Research On Three Dimensional Transient Thermal And Hydraulic Characteristics Of Pool-type Sodium-cooled Fast Reactor Under Asymmetric Conditions Of One Primary Pump Trip Superimposing Loss Of Off-site Power

The one primary pump trip is an initiating event that may occur during the operation of the double-loop pool-type sodium-cooled fast reactor.Under its influence,two pumps in the two loops will perform asymmetrical coast-down,leading to failure pump coast-down and backflow phenomenon.When one primary pump is out of service,it may be accompanied by the loss of off-site power and other different superposition conditions.The special flow and complex superposition conditions in the reactor further result in the special three-dimensional thermo-hydraulic asymmetry in the primary circuit sodium pool,which in turn leads to excessive temperature gradients and excessive thermal stresses in the internal components of the reactor.Therefore,it is important to ascertain the complex transient thermo-hydraulic distribution for the safe operation of the sodium-cooled fast reactor.The main components of the pool-type fast reactor primary circuit is soaking in sodium pool,that makes the flow distribution harder to determine under the working condition of one primary pump trip.Moreover,the two pumps coast-down and the failure pump backflow make the flow distribution more complex.At the same time,the complicated superposition conditions may occur,making the transient thermal hydraulic parameters more difficult to determine.This working condition is relatively complicated,and there are few numerical calculations and experimental studies at home and abroad.The three dimensional transient thermal and hydraulic characteristics of pool-type sodium-cooled fast reactor under asymmetric conditions of one primary pump trip superimposing loss of off-site power need to be further clarified.Based on the three-dimensional model of primary sodium pool of the research team,this study took the China Experimental Fast Reactor(CEFR)as the research object,using the software FLUENT to simulate the transient three-dimensional thermal hydraulic parameters of CEFR under the condition of one primary pump trip superposing loss of off-site power.The research team had fully verified the rationality of the model in the early stage,and completed the calculation of some working conditions through the model.The study was improved and optimized by adding the coasting model of the pump to realize the asymmetric coast-down and backflow processes under this condition.The three-dimensional asymmetric thermo-hydraulic distribution and the transient variation of key operating parameters were obtained.Then,these parameters were compared with the calculation of one primary pump trip superposing residual heat removal of single loop.The calculation showed that the hot sodium pool overall temperature decreased gradually.While,the cold sodium pool overall temperature increased gradually under the one primary pump trip superposing loss of off-site power transient operating condition in 1500s.And the thermal stratification gradually blurred.The overall temperature in the normal loop at the key positions in the reactor was significantly higher than that in the failure loop.Among the key operating parameters,the core outlet average temperature reached the lowest value of about 400.33℃ at about 600 s.Although the average temperature of core outlet occurred a certain rebound in the later stage,CEFR had enough design margin to ensure safety to meet the safety requirements of the reactor.And the overall temperature distribution in the sodium pool did not exceed the CEFR operating limit.Compared with the condition of superposition loss of off-site power,the outlet temperature of IHX in the normal loop was less than 365℃ under condition of residual heat removal of single loop,which ensures that large thermal shock did not occur in the cold sodium pool supporting structure.The simulation results offer an important three-dimensional numerical reference for the safe operation of CEFR under the one primary pump trip condition.