A method and judgment module for preventing accidental addition of chemicals to a containment spray system of a nuclear power plant

Abstract

The present invention belongs to the technical field of special safety facilities for nuclear power plants, and specifically relates to a method and a judgment module for preventing the accidental addition of drugs to a containment spray system of a nuclear power plant. The method is used for the opening permission logic of an injection valve of a chemical reagent adding box, and the chemical reagent adding box is used to inject a NaOH solution into a containment spray system in a containment. The opening permission logic of the injection valve is set to "'containment spray signal is turned on for 5 minutes' signal & 'high gamma dose rate of air in containment' signal & 'chemical reagent adding box non-low liquid level' signal". The present invention can ensure the containment spray action in the event of a secondary circuit breach in the containment, while avoiding a series of problems caused by unnecessary NaOH solution spraying, and can also ensure the containment spray action and NaOH solution spraying in the event of a coolant loss accident.

Description

Technical Field

[0001] The invention belongs to the technical field of special safety facilities for nuclear power plants, and in particular relates to a method and a judgment module for preventing accidental addition of chemicals to a containment spray system of a nuclear power plant. Background Art

[0002] When a nuclear power plant loses coolant or the main steam pipe breaks in the containment, high-temperature, high-pressure steam is released, causing the pressure and temperature in the containment to rise. To ensure the integrity of the containment under accident conditions, domestic pressurized water reactor nuclear power units are equipped with a dedicated safety facility - the containment spray system. When the pressure and temperature in the containment exceed the specified value, condensed water is sprayed into the containment through a large number of nozzles located under the dome of the containment to reduce the pressure and temperature in the containment to an acceptable level to maintain the integrity of the containment.

[0003] At present, the normal operation process of the containment spray system is:

[0004] (1) After a coolant loss accident or a main steam pipe rupture accident in the containment, the pressure and temperature in the containment increase. When the containment spray system receives the containment high pressure signal, it starts spraying and sprays condensed water into the containment.

[0005] (2) After the containment spray system has been running for 5 minutes, the injection valve corresponding to the chemical reagent adding tank is opened, the NaOH solution in the tank is mixed with the mainstream water, and NaOH is sprayed into the containment until the NaOH solution in the chemical reagent adding tank is emptied.

[0006] (3) At the later stage of spraying, the pump pumps hot water from the refueling water tank into the heat exchanger, and after cooling in the heat exchanger, it is continuously sprayed into the containment.

[0007] From the above system settings, it can be seen that 5 minutes after the containment spray system is started, the injection valve of the chemical reagent addition box must be opened to inject NaOH solution.

[0008] After a loss of coolant accident occurs, a large amount of radioactive nuclides in the core will be released into the atmosphere of the containment, especially radioactive iodine, which has a significant impact on workers and the public. By adding NaOH solution to the spray water, the removal efficiency of radioactive iodine can be greatly enhanced. However, in the event of a rupture of the main steam pipe in the containment, since the steam in the main steam pipe is secondary circuit steam and the accident is not expected to cause fuel damage and release a large amount of radioactive nuclides, adding NaOH solution is meaningless to the accident process and will bring a series of negative effects:

[0009] a) NaOH is a strong alkali. Once sprayed through the spray system, it will be dispersed throughout the reactor building. High-concentration NaOH solution may corrode the equipment and structural materials in the containment, causing damage to the equipment or structural materials or shortening their service life.

[0010] b) The aluminum corroded and dissolved by NaOH in the reactor building will combine with other chemical components to form a sticky sodium aluminum silicate. When it is collected into the pit with the water flow, it will cause the pit filter to be blocked, affecting the operation of other safety facilities in the recycling stage.

[0011] c) The strong alkaline NaOH solution sprayed into the reactor building brought many inconveniences to the post-accident cleaning and recovery work, greatly increasing the workload. Summary of the invention

[0012] The purpose of the present invention is to propose a method for preventing the nuclear power plant containment spray system from mistakenly adding drugs in a low-radioactivity risk accident in view of the design defects of the existing containment spray system, so as to ensure the smooth start-up of adding NaOH solution to the spray liquid in the event of a coolant loss accident; on the other hand, to avoid unnecessary NaOH solution spraying after the main steam pipeline rupture accident in the containment, and at the same time ensure the normal operation of the containment spray system.

[0013] To achieve the above purpose, the technical solution adopted by the present invention is a method for preventing the accidental dosing of a containment spray system of a nuclear power plant, which is used for the opening permission logic of an injection valve of a chemical reagent adding box, wherein the chemical reagent adding box is used to inject NaOH solution into the containment spray system in the containment, and the opening permission logic belongs to the dosing procedure of the containment spray system.

