Nuclear Transmutations in HFIR’s Beryllium Reflector and Their Impact on Reactor Operation and Reflector Disposal

TL;DRAbstract

The High Flux Isotope Reactor (HFIR) located at the Oak Ridge National Laboratory utilizes a large annular beryllium reflector that is subdivided into three concentric regions and encompasses the compact reactor core. Nuclear transmutations caused by neutron activation occur in the beryllium reflector regions, which leads to unwanted neutron-absorbing and radiation-emitting isotopes. During the past year, two topics related to the HFIR beryllium reflector were reviewed. The first topic included studying the neutron poison (3He and 6Li) buildup in the reflector regions and its effect on beginning-of-cycle reactivity. A new methodology was developed to predict the reactivity impact and estimated symmetrical critical control element positions as a function of outage time between cycles due to 3He buildup and was shown to be in better agreement with actual symmetrical critical control element position data than the current methodology. The second topic included studying the composition of

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