One of the possible consequences of a loss-of-coolant accident (LOCA) in a light-water reactor would be the rapid heatup of the fuel tubes in a steam environment. During the period of time in which the cladding was exposed to steam (provided both from boiloff of residual water in the pressure vessel and by the emergency coolant) at elevated temperatures, reaction of the Zircaloy with the steam would cause the formation of an oxide film on the cladding surface and an oxygen gradient into the wall. Since the ductility of Zircaloy is a direct function of oxygen content, and since the oxygen content is a function of time and temperature of steam exposure, a study of the degree of embrittlement to be expected in a LOCA necessitates the examination of specimens exposed to specific temperatures for given lengths of time in a steam environment. Correlations are developed among steam exposure, oxygen content, ductility, and hardness which permit estimating the degree of embrittlement the cladding would attain during any LOCA transient. Curve fitting to LOCA transient data and subsequent integration provide easy analysis of the amount of embrittlement expected.

This paper describes the results of two sets of experiments designed to characterize the ductile-brittle behavior of Zircaloy fuel element cladding in terms of amount of oxidation, degree of penetration of brittle phases into the tube wall, and type of deformation used in the tests.Ring specimens were cut from 0.422-in. OD x 0.027-in.-wall thickness Zircaloy-4 tubes previously steam-oxidized on both inner and outer surfaces at temperatures ranging from 1700 to 2400°F for various times. Two typas of deformation tests were employed: high-strain-rate coapression (flattening) tests in an argon atmosphere at teepeeatures from room temperature to 1900°F and slow-strain-rate compression t.s from room temperature to 300°F.The high (near iinpact)-strain-rate test results 1 showed thai: a correlation exists between deformation temperature and amount of oxidation.The ductile-brittle transition is defined by a zero-ductility temperature (ZDT) and the amount of oxidation by the parameter F , which is the fracw tion of the as-oxidized wall thickness that reverted to a-phase from the ,B-phase on quenching from the steam exposure temperature. The empirical correlation derived from the high-strain-rate tests is given bŷ

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