[0014] The opening permission logic of the injection valve is set to "'containment spray signal open for 5 minutes' signal & 'containment air gamma dose rate high' signal & 'chemical reagent addition box non-low liquid level' signal";

[0015] When the 'containment spray signal is turned on for 5 minutes' signal, the 'high gamma dose rate of air in the containment' signal and the 'chemical reagent addition tank non-low liquid level' signal are all true, the injection valve is opened, the dosing program is started, and the chemical reagent addition tank injects the NaOH solution into the containment spray system; otherwise, the injection valve remains closed and the dosing program is not started.

[0016] further,

[0017] The 'containment spray signal is turned on for 5 minutes' signal is used to start the containment spray system and start spraying condensed water into the containment; when the 'containment spray signal is turned on for 5 minutes' signal is not true, the containment spray system is not started; when the 'containment spray signal is turned on for 5 minutes' signal is true, the containment spray system is started, and the running time is greater than or equal to 5 minutes;

[0018] The 'high gamma dose rate of air in containment' signal is used to control the opening and closing of the injection valve; when the 'high gamma dose rate of air in containment' signal is not true, the injection valve remains closed; when the 'high gamma dose rate of air in containment' signal is true, the injection valve is allowed to open;

[0019] The 'chemical reagent addition tank non-low liquid level' signal is used to prevent the injection valve from being opened by mistake due to the absence of the NaOH solution in the chemical reagent addition tank, and is also used to close the injection valve when the liquid level of the NaOH solution in the chemical reagent addition tank is lower than a set value; when the 'chemical reagent addition tank non-low liquid level' signal is not true, the injection valve remains closed; when the 'chemical reagent addition tank non-low liquid level' signal is true, the injection valve is allowed to open, and the injection valve is closed when the liquid level of the NaOH solution in the chemical reagent addition tank is lower than a set value.

[0020] Further, the 'high gamma dose rate of air in containment' signal is provided by the accident and post-accident gamma dose rate monitoring channel of the air in containment located on the operating platform of the reactor building according to the gamma dose rate threshold of the air in containment; when the fourth gamma dose rate is lower than the gamma dose rate threshold of the air in containment, the 'high gamma dose rate of air in containment' signal is not true; when the fourth gamma dose rate is higher than the gamma dose rate threshold of the air in containment, the 'high gamma dose rate of air in containment' signal is true; the fourth gamma dose rate is the real-time monitored gamma dose rate of the air in containment.

[0021] further,

[0022] The air gamma dose rate threshold in the containment is provided by the air gamma dose rate monitoring channel in the accident and after the accident, and is used to distinguish between the first gamma dose rate and the second gamma dose rate;

[0023] The first gamma dose rate refers to the gamma dose rate of the air in the containment after the first accident, and the second gamma dose rate refers to the gamma dose rate of the air in the containment after the second accident;

[0024] The first accident refers to a coolant loss accident, and the second accident refers to a main steam pipe rupture accident in the containment.

[0025] Further, the determination of the air gamma dose rate threshold in the containment vessel comprises the following steps:

[0026] Step S1, considering the most realistic source term assumption of the first accident, calculating the air gamma dose rate in the containment after the accident as the first gamma dose rate;

[0027] Considering the most conservative source term assumption of the second accident, the gamma dose rate of the air in the containment after the accident is calculated as the second gamma dose rate;

[0028] Step S2, selecting a value lower than the first gamma dose rate and higher than the second gamma dose rate as the gamma dose rate threshold of the air in the containment, used to indicate whether the 'high gamma dose rate of the air in the containment' signal is true, so as to ensure that the first accident and the second accident can be distinguished;

[0029] Step S3 also includes collecting a third gamma dose rate, wherein the third gamma dose rate refers to the gamma dose rate at the location of the sensor for monitoring the gamma dose rate of the air in the containment during an accident or after an accident under normal operating conditions of the same type of unit, and combining the radiation zoning at the location to ensure that the third gamma dose rate is not lower than the gamma dose rate of the air in the containment under normal operating conditions.

[0030] further,

[0031] The most realistic source term assumption for the first accident is that 100% of the radionuclides in the reactor coolant system are released into the containment atmosphere, while taking into account the additional iodine activity concentration caused by the pre-existing iodine spike;

[0032] The most conservative source term assumption for the second accident is that all the radionuclides contained in the steam of all steam generators in the containment are discharged into the containment, while a more conservative accident-triggered iodine spike is considered.

[0033] further,

[0034] The radioactive nuclides are all released at the moment of occurrence of the first accident;

[0035] The radioactive nuclides are all released at the moment the second accident occurs.

[0036] Furthermore, the method for preventing the accidental addition of chemicals to the containment spray system of a nuclear power plant is used in low-radioactivity risk accidents of the containment.

