Reactor Pressure Vessel Characterization Methods Development for the High Flux Isotope Reactor to Support Future Vessel Replacement

This paper presents newly developed methods and results from a series of studies to characterize the High Flux Isotope Reactor's (HFIR) reactor pressure vessel (RPV) to support a preliminary RPV replacement design specification. The US Department of Energy Office of Science chartered a Basic Energy Sciences Advisory Committee (BESAC) subcommittee review to provide recommendations on the long-term strategy concerning HFIR, which has been operating for nearly six decades. Radiation bombardment on the RPV is causing embrittlement of the steel; thus, the BESAC subcommittee recommended it be replaced to maintain HFIR and its unparalleled neutron science capabilities for research in neutron scattering, isotope production, materials and fuels irradiation, and neutron activation analysis. A reactor physics methodology framework using the HFIRCON, MCNP, ADVANTG, and SCALE codes was developed to calculate key RPV heat deposition, displacements per atom (dpa), and source term metrics. A large region of the RPV was first analyzed on a coarse spatial mesh to determine the area experiencing the greatest heat deposition and damage rates. Then, a higher-fidelity analysis of the RPV surrounding HB-2, the most limiting area, was performed to characterize the key metrics. Assuming operations at HFIR's design power of 100 MWth, peak local metrics of 0.7 W/cm³, 2.4 × 10^-10 neutron dpa/s, 7.3 × 10^-12 gamma dpa/s, 1.1 × 10¹⁰ γ/cm³.s, and 2.8 Ci/cm³ were calculated for the RPV with the models, methods, and assumptions discussed in this paper.