Analyses Of Small Modular Reactor Loaded Accident Tolerant Fuel

The Fukushima nuclear accident made researchers from all over the world pay more attention to the safety of nuclear power plants.In order to reduce the heat load of the reactor,changing the traditional pressurized water reactor to the Small Modular Reactors（SMR）is a solution to improve safety.The small modular reactor has the advantages of small footprint,high inherent safety,flexible assembly and disassembly,and suitable for deployment and power generation of small and medium power grids.Compared with the fourth generation of new nuclear reactors,small modular PWRs are technically mature,economically feasible,and promising in terms of application prospects.In addition,the Accident Tolerant Fuel（ATF）can also effectively improve the safety of nuclear plants.It can make the fuel rod cladding withstand longer or better contain radioactive fission products and prolong the cooling failure time of the core in the accident.At present,although there are some research results about SMR or ATF,and there are also studies that apply ATF to SMR,the comprehensive analysis of SMR loaded with ATF is not much.In this article,Nu Scale,a SMR developed by Nu Scale Power,was selected as the research object.From the four aspects of reactor physical analysis,fuel performance analysis,thermal-hydraulic analysis of sub-channel and system,the safety of Nu Scale loaded with ATF was studied under accidents.Two kinds of ATF pellet materials U₃Si₅,U₃Si₂ and two kinds of ATF cladding materials Fe Cr Al,Si C/Si C composite were selected as the study objects of the Nu Scale.The research results show that the lifetime of Nu Scale has been proven to be satisfied by 4%low-enriched uranium.Due to the excellent safety performance of Nu Scale,both traditional fuel and ATF can ensure the safety of the reactor under REA.Then,Thorium-uranium mixed fuel Th_0.923U_0.077O₂ and two-layer Si C cladding ATF system was used to study the thermal hydraulic analysis of system and fuel performance analyses of Nu Scale under SGTR and on this basis,the other safety system failure without responding of operators.The research results show that the initial coolant and cladding temperature of the two fuel systems are basically the same,but the initial pellet temperature of the ATF system is143K lower than that of the traditional fuel system.The trend temperature of the coolant,pellet and cladding curve of the two fuel systems was basically the same.ATF can prolong the safety time under SGTR by 8s.Due to the superior performance of ATF,the gap of ATF system did not narrow significantly during the simulation.From the stress and strain failure criteria of the cladding,ATF system can extend the safety time by 17 seconds compared with the traditional fuel system.