Applicability Research And Application Of The System Safety Analysis Code On Supercritical Water-cooled Reactors And Sodium-cooled Fast Reactors

System safety analysis code is an important tool to perform transientsand accidents safety analysis for reactor systems. Under the context ofglobal R&D upsurge about Generation IV innovative nuclear systems,plenty of work has been done for Gen-IV reactor system codedevelopment. Because light water reactor system codes are well developedwith systematic V&V and extensive application, some of them aremodified for Gen-IV nuclear systems. However, feasibility and realiabilityof these modified codes are still to be further confirmed.This dissertation aims at development, validation and application ofthe system code for Supercritical water-cooled reactor (SCWR) andSodium-cooled fast reactor (SFR). Firstly, assess the applicability of thelight water reactor system code ATHLET for these two reactor types, anddevelop the multi-fluid model for supercritical water and sodium, to obtainthe system code ATHLET-MF (multi-fluid). Secondly, preliminaryverification of the multi-fluid model and validation with the French SFRPHENIX’s natural convection test. Thirdly, application of theATHLET-MF code to safety analysis and safety system designimprovement of the SCWR Fuel Qualification Test (SCWR-FQT) Loop. The main contents of this dissertation include:1. Applicability assessment of the ATHLET code and development ofthe multi-fluid model.(1) Applicability analysis of the ATHLET code forSCWR and SFR.(2) Implementation of property model, heat transfermodel, pressure drop model and critical flow model for supercritical water.(3) Implementation of property model, heat transfer model and pressuredrop model for sodium.(4) Introduction of the multi-fluid generalinterface to integrate code extensions for supercritical water and sodiuminto the multi-fluid model, and obtain the code version ATHLET-MF.2. Preliminary verification and validation of the multi-fluid model ofthe ATHLET-MF code.(1) Validation of the supercritical watermodifications by comparson with analytical calculation and other codes.(2) Validation of the sodium modifications with the SFR PHENIX naturalconvection test. Results show good applicability and accuration of theATHLET-MF code in transient simulation of SCWR and SFR systems.3. Application of the ATHLET-MF code to safety analysis of theSCWR-FQT loop.(1)5types of design basis accidents are simulated,including loss of coolant accident, primary pump seize, loss of power tothe test loop, blockage of any coolant supply line, and coolant bypassingthe test section due to crack in the internal structures of the pressure tube.(2) Improvement of the initial safety system design,2safety signals areadded, and the long term residual heat removal strategy is proposed and itsfeasibility is analyzed.(3) Sensitivity analysis of some design parametersof the safety system, and suggestions to control signal design as well as equipment selection are proposed.This dissertation focuses on development and validation of thesystem safety analysis tool for Gen-IV nuclear systems, mainly for SCWRand SFR, and its engineering application to safety analysis and safetysystem design improvement of the SCWR-FQT loop. The outcomings ofthis dissertation provide safety analysis tools and analysis results fordesign and licensing the SCWR-FQT loop, which give realistic referenceand guidance for the safty system design of the test loop.