Physics validation measurements for highly-reactive experiment packages in the INL advanced test reactor

The Korea Atomic Energy Research Institute is currently in the process of qualifying the Low-Enriched Uranium fuel element design for the new Ki-Jang Research Reactor (KJRR). As part of this effort, a prototype KJRR fuel element will be irradiated for several operating cycles in the Northeast Flux Trap of the Advanced Test Reactor (ATR) at the Idaho National Laboratory. The KJRR fuel element contains a very large quantity of fissile material (618g ²³⁵U) in comparison with historical ATR experiment standards and its presence in the ATR flux trap was expected to create a neutronic configuration that would be well outside of the current validation envelope for the reactor physics analysis methods used to support ATR operations. Accordingly it was necessary to conduct an extensive set of new low-power physics measurements in the ATR Critical Facility (ATRC), with the objective of expanding the validation envelope for the computational reactor physics tools used to support ATR operations and safety analysis to include the planned KJRR irradiation in the ATR and similar experiments that are anticipated in the future. The computational and experimental results demonstrated that the neutronic behavior of the KJRR fuel element in the ATRC is well-understood, both in terms of its general effects on ATRC core reactivity and fission power distributions as well as in terms of its own internal fission rate distribution and total fission power per unit ATRC core power. Taken as a whole, these results will help to extend the ATR physics validation envelope and they are expected to enable an entire new class of irradiation experiments in the ATR.