Research On The Security Features Of Accident Tolerant Chromium Coated Zirconium Alloy Cladding

Zirconium water reaction under accident condition of nuclear reactor was the main reason for the serious consequences of Fukushima nuclear accident in japan.Therefore,improving the high temperature steam oxidation resistance of nuclear fuel cladding can improve the overall safety performance of fuel cladding which was important for the safe operation of nuclear reactor,what is more,it also is one of the key problems to be solved in the field of global nuclear reactor safety.In order to solve it effectively,the concept of accident resistant nuclear fuel including high performance fuel cladding and high temperature fuel pellets was proposed by nuclear scientists and technicians.Modified the zirconium alloy surface coating is an important direction to research the accident resistance nuclear fuel cladding,which was designed to take advantage of surface coating to improve the function of zirconium alloy high temperature steam oxidation resistance and so on.This article was main to study the technology of fabrication of Cr coating on Zr-4 alloy,the basic performance and high temperature oxidation resistance of surface coating,so as to determine the overall safety characteristics of the Cr coated Zr-4 alloy.The surface coating of zirconium alloy was prepared by multi-arc ion plating.It explored the influence of different process parameters on the basic performance of the Cr coating on Zr-4 alloy.The main study was research the effect of four process parameters,which were arc current、deposition temperature、substrate bias and deposition time in multi arc ion plating process,to Cr coating surface morphology,phase composition,mechanical strength and the bonding strength between coating and substrate,to determine the best process parameters of the Cr coating prepared by multi arc ion plating.It mainly included the surface shape,section shape,phase,thickness,surface roughness and bonding strength in zirconium alloy coating at room temperature.The surface micromorphology of the coating was observed by SEM,and Phase can determined by XRD test analysis.The thickness of the coating can be determined by the backscattering of SEM and the element distribution of EDS.The bonding strength is generally obtained by indentation scratch text.For Cr coating on Zr-4 alloy,using the process parameters were 80 A arc current,-100V deposition temperature,350℃deposition temperature,10～15um coating thickness,which can obtain the ideal Cr coating.The high temperature property characterization,test method and high temperature oxidation mechanism of chrome-plated Zr-4 alloy were studied.It studied the high temperature oxidation mechanism of the Cr coated Zr-4 alloy in high temperature air environment.After oxidation at300 to 1200℃for a certain period of time,analyzing the surface morphology,phase composition and mechanical strength of coating.A dense Cr₂O₃ layer is formed on the surface of Cr after high temperature oxidation,which can prevent the inward diffusion of oxygen and without cracking.With the increase of oxidation degree,void and crack defects were formed in both Cr coating and Zr matrix,the appearance of defects accelerates the oxidation rate of the Zr matrix.But Cr coating can still cover the whole Zr matrix completelyThe oxidation characterization and oxidation kinetics of Cr coating on Zr-4 alloy in high temperature steam and air environment were studied.The oxidation rate of Cr coated Zr-4 alloy in steam was faster than it in the air.The oxidation rate of coated Zr-4 alloy cladding material was obviously lower than uncoated.The Cr coated Zr-4 alloy cladding had almost no oxidation reaction in steam environment below 900℃and air environment below 1000℃.Compared with the uncoated Zr-4 alloy cladding,Cr coating can improve the Zr matrix high temperature oxidation resistance.The Zr-4 alloy covered with Cr coating obeyed the linear parabola oxidation law in both steam and air environment.Based on the oxidation date from the oxidation experiment,establishing the oxidation kinetic modal.By Arrhenius formula fitting,the oxidation activation energy of the Cr coated Zr-4 alloy and the Zr-4 alloy in the high temperature steam environment from 600 to 1100℃was calculated separately as 129.1k J/mol and 221.8 k J/molThe oxidation bonding properties of chromium-plated Zr-4 alloy at high temperature were studied.Through the scratch test,testing the bonding properties of Zr-4 alloy coated with Cr coating which was oxidized by high temperature steam.In the range of 500～1100℃,with the increase of oxidation temperature,Cr-Zr diffusion layer becomes thicker,and the bonding force of the coating increase with the increase of oxidation temperature.In the range of 1000～1100℃,with the time of oxidation,the bonding force of the coating increase first and then decrease.Numerical analysis of safety characteristics of zirconium alloy surface coating under high temperature oxidation.Through analysis the influence of oxidation temperature and oxidation time to Cr coated Zr-4 alloy and Zr-4 alloy cladding,studying the relationship of the effect of the Cr coating on the shape variable of Zr-4 alloy cladding...