[0037] To achieve the above objectives, the present invention also discloses a judgment module for preventing accidental dosing of containment spray system of a nuclear power plant used in the above-mentioned method for preventing accidental dosing of containment spray system of a nuclear power plant, which is arranged in the dosing program of the containment spray system, and is used to judge whether the 'high γ dose rate of air in containment' signal is true according to the fourth γ dose rate and the γ dose rate threshold of air in containment; and is also used to control the opening of the injection valve when the 'containment spray signal is turned on for 5 minutes' signal, the 'high γ dose rate of air in containment' signal and the 'chemical reagent addition box non-low liquid level' signal are all true, so as to start the dosing program.

[0038] further,

[0039] The judgment module includes a first submodule, a second submodule and a third submodule;

[0040] The first submodule is used to obtain the fourth gamma dose rate;

[0041] The second submodule is used to obtain whether the 'containment spray signal is turned on for 5 minutes' signal is true, whether the 'air gamma dose rate in the containment is high' signal is true, and whether the 'chemical reagent addition box is not at low liquid level' signal is true, and output the obtained results to the third submodule;

[0042] When obtaining whether the 'high gamma dose rate of air in containment' signal is true, the second submodule compares the fourth gamma dose rate with the gamma dose rate threshold of air in containment, and when the fourth gamma dose rate is lower than the gamma dose rate threshold of air in containment, a comparison result indicating that the 'high gamma dose rate of air in containment' signal is not true is given; when the fourth gamma dose rate is higher than the gamma dose rate threshold of air in containment, a comparison result indicating that the 'high gamma dose rate of air in containment' signal is true is given;

[0043] The third submodule is used to output the result obtained by the second submodule to the opening permission logic of the injection valve; when the result is "the 'containment spray signal is turned on for 5 minutes' signal is true", "the 'gamma dose rate of air in the containment is high' signal is true" and "the 'chemical reagent addition tank is not at a low liquid level' signal is true", the injection valve is opened and the dosing program is started; when the result is that the 'containment spray signal is turned on for 5 minutes' signal, the 'gamma dose rate of air in the containment is high' signal and the 'chemical reagent addition tank is not at a low liquid level' signal are not all true, the injection valve remains closed and the dosing program is not started.

[0044] The beneficial effects of the present invention are:

[0045] The present invention provides a method for preventing a nuclear power plant containment spray system from being pressurized in a low-radioactivity risk accident. By adding permission logic to the opening of an injection valve, the opening of the injection valve is triggered by coupling three signals: "a 5-minute containment spray signal opening signal, a γ-dose rate high in the air in the containment, and a non-low liquid level signal in the chemical reagent adding box". Then, NaOH solution is sprayed into the containment. This can ensure the containment spray action in the event of a secondary circuit rupture accident in the containment, avoid a series of problems caused by unnecessary NaOH solution spraying, and ensure the containment spray action and NaOH solution spraying in the event of a coolant loss accident. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a control logic diagram of the opening of the injection valve provided by a method for preventing the accidental addition of chemicals to the containment spray system of a nuclear power plant described in a specific embodiment of the present invention (the chemical reagent addition box contains NaOH solution);

[0047] Figure 2 It is a schematic diagram of a method for determining a 'high gamma dose rate in the air in the containment' signal of an accident and post-accident air gamma dose rate monitoring channel in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention provides a method for preventing the accidental addition of drugs to the containment spray system of a nuclear power plant (applicable to low-radioactivity risk accidents of the containment), which is used for the opening permission logic of the injection valve on the chemical reagent adding box, and the chemical reagent adding box is used to inject NaOH solution into the containment spray system in the containment, and the opening permission logic belongs to the dosing procedure of the containment spray system, wherein the opening permission logic of the injection valve is increased with the "high gamma dose rate of air in the containment" logic, and the "'containment spray signal is turned on for 5 minutes' signal & 'chemical reagent adding box is not at a low liquid level' signal" is changed to "'containment spray signal is turned on for 5 minutes' signal & 'high gamma dose rate of air in the containment' signal & 'chemical reagent adding box is not at a low liquid level' signal" (see Figure 1 ); when the 'containment spray signal is turned on for 5 minutes' signal, the 'air gamma dose rate in the containment is high' signal and the 'chemical reagent adding box is not at low liquid level' signal are all true, the injection valve is opened, the dosing program is started, and the chemical reagent adding box injects NaOH solution into the containment spray system. The NaOH solution in the chemical reagent adding box is mixed with the mainstream water of the condensed water, and the NaOH solution is sprayed into the containment; otherwise, the injection valve remains closed and the dosing program is not started.

