Pressurized water reactor type fuel rods are being irradiated under postulated accident conditions in the Power Burst Facility at the Idaho National Engineering Laboratory as part of the Thermal Fuels Behavior Program. In these tests, film boiling was achieved by establishing a mismatch reactor power and coolant flow, while maintaining the coolant pressure at 15 MPa.

Cladding embrittlement resulting from film boiling operation of intact fuel rods was found to be consistent with previously established embrittlement criteria based on oxygen content in β-Zircaloy, but not with previously established criteria based on either fractional thickness of transformed β or equivalent cladding reacted.

Rods that were operated with breached cladding were embrittled to a greater degree than intact fuel rods under similar oxidizing conditions. This embrittlement appears to be associated with rim α and acicular α precipitation within the transformed β field as well as with enhanced hydrogen absorption.