FEED-AND-BLEED PROCEDURE MITIGATING THE CONSEQUENCES OF A STEAM-GENERATOR TUBE RUPTURE ACCIDENT

Two accident scenarios with a steam generator tube rupture and loss of secondary heat sink in the Krsko NPP have been analyzed. The analyses have been performed with relap5/mod2 computer code on a VAX-8650. In the first scenario, availability of one HPSI pump was assumed, combine d with loss of secondary heat sink, following the total loss of off-si te power soon after identification and isolation of the ruptured SG. I n the second case, the accident was managed by only two centrifugal ch arging pumps. Loss of all off-site power, causing loss of secondary he at sink, was assumed after the pump trip for this case. Emergency oper ating procedures for the Krsko NPP were strictly followed. The symptom s of the accident led the operator into the feed-and-bleed procedure i n both cases. The procedure instructs the operator to cool down the pl ant by injecting cold water from the HPSI system directly into the pri mary system and discharging it through the pressurizer relief valves. In the second case, when no HPSI flow could be provided, operator impr ovised the feed-and-bleed procedure using the only source of water ass umed to be available, the two centrifugal charging pumps, to fill the primary system.