| TMSR-SF2 is a SMR version of the experimental prototype SF1.This new reactor plant concept not only combines fluoride salt coolant,ceramic-coated assembly,high operation temperature,low pressure,considerable heat capacity,sufficient safety margins,high burnup pebble bed,on-line refueling and passive decay heat removal system based on natural circulation from FHR,but also brings in many attractive features inspired from the small module idea including simple in design,scale advantage,integration design,modular construction,transportation and assembly,flexible power regulation,commercial rolling development and heat utilization,indicating significent economic and safety advantages over SF1.Due to its innovative and design,it is of great research significance and strategic value to carry out its thermal-hydraulic design and accident analysis.The first part ot this essay proposes the concpetual design of SF2 based on various of investigation results of fluoride salt reactors and small module reactos and accomplishes the thermal hydraulic design process of reactor core by Fluent software,which includes the following key issues:(1)The pressure vessel downcomer and the lower plenum can effectively mitigate the impact of local coolant flow intensity of turbulence to the core contracture.(2)The reflector channels have decreased the total pressure loss in reactor core significantly and the bottom reflector and the inlet baffle aims at the balance of temperature non-uniformity in active zone.(3)The upper reflector and outlet baffle has guaranteed the homogenization degree and temperature uniformity of coolant in the upper plenum.(4)The steady and transient characteristics of pebble bed and TRISO elements have been studied and certain response time is obtained to provide reference for the equivalent process in accident analyze.Moreover,the preliminary calculation of fluoride salt heat exchanger and RVACS is completed by theoretical and empirical equations.The preliminary concept design is then determined by repeated iterations and optimization processes,providing basic parameters for further safety accident analysis.The second part is the safety accident analysis of SF2 accomplished by RELAP software with following sections:(1)The nodalization process is completed and the consistency of modification is verified.(2)The typical accident analysis proves the high degree of safety of SF2 and the excellent complementarity relationship between protection systems and inherent safety.(3)Results indicate that the small module idea has greatly simplified the accident types,accident progresses and physical phenomena.(4)The inherent safety proves its ability to stabilize when faced with temporary disturbances.(5)Moreover,several subsequent events and potential safety strategies have been taken into consideration,which indicates the main circulation pump as an effective method to remit and even eliminate the serious consequences of some beyond design basis accidents has been brought out and verified.The importance of thermal inertia in SF2 is confirmed and its intensify method is also developed.(6)The uncertainty analysis of protection systems is completed and detailed safety requirements for rod dropping delay,rod dropping speed and rod dropping number have been achieved.The RVACS shows its limitation capability in early stages and potential risk in long-term safety with corresponding improvement method developed.(7)The sensitivity analysis of key temperature reactivity feedback coefficients has been completed and the coolant coefficient turns out to be opposite to the thermal inertia.(8)Furthermore,an abnormal reflux and oscillating phenomenon is pointed out because of natural circulation.Finally,the safety features and accident strategy of SF2 is summarized and it proves that the current design of SF2 has satisfied the safety design criteria. |
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