Analysis of the hydrogen behaviour in compartments of the Ignalina nuclear power plant

The Accident Localisation System (ALS) of the Ignalina nuclear power plant is a ''pressure suppression'' type confinement, which protects the population, employees and environment from radiation hazards. According to the emergency operating procedures for the Ignalina nuclear power plant ∝ 110 m3 of hydrogen is released to the ALS compartments during the maximum design basis accident. However, in case of beyond design basis accidents, when the oxidation of zirconium starts, the amount of generated hydrogen could be significantly higher. The volume concentration of hydrogen in the compartment might reach 4% of a combustible mixture. To prevent a possible hydrogen accumulation in the ALS of the Ignalina nuclear power plant during an accident, the H2 control system is installed. The analysis performed resulted in the identification of places of possible H2 accumulation in the ALS compartments during transient processes and the assessment of the mixture combustibility in these places for a postulated accident scenario. The results also allow to evaluate the influence of the proposed severe accident management strategy on the ALS conditions. (orig.)