Results of the Level 1 Probabilistic Safety Assessment (PSA)of the Ignalina Nuclear Power Plant have shown that in topography of the risk, transients dominate above accidents with the loss of the coolant accidents. PSA has shown that failure of the core long-term cooling is the main contributor to frequency of the core damage. However, the transition to the condition of the reactor core due to loss of the long-term cooling specifies potential opportunities for the management of the accident consequences. The detail thermal-hydraulic analysis of long-term core cooling accidents should be performed for development of accident management strategy.
The most likely initiating event, which probably leads to the loss of long term cooling accident, is station blackout. The analysis of the station blackout was performed using the RELAP5/MOD3.2 model of Ignalina NPP reactor primary circuit and plant safety systems. The analysis results showed that the depressurisation of the reactor coolant system should be initiated if any other action of core cooling restoration does not success. The depressurisation creates the conditions for water supply from Emergency Core Cooling System (ECCS) hidroaccumulators and deaerators. Later the non-regular means (fire machine)for supply of firewater to the Main Circulation Circuit (MCC)should be employed.