Multi-Physics Coupling Simulation Within Porous CRUD Deposits On PWR Fuel Cladding

The Chalk River Unidentified Deposit(CRUD)on the surface of the fuel cladding in the Pressurized Water Reactor(PWR)causes problems such as Axial Offset Anomaly(AOA),enrichment of neutron moderator,and radionuclide enrichment in the reactor.Research on CRUD is necessary and urgent.However,due to the limitations of existing experimental methods and technical means,modeling and simulation calculation is an important research method,and can reduce the experimental cost.In this paper,theoretical model and numerical simulation are combined to establish the theoretical model and its governing equations under different physical fields,as well as the boundary conditions and initial conditions of each partial differential equation.Through the modeling software COMSOL Multiphysics(?),physical processes in CRUD are simulated such as heat transfer,fluid flow and mass transfer inside the porous medium under the coupling of multiple physics,and analyzes the influence of geometric size,CRUD porosity and heat flux density on different physical fields.The temperature in the porous medium near the surface of the fuel cladding can reach a maximum of 634K,and the temperature at the upper portion in contact with the coolant body reaches a minimum of 616K;the direction of the Darcy flow in the porous medium is from the coolant to the cladding.There is a tendency to flow toward the surface of the chimney,the flow velocity gradually becomes larger,the maximum flow velocity can reach 2.5×10-3m/s.There is a relatively low flow rate stagnation zone in the porous medium near the cladding;the concentration of boric acid in the vicinity of the contact surface with the coolant bulk is the largest,and the concentration of boric acid near the fuel cladding is lowered.With the increase of the radius of the chimney,the temperature of the porous medium near the surface of the cladding gradually increases,has little effect on the velocity distribution and concentration distribution;the flow velocity of the porous medium is negatively correlated with the porosity,and the porosity is related to the temperature distribution.The distribution of boric acid concentration has little effect;the higher the heat flux density of the fuel cladding,the higher the temperature,and the maximum flow velocity in the flow field also shows a nonlinear positive growth trend with the increase of the envelope heat flux.