阅读说明：本技术 一种核电厂避免压力容器上封头产汽的自然循环冷却方法 (Natural circulation cooling method for preventing upper seal head of pressure vessel from generating steam in nuclear power plant ) 是由 李峰 冉旭 吴清 刘昌文 冷贵君 喻娜 陈宏霞 蔡容 程坤 习蒙蒙 陆雅哲 杨 于 2021-07-22 设计创作，主要内容包括：为解决现有技术中存在的在将反应堆冷却至冷停堆状态过程中,自然循环冷却压力容器时,压力容器上封头流体温度达到饱和出现闪蒸现象导致冷却能力丧失危及安全的技术问题,本发明实施例提供一种避免核电站压力容器上封头产汽的自然循环冷却方法,包括：启动控制棒驱动机构风冷系统的冷却风机冷却压力容器上封头；主系统硼化至冷停堆硼浓度；主系统降温；检查热段温度,若热段温度小于284℃,则主系统第一次降压；维持主系统温度压力稳定；主系统第二次降压；主系统降温降压；主系统冷却至冷停堆；冷却主系统死区；检查主系统温度是否小于90℃,若是,则主系统完全卸压,若否,则主系统冷却至冷停堆。(In order to solve the technical problem that in the process of cooling a reactor to a cold shutdown state in the prior art, when the pressure vessel is cooled in a natural circulation manner, the temperature of the fluid of the upper end enclosure of the pressure vessel is saturated, so that a flash evaporation phenomenon occurs, and the cooling capacity is lost and the safety is endangered, the embodiment of the invention provides a natural circulation cooling method for preventing the upper end enclosure of the pressure vessel of a nuclear power station from generating steam, which comprises the following steps: starting a cooling fan of the control rod driving mechanism air cooling system to cool the upper end enclosure of the pressure vessel; boronizing the main system to the boron concentration of the cold shutdown reactor; cooling the main system; checking the temperature of the hot section, and if the temperature of the hot section is less than 284 ℃, reducing the pressure of the main system for the first time; maintaining the temperature and pressure of the main system stable; the main system reduces the pressure for the second time; cooling and depressurizing the main system; cooling the main system to a cold shutdown state; cooling the main system dead zone; and checking whether the temperature of the main system is less than 90 ℃, if so, completely relieving the pressure of the main system, and if not, cooling the main system to cold stop the reactor.)

1. A natural circulation cooling method for preventing an upper seal head of a pressure vessel from generating steam in a nuclear power plant is characterized by comprising the following steps:

starting a cooling fan of the control rod driving mechanism air cooling system to cool the upper end enclosure of the pressure vessel;

boronizing the main system to the boron concentration of the cold shutdown reactor;

cooling the main system;

checking whether the temperature of the hot section is less than 284 ℃, and if not, cooling the main system; if so, then

The main system reduces the pressure for the first time;

maintaining the temperature and pressure of the main system stable;

the main system reduces the pressure for the second time;

cooling and depressurizing the main system;

cooling the main system to a cold shutdown state;

cooling the main system dead zone;

and checking whether the temperature of the main system is less than 90 ℃, if so, completely relieving the pressure of the main system, and if not, cooling the main system to cold stop the reactor.

2. The natural circulation cooling method for avoiding the steam generation of the upper head of the pressure vessel in the nuclear power plant according to claim 1, further comprising: starting a main pump; and if the main pump cannot be started normally or cannot work normally, returning to the step of starting a cooling fan of the control rod driving mechanism air cooling system to cool the upper end enclosure of the pressure vessel.

3. The natural circulation cooling method for avoiding the steam generation of the upper head of the pressure vessel in the nuclear power plant according to claim 1, wherein the temperature reduction of the main system comprises the following steps: the cooling rate of the main system is less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; maintaining the temperature and pressure of the main system within the limits of the natural circulation pressure-temperature diagram; the water level of the steam generator is maintained to be 34-50%.

4. The natural circulation cooling method for avoiding the steam generation of the upper end enclosure of the pressure vessel in the nuclear power plant as claimed in claim 1, wherein the primary pressure reduction comprises: the main system is depressurized to 13.56MPa a by using an auxiliary spray or a safety valve.

