Method for analyzing a control rod uncontrolled lifting accident of a reactor

Abstract

The application provides a control rod uncontrolled lifting accident analysis method of a reactor, including providing a first neutron dynamics model, and setting a shutdown protection signal, the shutdown protection signal including an over-power protection signal and a period protection signal; carrying out power spectrum analysis according to the first neutron dynamics model to obtain a transient peak power; obtaining a transient MDNBR based on the transient peak power and initial thermal parameters of the reactor; comparing the transient MDNBR with a safety analysis limit value, if the transient MDNBR is less than or equal to the safety analysis limit value, then carrying out a system optimization operation and returning to carry out the power spectrum analysis until the transient MDNBR is greater than the safety analysis limit value. The application only carries out neutron dynamics calculation and does not carry out thermal flow and heat transfer calculation, the calculation process is the most conservative, for example, if the accident analysis process only carries out a first analysis stage, the analysis process is the most simple, and the work efficiency of the accident analysis can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of nuclear safety, and in particular to a method for analyzing an accident in which a control rod of a reactor is lifted out of control. Background Art

[0002] A reactor control rod uncontrolled lift accident is a key design basis accident. This occurs when the control rod assembly is withdrawn from the reactor due to a malfunction in the control rod control system, a malfunction in the control rod drive mechanism, or human error. This causes the system to continuously introduce excessive positive reactivity into the reactor core, significantly increasing the core's nuclear power. Therefore, an accident safety analysis is required to ensure reactor safety in the event of a zero-power uncontrolled lift accident. However, the safety analysis methods used in related technologies are complex and inefficient in order to ensure accuracy, which cannot guarantee reactor design efficiency. Summary of the Invention

[0003] The present invention provides a method for analyzing an accident of uncontrolled lifting of a control rod of a reactor, which can optimize the analysis process and improve the design efficiency of the reactor.

[0004] In a first aspect, the present application discloses a method for analyzing a runaway control rod lifting accident in a reactor, comprising executing a first analysis phase, the first analysis phase comprising:

[0005] Step A1: providing a first neutron kinetic model and setting a reactor shutdown protection signal; the reactor shutdown protection signal includes an overpower protection signal and a cycle protection signal;

[0006] Step B1: performing power spectrum analysis based on the first neutron kinetic model to obtain transient peak power;

[0007] Step C1: Obtaining the transient MDNBR based on the transient peak power and the initial thermal parameters of the reactor;

[0008] Step D1: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B1 until the transient MDNBR is greater than the safety analysis limit.

[0009] Optionally, further comprising executing a second analysis phase, step D1 further comprises: if the transient MDNBR is less than or equal to the safety analysis limit, performing a system optimization operation and then returning to executing step B1, or executing the second analysis phase;

[0010] The second analysis phase includes:

[0011] Step A2: providing a first coupled computational model, the first coupled computational model including a second thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model;

[0012] Step B2: Set the forced flow rate and perform power spectrum analysis based on the first coupled calculation model to obtain transient thermal parameters;

[0013] Step D2: Obtaining transient MDNBR based on transient thermal parameters;

[0014] Step E2: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B2 until the transient MDNBR is greater than the safety analysis limit.

[0015] Optionally, the second analysis phase also includes:

[0016] Step C2: Verify the conservatism of the forced flow in step B2; Step C2 includes:

[0017] Step C21: providing a natural circulation model;

[0018] Step C22: Based on the transient thermal parameters obtained in step B2, a steady-state natural circulation calculation is performed using a natural circulation model to obtain the maximum natural circulation flow rate under transient conditions;

[0019] Step C23: Check forced flow; if the maximum natural circulation flow ≥ forced flow, or , then adjust the forced flow and return to step B2 until .

[0020] Optionally, step C23 includes:

[0021] , then reduce the forced flow rate and return to step B2;

[0022] If the maximum natural circulation flow rate is greater than or equal to the forced flow rate, increase the forced flow rate and return to step B2.

[0023] Optionally, step D2 includes:

[0024] Based on transient thermal parameters, critical heat flux is obtained;

[0025] Outputting the transient core peak heat flux density through the first coupled calculation model;

[0026] The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

[0027] Optionally, the third analysis phase is further included. Step E2 further includes: if the transient MDNBR is less than or equal to the safety analysis limit, performing system optimization operations and then returning to step B2, or performing the third analysis phase. The third analysis phase includes:

[0028] Step A3: providing a second coupled calculation model, the second coupled calculation model including a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model;

[0029] Step B3: Perform power spectrum analysis based on the second coupled calculation model to obtain transient thermal parameters;

[0030] Step C3: Obtaining transient MDNBR based on transient thermal parameters;

[0031] Step D3: Compare the transient MDNBR with the safety analysis limit; if the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B3 until the transient MDNBR is greater than the safety analysis limit.

[0032] Optionally, step C3 includes:

[0033] Based on the transient thermal parameters in step C3, the critical heat flux is obtained;

[0034] Directly output the transient core peak heat flux density through the second coupled calculation model;

[0035] The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

[0036] Optionally, step B1 includes:

[0037] Step B11: Set the power range for switching the shutdown protection signal.

