Numerical Simulation Of Natural Circulation Characteristics Of Lead-based Pool Reactor

Due to the high inherent safety of the lead-based reactor,the China Initiative Accelerator Driven System(CiADS)adopts the scheme of pool-type lead-based fast reactor.And CiADS reactor adopts passive emergency residual heat removal system based on natural circulation.The natural circulation characteristics are the key operating characteristic of the primary circuit of the lead-based reactor,which has an important influence on the passive residual heat removal system of the reactor.In order to ensure the safety of reactor operation,it's of important academic significance and engineering application value to study the natural circulation and residual heat removal capacity of CiADS lead-based reactor primary circuit.Based on the design scheme of CiADS reactor and the porous media model,this paper established the flow heat transfer analysis model of CiADS reactor.In this paper,the model includes core assemblies,flow distributor,core shrouds,horizontal heat shield,main heat exchangers,main pumps and other major facility or structures.Through 3D CFD model,steady state calculations for three conditions were completed: full power mixed circulation,full power non-natural circulation and low power natural circulation.The key thermal-hydraulics parameters to evaluate the safety of operation under different conditions were focused,including the maximum temperature of cladding and coolant,the maximum velocity,and the coolant mass flow rate that characterizes the strength of natural circulation.Temperature distribution,velocity distribution and flow pressure drop in the reactor were observed and analyzed.The maximum coolant temperature,the maximum cladding temperature and the maximum flow rate of the CiADS lead-based reactor under rated condition are 656.3k,664.19 k and 0.61m/s,respectively,which are all lower than the safety limit.When operating at low power level,the maximum temperature in the reactor is 642.27 k,which is below the safety limit and has a large safety margin,indicating that the Ci ADS lead-based reactor has the ability to operate in the natural circulation at low power and has a certain degree of accident tolerance.Due to the low computational efficiency of the 3D model,it cannot meet the requirements of transient calculation.According to the principles of volume equivalence,heat transfer area equivalence,flow area equivalence and height equivalence,a 2D CFD model was established.By comparing the calculation results of 2D and 3D,it was found that the temperature distributions are similar,and the maximum relative deviation is 14.49%,which is derived from the momentum source item of the pump,which indicates that the equivalent method of the two-dimensional model is feasible.The transient calculation results show that the passive residual heat removal system can cope well with the station blackout accident,and the CiADS lead-based reactor has good passive safety performance.