[0049] The 'containment spray signal is turned on for 5 minutes' signal is used to start the containment spray system and start spraying condensate into the containment; when the 'containment spray signal is turned on for 5 minutes' signal is not true, the containment spray system will not start; when the 'containment spray signal is turned on for 5 minutes' signal is true, the containment spray system will start, and the running time is greater than or equal to 5 minutes;

[0050] The signal of 'high gamma dose rate of air in containment' is used to control the opening and closing of the injection valve; when the signal of 'high gamma dose rate of air in containment' is not true, the injection valve remains closed; when the signal of 'high gamma dose rate of air in containment' is true, the injection valve is allowed to open;

[0051] The 'chemical reagent addition tank non-low liquid level' signal is used to prevent the injection valve from being opened by mistake due to the absence of NaOH solution in the chemical reagent addition tank, and is also used to close the injection valve when the liquid level of the NaOH solution in the chemical reagent addition tank is lower than the set value; when the 'chemical reagent addition tank non-low liquid level' signal is not true, the injection valve remains closed; when the 'chemical reagent addition tank non-low liquid level' signal is true, the injection valve is allowed to open, and the injection valve is closed when the liquid level of the NaOH solution in the chemical reagent addition tank is lower than the set value.

[0052] The signal of 'high gamma dose rate of air in containment' is provided by the accident and post-accident gamma dose rate monitoring channel of the air in containment on the operating platform of the reactor building according to the gamma dose rate threshold of air in containment; when the fourth gamma dose rate is lower than the gamma dose rate threshold of air in containment, the signal of 'high gamma dose rate of air in containment' is not true; when the fourth gamma dose rate is higher than the gamma dose rate threshold of air in containment, the signal of 'high gamma dose rate of air in containment' is true; the fourth gamma dose rate is the real-time monitored gamma dose rate of air in containment. The operating platform is a place in the reactor building. During the reactor shutdown and maintenance, it is a workplace where a large number of maintenance personnel work. It is not an instrument for the control of the containment spray system.

[0053] The air gamma dose rate threshold in the containment is provided by the air gamma dose rate monitoring channel in the containment during the accident and after the accident, and is used to distinguish the first gamma dose rate from the second gamma dose rate;

[0054] The first gamma dose rate refers to the gamma dose rate of the air in the containment after the first accident, and the second gamma dose rate refers to the gamma dose rate of the air in the containment after the second accident;

[0055] The first accident refers to the coolant loss accident, and the second accident refers to the main steam pipe rupture accident in the containment.

[0056] The determination of the air gamma dose rate threshold in the containment includes the following steps:

[0057] Step S1, considering the most realistic source term assumption of the first accident (loss of coolant accident), calculating the air gamma dose rate in the containment after the accident as the first gamma dose rate;

[0058] Considering the most conservative source assumption of the second accident (rupture of the main steam pipeline in the containment), the gamma dose rate of the air in the containment after the accident was calculated as the second gamma dose rate;

[0059] Step S2, selecting a value lower than the first gamma dose rate and higher than the second gamma dose rate as a gamma dose rate threshold of the air in the containment, used to determine whether a signal of "high gamma dose rate of the air in the containment" is true, so as to ensure that the first accident and the second accident can be distinguished;

[0060] Step S3 also includes collecting a third gamma dose rate, which refers to the gamma dose rate at the location of the sensor for monitoring the gamma dose rate of the air in the containment during accidents and after accidents under normal operating conditions of the same type of units, and combining the radiation zoning at the location to ensure that the third gamma dose rate is not lower than the gamma dose rate of the air in the containment under normal operating conditions, so as to avoid frequent false alarms affecting the judgment of nuclear power plant operators.

[0061] The most realistic source term assumption for the first accident is that 100% of the radionuclides in the reactor coolant system are released into the containment atmosphere, while taking into account the additional iodine activity concentration caused by the pre-existing iodine spike;

[0062] The most conservative source assumption for the second accident is that all the radioactive nuclides contained in the steam of all steam generators in the containment are discharged into the containment, while considering more conservative accident-triggered iodine spike situations.

[0063] Iodine spike: The phenomenon of a sharp increase in iodine concentration in the primary coolant during the shutdown process after an accident. When the reactor is operating at power, iodine accumulates on the surface of the fuel pellets and the inner surface of the cladding in the form of soluble salts (mainly cesium iodide), and it is difficult to release from the cladding; when the reactor power or the primary coolant pressure changes, radioactive iodine enters the primary coolant through the damaged cladding, resulting in an iodine spike in the primary coolant;

[0064] Iodine activity concentration: the activity concentration of radioactive iodine in the coolant, that is, the radioactive iodine activity per unit mass of coolant.

[0065] The radionuclides were all released at the moment of the first accident;

[0066] All radionuclides were released at the moment of the second accident.

