阅读说明：本技术 一种压水堆核电厂中小破口失水事故应对方法 (Method for coping with small-sized crevasse loss of coolant accident in pressurized water reactor nuclear power plant ) 是由 吴丹 丁书华 冉旭 吴清 冷贵君 刘昌文 申亚欧 陈伟 党高健 杜思佳 钱立波 于 2020-05-15 设计创作，主要内容包括：本发明公开了一种压水堆核电厂中小破口失水事故应对方法,包括以下步骤：对主系统进行冷却降温和降压,并在其过程中,依次停运中压安注泵；停运所有中压安注泵之后,调节上充流量,维持稳压器水位,根据稳压器水位或堆芯出口过冷度重启中压安注泵；根据稳压器水位或堆芯出口过冷度重启中压安注泵或安注箱水量情况,隔离安注箱；若热管段温度和一回路系统压力下降一定水平,则接入余热排出系统；对主系统进行持续冷却,将压水堆核电厂带至冷停堆状态。本发明解决了对先进的三代核电厂中中小破口失水事故合理应对的问题,以保障核电厂出现中小破口失水事故时,能够安全有效的冷停堆。(The invention discloses a method for responding to small-sized crevasse water loss accidents in a pressurized water reactor nuclear power plant, which comprises the following steps of: cooling and depressurizing the main system, and sequentially stopping the medium-pressure safety injection pump in the process; after all the medium-pressure safety injection pumps are stopped, the upper charging quantity is adjusted, the water level of the voltage stabilizer is maintained, and the medium-pressure safety injection pumps are restarted according to the water level of the voltage stabilizer or the supercooling degree of the reactor core outlet; restarting a medium-pressure safety injection pump or a safety injection tank according to the water level of the pressure stabilizer or the supercooling degree of the reactor core outlet, and isolating the safety injection tank; if the temperature of the heat pipe section and the pressure of the loop system are reduced to certain levels, a waste heat discharge system is connected; and continuously cooling the main system, and bringing the pressurized water reactor nuclear power plant to a cold shutdown state. The invention solves the problem of reasonably dealing with medium and small break water loss accidents in advanced three-generation nuclear power plants, and can ensure that the nuclear power plants can be safely and effectively stopped in a cold mode when the medium and small break water loss accidents occur.)

1. A method for responding to small-break water loss accidents in a pressurized water reactor nuclear power plant is characterized by comprising the following steps:

s1: cooling the main system, wherein the cooling rate does not exceed a threshold cooling rate;

s2: the main system is subjected to pressure reduction through main spraying of the voltage stabilizer, auxiliary spraying of the voltage stabilizer or a safety valve of the voltage stabilizer;

s3: in the processes of cooling and reducing the pressure of the main system, the medium-pressure safety injection pump is stopped in sequence;

s4: after all the medium-pressure safety injection pumps are stopped, the upper filling flow is adjusted, the water level of the pressure stabilizer is maintained, and one medium-pressure safety injection pump is restarted if the water level of the pressure stabilizer or the supercooling degree of the reactor core outlet meets a first preset value;

s5: if the water level of the pressure stabilizer and the supercooling degree of the reactor core outlet are recovered to first preset values, or the water quantity of the safety injection tank is lower than the preset values, isolating the safety injection tank;

s7: if the temperature of the heat pipe section and the pressure of the loop system are reduced to second preset values, the waste heat discharge system is connected;

s8: and continuously cooling the main system, and bringing the pressurized water reactor nuclear power plant to a cold shutdown state.

2. The method for responding to the medium and small crevasse water loss accident in the pressurized water reactor nuclear power plant according to claim 1, wherein the method for judging the medium and small crevasse water loss accident in the pressurized water reactor nuclear power plant comprises the following steps: when a breach accident occurs, the upper charging flow cannot compensate for the breach flow, and all medium-pressure safety injection pumps cannot be stopped.

3. The method for responding to the small break loss of coolant accident in the pressurized water reactor nuclear power plant according to claim 1, wherein the step S1 includes: if the RHR system is not put into operation, exhausting steam to a condenser through a perfect steam generator or exhausting steam through an atmospheric release valve of the perfect steam generator; if the RHR system is already in operation, the main system is cooled by the RHR system.

4. The method for responding to the small-break fluid loss accident in the pressurized water reactor nuclear power plant according to claim 1, wherein the threshold cooling rate in step S1 is in a range of 50 ℃/h to 60 ℃/h.