5. The natural circulation cooling method for avoiding the steam generation of the upper head of the pressure vessel in the nuclear power plant according to claim 1, wherein the step of maintaining the temperature and the pressure of the main system stable comprises the following steps: maintaining the pressure of a main system of the main system at 13.56MPa a, and the cooling rate of the main system at less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; maintaining the main system temperature pressure within the natural circulation pressure-temperature map limits.

6. The natural circulation cooling method for avoiding the steam generation of the upper end enclosure of the pressure vessel in the nuclear power plant as claimed in claim 1, wherein the secondary depressurization of the main system comprises: the main system is depressurized to 7MPa a.

7. The natural circulation cooling method for avoiding the steam generation of the upper head of the pressure vessel in the nuclear power plant according to claim 6, wherein the pressure reduction of the main system to 7MPa a comprises the following steps: maintaining the supercooling degree of the reactor core outlet to be more than 20 ℃; maintaining the cooling rate of the cold section to be less than 14 ℃/h; the pressure of the pressure stabilizer is reduced by adopting a spray or a safety valve.

8. The natural circulation cooling method for avoiding the steam generation of the upper end enclosure of the pressure vessel in the nuclear power plant as claimed in claim 1, wherein the temperature and pressure reduction of the main system comprises the following steps: the cooling rate of the main system cold section is less than 14 ℃/h; the main system temperature and pressure are within the cool down and pressure reduction curve limits.

9. The natural circulation cooling method for avoiding the steam production of the upper head of the pressure vessel in the nuclear power plant according to claim 1, wherein the step of cooling the main system to the cold shutdown comprises the following steps: and cooling the reactor main system to a cold shutdown reactor by using the residual discharge system.

10. The natural circulation cooling method for avoiding the steam generation of the upper head of the pressure vessel in the nuclear power plant according to claim 1, wherein the cooling of the dead zone of the main system comprises the following steps: and cooling the upper end enclosure of the pressure vessel by using a cooling fan of the control rod driving mechanism, and cooling the U-shaped tube area of the steam generator through steam discharge.

Technical Field

The invention relates to a natural circulation cooling method for preventing an upper seal head of a pressure vessel from generating steam in a nuclear power plant.

Background

After a Hualongyi pressurized water reactor nuclear power plant generates a non-loss-of-coolant accident and triggers a reactor to be stopped emergently, an operator controls and relieves the accident consequence according to an emergency accident rule, and if the accident cannot be repaired in a hot state at first, the reactor needs to be cooled to a cold stop state for fault treatment. In this process, if the main pump is not operated, the reactor-loop system will be in a natural circulation state. The coolant flow driving pressure head under natural circulation is stronger and the forced circulation is low, so that the coolant flow is lower, and the temperature difference of the inlet and the outlet of the reactor is larger. In addition, a flow dead zone exists in the upper head area of the reactor pressure vessel, the cooling rate of the flow dead zone is possibly different from that of a primary loop, and the phenomenon of flash evaporation due to the fact that the temperature of the upper head fluid is saturated in the cooling process can occur. If the steam yield is large, the liquid level in the pressure vessel is lower than the upper surface of the heat pipe section, and the natural circulation of the primary loop is stopped, so that the waste heat of the reactor core cannot be discharged, and the safety of the reactor is endangered.

Disclosure of Invention

In order to solve the technical problem that in the process of cooling a reactor to a cold shutdown state in the prior art, when the pressure vessel is cooled in a natural circulation mode, the temperature of fluid at an upper end socket of the pressure vessel is saturated, so that a flash evaporation phenomenon occurs, the loss of cooling capacity is caused, and the safety is endangered, the embodiment of the invention provides the natural circulation cooling method for preventing the upper end socket of the pressure vessel of the nuclear power station from generating steam.

