hydrogen in the steam and chemically combines them into water, the excess gas that was not combined by the recombiner is condensed. We propose a boiling water nuclear power plant equipped with an off-gas return line that returns to the condensate pipe downstream of the reactor, and a hydrogen injector and an oxygen injector between the condenser and the feed water heater.

In addition, a pipe that can be opened and closed to short-circuit the inlet and outlet of the recombiner may be provided.

[Action]

The line connecting the outlet of the re-engager and the downstream of the condenser guides hydrogen, which is not recombined with oxygen in the re-combiner and exits from the outlet, to the reactor water via feed water or condensate. The hydrogen and oxygen injection facility provided downstream of the condenser is for injecting hydrogen to lower the dissolved oxygen in the reactor water and injecting oxygen to increase it. That is, when hydrogen is injected,
This hydrogen suppresses radiolysis of water in the core and reduces dissolved oxygen in the reactor water. At this time, the hydrogen that migrates to the steam side and enters the recombiner is combined with the same oxygen in the recombiner to form water, but the injected hydrogen remains as an excess and is returned from the recombiner outlet to the downstream of the condenser. Be done. If the hydrogen injection is stopped at this point, the hydrogen injected up to that point always circulates between the reactor water and the steam, and the radiolysis of water in the core is always suppressed, and the dissolved oxygen in the core is kept low.

When the plant is stopped, etc., it is better that the excess hydrogen is small from the viewpoint of explosion protection. When the dissolved oxygen in the reactor core is kept low to increase the dissolved oxygen in the reactor water in order to reduce excess hydrogen, oxygen is injected from the oxygen injection equipment. In this case, in feed water or condensate, hydrogen and injected oxygen that co-exist in the system coexist, but when they enter the reactor pressure vessel, they combine with each other to form water. That is, the hydrogen circulating in the system is reduced by the injected oxygen, but if the oxygen injection is stopped when the circulating hydrogen decreases to a predetermined amount, the dissolved oxygen concentration in the reactor water reaches the value corresponding to the circulating hydrogen amount. Increased and maintained at that value.

When hydrogen and oxygen are mixed in the condensate water or the feed water, excess hydrogen that remains when the condensed water becomes combined water suppresses radiolysis of the water in the core according to the amount. Therefore, even if the valve provided in the pipe bypassing the recombiner is opened and the hydrogen and oxygen transferred into the steam are returned to the condensate or feed water as they are, the dissolved oxygen concentration in the core can be stably controlled, and It is possible to stop the operation of the recombiner.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an outline of a system configuration of a boiling water nuclear power plant according to the present invention. In the figure, 1 is a reactor pressure vessel, 2 is a main steam pipe for taking out the steam, 3 is a turbine, 4 is a condenser, 5 is a condensate pump, 6 is a condensate pipe, and 7 is a condensate pipe.
Is a water heater, 8 is a water supply pipe, 9 is an off-gas line, 10 is an ejector driven by steam, and 11 is an ejector.
Eductor drive line for supplying steam to 10, 12 recombiner, 13 off gas condenser, 14 off gas return line, 15
Is a bypass pipe, 16 is a valve provided on the way, 17 is a hydrogen or oxygen injection line, 18 is a hydrogen injection valve, 19 is a hydrogen cylinder, 20 is an oxygen injection valve, 21 is an oxygen cylinder, 22 is a core, and 23 is A steam separator, 24 is a shroud, 25 is a downcomer, 26 is a hydrogen concentration meter, and 27 is an oxygen concentration meter.

The steam generated in the reactor pressure vessel 1 is guided to the turbine 3 by the main steam pipe 2, drives the turbine 3, is condensed by the condenser 4, is pressurized by the pump 5, and is condensed by the condenser pipe 6 and the feed water heater. It is returned to the reactor pressure vessel 1 via 7 and the water supply pipe 8.

Non-condensable gas components such as steam and hydrogen contained in the steam are recovered from the condenser 4 to the off-gas line 9 by the ejector 10 driven by the steam from the ejector drive line 11, and then recombined 12 At, oxygen and hydrogen combine to form water. The steam is turned into water by the offgas condenser 13, and is returned to the condensate pipe 6 from the offgas return line 14. Recombiner
The 12 inlets and outlets are connected by bypass piping 15 and valve 16
Opening bypasses the recombiner 12.

An injection line 17 is connected to the condenser 6, and when the hydrogen injection valve 18 or the oxygen injection valve 20 is opened, hydrogen or oxygen is injected into the condensate, respectively.

The dissolved oxygen concentration in the reactor water is controlled as follows. First, the hydrogen injection valve 18 is opened, and hydrogen is injected into the condensate pipe 6. This hydrogen is returned to the reactor pressure vessel 1 by the water supply system and reduces the dissolved oxygen concentration of the reactor water as follows.
In a boiling water reactor, the reactor water is boiled by the reactor water 22 to become steam. In the steam separator 23, the reactor water and steam are separated, and the steam is guided to the main steam pipe 2. The reactor water circulates down the downcomer 25 between the shell 24 surrounding the core 22 and the reactor pressure vessel 1, and is guided to the core 22 again. The injected hydrogen is combined with oxygen dissolved in the reactor water into water in the downcomer 25 due to the effect of radiation emitted from the core 22. Further, the remaining hydrogen reaches the core 22,
Suppress radiolysis of water here.

