Depletion and lifetime performance analysis of advanced manufactured control elements in the high flux isotope reactor (HFIR)

The application of advanced manufacturing to the fabrication of control elements (CEs) for the High Flux Isotope Reactor (HFIR) is under investigation at the Oak Ridge National Laboratory. Advanced manufacturing yields a unique CE design with lumped neutron absorbers, necessitating investigation of the neutronic implications of employing this novel CE design in HFIR. This work assesses the operational performance of advanced manufactured CEs in HFIR throughout their useful lifetime. CE depletion calculations are carried out for long residence time (50 cycles) under several predictor-corrector approximation schemes of varying rigor, with their reactivity worth evaluated at beginning, middle, and end of life. While coarse temporal divisions of the long CE irradiation time yield prominent discrepancies in the isotopic content predicted by each approximation, the corresponding reactivity worth predictions are reasonably consistent across approximations. Further, regardless of the approximation employed, the reactivity worth of the advanced manufactured CEs is found to be comparable to that of the original CEs throughout their useful lifetime. The core power distribution is also not prohibitively perturbed by the introduction of the new CE design at any time in the CE life. Pending irradiation characterization testing, it may thus be concluded that the advanced manufactured CE design can successfully replace the current design and is neutronically feasible for the operation of HFIR.