A fast calculation method for hydrogen concentration after containment spraying is opened

Abstract

The present invention relates to a method for quickly calculating the hydrogen concentration after the containment spray is turned on, comprising: (1) calculating the initial state of the containment at time t0 before the containment spray is turned on, including calculating the water vapor partial pressure, hydrogen partial pressure, air partial pressure, and the mass of the water vapor, air, and hydrogen in the containment; (2) calculating the containment atmospheric pressure P after the spray is turned on for t time according to the containment atmospheric pressure prediction relationship. t (3) Calculate the containment atmosphere state after the spray is activated for a period of time t, and obtain the relationship between the containment atmospheric pressure and the change in hydrogen concentration over time. The present invention can use the containment pressure prediction formula obtained by data fitting as a tool to quickly calculate the change in hydrogen concentration in the containment after the containment spray is activated, thereby achieving rapid prediction of hydrogen risks and providing technical support for operators to mitigate the consequences of nuclear power plant accidents.

Description

Technical Field

[0001] The present invention belongs to nuclear power design technology, and in particular relates to a method for quickly calculating hydrogen concentration after containment spraying is started. Background Art

[0002] In the event of a serious accident at a nuclear power plant, high-energy gases such as water vapor and hydrogen are generated for various reasons. These gases are released into the containment space, causing the containment to heat up and pressurize. Currently, all second- and third-generation nuclear power plants in China are equipped with containment spray systems. When the containment atmospheric pressure exceeds a set limit, the containment spray system is activated to reduce the pressure and mitigate the threat posed by high pressure to the containment's integrity. When the containment spray system is activated, the pressure and temperature within the containment drop, causing water vapor in the atmosphere to condense, increasing the hydrogen content within the containment and the risk of hydrogen contamination.

[0003] The severe accident management guidelines based on the US WOG provide a method for assessing hydrogen risk using the fuel cladding oxidation fraction and containment pressure as independent variables. However, in actual accidents, there is no instrumentation to indicate the oxidation state of the fuel cladding, and operators cannot determine the oxidation fraction of the fuel cladding under accident conditions. Therefore, this method is difficult to use for assessing hydrogen risk after the containment spray is activated. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the existing technology and provide a method for quickly calculating the hydrogen concentration after the containment spray is opened, so as to provide support for hydrogen risk assessment and severe accident management after the containment spray is opened in a nuclear power plant.

[0005] The technical solution of the present invention is as follows: a method for quickly calculating the hydrogen concentration after the containment spray is opened, comprising the following steps:

[0006] (1) Calculate the initial state of the containment at time t0 before the containment spray is opened, including the calculation of the water vapor partial pressure, hydrogen partial pressure, air partial pressure, and the mass of water vapor, air, and hydrogen in the containment;

[0007] (2) According to the following containment atmospheric pressure prediction relationship, the containment atmospheric pressure P after the spray is opened for t time is calculated. t ,

[0008] p t =p1+(p0-p1)e -rt

[0009] in,

[0010] P t is the atmospheric pressure of the containment after the spray is opened for t time,

[0011] P1 is the containment atmospheric equilibrium pressure,

[0012] P0 is the atmospheric pressure of the containment when the spray is opened,

[0013] t is the operating time of the sprinkler system,

[0014] r is the coefficient of the exponential;

[0015] (3) The atmospheric state of the containment is calculated after the spray is turned on for t time, and the relationship between the atmospheric pressure of the containment and the change of hydrogen concentration with time is obtained.

[0016] Furthermore, the above-mentioned method for quickly calculating the hydrogen concentration after the containment spray is opened is based on the following assumptions:

[0017] Assume that the atmosphere in the containment is a uniform mixture of gases, with the same temperature and concentration of each gas component at different locations;

[0018] Assume that the water vapor in the containment is always in a saturated state;

[0019] Assuming that all mixed gases in the containment are ideal gases, the ideal gas state equation can be used to solve the problem;

[0020] It is assumed that the decay heat is used to generate saturated water vapor to be released into the containment;

[0021] Assume that once the sprinkler system is turned on, it remains on continuously.