[0038] Step B12: Perform transient calculation on the power interval when the shutdown protection signal is switched to obtain the power interval when the period protection signal is triggered and the power interval when the overpower protection signal is triggered.

[0039] Step B13: Based on the power interval when the period protection signal is triggered and the power interval when the overpower protection signal is triggered, the power interval when the shutdown protection signal is switched is processed in a refined manner.

[0040] Step B14: Compare the full power range when the trip protection signal is switched and the interval threshold. If the full power range when the trip protection signal is switched is greater than the interval threshold, return to step B12 until the full power range when the trip protection signal is switched is less than or equal to the interval threshold; wherein, the full power range when the trip protection signal is switched = the maximum power interval value when the trip protection signal is switched - the minimum power interval value when the trip protection signal is switched.

[0041] Step B15: Obtain a transient operating condition based on the power range when the shutdown protection signal is switched.

[0042] Optionally, step C1 includes:

[0043] Obtaining the transient core peak heat flux based on the transient peak power;

[0044] Obtain critical heat flux based on initial thermal parameters;

[0045] The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

[0046] Optionally, the system optimization operation includes at least one of the following:

[0047] Reduce the control rod value and reduce the maximum rod lifting rate;

[0048] Added lifting rod locking protection signal;

[0049] Reduce the protection signal setting value;

[0050] Shorten the delay time for implementing the shutdown protection function.

[0051] In a second aspect, the present application discloses a method for analyzing a runaway control rod lifting accident in a reactor, including executing a second analysis phase, which includes:

[0052] Step A2: providing a first coupled computational model, the first coupled computational model including a second thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model;

[0053] Step B2: setting the forced flow rate and performing power spectrum analysis based on the first coupled calculation model to obtain transient operating conditions;

[0054] Step D2: Obtaining transient MDNBR based on transient thermal parameters;

[0055] Step E2: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B2 until the transient MDNBR is greater than the safety analysis limit.

[0056] Optionally, further comprising executing a third analysis phase, step E2 further comprises executing a system optimization operation and then returning to executing step B2 if the transient MDNBR is less than or equal to the safety analysis limit, or executing the third analysis phase;

[0057] The third analysis phase includes:

[0058] Step A3: providing a second coupled calculation model for accident analysis, the second coupled calculation model including a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; and setting a reactor trip protection signal; the reactor trip protection signal including an overpower protection signal and a cycle protection signal;

[0059] Step B3: Perform power spectrum analysis based on the second coupled calculation model to obtain transient thermal parameters;

[0060] Step C3: Obtaining transient MDNBR based on transient thermal parameters;

[0061] Step D3: Compare the transient MDNBR with the safety analysis limit; if MDNBR ≤ the safety analysis limit, perform system optimization operations and return to step B3 until the transient MDNBR > the safety analysis limit.

[0062] In a third aspect, the present application discloses a method for analyzing a runaway control rod lifting accident in a reactor, comprising executing a third analysis phase;

[0063] The third analysis phase includes:

[0064] Step A3: providing a second coupled calculation model, the second coupled calculation model including a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model;

[0065] Step B3: Perform power spectrum analysis based on the second coupled calculation model to obtain transient thermal parameters;

[0066] Step C3: Obtaining transient MDNBR based on transient thermal parameters;

[0067] Step D3: Compare the transient MDNBR with the safety analysis limit; if MDNBR ≤ the safety analysis limit, perform system optimization operations and return to step B3 until the transient MDNBR > the safety analysis limit.

[0068] The beneficial effects of the present invention are as follows:

[0069] The present application discloses a method for analyzing a control rod uncontrolled lifting accident in a reactor, comprising executing a first analysis phase, which includes:

[0070] Step A1: providing a first neutron kinetic model and setting a reactor shutdown protection signal; the reactor shutdown protection signal includes an overpower protection signal and a cycle protection signal;

[0071] Step B1: performing power spectrum analysis based on the first neutron kinetic model to obtain transient peak power;

[0072] Step C1: Obtaining the transient MDNBR based on the transient peak power and the initial thermal parameters of the reactor;

[0073] Step D1: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B1 until the transient MDNBR is greater than the safety analysis limit.

[0074] In the first analysis phase, only neutron dynamics calculations are performed, and no thermal flow and heat transfer calculations are performed. The calculation process is the most conservative. If the accident analysis process only performs the first analysis phase, the analysis process is the most concise, which can greatly improve the work efficiency of accident analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The above features and advantages of the present invention will be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or characteristics may have the same or similar reference numerals.

[0076] Figure 1 It is the accident analysis flow chart of the present invention;

[0077] Figure 2 It is a power spectrum analysis flow chart of the present invention;

[0078] Figure 3 This is a specific example of power spectrum analysis in the first stage of analysis of the present invention;

[0079] Figure 4 This is a forced flow verification flow chart of the present invention;

[0080] Figure 5 It is a flow chart of the system optimization operation of the present invention. DETAILED DESCRIPTION

[0081] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Further details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in various other ways than those described herein. Those skilled in the art may make similar generalizations and deductions based on actual applications without departing from the scope of the present invention. Therefore, the scope of protection of the present invention should not be limited by the contents of this specific embodiment.

