Study Of Corrosion And Deposition Processes On The Surface Of Nuclear Fuel Elements

In the primary loop of a nuclear reactor,the operation of the system can lead to the deposition of corrosion products on the surfaces of fuel elements.These corrosion products can impact the stability and heat transfer efficiency of the primary loop,causing hazards such as axial power offset,localized corrosion exacerbation,increased radioactivity,and shortened equipment lifespan.Analyzing the process of corrosion product deposition is beneficial for predicting the behavior of the system under different core conditions.By studying a large number of different models of corrosion product deposition(CRUD),two deposition models are integrated: the steam-dry deposition model and the water chemistry model.The process of corrosion product deposition is divided into non-steady-state deposition and steady-state deposition.There are four types of corrosion deposition: deposition of soluble impurities,deposition of insoluble particles,exchange deposition between impurities and particles,and steam-dry deposition.By combining the four deposition modes with the two deposition models,a model is constructed to describe the formation,growth,and stabilization process of corrosion products.In the non-steady-state deposition process,important factors that influence the corrosion product deposition rate,such as deposition coefficient,latent heat of evaporation,and bubble growth rate,were studied.A comprehensive experimental method was established.By using this model for calculations and validating it with experimental data,the correctness and feasibility of the model were demonstrated.The model successfully predicts the growth process of corrosion products.The model calculates the values of KQ/L and K for suspended deposits.When the circulation velocity is 0 m/s,the deposition rate is directly proportional to the heat flux density.When the heat flux density is fixed at 20 W,as the flow velocity increases from 0m/s to 2.6 m/s,the value of K decreases from around 2.31 to 0.35,and the value of KQ/L decreases from around 0.735 μg/cm2·s to 0.11 μg/cm2·s.Additionally,as the iron ion concentration increases,the deposition rate of corrosion products also increases.In the steady-state deposition process,several parameters of the most common corrosion products were studied,including the concentration of substances in the deposits,the temperature of the deposits,and the acidity or alkalinity.The research results indicate that when the deposit thickness is 59 μm,the p H value varies between 7.0 and 7.9.With an increase in the concentration of boron ions,the temperature of the deposit layer also increases.Furthermore,the temperature of the deposit layer increases with an increase in the thickness of the deposits.At a thickness position of 35 μm,the temperature of the deposit layer is 363°C,while it increases to 402°C when the thickness increases to 59 μm.Using the calculation results from this model,it is possible to accurately estimate the deposition thickness of corrosion products on the surfaces of fuel elements in actual operating nuclear power plant cores.It also allows for the accurate calculation of the heat transfer effects of the deposited products on the surface of the fuel elements.