In order to develop a thermal-hydraulic analysis model of the SG (steam-generator) to simulate transient phenomena in the FBR (sodium cooled fast breeder reactor) MONJU, JNES (Japan Nuclear Energy Safety Organization) validated a SG analysis model using the RELAP5/3D code against the results of turbine trip test at a 40% power load. The modeling by using the code was performed to explain main observed behaviors of the pressure and the temperature of the EV (evaporator) steam outlet, and the temperature of water supply distributing piping (near the water supply chamber) until 600 seconds after the turbine trip. The analysis results of these behaviors showed good agreement with the test results on parameter study of the blow efficiency (release coefficient.). It was found that RELAP5/3D with a two-fluid model of water/steam and a sodium fluid model for tube outside predicted well the physical behaviors: the void of steam generated by the depressurization boiling moves upward in the down-comer tubes accompanied by the enthalpy, increases the temperature of the water supply chambers; and that the pressure change of a “shoulder” like shape is induced by the mass balance between the steam mass generated in the down-comer tubes and the steam mass blown from the SG. The applicability of RELAP5/3D to the SG modeling was confirmed by the well simulation of the actual FBR system.

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