5. The method for responding to the small-break water loss accident in the pressurized water reactor nuclear power plant according to claim 1, wherein the first preset value is as follows: the supercooling degree of the reactor core outlet is smaller than a specific difference or the water level of the pressure stabilizer is smaller than a specific ratio, the range of the fixed difference is 15K-25K, and the range of the specific ratio is 25% -35%; the second preset value is as follows: the temperature of the heat pipe section is smaller than a temperature threshold value, the pressure of the primary circuit is smaller than a pressure threshold value, the temperature threshold value range is 170-185 ℃, and the pressure threshold value range is 2.3-3.3 MPa.

6. The method for responding to the small breach loss of coolant accident in the pressurized water reactor nuclear power plant as recited in claim 1, wherein in step S2, when one or two medium pressure safety injection pumps have been shut down, the spraying flow rate is adjusted to prevent the medium pressure safety injection from being restarted due to the loss of supercooling degree.

7. The method according to claim 1, wherein in step S2, when external power is lost, the auxiliary spray pump or the charge pump is alternately started according to the state and demand of the pressurized water reactor nuclear power plant.

8. The method according to claim 7, wherein the charge pump is mainly started if the supercooling degree decreases rapidly, and the auxiliary spray is mainly started if the supercooling degree is high.

9. The method for responding to the small break loss of coolant accident in the pressurized water reactor nuclear power plant according to claim 1, wherein the step S3 includes: when the water level of the pressure stabilizer and the supercooling degree of the reactor core outlet meet the requirements, the medium-pressure safety injection pumps are stopped in sequence, the pressure of the main system is checked after one medium-pressure safety injection pump is stopped, and when the pressure of the main system is stable or increased, the other medium-pressure safety injection pump is stopped.

10. The method for dealing with the small-break water loss accident in the pressurized water reactor nuclear power plant as recited in any one of the preceding claims, wherein the low-pressure safety injection pump is started if the pressure of the main system is lower than the low-pressure safety injection cut-off pressure head.

Technical Field

The invention relates to the field of nuclear safety, in particular to a method for coping with small-sized break water loss accidents in a pressurized water reactor nuclear power plant.

Background

When a nuclear power plant breaks, accidents with the same size of the break are difficult to deal with, namely medium and small break water loss accidents. Because the accidents do not need to be like the small-break water loss accidents, the break flow can be compensated through the upper charging flow, the quick pressure relief can be realized unlike the large-break water loss accidents, and the low-pressure safety injection can be quickly put into use. Therefore, it is necessary to take reasonable countermeasures to bring the system to a cold shutdown state.

The method for reasonably dealing with the medium and small-sized crevasse water loss accidents is very important, and the configuration of a safety injection system, the design of safety injection flow and the like are improved in the advanced three-generation nuclear power plant design, so that the conventional method for dealing with the medium and small-sized crevasse water loss accidents is not applicable any more, a large number of crevasse spectrum analysis and demonstration are required to be carried out on the basis of analyzing the configuration characteristics of the safety injection system, and a set of reasonable coping method is further obtained.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method aims to provide a method for coping the small and medium-sized crevasse water loss accidents in a pressurized water reactor nuclear power plant, solves the problem of reasonably coping the small and medium-sized crevasse water loss accidents in the third-generation nuclear power plant, and can safely and effectively carry out cold shutdown on a system when the small and medium-sized crevasse water loss accidents occur in the nuclear power plant.

The invention is realized by the following technical scheme:

a method for responding to small-break water loss accidents in a pressurized water reactor nuclear power plant comprises the following steps: s1: cooling the main system, wherein the cooling rate does not exceed a threshold cooling rate; s2: the main system is subjected to pressure reduction through main spraying of the voltage stabilizer, auxiliary spraying of the voltage stabilizer or a safety valve of the voltage stabilizer; s3: in the processes of cooling and reducing the pressure of the main system, the medium-pressure safety injection pump is stopped in sequence; s4: after all the medium-pressure safety injection pumps are stopped, the upper filling flow is adjusted, the water level of the pressure stabilizer is maintained, and one medium-pressure safety injection pump is restarted if the water level of the pressure stabilizer or the supercooling degree of the reactor core outlet meets a first preset value; s5: if the water level of the pressure stabilizer and the supercooling degree of the reactor core outlet are recovered to first preset values, or the water quantity of the safety injection tank is lower than the preset values, isolating the safety injection tank; s7: if the temperature of the heat pipe section and the pressure of the loop system are reduced to second preset values, the waste heat discharge system is connected; s8: and continuously cooling the main system, and bringing the pressurized water reactor nuclear power plant to a cold shutdown state.

