This test method is intended to include a concise description of an orderly procedure for conducting high-temperature oxidation of samples of zirconium-based nuclear fuel cladding in a steam atmosphere, in order to determine the onset (time) of a mechanism referred to as a breakaway oxidation. These testing conditions are related to postulated loss-of-coolant accidents (LOCA) in nuclear reactors.
Breakaway oxidation is defined as the acceleration of oxidation rate under certain conditions, and is related to the degradation of a protective oxide due to phase transformation. Breakaway oxidation is associated with accelerated hydrogen pickup, which embrittles the material. The U.S. Nuclear Regulatory Commission (NRC) is preparing a Regulatory Guide (Draft Regulatory Guide DG-1261) describing an experimental technique to measure the onset of breakaway oxidation. The purpose is to support a specified and acceptable limit on the total accumulated time that a cladding may remain at high temperature, aiming to prevent cladding embrittlement during a loss-of-coolant accident (LOCA), thus ensuring that the general core geometry will be maintained and be coolable. The experimental technique currently proposed by the NRC is based on the experience of a single laboratory and a limited range of test parameters, and may impose acceptance criteria without taking into account concerns of the nuclear power industry on uncertainty and repeatability of results. For this reason, the nuclear power industry is aiming to establish an ASTM (i.e. a consensus) standard test method to conduct these tests, for which a round robin program has been started. The standard test method will be used by nuclear fuel vendors, zirconium alloy vendors and contracted laboratories to test different zirconium-based cladding materials and assess compliance with the NRC regulations.
Keywordsbreakaway oxidation; zirconium cladding; LOCA
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
Draft Under Development