Modelling operator rediagnosis during an SGTR event

A parametric analysis has been performed analysing the hypothetical steam generator tube rupture (SGTR) accident combined with the total loss of secondary heat sink. The analyses have been performed by Relap5/Mod2/36.05 and Mod3 5M5 computer code versions using universal Krško NPP input deck, developed at IJS. Two break sizes have been chosen for the SGTR event: two and five double-ended broken tubes have been assumed. Total loss of secondary heat sink has been assumed from the beginning of the calculation with no possibility of initiating secondary-side feed and bleed. The ways of cooling down the plant after the postulated accidents have been investigated. A scenario has been analysed, when the operator applies rediagnosis procedure, during the period of loss of secondary heat sink threat, and manages SGTR consequences first. The Krško nuclear power plant emergency operating procedures have been verified for this case