Blowdown transient for sodium-steam water SG for prototype fast breeder reactor

Prototype Fast Breeder Test Reactor (PFBR) Steam Generator is once through steam generator in which water flows from bottom to top in 547 tubes, changing its state from highly subcooled to superheated state as it receives heat from sodium flowing from top to bottom in the shell side. Depressurization of steam generator from the dump valve provided at bottom is protective action. It prevents further possibility of water steam leak into sodium and subsequent sodium - water reaction. To perform depressurization transient analysis of PFBR appropriate thermal hydraulic modeling of SG is essential. Correct thermal hydraulic modelling needs simulation of sodium system, steam water system with different states from highly subcooled to superheated, coupling between sodium and steam-water system, SG tube and shell and different valve action. The computer code DPPFBR is developed with capability to simulate all these systems and phenomena encountered during transient. Different models of the code have been validated and code has been used for analysing depressurization transient. This paper describes various models used in the code and results of analysis for typical scenario. (author)