[0022] Furthermore, in the method for quickly calculating the hydrogen concentration after the containment spray is started, the calculation of the initial state of the containment at time t0 before the containment spray is started in step (1) includes the following steps:

[0023] (1-1) Assuming that the water vapor in the containment is in a saturated state at time t0, the water vapor partial pressure P in the containment is calculated based on the thermodynamic properties of industrial water and water vapor IAPWS IF-97 and the containment temperature T0. 0,steam ;

[0024] (1-2) According to the containment atmospheric pressure P0 and hydrogen molar concentration N at time t0 0,H2 , calculate the hydrogen partial pressure P 0,H2 =P0*N 0,H2 , and then get the air partial pressure P in the containment 0,air =P0-P 0,steam -P 0,H2 ;

[0025] (1-3) According to the ideal gas equation PV = nRT, the mass m of water vapor, air, and hydrogen in the containment at time t0 are obtained respectively. 0,steam 、m 0,H2 、m0,air .

[0026] Furthermore, in the above-mentioned method for quickly calculating the hydrogen concentration after the containment spray is turned on, in step (2), the containment atmospheric pressure prediction relationship is fitted in two steps:

[0027] The first step is fitting, for different initial operating conditions, fitting the corresponding containment atmospheric pressure prediction relationship, where the parameters P1 and r in each relationship are functions of the operating condition parameters initial pressure P0 and decay heat power Q;

[0028] In the second step of fitting, according to the variation characteristics of the parameters P1 and r obtained in the first step of fitting, the following second-order polynomial is used to fit the parameters P1 and r:

[0029] Y=a+b*Q+c*P0+d*Q 2 +e*P0 2 +f*Q*P0

[0030] Where,

[0031] Y is the parameter P1 or r,

[0032] Q is the decay heat power,

[0033] P0 is the initial pressure of the containment atmosphere,

[0034] a, b, c, d, e, and f are polynomial coefficients.

[0035] Furthermore, when the initial working conditions are selected in the first fitting step, the initial pressure P0 is in the range of 0.2-0.6 MPa.a, and the decay heat power Q is in the range of 10-60 MW.

[0036] Furthermore, in the method for quickly calculating the hydrogen concentration after the containment spray is turned on, the calculation of the containment atmosphere state after the spray is turned on for t time in step (3) includes the following steps:

[0037] (3-1) Assume that the water vapor in the containment is saturated after the spray is turned on for t time, and the containment atmosphere temperature is T t According to the thermodynamic properties calculation formula of industrial water and water vapor IAPWS IF-97, the water vapor partial pressure P in the containment is calculated. t,steam ;

[0038] (3-2) The mass of air and hydrogen in the containment does not change. According to the ideal gas state equation PV=nRT, the air partial pressure P at time t is calculated respectively. t,air and hydrogen partial pressure P t,H2 ;

[0039] (3-3) Determine the temperature Tt The sum of the lower containment gas partial pressures P sum =P t,steam +P t,air +P t,H2 and containment atmospheric pressure P t Are they equal? ​​If not, update the atmospheric temperature T. t , return to step (3-1) and recalculate until the iterative calculation converges;

[0040] (3-4) After the calculation converges, according to the partial pressure P of water vapor, air and hydrogen at time t t,steam 、P t,air 、P t,H2 , the hydrogen molar concentration D is calculated by the following formula t,H2 ,

[0041] D t,H2 =P t,H2 / (P t,steam +P t,air +P t,H2 ).

[0042] Furthermore, in the above-mentioned method for quickly calculating the hydrogen concentration after the containment spray is opened, in step (3-3), the atmospheric temperature T is updated according to the following formula: t :

[0043] T t (new) = T t (old)-(P sum -P t ) / 10 5

[0044] Among them, T t (old) is the original atmospheric temperature,

[0045] T t (new) is the updated atmospheric temperature,

[0046] P sum is the temperature T t (old) The sum of the lower containment gas partial pressures,

[0047] P t It is the atmospheric pressure of the containment after the spray is turned on for t time.

[0048] The beneficial effects of the present invention are as follows: The present invention provides a method for calculating the hydrogen concentration after the containment spray is turned on. The method uses the current containment temperature, pressure and hydrogen concentration given by the containment instrument as independent variables, and uses the containment pressure prediction formula obtained by data fitting as a tool to quickly calculate the change in hydrogen concentration in the containment after the containment spray is turned on, thereby realizing rapid prediction of hydrogen risks and providing technical support for operators to mitigate the consequences of nuclear power plant accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a flow chart of the calculation method of the present invention;

[0050] Figure 2 Schematic diagram of atmospheric pressure changes in the containment vessel under typical working conditions in an embodiment of the present invention;