[0082] It should be noted that these and other subsequent drawings are only examples and are not drawn to scale, and should not be used to limit the actual scope of protection required by the present invention.

[0083] The following combination Figures 1 to 5 Analysis of the accident analysis method for this application:

[0084] The technical solution of this application is primarily targeted at plate-type fuel pool reactors. The operating mode of plate-type fuel pool reactors includes a natural circulation cooling mode at low power. Therefore, after an accident, the power increases rapidly, but its flow rate gradually increases after passing through the core heating fluid, resulting in an increase in density difference. That is, the increase in flow rate lags behind the power. Therefore, the degree of power (heat flow) increase after the accident and the natural circulation flow rate are the key concerns of this accident. However, due to the large uncertainty in the calculation of natural circulation flow rate, and the fact that natural circulation flow rate also affects the calculation of heat flow, the program needs to be fully verified, which will lead to a cumbersome analysis process and cannot guarantee the design efficiency of the reactor. Therefore, this solution proposes a staged accident analysis method for the reactor, which is detailed as follows:

[0085] Execute the first analysis phase. The first analysis phase only performs neutron dynamics calculations and does not perform thermal flow and heat transfer calculations. The calculation process is the most conservative. If the accident analysis process only performs the first analysis phase, the analysis process is the most concise and can greatly improve the work efficiency of the accident analysis. The first analysis phase includes:

[0086] Step A1: Use the RELAP5 program or other programs as the accident analysis system program, provide the first neutron kinetic model for accident analysis, and set the reactor trip protection signal. RELAP5 is a one-dimensional system safety analysis program, a specialized computational tool for simulating and analyzing the thermodynamic behavior and reactor dynamics of nuclear power plants. RELAP5 simulates the flow and heat transfer of fluids such as coolant and steam within nuclear equipment, as well as the nuclear reaction processes in the core. The reactor trip protection signals include an overpower protection signal and a periodic protection signal. The overpower protection signal is used to protect against excessive neutron flux, while the periodic protection signal is used to protect against excessively rapid power increases. The neutron kinetic model is used to calculate post-accident power changes. After an accident, control rods are raised, introducing positive reactivity and increasing power. When the trip protection signal is reached, a trip is triggered, the control rods are lowered, introducing negative reactivity and decreasing power. This calculation process can be completed using the RELAP5 program.

[0087] Step B1: Perform power spectrum analysis on the trip protection signal according to the first neutron kinetic model to obtain the transient peak power during the accident transient process. Step B1 is as follows: Figure 2 and Figure 3 As shown, the details are as follows:

[0088] Step B11: Set the power range when the shutdown protection signal switches; the shutdown protection signal switching is the mutual switching between the overpower protection signal and the periodic protection signal. For example, the power range when the shutdown protection signal switches is 10 -9 FP~10 -5 FP, which is 10 -9 ~10 -5times the rated power, for example, if the reactor rated power is 100MW, then 10 -9 times the rated power is 0.1W;

[0089] Step B12: Perform transient calculation on the power range when the shutdown protection signal is switched based on the first neutron kinetic model to obtain the power range when the periodic protection signal is triggered and the power range when the overpower protection signal is triggered; wherein the power range when the periodic protection signal is triggered and the power range when the overpower protection signal is triggered are both within the power range when the shutdown protection signal is switched. For example, for the rated power 10 when the shutdown protection signal is switched, -9 FP, 10 -8 FP, 10 -7 FP, 10 - 6 FP, 10 -5 FP separately carries out transient calculation to determine the power range when the period protection signal is triggered. -9 FP~10 -8 FP, power range when over power protection signal is triggered 10 -7 FP~10 -5 FP.

[0090] Step B13: Based on the power interval when the periodic protection signal is triggered and the power interval when the overpower protection signal is triggered, the power interval when the shutdown protection signal is switched is refined. The power interval when the shutdown protection signal is switched will be reduced after the refined processing. For example, based on the power interval 10 when the periodic protection signal is triggered, -9 FP~10 -8 FP, power range when over power protection signal is triggered 10 -7 FP~10 -5 FP, power range when the shutdown protection signal switches 10 -9 FP~10 - 5 After FP is refined, the power range when the shutdown protection signal is switched is reduced to 10 -8 FP~10 -7 FP; It can be seen that after the refined processing, the power interval when the stack protection signal switches is between the power interval when the periodic protection signal is triggered and the power interval when the overpower protection signal is triggered, and the minimum value of the power interval when the shutdown protection signal switches is the maximum value of the power interval when the periodic protection signal is triggered. -8 FP, the maximum value of the power range when the shutdown protection signal switches is the minimum value of the power range when the overpower protection signal is triggered. -7 FP.

[0091] Step B14: compare the power full range at the trip protection signal switching time with the interval threshold value, if the power full range at the trip protection signal switching time ≤ the interval threshold value, continue step B15, if the power full range at the trip protection signal switching time > the interval threshold value, return to step B12 until the power full range at the trip protection signal switching time ≤ the interval threshold value. The power full range at the trip protection signal switching time = the power interval maximum value at the trip protection signal switching time - the power interval minimum value at the trip protection signal switching time.

