The Study On The Performance And Applicability Of A Passive Containment Cooling System Based On Open-loop Natural Circulation

The lessons learned from several severe nuclear accidents around the world showed that the active safety system might not be reliable in nuclear power plant.Therefore,in HPR-1000 nuclear system,the passive containment cooling system based on open-loop natural circulation was incorporated.Under such background,different types of natural circulation systems were investigated by using numerical modeling,codes development,theoretical analysis,system codes,severe accident analysis code and possibility safety analysis(PSA)code etc.The operational principles,the performance of different schemes,experimental measurement,two-phase flow instabilities,the configuration method and the reliability of the system were comprehensively studied.Eventually,the applicability of passive containment cooling system based on open-loop natural circulation was evaluated.On the operation modes of natural circulation for the background of passive containment cooling system,the numerical models were set up and house-code was developed for analysis of steady state performance.The performances of open-loop natural circulation system,close-loop two-phase and single-phase natural circulation systems were numerically simulated and compared in different aspects and the recommendation was made by analyzing the results.Among three candidate schemes proposed in this thesis,the overall performance of open-loop natural circulation system took the advantages of that of two close-loop systems.On the scaling analysis and experimental observation of passive containment cooling system,the scaling analysis theory was applied to decide the main criteria and get the scale of the model system.The experimental study was conducted to verify the requirements on the heat removal capacity and flow characteristics.The scale-down of the open-loop natural circulation system was recommended to use identical height,pressure and material scheme.The non-dimensional flashing number was import for the modeling of the long-term characteristics of open-loop natural circulation system.The proper distribution of flow resistance was an easy way to simulate the heat removal capacity of the prototype system with model system.For two typical experimental operation conditions,the model system proposed could supply enough heat removal capacity for two cases.On the two-phase flow instability observed in open-loop natural circulation system,the system code RELAP5 and house code were used to simulate and analyze the phenomena and mechanisms from both time-domain and frequency-domain points of view.The dominated factors which induce flow instability in natural circulation system and the steady operating points of the system were determined through the analysis.On the reliability analysis and the response of the system after postulated accidents,the analysis of different configuration scheme,the system codes such as RELAP5,MELCOR and MAPP were used to evaluate the applicability of the passive containment cooling system for HPR-1000.The capability of the passive containment cooling system to reduce the frequency of core damage and massive release of radioactive materials was studied and analyzed.The capability of the passive containment cooling system in HPR1000 was numerically verified to alleviate the consequences of design basis accident and severe accident scenario.The design function of passive containment cooling system could be guaranteed to limit the pressure and temperature inside the containment after above-mentioned accidents to allowable values.The passive containment cooling system in HPR1000 could supply positive effects to reduce the frequency of core damage and massive release of radioactive materials.