Preparing SCALE and MELCOR for source term analysis of heat-pipe microreactors

Abstract Heat-pipe microreactors represent an emerging class of advanced nuclear reactor designs optimized for transportability, factory fabrication, and long-duration autonomous operation. Their unique design features introduce neutronic, thermal, and severe-accident characteristics that differ significantly from traditional LWR technologies. Preparing analytical tools to evaluate beyond-design-basis accidents (BDBAs) and fuel-cycle source terms is therefore essential for future licensing activities. The U.S. Nuclear Regulatory Commission (NRC) Office of Research has strengthened the capabilities of the SCALE and MELCOR computer codes to facilitate the modeling of these unique designs and demonstrated the new code features with select scenarios. This article discusses the motivation, modeling workflow, representative scenarios analyzed, and highlights insights gained that inform future license reviews and ongoing code development.