RELAP5 Numerical Simulation Model Of AP1000 On Small Break LOCAs

As China's first introduction of the third generation ? nuclear power plant,the AP1000 which developed on basis of AP600 employs passive safety features for their outstanding advantage.It is the passive safety features that greatly reduces the possibility of accidents caused by human action and greatly simplifies the design of system,which makes AP1000 more competitive in economy and security.Since the TMI-2 accident,small break loss of coolant accidents(SB-LOCAs)has been more extensively concerned.However,the themal hydraulic phenomena related to SB-LOCAs in AP1000 have not been fully understood and further studies are still needed.The RELAP5 nodes model for whole primary coolant system of AP1000 is established in this paper.DEDVI accident is simulated with conservative parameters and analyzed.The predictions calculated by RELAP5 are compared to the results obtained by NOTRUMP code of Westinghouse.The comparison result shows a good agreement and verifys the accuracy of the model established.Based on the model mentioned,the responses of AP1000 plant to a spectrum of cold leg small break LOCAs are simulated and analyzed,including 2-inch break,4-inch break,6-inch break,8-inch break,10-inch break.Furthermore,the parametric variations and evolution of system under PRHR SB-LOCA condition are analyzed though sensitivity analysis for inputing delay times of CMT;The relaiability of passive safety features is also verified by determining the influence of delay time on evolution of PRHR SB-LOCA scenario and phenomena.The results calculated by RELAP5 and NOTRUMP has good agreement in DEDVI accident,including system pressure,break flow,CMT injection mass flow rate,ACC injection mass flow rate,and so on.RELAP5 can accurately simulate the DEDVI accident.In the cold leg SB-LOCA,evolution of accident scenario is accelerated as the break size increases.However,AP1000 systems could finally achieve safety state n long term cooling as CMT,ACC,IRWST and other passive safety features are put into use.In PRHR SB-LOCA,the accident process behaves more slowly compared to that for DEDVI and cold leg SB-LOCA.What is more,the safety of the reactor could be maintained so long as passive safety system injecte successfully.The results of parameter sensitivity analysis for PRHR SB-LOCA show that the process of accident are delayed due to increasement of delay time,while the core power,system pressure and flow rate are nearly the same.In addition,flow fluctuations that show differences between ADS1-4 and IRWST flow rates become lager as inputing delay time increases.