[0092] Specifically, as shown in Figure 2 and Figure 3 , since the transient calculation cannot be infinitely fine, the interval threshold value can be used to control the fineness of the transient calculation result, for example, the interval threshold value is set to 10 -8 FP; after the fine processing in step B13, the power interval at the trip protection signal switching time is 10 -8 FP~10 -7 FP, the power full range at the trip protection signal switching time = 10 -7 FP-10 -8 FP=9×10 -8 FP, the power full range at the trip protection signal switching time is 9×10 -8 FP> the interval threshold value 10 -8 FP; return to step B12 to continue the fine processing of the power interval 10 -8 FP~10 -7 FP at the trip protection signal switching time (for example, the rated power 10 -8 FP, 2×10 -8 FP, 3×10 -8 FP,... 10 -7 FP respectively), to obtain the power interval 10 -8 FP~5×10 -8 FP at the periodic protection signal triggering time, the power interval 6×10 - 8 FP~10 -7 FP; then perform step B13, based on the power interval 10 -8 FP~5×10 -8 FP at the periodic protection signal triggering time, the power interval 6×10 -8 FP~10 -7 FP, the fine processing of the power interval 10 -8 FP~10 -7 FP at the trip protection signal switching time, to reduce the power interval at the trip protection signal switching time to 5×10 -8 FP~6×10 -8FP; After refined processing, the power range when the shutdown protection signal switches is 6×10 -8 -5×10 -8 =10 -8 FP, the power range when the shutdown protection signal switches is 10 -8 FP=interval threshold 10 -8 FP, proceed to step B15.

[0093] Step B15: Obtain the transient operating condition based on the power interval when the shutdown protection signal switches. Specifically, select the lower power in the power interval when the shutdown protection signal switches as the initial power of the transient operating condition, and do not trust the short-period signal to obtain a reasonable and conservative transient operating condition; for example, select the power interval 5×10 -8 FP~6×10 -8 Minimum value in FP 5×10 -8 FP is the transient initial power of the transient condition. In the transient calculation, the periodic protection is not considered and only the overpower protection is used. Then, during the transient process of the accident, the initial power of the transient condition is 5×10 -8 The maximum power to which FP can be increased is taken as the transient peak power of the transient condition. The transient initial power and the transient peak power of the transient condition are both determined. The transient peak power of the transient condition obtained in this way is the largest and most conservative.

[0094] Step C1: Based on the transient peak power and the initial thermal parameters of the reactor, obtain the transient MDNBR corresponding to the first analysis stage, including:

[0095] The transient core peak heat flux is obtained based on the transient peak power. In actual accidents, the heat flux is lower than the power. However, since only neutron dynamics calculations were performed in the first analysis phase, a conservative assumption was made that the transient heat flux and power change synchronously. Based on the influence of core structural parameters, core axial power distribution, and radial power peaking factor, a conservative assumption was made that the transient core peak heat flux / reactor initial heat flux = transient peak power / reactor initial power.

[0096] The critical heat flux is obtained based on the initial thermal parameters. Specifically, the core inlet parameters remain essentially unchanged, and no thermal transmission calculations are performed in this phase. Therefore, in the first analysis phase, the initial thermal parameters can be used, conservatively assuming the core flow velocity is zero. These initial thermal parameters are substituted into the zero-flow CHF relationship to calculate the critical heat flux. The zero-flow CHF relationship can be constructed using, for example, the SUDO zero-flow relationship.

[0097] The MDNBR in the transient is obtained based on the peak heat flux density in the core in the transient and the critical heat flux density, wherein the DNBR (Departure from Nucleate Boiling Ratio) is a core departure from nucleate boiling ratio, and the MDNBR is a minimum core departure from nucleate boiling ratio. Specifically, the MDNBR in the transient satisfies:

[0098] .

[0099] Step D1: verifying whether the MDNBR in the transient corresponding to the first analysis stage satisfies the acceptance criterion, comprising:

[0100] comparing the MDNBR in the transient with a safety analysis limit value, the safety analysis limit value being a safety limit value specified in the DNBR acceptance criterion, the DNBR acceptance criterion being a safety criterion for preventing the fuel element from departing from nucleate boiling in the reactor thermal hydraulic design, and the safety analysis limit value being a number greater than 1, such as 1.3, 1.5, etc. If the MDNBR in the transient > the safety analysis limit value, the acceptance criterion is satisfied, and the accident analysis is ended; if the MDNBR in the transient ≤ the safety analysis limit value, a system optimization operation is performed, and then step B1 is executed, or a second analysis stage is executed until the MDNBR in the transient > the safety analysis limit value. The system optimization operation comprises at least one of the following:

[0101] reducing the control rod value and reducing the maximum rod withdrawal rate to minimize the post-accident reactivity introduction rate under the premise of meeting the reactor power regulation requirement;

[0102] increasing the rod withdrawal lockout protection signal, including setting the maximum one-time continuous rod withdrawal distance and the rod withdrawal lockout setting value lower than the shutdown setting value;

[0103] minimizing the protection signal setting value under the premise of meeting the operation band to trigger the shutdown protection as soon as possible after the accident;

[0104] optimizing the protection logic, instrument equipment, etc. to shorten the delay time for realizing the shutdown protection function;

[0105] limiting the one-time rod withdrawal distance under the premise that the rod control system meets the normal power increase requirement;

[0106] optimizing the loop structure of the natural circulation model to reduce the loop resistance of the natural circulation model.

