The influence of the oxidation on the emissivity of Zircaloy - 4 alloy

The purpose of this work was to generate transient oxidation data at high temperature (800 - 1200{sup o} C) on Zircaloy - 4 specimens, tested in steam, under conditions simulating a loss of coolant accident (LOCA). The zirconium oxide, oxygen-stabilised {alpha}-Zr and transformed {beta} layers thickness are measured and characterised by means of the metallographic analyses and microhardness tests. The growth rate of zirconium oxide was correlated with the testing conditions by expression of the form: x=f(R, T, t{sub h}), where x=thickness of zirconium oxide ({mu}m), R=heating rate ({sup o} C/s), t{sub h}=holding time under isothermal conditions (s), T=the transient temperature (T). Taking into account the heat transfer mechanisms for the experimental testing system, the cooling range of the temperature-time diagram was used to obtain the effective emissivity of the Zircaloy - 4 alloy oxidised in steam. A correlation was proposed between the emissivity and zirconium oxide thickness, as follows: {epsilon} = {epsilon}{sup 0} + C x{sup a} where {epsilon} is the emissivity of the oxidised alloy, {epsilon}{sup 0} is the emissivity of the unoxidized alloy surface, C and a are constants. The above mentioned relationships shall introduced in the computer models describing the oxidation of Zircaloy - 4 cladding under nonisothermal conditions. (Author) 11 Figs., 3 Refs.