The analyses of more probable scenarios of accidents with a loss of core cooling, potentially resulting in core damage, and PRA results show that the most critical LOCA scenario is that accompanied by a failure of ‘normal’ ECCS channels, caused by the failure of active elements (pumps or connecting valves of the same type).

To cope with such situation, the KLT-40S design provides for an option to supply water to the reactor via the pipelines of the purification system, using the turbine plant pumps.

Measures on accident mitigation include measures on limitation of the core damage fraction, measures on in-vessel retention of the corium, and measures on limitation of radiological consequences.

Measures on limitation of core damage fraction

Core damage process in the KLT-40S nuclear installation is relatively slow due to the injection of water from the hydro-accumulator that cools overheated and partially degraded core elements. Successful realization of the measures on water supply to the reactor at this stage of an accident will lead to the flooding and cooling of core materials, and would allow prevention of a molten pool formation on the reactor bottom head and exclude an impact of the corium on the reactor vessel.

Measures on in-vessel retention of corium

For retention of the molten core inside the reactor vessel, a special system is provided for in the reactor unit design that secures external cooling of the reactor vessel in accidents with core damage and core melt relocated to the reactor vessel bottom. In-vessel retention of the corium allows for exclusion of negative phenomena associated with corium release to the containment.

Measures on limitation of radiological consequences

To exclude irradiation of the personnel and population in case of a severe accident, the following protective measures need to be implemented:

(1) To ensure protection of the personnel, it is necessary to exclude staff presence in the compartments adjacent to the containment and in other compartments with high radiation levels;

(2) To limit radiation dose to the population living within a 1 km radius from the floating NPP, it may be required (depending on the actual radiation situation) that some protective measures, such as iodine prophylaxis or sheltering, are implemented. As a protective measure, a temporary limitation should be established on the consumption of separate agricultural products grown within a radius of up to 5 km from the floating NPP and contaminated by radioactive release.

Evacuation of the population is not required at any distance from the floating NPP.