[0107] The system optimization operation is an optimization design in the common accident analysis process, which is not described in detail here.

[0108] The second analysis stage is performed, compared with the first analysis stage, the neutron kinetics calculation and the thermal hydraulic calculation are carried out simultaneously in the second analysis stage, and the reactivity feedback in the transient condition is considered, which is equivalent to considering the phenomenon that the peak heat flux density of the reactor core after the accident / the initial heat flux density of the reactor < the peak power of the transient / the initial power of the reactor, which releases the conservatism in the first analysis stage that the peak heat flux density of the reactor core after the accident / the initial heat flux density of the reactor = the peak power of the transient / the initial power of the reactor, so that the conservative margin can be released, and the accuracy of the MDNBR in the transient is higher, specifically, the second analysis stage includes:

[0109] Step A2: providing a first coupled calculation model for accident analysis, the first coupled calculation model comprising a second thermal hydraulic model, a reactor core thermal component model and a second neutron kinetics model. Wherein, the second thermal hydraulic model, the reactor core thermal component model and the second neutron kinetics model have a coupling relationship; the second thermal hydraulic model is a fixed flow boundary model with forced flow; the reactor core thermal component model can cooperate with the second neutron kinetics model and the second thermal hydraulic model to calculate to obtain the change of the fluid parameter in the transient, the peak heat flux density of the reactor core in the transient; the second neutron kinetics model contains reactivity feedback, which can affect the calculation of the peak power in the transient.

[0110] Step B2: setting forced flow in the second thermal hydraulic model, and under the forced flow set in the second thermal hydraulic model, performing power spectrum analysis on the shutdown protection signal according to the first coupled calculation model comprising the second thermal hydraulic model, the reactor core thermal component model and the second neutron kinetics model, to determine the transient condition in the accident transient process, and then obtain the transient thermal parameter corresponding to the transient condition.

[0111] Wherein, the power spectrum analysis in step B2 can be performed according to step B1, specifically including:

[0112] Step B21: setting the power interval when the shutdown protection signal switches;

[0113] Step B22: first, under the set forced flow, combining the first coupled calculation model, performing transient calculation on the power interval when the shutdown protection signal switches, to obtain the power interval when the cycle protection signal triggers, the power interval when the over-power protection signal triggers;

[0114] Step B23: based on the power interval when the cycle protection signal triggers, the power interval when the over-power protection signal triggers, finely processing the power interval when the shutdown protection signal switches;

[0115] Step B24: Compare the full power range when the trip protection signal is switched with the interval threshold. If the full power range when the trip protection signal is switched is less than or equal to the interval threshold, proceed to step B25. If the full power range when the trip protection signal is switched is greater than the interval threshold, return to step B22 until the full power range when the trip protection signal is switched is less than or equal to the interval threshold.

[0116] Step B25: Obtain a transient operating condition based on the power range when the shutdown protection signal is switched.

[0117] The transient operating condition obtained in step B2 is similar to the transient operating condition obtained in step B1. The two can be the same or different. For example, in the transient operating condition obtained in step B2, the initial power is 5.2×10 -8 FP, peak power is the initial power 5.2×10 -8 The maximum power that FP can reach during an accident transient is provided here for illustrative purposes only. The specific power is subject to calculation results and is not detailed here. Transient thermal parameters include transient power, transient heat flux, transient temperature, and transient pressure. The set forced flow rate affects the final results of these transient thermal parameters.

[0118] Step C2: Verify the conservatism of the forced flow in step B2. Specifically include:

[0119] Step C21: Provide a natural circulation model for analyzing forced flow.

[0120] Step C22: Based on the transient peak power of the transient thermal parameters obtained in step B2, a steady-state natural circulation calculation is performed using a natural circulation model to obtain the maximum natural circulation flow rate under the accident transient condition.

[0121] Step C23: Check the forced flow rate.

[0122] like ; The maximum natural circulation flow is much smaller than the forced flow, and the set forced flow is too conservative, so the forced flow is reduced to release the margin and return to step B2; wherein, the flow conservative threshold is used to control the conservative degree of the forced flow, and the flow conservative threshold can be taken as 20%.

[0123] If the maximum natural circulation flow rate is greater than or equal to the forced flow rate, the set forced flow rate is not conservative, and the forced flow rate is increased to release the margin, and the process returns to step B2.

[0124] like ; The set forced flow is conservative, then the conservative verification of the forced flow is completed and the process goes to step D2.

