Accident Analysis Of The High Temperature And High Pressure Loop In The Reactor

The localization of fuel components is an important condition for the independent production and export of nuclear plants in China.The design and manufacture of new fuel elements requires an irradiation test,and the fuel test loop based on research reactors can provide an irradiation test platform that simulates the real pressurized water reactor thermal-hydraulic environment.The high-pressure and high-temperature coolant flows in the pipes of main loop when the fuel test loop runs with a high fission power.Once an accident occurs,high-temperature and high-pressure coolant will spew out,accompanied by a large amount of radioactive material leakage.Therefore,an accident analysis must be performed at the time of design to verify the safety of the design.Based on the primary design of the fuel test loop in the CMRR reactor,this paper uses RELAP5 to build a model and adjust the steady-state operation to match the design parameters.The results show that the operating parameters of the RELAP5 model of the loop design scheme are basically consistent with the design values,which meet the requirements of transient calculation.On this basis,three typical accidents are calculated respectively:1.Loss-of-flow accident:The main loop consists of one circuit.Therefore,two typical accidents,total loss-of-flow accident and clamp shaft accident,are selected,and comparative analysis is carried out.The results are checked according to the safety criteria.2.Loss-of-coolant accident:In this paper,the small-break loss-of-coolant accident of the test circuit is analyzed,which includes the cold/hot leg accidents and the sensitivity analysis of the fracture size.Later,the inner pressure tube rupture accident with greater influence on the research reactor is also calculated.The calculation results are as follows:The pressure of the clamp shaft accident/total loss-of-flow accident is smaller than 110%design value,the cladding temperature in the clamp shaft accident is 734.1? which is lower than 1482?,and the MDNBR during the loss-of-flow accident is greater than 1.5,which means there is no nucleate boiling on the surface of the fuel rods.In the cold/hot leg loss-of-coolant accident,the peak cladding temperature is 880.60C and 367.6 ? respectively,which is below the limit temperature of 1204 ?.The loop safety can be ensured for small-break loss-of-coolant accidents with different break size.There is no significant change in the reactor coolant temperature and the argon gap pressure.In the inner pressure tube rupture accident,the peak cladding temperature is 985.7 ?,which is lower than the limit temperature of 1204?.The CMRR coolant temperature is 86.7 °C,which means there is large impact on the research reactor.The argon gap pressure is up to 2.3 MPa,which poses a challenge to the double-layer pressure tube structure.The results of the accident analysis will provide feedback to the loop design and promote the improvement of the loop design.