压水堆沉积物对包壳表面性能影响的模拟研究OA北大核心CSTPCD

With the increase of fuel cycle period of the new generation pressurized water reactor,the influence of corrosion product deposition in the core is becoming more and more serious.The cladding surface temperature and species concentration changes caused by deposits(also called Chalk River Unidentified Deposit(CRUD))increase the risks of core power shift induced by boron accumulation,radiation dose increase and cladding corrosion.In order to predict the risks induced by the CRUD on the cladding in the pressurized water reactor,a multi-physics process model was established and optimized for the heat transfer,mass transfer,fluid flow and chemical process of the cladding surface with CRUD.The heat transfer parameters and mass transfer parame-ters on the cladding surface were carried out under different operating conditions,hydrochemical conditions and CRUD structures.Combined with the relationship of multi-physics processes,the effects of the heat flux,the coolant temperature,the boron and lithium concentrations in coolant and the structural parameters of CRUD on the performance of the cladding surface were discussed,and the essential reasons of CRUD induced boron accumulation were discussed.The risk equation to evaluate the CRUD induced boron accumulation under different operating parameters,hydrochemical param-eters and CRUD structural parameters was proposed.The results show that when boiling occurs in CRUD,the temperature distribution can be obtained more accurately by considering the volatilization of boric acid.The presence of CRUD leads to a dramatic increase of the outer surface temperature of the cladding.The increase degree of clad-ding temperature increases with the CRUD thickness,the CRUD porosity and the boron concentration,and decreases with the increase of heat flux,coolant temperature and CRUD stack density.The thermal driving force from cladding to coolant increases when the CRUD thickness is less than 50 μm,the heat flux is 0.4-1 MW/m2 and the coolant temperature is less than 300 ℃.Beyond the above ranges,the presence of CRUD reduces the heat transfer from cladding to coolant.Under the classical pressurized water reactor condition,the boron accumulation in the void structure of 40 μm CRUD mainly derives from boric acid(0.057 4 g/m2)and the adsorbed boron(4.61× 10-2 g/m2).The deposited boron in the void structure of CRUD in the form of Li2B4O7 is 8.34 × 10-5 g/m2,while LiBO2 can not deposit in 40 μm CRUD.At 1 MW/m2,a power shift of 1.5％occurs when 1/8 of the core attaching to 80 μm thick cladding CRUD.The effects on the CRUD induced boron accumulation risk from large to small are as follows:CRUD thickness,coolant temperature,pore diameter,coolant boron concentration,heat flux,porosity,while the coolant lithium concentration and chimney density of CRUD have little effect.