The embodiment of the invention is realized by the following technical scheme:

a natural circulation cooling method for preventing an upper seal head of a pressure vessel from generating steam in a nuclear power plant comprises the following steps:

starting a cooling fan of the control rod driving mechanism air cooling system to cool the upper end enclosure of the pressure vessel;

boronizing the main system to the boron concentration of the cold shutdown reactor;

cooling the main system;

checking whether the temperature of the hot section is less than 284 ℃, and if not, cooling the main system; if so, then

The main system reduces the pressure for the first time;

maintaining the temperature and pressure of the main system stable;

the main system reduces the pressure for the second time;

cooling and depressurizing the main system;

cooling the main system to a cold shutdown state;

cooling the main system dead zone;

and checking whether the temperature of the main system is less than 90 ℃, if so, completely relieving the pressure of the main system, and if not, cooling the main system to cold stop the reactor.

Further, the method also comprises the following steps: starting a main pump; and if the main pump cannot be started normally or cannot work normally, returning to the step of starting the cooling fan of the air cooling system of the control rod driving mechanism to cool the upper end enclosure of the pressure vessel.

Further, the cooling of the main system comprises: the cooling rate of the main system is less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; maintaining the temperature and pressure of the main system within the limits of the natural circulation pressure-temperature diagram; the water level of the steam generator is maintained to be 34-50%.

Further, the primary system step-down for the first time includes: the main system is depressurized to 13.56MPa a by using an auxiliary spray or a safety valve.

Further, maintaining the temperature and pressure of the main system stable comprises: maintaining the pressure of a main system of the main system at 13.56MPa a, and the cooling rate of the main system at less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; the main system temperature pressure is maintained within the native cycle pressure-temperature map limits.

Further, the second voltage reduction of the main system comprises: the main system is depressurized to 7MPa a.

Further, the main system is depressurized to 7MPa a, and the method comprises the following steps: maintaining the supercooling degree of the reactor core outlet to be more than 20 ℃; maintaining the cooling rate of the cold section to be less than 14 ℃/h; the pressure of the pressure stabilizer is reduced by adopting a spray or a safety valve.

Further, the temperature and pressure reduction of the main system comprises: the cooling rate of the main system cold section is less than 14 ℃/h; the main system temperature and pressure are within the cool-down and pressure-down curve limits.

Further, the primary system is cooled to a cold shutdown stack, comprising: and cooling the reactor main system to a cold shutdown reactor by using the residual discharge system.

Further, cooling the main system dead zone, comprising: and cooling the upper end enclosure of the pressure vessel by using a cooling fan of the control rod driving mechanism, and cooling the U-shaped tube area of the steam generator through steam discharge.

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

according to the natural circulation cooling method for preventing the upper end socket of the pressure vessel from generating steam in the nuclear power plant, provided by the embodiment of the invention, the generation of water vapor of the upper end socket of the pressure vessel in the process of temperature and pressure reduction is avoided by carrying out a series of temperature and pressure reduction operations on the main system; therefore, waste heat is discharged from the reactor core in the pressure vessel, and the safe use of the reactor is guaranteed.

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 diagram of a pressure vessel cooling system.

Fig. 2 is a schematic flow chart of a natural circulation cooling method for preventing the upper end socket of the pressure vessel from generating steam in the nuclear power plant.

Reference numbers and corresponding part names in the drawings:

1-a pressure vessel; 2-control rod drive mechanism; 3-a voltage stabilizer; 4-a steam generator; 5-main pump; 6-a pressurizer safety valve; 7-pressure relief box; 8, supplying water by an auxiliary spraying system; 9-a spray valve; 10-a waste heat discharge pump; 11-residual heat removal heat exchanger; 12-a water supply channel; 13-a steam channel; 14-chemical and solvent control systems; 15-a cold section; 16-a transition section; 17-safety injection box; 18-hot section; 19-upper end enclosure; 20-dead zone; 21-hot gas zone.

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 used as limitations of the present invention.

Examples

Referring to fig. 1, the pressure vessel cooling system includes a pressure vessel 1, a control rod drive mechanism 2, a pressure stabilizer 3, a steam generator 4, a main pump 5, a pressure stabilizer safety valve 6, a pressure relief tank 7, an auxiliary spray 8, a spray valve 9, a residual heat removal pump 10, a residual heat removal heat exchanger 11, a chemical and solvent control system 14, and a safety injection tank 17.

