Regulatory requirements and implications of probabilistic safety studies for the Italian NPPs

At present, the Italian licensing process of nuclear power plants is set on the basis of deterministic criteria and review guides. Nevertheless in the safety assessment of plant design and in the definition of new design criteria for future plants, there is now a trend towards a systematic use of probabilistic risk assessment (PRA) techniques, willing to provide assurance that accidents which cause plant degraded conditions are very unlikely to occur. This approach is in line with the Italian policy which enhances prevention of accidents rather than their mitigation. In practical applications, the use of PRA techniques has been and is being implemented gradually, depending on their level of maturity and in view of uncertainties which affect the results of the analyses. As a matter of fact, the last two applications of PRA techniques were conducted in Italy in a different manner and different probabilistic requirements were set by the Italian Regulatory Body for decision making purposes. The first application concerns the Alto Lazio NPP, a BWR plant now under construction in an area about 100 km far from Rome. The second one is related to PUN, namely the Italian PWR Standard Plant to be developed in the framework of the present National Energy Plan. Information is given on the main technical aspects characterizing the two applications. Consideration is also given to those aspects of applications and issues that have been accounted for by the Regulatory Body before making decisions for licensing or regulatory purposes