[0051] Figure 3 This is a comparison chart of containment atmospheric pressure results for working condition 1 in an embodiment of the present invention;

[0052] Figure 4 This is a comparison chart of containment atmospheric temperature results for working condition 1 in an embodiment of the present invention;

[0053] Figure 5 This is a comparison chart of the gas component results of working condition 1 in an embodiment of the present invention;

[0054] Figure 6 This is a comparison chart of containment atmospheric pressure results for working condition 2 in an embodiment of the present invention;

[0055] Figure 7 This is a comparison chart of containment atmospheric temperature results for working condition 2 in an embodiment of the present invention;

[0056] Figure 8 This is a comparison chart of the gas component results of working condition 2 in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0058] The input data required by the present invention are:

[0059] 1) Atmospheric pressure P0 before the spray is opened;

[0060] 2) Atmospheric temperature T0 before spraying is turned on;

[0061] 3) Hydrogen molar concentration N before spraying 0,H2 ;

[0062] 4) Free volume of containment;

[0063] 5) Decay heat Q.

[0064] The following assumptions need to be made during the calculation process of this method:

[0065] (1) Assume that the atmosphere in the containment is a uniform mixture of gases, with the same temperature and concentration of each gas component at different locations;

[0066] (2) Assume that the water vapor in the containment is always saturated;

[0067] (3) Assuming that all mixed gases in the containment are ideal gases, the ideal gas state equation can be used to solve the problem;

[0068] (4) Assume that decay heat is used to generate saturated water vapor to be released into the containment;

[0069] (5) Assume that the sprinkler system is turned on and remains on continuously.

[0070] This paper develops a containment pressure prediction equation, uses a data fitting method to predict changes in containment atmospheric pressure, and then provides changes in the containment atmosphere state. The development process of the containment atmospheric pressure prediction equation after the spray system is turned on is as follows:

[0071] An integrated severe accident analysis program was used to calculate the change in containment atmospheric pressure after the sprinkler system was activated under different initial operating conditions. The selected initial operating conditions ranged from pressure (0.2-0.6 MPa.a) to decay heat power (10-60 MW). Figure 2 The calculation results of the containment atmospheric pressure after the spray system is opened are given under the conditions of initial pressure 0.5MPa.a and decay heat power 30MW.

[0072] from Figure 2 It can be seen that after the spray system is turned on, the atmospheric pressure in the containment shows an exponential decrease characteristic. Therefore, the exponential relationship in the form of formula (1) is used to fit the atmospheric pressure in the containment in two steps.

[0073] p t =p1+(p0-p1)e -rt (1)

[0074] Where:

[0075] P t : atmospheric pressure of containment after spraying is started for t time, MPa.a;

[0076] P1: containment atmospheric equilibrium pressure, MPa.a;

[0077] P0: containment atmospheric pressure at the moment of spray opening, MPa.a;

[0078] t: sprinkler system operating time, s;

[0079] r: coefficient of the exponential.

[0080] In the first step of fitting, for each initial operating condition (initial pressure, decay heat power), an exponential relationship of the form of equation (1) is fitted. The parameters P1 and r in each relationship are functions of the operating condition parameters initial pressure P0 and decay heat power Q.

[0081] In the second step of fitting, according to the variation characteristics of the parameters P1 and r obtained in the first step of fitting, a second-order polynomial in the form of formula (2) is used to fit the parameters P1 and r.

[0082] Y=a+b*Q+c*P0+d*Q 2 +e*P0 2 +f*Q*P0 (2)

[0083] Where:

[0084] Y: parameter P1 or r

[0085] Q: decay heat power, MW;

[0086] P0: initial pressure of containment atmosphere, MPa.a;

[0087] a, b, c, d, e, f: polynomial coefficients.