[0067] The present invention also discloses a judgment module for preventing accidental dosing of a nuclear power plant containment spray system in the above-mentioned method for preventing accidental dosing of a nuclear power plant containment spray system. The judgment module is arranged in the dosing program of the containment spray system, and is used to judge whether the 'high γ dose rate of air in containment' signal is true according to the fourth γ dose rate and the γ dose rate threshold of the air in the containment; and is also used to control the injection valve to open when the 'containment spray signal is turned on for 5 minutes' signal, the 'high γ dose rate of air in containment' signal and the 'chemical reagent addition box non-low liquid level' signal are all true, so as to start the dosing program.

[0068] The judgment module includes a first submodule, a second submodule and a third submodule;

[0069] The first submodule is used to obtain a fourth gamma dose rate;

[0070] The second submodule is used to obtain whether the signal of 'containment spray signal turned on for 5 minutes' is true, whether the signal of 'high gamma dose rate of air in containment' is true, and whether the signal of 'chemical reagent adding box non-low liquid level' is true, and output the obtained results to the third submodule;

[0071] When obtaining whether the signal of 'high gamma dose rate of air in containment' is true, the second submodule compares the fourth gamma dose rate with the threshold of gamma dose rate of air in containment, and when the fourth gamma dose rate is lower than the threshold of gamma dose rate of air in containment, a comparison result indicating that the signal of 'high gamma dose rate of air in containment' is not true is given; when the fourth gamma dose rate is higher than the threshold of gamma dose rate of air in containment, a comparison result indicating that the signal of 'high gamma dose rate of air in containment' is true is given;

[0072] The third submodule is used to output the result obtained by the second submodule to the opening permission logic of the injection valve. When the result is "the signal of 'containment spray signal turned on for 5 minutes' is true", "the signal of 'high gamma dose rate of air in containment' is true" and "the signal of 'chemical reagent addition box is not at low liquid level' is true", the injection valve is opened and the dosing program is started; when the result is that the signal of 'containment spray signal turned on for 5 minutes', 'high gamma dose rate of air in containment' and 'chemical reagent addition box is not at low liquid level' are not all true, the injection valve remains closed and the dosing program is not started.

[0073] The present invention is described in detail below with reference to the accompanying drawings and implementation examples.

[0074] The present invention provides a method for preventing the accidental addition of drugs to a containment spray system of a nuclear power plant, comprising the following processes: analyzing the gamma dose rate of air in the containment after a loss of coolant accident, analyzing the gamma dose rate of air in the containment after a main steam pipeline rupture accident in the containment, determining a signal value of 'high gamma dose rate of air in the containment', and modifying the logic of increasing the opening permission of an injection valve based on the determined signal value of 'high gamma dose rate of air in the containment'.

[0075] Firstly, the signal value of 'high gamma dose rate in the air inside the containment' is determined, that is, the gamma dose rate threshold of the gamma dose rate monitoring channel of the air inside the containment during and after the accident.

[0076] For the loss of coolant accident (first accident), the most realistic source term assumption is considered, assuming that 100% of the radionuclides in the reactor coolant system are released into the containment atmosphere, and considering the additional iodine activity concentration caused by the pre-existing iodine spike. The iodine spike can be considered as the transient value under the extreme operating conditions. It is assumed that the above radionuclides are released into the containment instantaneously. The radionuclides are immediately mixed and evenly distributed in the containment atmosphere at the moment of release into the containment, and the removal factors such as the decay of radionuclides over time and the leakage of the containment are considered. Based on the above assumptions and calculation methods, the air gamma dose rate (first gamma dose rate) in the containment after the loss of coolant accident of a million-kilowatt unit can be calculated to be 45.0mSv / h.

[0077] For the main steam pipe rupture accident in the containment (the second accident), the most conservative source term assumption is considered, assuming that all the radionuclides contained in the steam of all steam generators in the containment are discharged into the containment, and all are released at the moment of the main steam pipe rupture accident. The radionuclides are immediately mixed and evenly distributed in the containment atmosphere at the moment of release into the containment, and the removal factors such as the decay of radionuclides over time and the leakage of the containment are considered. Based on the above assumptions, the γ dose rate of the air in the containment after the main steam pipe rupture accident in the containment of a million-kilowatt unit (the first γ dose rate) can be calculated to be 8.0mSv / h.

[0078] Based on the gamma dose rate (third gamma dose rate) at the sensor position of the air gamma dose rate monitoring channel in the containment under normal operating conditions of the same type of units during accidents and after accidents, the maximum value is less than 1.0mSv / h. The radiation partition dose rate limit here is 10.0mSv / h.