[0125] Step D2: Based on the transient thermal parameters, obtain the transient MDNBR corresponding to the second analysis stage, including:

[0126] The critical heat flux is obtained based on the transient thermal parameters of the verified forced flow rate in step C2. Specifically, the core flow rate can be conservatively assumed to be zero. The transient thermal parameters of the verified forced flow rate are substituted into the zero-flow CHF relationship constructed using the SUDO zero-flow relationship, etc., to calculate the critical heat flux.

[0127] The first coupled calculation model directly outputs the transient core peak heat flux density. Specifically, the first coupled calculation model performs calculations to output a transformation curve for the transient core peak heat flux density. The transient core peak heat flux density obtained in the second analysis phase is smaller than that obtained in the first analysis phase, but still greater than the actual core peak heat flux density, indicating that the result is conservative.

[0128] The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state, that is,

[0129] .

[0130] Step E2: Verify whether the transient MDNBR corresponding to the second analysis phase meets the acceptance criteria, including:

[0131] Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is greater than the safety analysis limit, the acceptance criteria are met and the accident analysis ends. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B2, or execute the third analysis phase until the transient MDNBR is greater than the safety analysis limit.

[0132] The third analysis phase is executed. Natural circulation calculations are performed in the third analysis phase, and the critical heat flux density under natural circulation flow is considered. This further releases the conservative margin in transient heat flux and critical heat flux calculations. The obtained transient MDNBR is more accurate. Specifically, the third analysis phase includes:

[0133] Step A3: Provide a second coupled computational model for accident analysis. This second coupled computational model includes a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model. The third thermal-hydraulic model includes a natural circulation loop. Loop resistance affects the natural circulation flow rate. A greater loop resistance results in a smaller natural circulation flow rate and, consequently, a poorer ability to remove core heat. Loop resistance can be determined using reliable methods such as empirical formulas, computational fluid dynamics (CFD), or hydraulic testing, and will not be detailed here.

[0134] Step B3: Perform power spectrum analysis on the shutdown protection signal according to the second coupling calculation model to determine the transient operating conditions during the accident transient process, and then obtain the transient thermal parameters corresponding to the transient operating conditions. The power spectrum analysis in step B3 can be performed with reference to step B1; specifically, first, combine the second coupling calculation model to perform transient calculation on the initial power interval when the shutdown protection signal switches, and finally determine the power interval when the shutdown protection signal switches, and then obtain the transient operating conditions based on the power interval when the shutdown protection signal switches. The transient operating conditions obtained in step B3 can be the same as or different from the transient operating conditions obtained in step B1. For example, in the transient operating conditions obtained in step B3, the initial power is 5.3×10 - 8 FP, peak power is the initial power 5.3×10 -8 The maximum power to which FP can be increased during the transient process of an accident.

[0135] Step C3: Obtaining the transient MDNBR corresponding to the third analysis stage based on the transient thermal parameters, including:

[0136] Based on the transient thermal parameters in step C3, the parameters are substituted into the zero flow CHF relationship formed by the SUDO zero flow relationship and the like to perform calculations, thereby obtaining the critical heat flux.

[0137] The second coupled calculation model directly outputs the transient core peak heat flux. Specifically, the second coupled calculation model performs calculations to output a transformation curve for the transient core peak heat flux. The transient core peak heat flux obtained in the third analysis phase is smaller than that obtained in the second analysis phase.

[0138] The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state, that is,

[0139] .

[0140] Step D3: Verify whether the transient MDNBR corresponding to the third analysis stage meets the acceptance criteria, including:

[0141] Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is greater than the safety analysis limit, the acceptance criteria are met and the accident analysis ends. If the MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B3 until the transient MDNBR is greater than the safety analysis limit.

[0142] In summary, this scheme proposes a staged accident analysis method for plate fuel pool reactors. Specifically, in the first analysis stage, only neutron dynamics calculations are carried out, avoiding the calculation of natural circulation flow and heat flux. It is conservatively assumed that transient peak power / reactor initial power = core transient peak heat flux density / reactor initial heat flux density. At the same time, it is conservatively considered that heat flux and power change synchronously in the transient state. The analysis process is the simplest and can greatly improve the work efficiency of accident analysis. In the second analysis stage, the first coupled calculation model including the second thermal-hydraulic model, the core thermal component model and the second neutron dynamics model is adopted. Compared with the first analysis stage, the verification of forced flow and the acquisition of transient thermal parameters are added, which can release the conservative margin and improve the work efficiency to a certain extent. In the third analysis stage, the natural circulation flow is calculated to further release the conservative margin.

