High-fidelity gamma transport analysis for the advanced test reactor fuel storage canal

The Advanced Test Reactor (ATR) at the Idaho National Laboratory supports a variety of missions involving accelerated testing of nuclear fuel and other materials in a high neutron flux (5.0 x 1014 n/cm2-s) environment, as well as medical and industrial isotope production, and other applications. It typically runs several cycles per year with cycle lengths varying from 40 to 60 days, depending on specific experimental requirements. The highly radioactive used fuel elements that are discharged from the ATR after each cycle are stored in an adjacent heavily shielded canal with concrete walls that are approximately 1.8 m (6 ft) thick. These fuel elements are sufficiently radioactive to induce levels of gamma heating and integrated dose in the walls of the canal that are of potential concern with regard to damage of the canal walls. An early design study for the ATR canal quantified this phenomenon using limited one-dimensional computational transport techniques that were practical at the time (1962) and concluded that irradiated ATR fuel elements should be positioned at least 0.305 m (12 in.) from the canal wall to conservatively avoid excessive gamma heating in the concrete structure of the wall itself. A new study has now been completed using modern high-fidelity three-dimensional radiation transport computational techniques to verify the earlier results, to assess the degree of conservatism in those results, and to provide a new, much more comprehensive and detailed database for quantification of the canal wall heating induced by radiation from nearby ATR fuel elements stored in the canal.