[0079] According to the attached Figure 2The method for determining the 'high gamma dose rate of air in containment' signal of the gamma dose rate monitoring channel of the containment air in the accident and after the accident shown in the figure selects a value which is lower than the most realistic gamma dose rate of air in containment after the loss of coolant accident (the first gamma dose rate) and higher than the most conservative gamma dose rate of air in containment after the main steam pipe rupture accident in the containment (the second gamma dose rate) and the maximum gamma dose rate value that may be achieved under normal operating conditions, that is, any value between less than 45.0 mSv / h and greater than 10.0 mSv / h, which is 20.0 mSv / h in this embodiment.

[0080] Secondly, based on the determined threshold, the logic of increasing the opening permission of the injection valve is modified to "'Containment spray signal open 5min' signal & 'Containment air gamma dose rate higher than 20.0mSv / h' signal & 'Chemical reagent addition tank non-low liquid level' signal". After the logic is modified, according to the attached Figure 2 It can be seen that the operation mode of the containment spray system after the two types of accidents, namely, the loss of coolant accident and the rupture of the main steam pipe in the containment, is:

[0081] (I) Operation mode of containment spray system after loss of coolant accident:

[0082] (1) After a coolant loss accident occurs, the pressure and temperature inside the containment increase. When the containment spray system receives the containment high pressure signal, it starts spraying and begins to spray condensed water into the containment.

[0083] (2) After the containment spray system has been in operation for 5 minutes, the gamma dose rate of the air in the containment (the fourth gamma dose rate) exceeds 20 mSv / h. After receiving the signal "the gamma dose rate of the air in the containment is higher than 20.0 mSv / h" from the accident and post-accident containment gamma dose rate monitoring channel (i.e., the signal of 'high gamma dose rate of the air in the containment' is true), the injection valve corresponding to the chemical reagent adding tank is opened, the NaOH solution is mixed with the mainstream water, and NaOH is sprayed into the containment until the NaOH solution in the chemical reagent adding tank is emptied.

[0084] (3) At the later stage of spraying, the pump pumps hot water from the refueling water tank into the heat exchanger, and after cooling in the heat exchanger, it is continuously sprayed into the containment.

[0085] Under the above-mentioned operating mode, the operation process of the containment spray system is exactly the same as before the improvement and will not affect the original design.

[0086] If the air gamma dose rate (fourth gamma dose rate) in the containment does not exceed 20mSv / h after a loss of coolant accident, the operation mode of the containment spray system will become:

[0087] (1) After a coolant loss accident occurs, the pressure and temperature inside the containment increase. When the containment spray system receives the containment high pressure signal, it starts spraying and begins to spray condensed water into the containment.

[0088] (2) After the containment spray system has been running for 5 minutes, the gamma dose rate of the air in the containment (the fourth gamma dose rate) remains below 20 mSv / h. The “gamma dose rate of the air in the containment is higher than 20.0 mSv / h” signal is not received from the accident and post-accident containment gamma dose rate monitoring channel (i.e., the signal of ‘high gamma dose rate of the air in the containment’ is not true), the injection valve remains closed, and the dosing procedure is not started.

[0089] (3) At the later stage of spraying, the pump pumps hot water from the refueling water tank into the heat exchanger, and after cooling in the heat exchanger, it is sprayed into the containment.

[0090] At this time, although the dosing procedure of the containment spray system has not been started, it also means that the radiation level inside the shell is very low, and the amount of radionuclides released into other plant buildings and the environment through the containment will be even lower. The radiation consequences of the coolant loss accident will be much lower than the analysis results using conservative source term assumptions, and are therefore also at an acceptable level.

[0091] (II) Main steam pipe rupture accident in containment

[0092] Since a very conservative assumption is used for the accident source item of the main steam pipe rupture accident in the containment, the actual radioactivity level in the containment is very likely not to exceed the above-mentioned assumed value. The operation mode of the containment spray system is:

[0093] (1) After the main steam pipe rupture accident occurs in the containment, the pressure and temperature in the containment increase. When the containment spray system receives the containment high pressure signal, it starts spraying and begins to spray condensed water into the containment.

[0094] (2) After the containment spray system had been operating for 5 minutes, the gamma dose rate of the air in the containment (the fourth gamma dose rate) remained below 20 mSv / h. No signal indicating that the gamma dose rate of the air in the containment was higher than 20 mSv / h was received from the accident and post-accident containment gamma dose rate monitoring channel (i.e., the signal indicating that the gamma dose rate of the air in the containment was high was not true). The injection valve remained closed and the dosing procedure was not started.

[0095] (3) At the later stage of spraying, the pump pumps hot water from the refueling water tank into the heat exchanger, and after cooling in the heat exchanger, it is sprayed into the containment.