[0143] In the accident analysis method of the present application, the first analysis stage to the third analysis stage can not only independently complete the analysis of the accident, but also progressively complete the analysis of the accident stage by stage. For example, the first analysis stage to the second analysis stage are sequentially executed to complete the analysis of the accident, or the second analysis stage to the third analysis stage are sequentially executed to complete the analysis of the accident, or the first analysis stage to the third analysis stage are sequentially executed to complete the analysis of the accident. For the accident analysis that is completed step by step from the first analysis stage to the third analysis stage, if the rod-related design requirements in the reactor design are not high, the conservative use of the first analysis stage can also pass the acceptance of the MDNBR in the transient state, which greatly improves the design efficiency; if the first analysis stage cannot pass the acceptance of the MDNBR in the transient state, further system optimization operations can be carried out or the second analysis stage can be entered to release the margin, which can also relatively improve a certain efficiency; if the second analysis stage cannot pass the acceptance of the MDNBR in the transient state, further system optimization operations can be carried out or the third analysis stage can be entered to release the margin, and the third analysis stage requires additional natural circulation simulation verification work; if the third analysis stage cannot pass the acceptance of the MDNBR in the transient state, further system optimization operations can be carried out until the acceptance of the MDNBR in the transient state is achieved.

[0144] In summary, by analyzing the accident in a progressive stage-by-stage manner, while ensuring the accuracy of the accident analysis, the analysis process can be simplified and redundant steps can be reduced, thereby ensuring the design efficiency of the reactor.

[0145] Although the present invention is disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for analyzing an uncontrolled lifting accident of a control rod in a reactor, characterized in that: The method includes performing a first analysis phase, wherein the first analysis phase includes: Step A1: providing a first neutron kinetic model for accident analysis and setting a reactor trip protection signal; the reactor trip protection signal includes an overpower protection signal and a cycle protection signal; Step B1: performing power spectrum analysis on the trip protection signal according to the first neutron kinetic model to obtain transient peak power during the accident transient process; Step B1 includes: Step B11: setting the power range for switching the shutdown protection signal; Step B12: performing transient calculation on the power range when the trip protection signal is switched according to the first neutron kinetic model to obtain the power range when the periodic protection signal is triggered and the power range when the overpower protection signal is triggered; Step B13: Based on the power interval when the period protection signal is triggered and the power interval when the overpower protection signal is triggered, finely processing the power interval when the shutdown protection signal is switched; Step B14: Compare the full power range when the trip protection signal is switched with the interval threshold. If the full power range when the trip protection signal is switched is greater than the interval threshold, return to step B12 until the full power range when the trip protection signal is switched is less than or equal to the interval threshold. Here, the full power range when the trip protection signal is switched = the maximum power interval value when the trip protection signal is switched - the minimum power interval value when the trip protection signal is switched. Step B15: obtaining a transient operating condition based on the power range when the shutdown protection signal is switched; Step C1: Obtaining the transient MDNBR based on the transient peak power and the initial thermal parameters of the reactor; Step D1: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and then return to step B1 until the transient MDNBR is greater than or equal to the safety analysis limit, wherein the safety analysis limit is greater than 1.

2. The accident analysis method according to claim 1, characterized in that: It also includes executing the second analysis phase, and the step D1 further includes: if the MDNBR in the transient state is less than or equal to the safety analysis limit, then executing the system optimization operation and then returning to executing step B1, or executing the second analysis phase; The second analysis phase includes: Step A2: providing a first coupled computational model for accident analysis, the first coupled computational model including a second thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; Step B2: setting a forced flow rate in the second thermal-hydraulic model, and performing a power spectrum analysis on the trip protection signal according to the first coupled calculation model to obtain transient thermal parameters during the accident transient process; Step D2: obtaining the transient MDNBR based on the transient thermal parameters; Step E2: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B2 until the transient MDNBR is greater than or equal to the safety analysis limit.

3. The accident analysis method according to claim 2, characterized in that: The second analysis phase also includes: Step C2: Verify the conservatism of the forced flow in step B2; Step C2 includes: Step C21: providing a natural circulation model for analyzing forced flow; Step C22: Perform steady-state natural circulation calculations on the transient thermal parameters obtained in step B2 according to the natural circulation model to obtain the maximum natural circulation flow rate under the accident transient condition; Step C23: Check forced flow; if the maximum natural circulation flow ≥ forced flow, or , then adjust the forced flow and return to step B2 until .

4. The accident analysis method according to claim 3, characterized in that: The step C23 includes: , then reduce the forced flow rate and return to step B2; If the maximum natural circulation flow rate is greater than or equal to the forced flow rate, increase the forced flow rate and return to step B2.

5. The accident analysis method according to claim 3, characterized in that: The step D2 comprises: Based on transient thermal parameters, critical heat flux is obtained; Outputting the transient core peak heat flux density through the first coupled calculation model; The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

6. The accident analysis method according to claim 2, characterized in that: The method further includes executing a third analysis phase, wherein step E2 further includes: if the transient MDNBR is less than or equal to the safety analysis limit, performing system optimization operations and then returning to step B2, or executing the third analysis phase; the third analysis phase includes: Step A3: providing a second coupled computational model for accident analysis, the second coupled computational model including a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; Step B3: performing power spectrum analysis on the trip protection signal according to the second coupling calculation model to obtain transient thermal parameters during the transient accident process; Step C3: Obtaining transient MDNBR based on transient thermal parameters; Step D3: Compare the transient MDNBR with the safety analysis limit; if the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B3 until the transient MDNBR is greater than the safety analysis limit.