[0088] Taking the independent third-generation nuclear power plant as an example, after fitting calculation, the second-order polynomial coefficients of parameters P1 and r are obtained as shown in Table 1;

[0089] Table 1 Fitting coefficients of parameters P1 and r

[0090]

[0091] Based on the developed containment pressure prediction relationship, the method for quickly calculating the hydrogen concentration after the containment spray is turned on provided by the present invention includes the following steps:

[0092] Step 1: Calculation of containment atmosphere state before containment spraying is started (at time t0):

[0093] (1-1) Assuming that the water vapor in the containment is in a saturated state at time t0, the water vapor partial pressure (saturation pressure) P in the containment is calculated based on the thermodynamic properties of industrial water and water vapor IAPWSIF-97 and the containment temperature T0. 0,steam ;

[0094] (1-2) The containment atmospheric pressure P0 and hydrogen molar concentration N at time t0 are known. 0,H2 , calculate the hydrogen partial pressure P 0,H2=P0*N 0,H2 , and then get the air partial pressure P in the containment 0,air =P0-P 0,steam -P 0,H2 ;

[0095] (1-3) According to the ideal gas equation PV = nRT, the mass m of water vapor, air, and hydrogen in the containment at time t0 are obtained respectively. 0,steam 、m 0,H2 、m 0,air .

[0096] Step 2: Calculation of containment pressure after containment spraying is started for t time:

[0097] Given the containment atmospheric pressure P0 and core decay heat power Q at time t0, the containment atmospheric pressure P at time t can be calculated based on the above-developed containment atmospheric pressure prediction relationship. t .

[0098] Step 3: Calculation of containment atmosphere state after containment spraying is started for time t:

[0099] (3-1) Assume that the water vapor in the containment is saturated after the spray is turned on for t time, and the containment atmosphere temperature is T t According to the thermodynamic properties calculation formula of industrial water and water vapor IAPWSIF-97, the water vapor partial pressure P in the containment is calculated. t,steam ;

[0100] (3-2) The mass of air and hydrogen in the containment does not change. According to the ideal gas state equation PV=nRT, the air partial pressure P at time t is calculated respectively. t,air and hydrogen partial pressure P t,H2 ;

[0101] (3-3) Determine the assumed temperature T t The sum of the lower containment gas partial pressures P sum =P t,steam +P t,air +P t,H2 and containment atmospheric pressure P t If they are not equal, update the atmospheric temperature T according to the following formula: t , return to step (3-1) and recalculate until the iterative calculation converges;

[0102] T t (new) = T t (old)-(P sum -P t ) / 10 5

[0103] Among them, T t(old) is the original atmospheric temperature,

[0104] T t (new) is the updated atmospheric temperature,

[0105] P sum is the temperature T t (old) The sum of the lower containment gas partial pressures,

[0106] P t The atmospheric pressure of the containment after the spray is turned on for t time;

[0107] (3-4) After the calculation converges, according to the partial pressure P of each gas at time t t,steam 、P t,air 、P t,H2 , the hydrogen concentration (molar fraction) D is calculated by the following formula t,H2 .

[0108] D t,H2 =P t,H2 / (P t,steam +P t,air +P t,H2 ).

[0109] By adopting the above steps, the relationship between the containment pressure and the hydrogen concentration changing with time after the containment spraying is started can be obtained.

[0110] The above calculation method was verified using the Severe Accident Integrated Analysis Program. Two different initial containment states were selected as verification conditions. The initial containment states are shown in Table 2. The two different initial containment states represent two different atmospheric conditions.

[0111] Figure 3-Figure 8 The comparison of the results of the following parameters under two working conditions is given respectively:

[0112] 1) Containment atmospheric pressure;

[0113] 2) containment atmosphere temperature;

[0114] 3) Concentrations of atmospheric components, including water vapor, nitrogen, oxygen, and hydrogen.

[0115] It can be seen from the results that the calculation results using the fast calculation method are in good agreement with those calculated using the integrated analysis program.

[0116] Table 2 Initial state of containment

[0117] Calculation conditions Decay heat power / MW Containment atmospheric pressure / MPa Hydrogen molar concentration Working condition 1 50 0.5 0.022313 Working condition 2 30 0.3 0.034578

