Deploying Experiments To Support Internal Hazard Management

A typical feature of internal hazards and a special concern of accident progression in nuclear power plants are that such hazards challenge simultaneously various levels and barriers of the Defence in Depth concept. Internal hazards can themselves be initiating events, or they are created during the accident progression. This paper describes how the owner and operator has deployed thermal-hydraulic experiments in order to solve the plant-specific issues related to internal hazards at the Loviisa power plant. The presented cases are experiments for investigating thermal mixing, loop seal issue, counter-current flow limitation, boron crystallization, sump screen clogging and effects of non-uniform ice sublimation.