Application of RELAP/SCDAPSIM/MOD 4.1 to the Analysis of Molten Salt Small Modular Reactor System: Mark-1 Pb-Fhr

Abstract

The Mark 1 Pebble-Bed Fluoride –Salt –Cooled High-Temperature-Reactor (Mk1 PB-FHR) is a small, modular 236MWth graphite-moderated pebble-bed fluoride-salt-cooled, high-temperature reactor, developed by University of California, Berkeley (UCB). One of the most important tasks for the design and assessment of Mk1 PB-FHR performance is to develop system analysis codes. A new version called RELAP/SCDAPSIM/MOD4.1 code has been developed by Innovative System Software (ISS). RELAP/SCDAPSIM/MOD4.1 version is developed by ISS, which is powerful enough to treat liquid molten salts in the presence of non-condensable gases and also can simulate liquid-fuel molten-saltreactors. The Mk1 PB-FHR design uses three modular 50% capacity DRACS units for emergency decay heat removal, the DRACS are passive and function by natural circulation. Therefore, to determine whether the DRACS system as designed could remove the decay heat during a Station Blackout (SBO) event, RELAP/SCDAPSIM/MOD4.1 code is used to analyze Mk1 PB-FHR SBO transient. Results from the transient calculations show that the maximum temperature of fuel element is 1312K and the maximum salt temperature of the molten salt is 1060 K, which is far below the safety limit temperatures 1873.15K and 1123.15 K.