[0118] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0119] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for quickly calculating the hydrogen concentration after the containment spray is opened, characterized in that: The steps include: (1) Calculate the initial state of the containment at time t0 before the containment spray is opened, including the calculation of the water vapor partial pressure, hydrogen partial pressure, air partial pressure, and the mass of water vapor, air, and hydrogen in the containment; (2) According to the following containment atmospheric pressure prediction relationship, the containment atmospheric pressure P after the spray is opened for t time is calculated. t , p t =p1+(p0-p1)e -rt in, P t is the atmospheric pressure of the containment after the spray is opened for t time, P1 is the containment atmospheric equilibrium pressure, P0 is the atmospheric pressure of the containment when the spray is opened, t is the operating time of the sprinkler system, r is the coefficient of the exponential; (3) Calculating the atmospheric state of the containment vessel after the spray is turned on for a period of time t to obtain the relationship between the atmospheric pressure of the containment vessel and the hydrogen concentration over time, including the following steps: (3-1) Assume that the water vapor in the containment is saturated after the spray is turned on for t time, and the containment atmosphere temperature is T t According to the thermodynamic properties calculation formula of industrial water and water vapor IAPWSIF-97, the water vapor partial pressure P in the containment is calculated. t,steam ; (3-2) The mass of air and hydrogen in the containment does not change. According to the ideal gas state equation PV=nRT, the air partial pressure P at time t is calculated respectively. t,air and hydrogen partial pressure P t,H2 ; (3-3) Determine the temperature T t The sum of the lower containment gas partial pressures P sum =P t,steam +P t,air +P t,H2 and containment atmospheric pressure P t Are they equal? ​​If not, update the atmospheric temperature T. t , return to step (3-1) and recalculate until the iterative calculation converges; (3-4) After the calculation converges, according to the partial pressure P of water vapor, air and hydrogen at time t t,steam 、P t,air 、P t,H2 , the hydrogen molar concentration D is calculated by the following formula t,H2 , D t,H2 =P t,H2 / (P t,steam +P t,air +P t,H2 )。 2. The method for rapidly calculating the hydrogen concentration after the containment spray is opened according to claim 1, characterized in that: The calculation process of this method is based on the following assumptions: Assume that the atmosphere in the containment is a uniform mixture of gases, with the same temperature and concentration of each gas component at different locations; Assume that the water vapor in the containment is always in a saturated state; Assuming that all mixed gases in the containment are ideal gases, the ideal gas state equation can be used to solve the problem; It is assumed that the decay heat is used to generate saturated water vapor to be released into the containment; Assume that once the sprinkler system is turned on, it remains on continuously.

3. The method for rapidly calculating the hydrogen concentration after the containment spray is opened according to claim 1 or 2, characterized in that: The calculation of the initial state of the containment at time t0 before the containment spray is started in step (1) includes the following steps: (1-1) Assuming that the water vapor in the containment is in a saturated state at time t0, the water vapor partial pressure P in the containment is calculated based on the thermodynamic properties of industrial water and water vapor IAPWS IF-97 and the containment temperature T0. 0,steam ; (1-2) According to the containment atmospheric pressure P0 and hydrogen molar concentration N at time t0 0,H2 , calculate the hydrogen partial pressure P 0,H2 =P0*N 0,H2 , and then get the air partial pressure P in the containment 0,air =P0-P 0,steam -P 0,H2 ; (1-3) According to the ideal gas equation PV = nRT, the mass m of water vapor, air, and hydrogen in the containment at time t0 are obtained respectively. 0,steam 、m 0,H2 、m 0,air .

4. The method for rapidly calculating the hydrogen concentration after the containment spray is opened according to claim 1 or 2, characterized in that: In step (2), the containment atmospheric pressure prediction equation is fitted in two steps: The first step is fitting, for different initial operating conditions, fitting the corresponding containment atmospheric pressure prediction relationship, where the parameters P1 and r in each relationship are functions of the operating condition parameters initial pressure P0 and decay heat power Q; In the second step of fitting, according to the variation characteristics of the parameters P1 and r obtained in the first step of fitting, the following second-order polynomial is used to fit the parameters P1 and r: Y=a+b*Q+c*P0+d*Q 2 +e*P0 2 +f*Q*P0 Where, Y is the parameter P1 or r, Q is the decay heat power, P0 is the initial pressure of the containment atmosphere, a, b, c, d, e, and f are polynomial coefficients.

5. The method for rapidly calculating the hydrogen concentration after the containment spray is opened according to claim 4, characterized in that: When the initial working condition is selected in the first step of fitting, the initial pressure P0 is in the range of 0.2-0.6 MPa.a, and the decay heat power Q is in the range of 10-60 MW.

6. The method for rapidly calculating the hydrogen concentration after the containment spray is opened according to claim 1, characterized in that: In step (3-3), the atmospheric temperature T is updated according to the following formula: t : T t (new)=T t (old)-(P sum -P t ) / 10 5 Among them, T t (old) is the original atmospheric temperature, T t (new) is the updated atmospheric temperature, P sum is the temperature T t (old) The sum of the lower containment gas partial pressures, P t It is the atmospheric pressure of the containment after the spray is turned on for t time.

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