| Small Modular Reactors(SMRs)have been gaining significant attention from the nuclear field due to its flexibility,safety and economical.However,due to the inherent safety characteristics of the integrated design of SMR,the phenomenon and characteristics during the accident process are different from those of the conventional pressurized water reactors(PWRs),therefore its safety needs further analysis and verification.In this thesis,the analysis model of International Reactor Innovative and Secure(IRIS)was developed by RELAP5/MOD3.3 program,the simulation and analysis of several typical loss of coolant accident(LOCA)conditions were carried out,and the thermal hydraulic pernomenon and passive safety charcteristics of the transient process were ananlyzed,based on the calculation results of 2-in.SBLOCA,the preliminary uncertainty analysis was carried out.Firstly,based on the investigation of the status of the SMRs all around the world,and the evaluation of the key models of RELAP5,the RELAP5/ MOD3.3 analysis model of IRIS was established.After the steady state operation,the DVI SB-LOCA transient simulation was carried out,and the important thermal hydraulic parameters and safety characteristics of the transient process of the accidents were analyzed.The simulation results were compared with other simulation results to show the feasibility of the model.And then through the simulation of different conditions,such as 1 in.SBLOCA,0.5 in.SBLOCA and chemical and volume control system(CVCS)SBLOCA,the influence of the safety characteristics of the SMR caused by the differernt sizes and break locations were analyzed,the results showed that the break size decreased,and the minimum core collapse level was delayed by about 600s(1in.)and 1200s(0.5in)respectively.The break location is increased,and the time which converted into two-phase discharge moved up from 1625 s to 410 s.Then,the mitigation ability of the passive safety system of the IRIS were studied through the base case of SBLOCA with the failure of some components,such as SBLOCA with emergency heat removal system(EHRS)failure,SBLOCA with auto depression system(ADS)failure and SBLOCA with emergrncy boration tank(EBT)failure.The analysis of thermal hydraulic processes and phenomena showed that the EHRS was the most important for depression and cooling during the accident conditions..Finally,the uncertainty and sensitivity analysis of the DVI SBLOCA of IRIS were carried out.The uncertainty calculation platform coupled with the RELAP5 thermal hydraulic program and DAKOTA statistical program was established.Then,according to the phenomena identification and ranking table(PIRT)and related literature of IRIS SBLOCA,the important uncertainty input parameters were selected and their distribution of scope and probability were determined.Through the DAKOTA program,the uncertainty input parameters were randomly sampled to obtain different input conditions,and the various conditions were automatically parallelized calculated in the RELAP5 program,and the uncertainty envelope of important parameters was obtained,the results showed that the uncertainty of different input parameters has different effects on the uncertainty envelope of the output parameters at different times.Based on the Spearman rank correlation coefficient,the uncertainty and sensitivity analysis were caried out,and the important influence parameters were obtained,which showed RWST initial temperature is the most important influence parameter.And the influence of each parameter to the minimum core collapse level was quantitatively analyzed,the results showed that the initial temperature change of RWST is ±3.3%,and the minimum core collapse level is(-2.9%,+5.2%)respectively.In this thesis,a variety of typical SBLOCA conditions of the IRIS were simulated,and the uncertainty analysis of the transient simulation results were carried out,providing some references and guidances to the design of SMRs and the application of best estimate plus uncertainty(BEPU)analysis approach. |
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