Radiation-Induced Sharpening in Cr-Coated Zirconium Alloy

Abstract

To improve the safety of nuclear power plants, a Cr protective layer is deposited on zirconium alloys to enhance oxidation resistance of the nuclear fuel cladding during both in-service and hypothetical accidental transients at High Temperature (HT) in Light Water Reactors. The formation of the Cr2O3 film on the coating surface considerably helps in reducing the oxidation kinetics of the zirconium alloy, especially during hypothetic Loss of Coolant Accident (LOCA). However, if the Cr coating is successful to increase the oxidation resistance at HT of the zirconium substrate, for in-service conditions, under neutron irradiation, Cr desquamation has to be avoided to guarantee a safe use of the Cr-coated zirconium alloys. Therefore, the adhesion properties have to be maintained despite the structural defects created by sustained neutron irradiation in the reactor environment. This paper proposes to study the behavior of the Zircaloy-Cr interface of a first generation Cr-coated material during a specific in situ ion irradiation. As deposited, the Cr-coated sample presents a f.c.c. C15 Laves-type intermetallic phase at the interface with off-stoichiometric composition. After irradiation and for the specific conditions applied, this interfacial phase has significantly dissolved. Energy Dispersion Spectroscopy revealed that the dissolution was accompanied by a counterintuitive “sharpening” effect.

An Orthogonal Experimental Study on the Preparation of Cr Coatings on Long-Size Zr Alloy Tubes by Arc Ion Plating

“…Consequently, many coatings such as Cr and Cr-based alloys [ 14 , 15 , 16 ], nitride ceramics [ 17 , 18 , 19 ], FeCrAl alloys [ 20 , 21 , 22 ] and MAX phase ceramics [ 23 , 24 , 25 ] are used worldwide. Among them, Cr coatings show resistance to pressurized-water corrosion [ 26 , 27 ], friction and wear [ 16 , 28 ], high-temperature steam oxidation [ 29 , 30 , 31 , 32 ] and ion or neutron irradiation [ 33 , 34 , 35 , 36 ], and hence become the most promising candidate for advanced ATF cladding coatings. At present, the most important task for the development of pure Cr coatings on Zr alloy claddings is to precisely control the coating to meet the requirements of engineering design.…”