Modeling Of Heat Transfer Process Of Corrosion Products On The Surface Of PWR Fuel

The formation of porous corrosion deposits on nuclear fuel cladding(CRUD),is a significant challenge to safe operation in PWR.CRUD can accelerate corrosion of the fuel cladding,increase radiation fields,and induce power shift,resulting in an imbalance in core power distribution.These hazards are related to the heat transfer process of CRUD.In order to predict the negative effects of corrosion products on reactor,it is urgent to establish a CRUD heat transfer model suitable for various conditions.However,existing studies have focused on loosely coupled processes,and there are too many model assumptions with limited simulation conditions.Therefore,it is of great significance to establish a fully coupled CRUD heat transfer model suitable for various working conditions.Firstly,the nodes in the core area of PWR are divided according to the temperature difference,and the calculation model of corrosion products deposition thickness on the cladding is established by MATLAB.The model divides the core area into six nodes,including hot leg,core top,boiling fuel surface,bottom of core,non-boiling fuel surface and cold leg.According to the mass transfer equation between nodes and related chemical reactions,the relationship of ion concentration with time is calculated,and then the deposition thickness of corrosion products on the cladding is calculated.Secondly,based on the wick boiling heat transfer mechanism,this paper establishes a model coupling three physical processes of heat transfer,fluid flow and mass transfer which are fully coupled.The model reasonably predicts the internal temperature distribution,pressure distribution and concentration distribution of CRUD.The mechanism of porosity affecting heat transfer process is discussed in this paper.In addition,the assumption of liquid saturation in CRUD associated with wick boiling heat transfer mechanism is discussed,and a film boiling heat transfer mechanism with coexistence of liquid-saturation region and vapor-saturation region under high heat flux is proposed.Finally,according to the film boiling heat transfer mechanism,the control region is divided into two parts: the liquid-saturation region near the bulk coolant and the vapor-saturation region near the fuel cladding.The two regions apply different parameters and boundary conditions.The sensitivity analysis of typical reactor parameters is carried out.The calculation results show that porosity is the key parameter affecting CRUD heat transfer process.In addition,the model is verified by WALT loop tests,and the simulation results verify the correctness of the model.The results show that the film boiling heat transfer mechanism is more in line with the actual situation under the condition of high heat flux.