The purpose of this paper is to illustrate RELAP4/MOD5 applications and adaptability to a proposed Power Burst Facility (PBF) loop modification. RELAP4 is used to predict loop pressures resulting from thermal swell generated by fuel pin disassembly during a reactivity initiated event. Also, RELAP4 is applied to a blowdown problem requiring several code modifications for modeling specific hydraulic and fuel rod conditions. Thermal hydraulic responses resulting from (1) a design basis fuel pin energy transient and (2) an accidental rapid loop depressurization are presented
