Irradiation of advanced neutron absorbing material to support accident tolerant fuel applications

Development of enhanced accident tolerant fuel (E-ATF) concepts is a strong focus of the nuclear industry. The limiting components during Design Basis Accidents (DBAs) and Beyond Design Basis Accidents (BDBAs) will be the control components once application of E-ATF cladding and fuel concepts enable the fuel rod cladding to survive to higher temperatures. Post-accident evaluation of the performance of current absorber materials during the Three Mile Island and the Fukushima Daiichi accidents has provided indications that improving the high temperature stability of absorber materials will improve margins during accident conditions. During DBAs conditions at peak fuel rod cladding temperatures, control rod temperatures are predicted to be high enough that current absorber materials (Ag-In-Cd) will melt with vaporization of portions of the material. At about 1150 °C, B₄C will form a eutectic with the iron of the stainless steel control rod cladding. These behaviors lead to a loss of absorber material integrity and accelerated control component degradation. Framatome has developed new absorbers using neutron absorber materials with melting points more than three times that of the current absorber materials and predicted stability to BDBAs temperatures. While out of pile properties have been extensively characterized, these absorber materials have not yet been irradiated in test or commercial light water reactors. An irradiation test program has been defined for the neutron absorber materials to validate performance under irradiation and characterize irradiation-induced swelling. The test program is designed to evaluate the materials at middle and end of life fluence ranges, which are achieved in an accelerated time frame via irradiation at Oak Ridge National Laboratory's High Flux Isotope Reactor (HFIR). The goals of this experiment, test plans, and irradiation program status are presented. Sample information and pre-characterization results are provided. Development of accident tolerant neutron absorbing materials is a key aspect necessary to ensure the accident tolerance of the commercial nuclear fleet. Once irradiation of these materials is complete and the results incorporated into design models, the neutron absorbing materials can be deployed to commercial reactors worldwide. When used in conjunction with accident tolerant fuel designs, such as Framatome's PROtect technology short- and long-term solutions, the enhanced accident tolerant control rods will enable reactors to achieve maximum accident margin gains.