The main system comprises a pressure vessel 1, a control rod driving mechanism 2, a voltage stabilizer 3 and a steam generator 4; the pressure container 1 is respectively communicated with the voltage stabilizer 3 through a hot section 18; the pressure vessel is communicated with the steam generator 4 through the hot section; the steam generator is connected with the main pump 5 through a transition section 16 and then communicated with the cold section 15; the cold leg returns to the pressure vessel.

The hot section 18 is also connected with a safety injection tank 17.

The primary system pressure refers to the internal pressure of the system consisting of the pressure vessel 1, the control rod drive mechanism 2, the pressurizer 3, the steam generator 4, and the main pump 5, as well as the hot leg, the transition leg, and the cold leg.

The residual heat discharging system comprises a residual heat discharging pump 10 and a residual heat discharging heat exchanger 11, and the hot section 18 is communicated with the cold section 15 sequentially through the residual heat discharging pump and the residual heat discharging heat exchanger 11.

The pressure stabilizer 3 is communicated with the pressure relief tank 7 through a safety valve 6 of the pressure stabilizer.

Wherein, the hot section, the cold section and the transition section are pipelines.

The cold section 15 is also communicated with a hot air area 21 in the voltage stabilizer 3 through a spray valve 9; the hot gas zone 21 is also sprayed with water 8 by means of an auxiliary spraying system.

The upper part of the pressure vessel 1 has an upper closure head 19, i.e. a dead space 20 section. And the chemical and solvent control system is used for conveying the boronizing liquid to the inside of the pressure container and the pressure stabilizer 3 to cool the pressure container and the pressure stabilizer.

The steam generator 4 cools the main system through a U-shaped pipe of the steam generator, and the steam generator discharges steam through a steam channel 13; the steam generator injects water into the steam generator through the feed water channel 12.

When the whole system needs to be cooled, safety accidents are easily caused by flash evaporation caused by steam in the upper end enclosure. In order to avoid steam generation in the upper end socket, the inventor sets out the following method from the concept of avoiding steam generation of the upper end socket.

The method is carried out under the condition that the main pump cannot be started normally or cannot work normally, and when the main pump can be used normally, the main pump is preferentially adopted for carrying out circulating cooling.

Referring to fig. 2, a natural circulation cooling method for avoiding steam generation of an upper head of a pressure vessel in a nuclear power plant comprises the following steps:

starting a cooling fan of the control rod driving mechanism air cooling system to cool the upper end enclosure of the pressure vessel;

boronizing the main system to the boron concentration of the cold shutdown reactor;

cooling the main system;

checking whether the temperature of the hot section is less than 284 ℃, and if not, cooling the main system; if yes, continuing to execute downwards;

the main system reduces the pressure for the first time;

locking the low-pressure safety injection signal of the voltage stabilizer; maintaining the temperature and pressure of the main system stable;

the main system reduces the pressure for the second time;

isolating the safety injection box;

cooling and depressurizing the main system;

cooling the main system to a cold shutdown state;

cooling the main system dead zone;

and checking whether the temperature of the main system is less than 90 ℃, if so, completely relieving the pressure of the main system, and if not, cooling the main system to cold stop the reactor.

Further, the method also comprises the following steps: starting a main pump; and if the main pump cannot be started normally or cannot work normally, returning to the step of starting the cooling fan of the air cooling system of the control rod driving mechanism to cool the upper end enclosure of the pressure vessel.

Further, the cooling of the main system comprises: the cooling rate of the main system is less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; maintaining the temperature and pressure of the main system within the limits of the natural circulation pressure-temperature diagram; the water level of the steam generator is maintained to be 34-50%.

Further, the primary system step-down for the first time includes: the main system is depressurized to 13.56MPa a by using an auxiliary spray or a safety valve.

Further, the low safety injection signal of locking stabiliser pressure includes: the potentiostat pressure low safety injection signal is latched after the signal is allowed to appear at P11.

