Rappel Application to Accident Analysis of the Nist Research Reactor

Detailed safety analyses have been performed for the 20 MW D2O moderated research reactor (NIST) at the National Institute of Standards and Technology (Nist). The time-dependent analysis of the primary system is determined with a RELAR5 transient analysis model that includes the reactor vessel, the pump, heat exchanger, fuel element geometry, and flow channels for both the six inner and twenty-four outer fuel elements. A post-processing of the simulation results has been conducted to evaluate minimum critical heat flux ratio (CHFR) using the Sudo-Kaminaga correlation. Evaluations are performed for the following accidents: the control rod withdrawal startup accident and the maximum reactivity insertion accident. In both cases the RELAR5 results indicate that there is adequate margin to CHF and no damage to the fuel will occur because of sufficient coolant flow through the fuel channels and the negative scram reactivity insertion