[0096] If, in extreme cases, the main steam pipe rupture accident in the containment vessel causes more serious accident consequences, such as excessive core temperature affecting the integrity of the fuel elements, resulting in the air gamma dose rate (the fourth gamma dose rate) in the containment vessel exceeding 20mSv / h, the operation mode of the containment spray system will become:

[0097] (1) After the main steam pipe rupture accident occurs in the containment, the pressure and temperature in the containment increase. When the containment spray system receives the containment high pressure signal, it starts spraying and begins to spray condensed water into the containment.

[0098] (2) After the containment spray system had been in operation for 5 minutes, the gamma dose rate of the air in the containment (the fourth gamma dose rate) exceeded the level of 20 mSv / h. Upon receiving the signal "the gamma dose rate of the air in the containment is higher than 20 mSv / h" from the accident and post-accident gamma dose rate monitoring channel of the air in the containment (i.e., the signal of 'high gamma dose rate of the air in the containment' is true), the injection valve is opened, and the dosing procedure is started.

[0099] (3) At the later stage of spraying, the pump pumps hot water from the refueling water tank into the heat exchanger, and after cooling in the heat exchanger, it is sprayed into the containment.

[0100] The air gamma dose rate (the fourth gamma dose rate) in the containment is higher than 20mSv / h. The release of radionuclides in the containment caused by the main steam pipe rupture accident in the containment has greatly exceeded the expected level, which means that more serious accident consequences have been caused and may have exceeded the scope of the design basis accident. By starting the dosing procedure of the containment spray system, the amount of radionuclides released from the containment to other plant buildings and the environment can be reduced, which is of great positive significance for reducing the off-site consequences of the accident.

[0101] The device described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the technical innovation scope of the present invention.

Claims

1. A method for preventing accidental dosing of a containment spray system of a nuclear power plant, for the opening permission logic of an injection valve of a chemical reagent adding box, wherein the chemical reagent adding box is used to inject NaOH solution into the containment spray system in the containment, and the opening permission logic belongs to the dosing procedure of the containment spray system, and is characterized by: The opening permission logic of the injection valve is set to "'containment spray signal open 5min' signal & 'containment air gamma dose rate high' signal & 'chemical reagent addition box non-low liquid level' signal"; When the 'containment spray signal is turned on for 5 minutes' signal, the 'containment air gamma dose rate is high' signal and the 'chemical reagent addition tank is not at low liquid level' signal are all true, the injection valve is opened, the dosing program is started, and the chemical reagent addition tank injects the NaOH solution into the containment spray system, otherwise the injection valve remains closed and the dosing program is not started; The 'containment spray signal is turned on for 5 minutes' signal is used to start the containment spray system and start spraying condensed water into the containment; when the 'containment spray signal is turned on for 5 minutes' signal is not true, the containment spray system is not started; when the 'containment spray signal is turned on for 5 minutes' signal is true, the containment spray system is started, and the running time is greater than or equal to 5 minutes; The 'high gamma dose rate of air in containment' signal is used to control the opening and closing of the injection valve; when the 'high gamma dose rate of air in containment' signal is not true, the injection valve remains closed; when the 'high gamma dose rate of air in containment' signal is true, the injection valve is allowed to open; The 'chemical reagent adding tank non-low liquid level' signal is used to prevent the injection valve from being opened by mistake due to the absence of the NaOH solution in the chemical reagent adding tank, and is also used to close the injection valve when the liquid level of the NaOH solution in the chemical reagent adding tank is lower than a set value; when the 'chemical reagent adding tank non-low liquid level' signal is not true, the injection valve remains closed; when the 'chemical reagent adding tank non-low liquid level' signal is true, the injection valve is allowed to open, and the injection valve is closed when the liquid level of the NaOH solution in the chemical reagent adding tank is lower than a set value; The 'high gamma dose rate of air in containment' signal is provided by the accident and post-accident gamma dose rate monitoring channel of the air in containment arranged on the operating platform of the reactor building according to the gamma dose rate threshold of air in containment; when the fourth gamma dose rate is lower than the gamma dose rate threshold of air in containment, the 'high gamma dose rate of air in containment' signal is not true; when the fourth gamma dose rate is higher than the gamma dose rate threshold of air in containment, the 'high gamma dose rate of air in containment' signal is true; the fourth gamma dose rate is the gamma dose rate of air in containment monitored in real time; The air gamma dose rate threshold in the containment is provided by the air gamma dose rate monitoring channel in the accident and after the accident, and is used to distinguish between the first gamma dose rate and the second gamma dose rate; The first gamma dose rate refers to the gamma dose rate of the air in the containment after the first accident, and the second gamma dose rate refers to the gamma dose rate of the air in the containment after the second accident; The first accident refers to a coolant loss accident, and the second accident refers to a main steam pipe rupture accident in the containment; Determination of the air gamma dose rate threshold in the containment vessel comprises the following steps: Step S1, considering the most realistic source term assumption of the first accident, calculating the air gamma dose rate in the containment after the accident as the first gamma dose rate; Considering the most conservative source term assumption of the second accident, the gamma dose rate of the air in the containment after the accident is calculated as the second gamma dose rate; Step S2, selecting a value lower than the first gamma dose rate and higher than the second gamma dose rate as the gamma dose rate threshold of the air in the containment, used to indicate whether the 'high gamma dose rate of the air in the containment' signal is true, so as to ensure that the first accident and the second accident can be distinguished; Step S3 also includes collecting a third gamma dose rate, wherein the third gamma dose rate refers to the gamma dose rate at the location of the sensor for monitoring the gamma dose rate of the air in the containment during an accident or after an accident under normal operating conditions of the same type of unit, and combining the radiation partition at the location to ensure that the third gamma dose rate is not lower than the gamma dose rate of the air in the containment under normal operating conditions, so as to avoid frequent false alarms affecting the judgment of the nuclear power plant operator; determining the range of the gamma dose rate threshold of the air in the containment according to the first gamma dose rate and the third gamma dose rate, wherein the gamma dose rate threshold of the air in the containment is any value less than the first gamma dose rate and greater than the dose rate limit of the radiation partition at the location of the sensor for monitoring the gamma dose rate of the air in the containment during an accident or after an accident.

