Evolution of accident management strategies from the present to the next generation nuclear power plants

The knowledge gained in Accident Management (A.M.) by means of studies and experiments performed for the current NPPs can be largely implemented in the advanced, passive safety NPPs, for which A.M. is still an application step of the defence in depth principle. Obviously, such implementation will take into account the safety philosophy peculiarities of the concerned plants, and the role assigned to their operators, which is largely determined by the objective of drastically reducing human errors and their potential effects on the plant safety. Indeed, in comparison with the current NPPs, the operators of the considered advanced plants are not strictly required to perform safety actions early in accidents progression, but are entrusted to follow-up and support automatic interventions of active and passive systems, and to manage the post accident plant conditions. A preliminary analysis shows that the A.M. implementation in advanced, passive safety plants could undergo as from now recognizable problems, mainly regarding: supervision needs and equipment requirements; utilization strategies for A.M. supporting equipment; staffing and training of operators; technical bases and procedures to cope with severe accidents. The related safety issues should be solved by appropriate analyses, strictly interacting with the design development. Operator's role and needs for (modes of) human intervention should be taken into account in every development stage of the concerned plants designs and should be carefully evaluated in assessing the plant response to the considered events, with deterministic and probabilistic methods. Also, specific studies and experiments should be performed, to support the development of A.M. bases and procedures, and to determine the equipment effectiveness as well. In summary: The knowledge in A.M. gained by studies and experiments performed for the current NPPs must be transferred to the advanced, passive safety NPPs, for which A. M. is still a step of defence in depth strategy. Such implementation must take into account some peculiarities of the concerned plants safety philosophy, including the operator role, and require adequate solution for some safety issues, a number of which has been recognized by the previously exposed preliminary analysis. The main issues pointed out regard: monitoring and control problems; design requirements and strategy for utilization of hardware supports; staffing problems; technical bases and possibility of severe accident simulation for development of A. M. procedures and for operator training. Such peculiarities in A. M. demands for advanced, passive safety plants should be timely addressed, to find prompt solutions for the related issues, and the required research and development effort should be adequately addressed. Also, these activities must effectively interact with the design development, in order to allow the attainment of the required objectives with the best level of simplicity and effectiveness