Actions taken in the Belgian nuclear power plants for the resolution of the GSI-191

The emergency core cooling system (ECCS) of a nuclear power plant supplies cooling water to the reactor vessel in the case of a loss of coolant accident (LOCA). A LOCA generates debris by the force of coolant impinging upon pipe insulation and entraining a wide variety of particulate matter from the reactor building surfaces that the coolant flows over. During the recirculation phase following a LOCA, if a sufficient quantity of debris accumulates on the sump screens, the ECCS pumps' suction flow path can be reduced significantly, causing a drop in the available NPSH and, eventually, a loss of pump flow. If the ECCS flow is lost for a sufficiently long time, the core may become uncovered and overheat, causing severe damage to the fuel. Since the Barsebaeck strainer event (July 1992), studies and experiments are being undertaken all over the world to provide a better understanding of how the different types of debris are generated, distributed, transported, and how they accumulate on the sump screens. All results of current experiments and research are not yet available. Nevertheless, a compensatory action plan was defined early last year to be applied to all Belgian units: - Each nuclear power plant in Belgium has been inspected by a team of engineers who examined and documented their particular situations with respect to debris generation and potential sump blockage. During these inspections (called 'walk-downs'), the physical configuration of the sumps, the type and state of thermal insulation and coatings are noted, along with any potential sources of debris and all information that may be useful for future assessment. - Plant housekeeping procedures were analysed for any possible links to debris generation and adaptations were proposed when required. - To reduce the risk of sump clogging, modifications of the post-accident operating procedures were analysed and mitigating actions were proposed. Solutions which have been applied at foreign power plants are being scrutinized. Lessons learned from a global study of the problem will yield a palette of possible solution elements which may be tailored to solve the problems encountered at any particular plant. (authors)