Further, maintaining the temperature and pressure of the main system stable comprises: maintaining the pressure of a main system of the main system at 13.56MPa a, and the cooling rate of the main system at less than 14 ℃/h; maintaining the water level of the voltage stabilizer at a zero load water level; the main system temperature pressure is maintained within the native cycle pressure-temperature map limits.

Further, the second voltage reduction of the main system comprises: the main system was depressurized to 7 MPaa.

Further, the main system is depressurized to 7MPa a, and the method comprises the following steps: maintaining the supercooling degree of the reactor core outlet to be more than 20 ℃; maintaining the cooling rate of the cold section to be less than 14 ℃/h; the pressure of the pressure stabilizer is reduced by adopting a spray or a safety valve.

Further, keep apart safety injection case includes: and closing the outlet isolation valve of the safety injection tank.

Further, the temperature and pressure reduction of the main system comprises: the cooling rate of the main system cold section is less than 14 ℃/h; the main system temperature and pressure are within the cool-down and pressure-down curve limits.

Further, the primary system is cooled to a cold shutdown stack, comprising: and cooling the reactor main system to a cold shutdown reactor by using the residual discharge system.

Further, cooling the main system dead zone, comprising: and cooling the upper end enclosure of the pressure vessel by using a cooling fan of the control rod driving mechanism, and cooling the U-shaped tube area of the steam generator through steam discharge.

The operation can be specifically carried out in the following way:

step 1: a main pump is tried to be started. If the main pump cannot be started, continuing to step 2;

step 2: starting a cooling fan of the control rod driving mechanism air cooling system;

and step 3: boronizing the main system to the boron concentration of the cold shutdown reactor;

and 4, step 4: the main system cooling is started according to the following operations:

a. the cooling rate of the main system is-less than 14 ℃/h;

b. maintaining the water level of the voltage stabilizer to be zero load water level;

c. maintaining the temperature and pressure of the main system within the limits of the natural circulation pressure-temperature diagram;

d. maintaining the water level of the steam generator to be 34-50%;

and 5: checking the temperature of the hot section to be less than 284 ℃;

step 6: reducing the pressure of the main system to 13.56MPa a by using an auxiliary spray or a safety valve;

and 7: after the permission of P-11, locking the low voltage stabilizer pressure safety injection signal;

and 8: the main system is maintained stable in the following states:

□ a main system pressure- -13.56MPa a;

□ b, potentiostat level-zero load level;

□ c, the cooling rate of the main system cold section is less than 14 ℃/h;

□ d. the main system temperature and pressure are within the natural circulation pressure-temperature map limits.

And step 9: the main system is depressurized to 7MPa a according to the following limiting conditions;

a. maintaining the supercooling degree of the reactor core outlet to be more than 20 ℃;

b. maintaining the cooling rate of the cold section to be less than 14 ℃/h;

c. the pressure of the pressure stabilizer is reduced by adopting spraying or a safety valve;

step 10: isolating the safety injection box;

step 11: continuing to cool and reduce the pressure of the main system according to the following limiting conditions;

a. the cooling rate of the main system cold section is less than 14 ℃/h;

b. the temperature and pressure of the main system are within the limit values of a temperature reduction and pressure reduction curve;

step 12: checking whether the waste heat discharge system can be put into operation;

a. the cold water and seawater system operates normally;

b. putting into a waste heat discharge system;

step 13: the main system is continuously cooled to a cold shutdown working condition;

step 14: checking the LTOP input of low-temperature overpressure protection;

step 15: continuously cooling the dead zone of the main system, cooling the upper end enclosure of the pressure vessel by using a cooling fan of the control rod driving mechanism, and cooling the U-shaped tube area of the steam generator through steam discharge;

step 16: it is determined whether the main system requires full pressure relief.

The embodiment of the invention avoids the problem that the cooling capacity is lost due to the steam generated by the upper end enclosure when the upper end enclosure of the pressure container is cooled by adopting natural circulation, has clear processing steps, is simple and convenient to operate, has small operation burden on operators, and effectively reduces the probability of misoperation.

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.