The effect of hydrogen for reducing dissolved oxygen in reactor water is shown by curve A in FIG. Increasing the hydrogen concentration in the feedwater dilutes the dissolved oxygen concentration in the reactor water. The concrete control of the concentration of dissolved oxygen in the furnace is carried out as follows. First, from the relationship shown in FIG. 2, the hydrogen concentration in the feed water corresponding to the predetermined dissolved oxygen concentration is read, and hydrogen corresponding to this is injected. The injected hydrogen is returned to the condensate pipe 6 with a slight time delay through the main steam pipe 2, the off-gas line 9 and the off-gas return line 14 in the same amount. This time delay is
It usually takes a few tens of seconds to a few minutes. Injection line to condensate pipe 6
When the hydrogen concentration meter 26 provided upstream of the connection point of 17 confirmed that the injected hydrogen had returned, the hydrogen injection valve 18
Close. Hydrogen injected in this state is the reactor pressure vessel.
1, main steam pipe 2, off-gas line 9, off-gas return line 1
4. The condensate pipe 6 and the feed water pipe 8 are constantly circulating in the system to maintain the dissolved oxygen concentration in the reactor water at the initially set value.

In such a state, the operation to further reduce or increase the dissolved oxygen concentration in the furnace is performed as follows.To further reduce the dissolved oxygen concentration, in order to further reduce the dissolved oxygen concentration set value, Is read, and hydrogen corresponding to the difference between this value and the reading of the hydrogen concentration meter 26 is injected. After that, when the readings of the hydrogen concentration meter 26 show that the hydrogen concentrations obtained from FIG. 2 are equal, the hydrogen injection valve 18 is turned on. Close and stop hydrogen injection.

Next, a method for increasing the dissolved oxygen concentration will be described. Also in this case, the hydrogen concentration in the feed water with respect to the target oxygen concentration in the reactor water is read from FIG. To the difference, oxygen is injected at a concentration corresponding to the stoichiometric ratio of water. The injected oxygen is combined with hydrogen circulating in the system in the downcomer 25 to become water, and this hydrogen is consumed. The reading of the hydrogen concentration meter 26 is second
The oxygen injection valve 20 is closed and the oxygen injection is stopped when the hydrogen concentration in the feed water becomes equal to that read from the figure.

In the above control method, the bypass can be performed without using the recombiner 12. That is, the valve 16 is opened and the recombiner 12 is bypassed by the bypass pipe 15. In this case, in order to control the dissolved oxygen concentration of the reactor water, the reading of the hydrogen concentration meter 26 in the above method is corresponded to the reading of the oxygen concentration meter 27 from the reading of the hydrogen concentration meter 26 by the stoichiometric ratio of water. It can be read as a value obtained by subtracting the hydrogen concentration value.

〔The invention's effect〕

According to the present invention, in controlling the dissolved oxygen concentration of reactor water, it is not necessary to constantly supply hydrogen and oxygen from outside the system, and it is possible to reduce enormous costs of hydrogen and oxygen.
Further, the dissolved oxygen concentration in the reactor water can be arbitrarily adjusted by injecting hydrogen and oxygen.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the system configuration of a boiling water nuclear power plant according to the present invention, and FIG. 2 is a diagram showing the relationship between the hydrogen concentration in feed water and the concentration of dissolved oxygen in reactor water in the embodiment of FIG. 1 ... Reactor pressure vessel, 3 ... Turbine, 4 ... Condenser, 6 ... Condensation pipe, 7 ... Feed water heater, 8 ... Feed pipe, 10 ... Ejector, 12 ... Rejoin Vessel, 13 …… off gas condenser, 14 …… off gas return line, 15 …… bypass piping, 19 …… hydrogen cylinder, 21 …… oxygen cylinder.

Claims (1)

[Claims] 1. A condenser for returning steam generated in a reactor pressure vessel and worked in a turbine to water, a feed water heater for heating the returned water and supplying the water to the pressure vessel, and the steam in the steam. In a boiling water nuclear power plant having a recombiner that recovers oxygen and hydrogen of the above and chemically combines them into water, the excess gas that was not combined in the recombiner is recovered in the downstream of the condenser. An off-gas return line for returning to the water pipe is provided, and a hydrogen injection device for supplying hydrogen to the reactor to reduce the dissolved oxygen concentration in the reactor water between the condenser and the feed water heater and the dissolved oxygen concentration. Is provided with an oxygen injection device for supplying oxygen to the reactor in order to adjust the degree to reduce the boiling water type, which is provided with a pipe that can be opened and closed to short-circuit the inlet and outlet of the recombiner. Nuclear power plant.