Because the medium and small-sized crevasse water loss accidents do not need to be similar to the minimum crevasse water loss accidents, the crevasse flow can be compensated through the upper charging flow, the rapid pressure relief of the large-sized crevasse water loss accidents is not needed, and the low-pressure safety injection can be rapidly put into use, a large number of crevasse spectrum analysis and demonstration are needed on the basis of analyzing the configuration characteristics of a safety injection system, and a set of reasonable coping method is further obtained. After a series of resetting and checking works are carried out firstly, (including checking whether a main pump stops, safety injection resetting, rapid cooling resetting and the like), the medium and small break water loss accidents are judged to occur, cooling and depressurization are carried out on a main system, medium-pressure safety injection pumps are stopped in sequence in the cooling and depressurization processes, the upper charging flow is adjusted after all the medium-pressure safety injection pumps are stopped, the water level of a voltage stabilizer is maintained, the medium-pressure safety injection flow is no longer needed to be confirmed, if the water level of the voltage stabilizer drops or the supercooling degree of a reactor core outlet is reduced to be less than a certain value at the moment, one medium-pressure safety injection pump needs to be restarted, whether a safety injection box needs to be isolated or not is checked, whether a waste heat discharge system can be put into operation is checked, the system is cooled continuously, and a power plant is brought to a cold. The design of the third-generation independent nuclear power plant is different from that of the second-generation and the second-generation power plants, including the design of a voltage stabilizer and the design of a safety injection system, so that the regulation development is required to be specially carried out on the third-generation independent nuclear power plant. The method is designed according to the special configuration of the advanced third-generation nuclear power plant (different from the second-generation nuclear power plant) and is specially used for coping with small-break water loss accidents in a pressurized water reactor nuclear power plant of the advanced third-generation nuclear power plant.

Further, the method for judging the occurrence of the medium and small break water loss accident in the pressurized water reactor nuclear power plant comprises the following steps: when a breach accident occurs, the upper charging flow cannot compensate for the breach flow, and all medium-pressure safety injection pumps cannot be stopped.

Further, the step S1 includes: if the RHR system is not put into operation, exhausting steam to a condenser through a perfect steam generator or exhausting steam through an atmospheric release valve of the perfect steam generator; if the RHR system is already in operation, the main system is cooled by the RHR system.

Further, the threshold temperature reduction rate in step S1 ranges from 50 ℃/h to 60 ℃/h.

Further, the first preset value is as follows: the supercooling degree of the reactor core outlet is smaller than a specific difference or the water level of the pressure stabilizer is smaller than a specific ratio, the range of the fixed difference is 15K-25K, and the range of the specific ratio is 25% -35%; the second preset value is as follows: the temperature of the heat pipe section is smaller than a temperature threshold value, the pressure of the primary circuit is smaller than a pressure threshold value, the temperature threshold value range is 170-185 ℃, and the pressure threshold value range is 2.3-3.3 MPa.

Further, in step S2, when one or two middle pressure safety injection pumps have been shut down, the spraying flow rate is adjusted to prevent the loss of supercooling degree and restart the middle pressure safety injection.

Further, in step S2, when the off-site power is lost, the auxiliary spray or the charge pump is alternately activated according to the status and demand of the pressurized water reactor nuclear power plant.

Furthermore, if the supercooling degree is reduced quickly, the charging pump is started mainly, and if the supercooling degree is high, the auxiliary spraying is started mainly.

Further, the step S3 includes: when the water level of the pressure stabilizer and the supercooling degree of the reactor core outlet meet the requirements, the medium-pressure safety injection pumps are stopped in sequence, the pressure of the main system is checked after one medium-pressure safety injection pump is stopped, and when the pressure of the main system is stable or increased, the other medium-pressure safety injection pump is stopped.

Further, if the pressure of the main system is lower than the low-pressure safety injection stop pressure head, the low-pressure safety injection pump is started.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention relates to a disposal method for medium and small break water loss accidents in a pressurized water reactor nuclear power plant (station). By applying the method, an operator can be guided to correctly execute relevant important operations, such as: starting main system cooling, starting/stopping depressurization, sequentially stopping all safety injection pumps, connecting a waste heat discharge system and the like. The method can bring the system to a safe cold shutdown state when medium and small crevasses loss of coolant accidents of different sizes and different positions of the novel three-generation nuclear reactor occur. On the basis of obvious improvement of the safety injection system design of a third-generation pressurized water nuclear power plant, the method can still bring the reactor to a cold shutdown state when medium and small break loss of coolant accidents at different sizes and different positions occur, has an internationally leading technical level, and has very important significance for the development of the current third-generation nuclear power plant technology in China. The invention fills up the blank field related to the domestic third-generation nuclear power design, and has the potential of entering the military and international markets.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic view of embodiment 5 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.