| In the 2011 Fukushima accident in Japan,the sation blackout(SBO)caused by the tsunami eventually caused serious consequences such as melting of the core and explosion of hydrogen.After this accident,the passive safety features of nuclear power plants have been valued by countries all over the world.Research institutes in various countries have put forward their own non-competent safety programs.In the passive safety system,the passive waste heat removal system plays the role of finally discharging the core decay heat from the primary circuit to the atmospheric space during serious accidents such as power failure of the whole plant.Among them,the primary loop system is coupled with the passive waste heat removal system multi-system to establish a stable natural cycle to achieve this function.Therefore,studying the full-pressure natural circulation characteristics is the key to designing passive safety systems.To this end,SPIC and China Guangdong Nuclear Power Group built a full-pressure natural circulation test device based on Hualong No.1,which can study the influence of various parameters on the coupling of the primary circuit system and the passive waste heat removal system to establish a multi-system natural circulation And the uncertainty and sensitivity evaluation of the analysis model of the CosSyst system program,one of the neutron programs of COSINE,the first independently developed nuclear power software package in China.In this study,the CosSyst system code was used to physically model the PWR full-pressure natural circulation system,and the calculation results obtained by CosSyst were compared with the test results.Evaluate the accuracy of the CosSyst program’s calculation results for such conditions.Then,based on the successful verification,the uncertainty and sensitivity analysis of the CosSyst program analysis model was carried out within the framework of the best international estimation method plus uncertainty analysis method(Best-Estimate Plus Uncertainty analyses,BEPU).The calculation results of the CosSyst program show that the natural circulation flow rate has little effect under different system pressures.The natural circulation flow rate and the system increase with the increase of power when other conditions remain unchanged.The difference between the calculated result and the test value is less than1%,indicating that the calculated result is accurate and reliable.In transient operating conditions,such as the transient changes in power reduction and pressure reduction,the final state value of the natural circulation flow rate is related to the core power,and is not related to the rate of decrease of the pressure power.The calculation result is in accordance with the test conclusion,and the error from the test value is less than 1%.The CosSyst program has good steady-state and transient analysis capabilities.Based on this,the uncertainty quantification method will be selected within the framework of the BEPU method as a steady-state operating condition and a transient operating condition as the test conditions for uncertainty and sensitivity analysis.Uncertainty and sensitivity analysis results show that the CosSyst calculation result has a small uncertainty band,and the upper and lower limits of the natural circulation flow uncertainty band are divided into 1.32 kg / s ～ 1.42 kg / s.The power of the core,the opening of the regulating valve,the potential difference of the core,the isothermal hydraulic parameters and the structural parameters of the test device have a greater impact on the natural circulation flow,and the temperature of the heat exchange water tank and the ambient temperature also have a greater impact on the system.The wall resistance coefficient also has a certain effect on the natural circulation flow. |
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