7. The accident analysis method according to claim 6, characterized in that: The step C3 comprises: Based on the transient thermal parameters in step C3, the critical heat flux is obtained; Outputting the core peak heat flux density in transient state through the second coupled calculation model; The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

8. The accident analysis method according to claim 1, characterized in that: The step C1 comprises: Obtaining the transient core peak heat flux based on the transient peak power; Obtain critical heat flux based on initial thermal parameters; The transient MDNBR is obtained based on the core peak heat flux and critical heat flux in the transient state.

9. The accident analysis method according to claim 1, characterized in that: System optimization operations include at least one of the following: Reduce the control rod value and reduce the maximum rod lifting rate; Added lifting rod locking protection signal; Reduce the setting value of the reactor protection signal; Shorten the delay time for implementing the shutdown protection function.

10. A method for analyzing an uncontrolled lifting accident of a control rod in a reactor, characterized in that: The method includes performing a second analysis phase, wherein the second analysis phase includes: Step A2: providing a first coupled computational model for accident analysis and setting a reactor trip protection signal; the reactor trip protection signal includes an overpower protection signal and a cycle protection signal; wherein the first coupled computational model includes a second thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; Step B2: setting a forced flow rate and performing a power spectrum analysis on the trip protection signal according to the first coupling calculation model to obtain a transient operating condition; Step B2 includes: Step B21: setting the power range for switching the shutdown protection signal; Step B22: Under the set forced flow rate and in combination with the first coupled calculation model, perform transient calculation on the power range when the trip protection signal is switched to obtain the power range when the period protection signal is triggered and the power range when the overpower protection signal is triggered; Step B23: Based on the power interval when the period protection signal is triggered and the power interval when the overpower protection signal is triggered, the power interval when the shutdown protection signal is switched is processed in a refined manner; Step B24: Compare the full power range when the trip protection signal is switched with the interval threshold. If the full power range when the trip protection signal is switched is greater than the interval threshold, return to step B22 until the full power range when the trip protection signal is switched is less than or equal to the interval threshold. Here, the full power range when the trip protection signal is switched = the maximum power interval value when the trip protection signal is switched - the minimum power interval value when the trip protection signal is switched. Step B25: obtaining a transient operating condition based on the power range when the shutdown protection signal is switched; Step D2: Obtaining transient MDNBR based on transient thermal parameters; Step E2: Compare the transient MDNBR with the safety analysis limit. If the transient MDNBR is less than or equal to the safety analysis limit, perform system optimization and return to step B2 until the transient MDNBR is greater than the safety analysis limit.

11. The accident analysis method according to claim 10, characterized in that: It also includes executing the third analysis phase, and the step E2 further includes executing the system optimization operation and returning to the step B2 if the transient MDNBR is less than or equal to the safety analysis limit, or executing the third analysis phase; The third analysis phase includes: Step A3: providing a second coupled computational model for accident analysis and setting a reactor trip protection signal; the reactor trip protection signal includes an overpower protection signal and a cycle protection signal; wherein the second coupled computational model includes a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; Step B3: performing power spectrum analysis on the trip protection signal according to the second coupling calculation model to obtain transient thermal parameters; Step C3: Obtaining transient MDNBR based on transient thermal parameters; Step D3: Compare the transient MDNBR with the safety analysis limit; if MDNBR ≤ the safety analysis limit, perform system optimization operations and return to step B3 until the transient MDNBR > the safety analysis limit.

12. A method for analyzing an uncontrolled lifting accident of a control rod in a reactor, characterized in that: This includes conducting the third phase of analysis; The third analysis phase includes: Step A3: providing a second coupled computational model for accident analysis and setting a reactor trip protection signal; the reactor trip protection signal includes an overpower protection signal and a cycle protection signal; wherein the second coupled computational model includes a third thermal-hydraulic model, a core thermal component model, and a second neutron kinetic model; Step B3: performing power spectrum analysis on the trip protection signal according to the second coupling calculation model to obtain transient thermal parameters. Step B3 includes: Step B31: setting the power range for switching the shutdown protection signal; Step B32: In combination with the second coupled calculation model, performing transient calculation on the power range when the trip protection signal switches to obtain the power range when the period protection signal is triggered and the power range when the overpower protection signal is triggered; the trip protection signal includes the overpower protection signal and the period protection signal; Step B33: Based on the power interval when the period protection signal is triggered and the power interval when the overpower protection signal is triggered, finely processing the power interval when the shutdown protection signal is switched; Step B34: Compare the full power range when the trip protection signal is switched with the interval threshold. If the full power range when the trip protection signal is switched is greater than the interval threshold, return to step B32 until the full power range when the trip protection signal is switched is less than or equal to the interval threshold. Here, the full power range when the trip protection signal is switched = the maximum power interval value when the trip protection signal is switched - the minimum power interval value when the trip protection signal is switched. Step B35: obtaining a transient operating condition based on the power range when the shutdown protection signal is switched; Step C3: Obtaining transient MDNBR based on transient thermal parameters; Step D3: Compare the transient MDNBR with the safety analysis limit; if MDNBR ≤ the safety analysis limit, perform system optimization operations and return to step B3 until the transient MDNBR > the safety analysis limit.

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