2. A method for preventing accidental dosing of a containment spray system of a nuclear power plant according to claim 1, characterized in that: The most realistic source term assumption for the first accident is that 100% of the radionuclides in the reactor coolant system are released into the containment atmosphere, while taking into account the additional iodine activity concentration caused by the pre-existing iodine spike; The most conservative source term assumption for the second accident is that all the radionuclides contained in the steam of all steam generators in the containment are discharged into the containment, while a more conservative accident-triggered iodine spike is considered.

3. A method for preventing accidental dosing of a containment spray system of a nuclear power plant as claimed in claim 2, characterized in that: The radioactive nuclides are all released at the moment of occurrence of the first accident; The radioactive nuclides are all released at the moment the second accident occurs.

4. A method for preventing accidental dosing of a containment spray system of a nuclear power plant as claimed in claim 3, characterized in that: The method for preventing the accidental addition of drugs to a containment spray system of a nuclear power plant is used in low-radioactivity risk accidents of the containment.

5. A judgment module for preventing the mis-dosing of a containment spray system of a nuclear power plant used in the method for preventing the mis-dosing of a containment spray system of a nuclear power plant as claimed in claim 4, characterized in that: It is arranged in the dosing program of the containment spray system, and is used to determine whether the 'high gamma dose rate of air in containment' signal is true according to the fourth gamma dose rate and the gamma dose rate threshold of the air in containment; and is also used to control the opening of the injection valve when the 'containment spray signal is turned on for 5 minutes' signal, the 'high gamma dose rate of air in containment' signal and the 'chemical reagent addition box non-low liquid level' signal are all true, so as to start the dosing program.

6. The judgment module of the method for preventing the mis-dosing of the containment spray system of a nuclear power plant according to claim 5, characterized in that: The judgment module includes a first submodule, a second submodule and a third submodule; The first submodule is used to obtain the fourth gamma dose rate; The second submodule is used to obtain whether the 'containment spray signal is turned on for 5 minutes' signal is true, whether the 'air gamma dose rate in the containment is high' signal is true, and whether the 'chemical reagent addition box is not at low liquid level' signal is true, and output the obtained results to the third submodule; When obtaining whether the 'high gamma dose rate of air in containment' signal is true, the second submodule compares the fourth gamma dose rate with the gamma dose rate threshold of air in containment, and when the fourth gamma dose rate is lower than the gamma dose rate threshold of air in containment, a comparison result indicating that the 'high gamma dose rate of air in containment' signal is not true is given; when the fourth gamma dose rate is higher than the gamma dose rate threshold of air in containment, a comparison result indicating that the 'high gamma dose rate of air in containment' signal is true is given; The third submodule is used to output the result obtained by the second submodule to the opening permission logic of the injection valve; when the result is "the 'containment spray signal is turned on for 5 minutes' signal is true", "the 'gamma dose rate of air in the containment is high' signal is true" and "the 'chemical reagent addition tank is not at a low liquid level' signal is true", the injection valve is opened and the dosing program is started; when the result is that the 'containment spray signal is turned on for 5 minutes' signal, the 'gamma dose rate of air in the containment is high' signal and the 'chemical reagent addition tank is not at a low liquid level' signal are not all true, the injection valve remains closed and the dosing program is not started.

Images