b'Performance of the HERA PreHydrided ExperimentsPrincipal Investigator: Charlie Folsom, Jason Schulthess, David KamermanTeam Members/Collaborators: J. Stinger, J. Burns, P. Petersen, M. Ramirez, S. Seo, C. Jensen, D. WachsI daho National Laboratory (INL)called High-burnup Experiments in in collaboration with the JapanReactivity-initiated Accidents (HERA). Atomic Energy Agency (JAEA),The purposes of this test series include under the Nuclear Energy Agenciesevaluating PCMI presence and (NEA) Framework for Irradiationseverity at different pulse widths on Experiments (FIDES) initiative havefuel rods specifically manufactured to tested four fuel rodlets made of UO 2 be representative of high-burnup fuel pellets in Zirconium-4 cladding withrods, namely Zircaloy cladding with a pre hydrided microstructure tohydride rims and sized to reduce the simulate high-burnup conditions.fuel-cladding gap. The experiments were performedThe HERA project will include in Transient Reactor Test (TREAT)multiple experiments in the TREAT Facility at INL and the Nuclearreactor with a ~90 ms full-width-at-Safety Research Reactor (NSRR) athalf-max (FWHM) pulse and NSRR JAEA as part of a larger campaign towith a ~7 ms FWHM pulse width. evaluate the effect of pulse-widthThe experiments are targeting test during a reactivity-initiated accidentconditions to achieve fuel radial (RIA). It is hypothesized that theaverage enthalpy increases during the pulse width in an RIA may affect rodtransient around the current failure failure by pellet-cladding mechan- limit of 711 J/gUO 2 .ical interaction, specifically, longer pulse widths may be less severe thanA modeling and simulation (M&S) shorter pulse widths. exercise was also organized under the HERA project. The M&S exercise Project Description: included participants from over 20 The RIAs are a postulated accidentorganizations around the world using condition in light-water nuclear14 different fuel performance codes. reactors. In these accidents, theThe goal of the M&S exercise was to rapid ejection of a control rod fromprovide pre-test blind predictions to the core results in a reactivity addi- help design the targets for the actual tion and a rapid rise of power. Oneexperiments. The M&S work will potential consequence of this rapidcontinue with post-test as-run results rise of power is a condition, known asthat will provide valuable validation pellet-cladding mechanical interac- data for codes.tion (PCMI), in which the rapid rise of power causes thermal expansionAccomplishments:of the fuel pellets. The pellets thenExperiment design, fabrication contact the still relatively coldand irradiation was completed for cladding and cause failure of thethe first two TREAT tests in this cladding due to excessive strain. Toseries, which included fresh fuel evaluate this potential failure mode, apellets assembled into rodlets with series of experiments were developedprecharged hydrogen in the clad-98 2023|AFC ACCOMPLISHMENTS'