Hypothetical accident analyses on the conceptual NIST reactor with a split core using RELAP5-3D

This paper performs steady-state and transient analyses for the recently proposed NIST research reactor. The primary purpose of this work is to examine the RELAP5-3D models for the study of the thermal-hydraulics (T/H) safety characteristics of the new reactor configured with a horizontally split core. Previously, the multi-channel T/H safety analysis code ANL-PARET was employed to model the transient behavior of the reactor during normal and off-normal design basis accidental conditions. These analyses were restricted to the reactor core portion due to limited modeling features of the PARET code. This investigation extends the reactor safety analyses using the more widely known systematic safety analysis code – RELAP5-3D. A nodalization of the core consisting important heat structures and hydraulics components in the primary cooling system of the reactor is realized in the RELAP5-3D. Both steady state and reactivity insertion accidental transient calculations are performed. For verification purpose, the RELAP5-3D simulation results are compared to the previous PARET results. These comparisons show that the RELAP5-3D outcomes have a very good agreement with the ones from the PARET code, which verifies the feasibility of the current model in a certain degree.