| With the increasing attention and demand for safety in nuclear power development,the passive safety technology based on natural circulation has been widely applied in the pool-type sodium cold fast reactor.When accidents occur,the Decay Heat Removal System(DHRS)can help establish and maintain natural circulation flow of coolant inside the pool-type fast reactor,and remove the residual heat from the core.Therefore,it is of great reference value for the design and safety analysis of fast reactor system to study the variation of thermal hydraulic characteristics in DHRS operation and the primary cooling system of fast reactor.However,due to the complex equipment structure and large size of the primary cooling system and DHRS of the pool-type fast reactor,it is difficult to carry out experimental research.It is difficult for traditional one-dimensional,two-dimensional and local three-dimensional thermal-hydraulic analysis programs to obtain detailed three-dimensional thermal-hydraulic characteristics in the whole reactor.When using the three-dimensional Computational Fluid Dynamics(CFD)method for full-size three-dimensional modeling and calculation of the first,second,and third circuits of the pool-type fast reactor,a huge amount of computational resources is required,and the computation time is very long,making it difficult to carry out engineering applications.Therefore,the coupling calculation method of one-dimensional and three-dimensional is necessary to study the natural circulation characteristics of the pool-type fast reactor.This paper established a heat transfer model for the DHX shell and sodium pool fluid,and coupled it into the DHRS analysis program SAC-DRACS independently developed by North China Electric Power University.The coupling interface program was self-written to realize the coupling of the one-dimensional program SAC-DRACS with the three-dimensional CFD software FLUENT.Based on the experimental results of the Japanese Large-Scale Sodium Experiment Plant Dynamics Test Loop(PLANDTL),the applicability of the one-dimensional and three-dimensional coupling calculation method was verified.Then,the one-dimensional and three-dimensional coupling calculation method was used to simulate the transient process of the primary cooling system and DHRS of the China Experimental Fast Reactor(CEFR)under a complete blackout(SBO)accident for 4000 seconds.According to the calculation results,the influence of the flow characteristics caused by the operation of DHRS on the temperature distribution inside the core was analyzed,and the residual heat removal capacity of DHRS was evaluated.The results showed that in the SBO accident,the cooling power growth of DHX lagged behind AHX after DHRS was put into operation.In the early stage of the accident,the operation of DHRS had a time lag effect on the cooling effect inside the primary cooling system.In terms of temperature distribution,the overall temperature of the first circuit hot pool in CEFR was high at the top and low at the bottom,and there was an obvious temperature stratification phenomenon inside the pool.However,with the continuous action of DHRS,the stratification phenomenon gradually disappeared.After entering natural circulation,the peak value of the average temperature at the outlet of the core appeared at about 1300 seconds,with a value of 500.3℃.In addition,the proportion of Inter-Wrapper Flow(IWF)affected by DHRS in the discharge of residual heat during natural circulation gradually increased over time.At 4000 seconds,the heat dissipation of IWF accounted for about 33.74%of the total residual heat of the core,which had an important role in the discharge of residual heat from the core.Application of One-dimensional and Three-dimensional Coupled Calculation Analysis Method on CEFR Shows that DHRS’s Waste Heat Discharge Capability Provides Important Safeguard for the Safety of Equipment and Core in the CEFR Pool.The work in this paper can provide key numerical references and research method extensions for the safety analysis of natural circulation conditions in pool-type fast reactors.Based on the application of one-dimensional and three-dimensional coupling calculation method on CEFR,the results show that the residual heat removal capacity of DHRS is important for the safety of the equipment in the CEFR pool and the core.The work in this paper can provide a key numerical reference and extend the research method for the safety analysis of the natural circulation of the pool-type fast reactor. |
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