REVIEWING THE SAFETY OF WWER-440 UNITS IN SLOVAKIA A REGULATORY APPROACH

摘要

A safety review of nuclear power plants (NPPs) is an essential component of the measures required to maintain a high level of nuclear safety, to recognize the scope and the potential consequences of deviations from safe conditions and to define the scope of safety upgrading. Safety review and safety upgrading of NPPs represent a very complex task in Slovakia, which has two different types of WWER-440 reactors in operation and under construction, a considerable lack of energy resources and limited financial resources. Regulatory involvement in safety review and upgrading is based mainly on Act No. 28/1984 on State Supervision on Nuclear Safety of Nuclear Installations, which gives the regulatory body the right to issue supplementary licensing conditions. At present, the general approach to each of the different reactor designs is to handle the bulk of safety issues by means of long term plans in a consistent, complex way. The entire spectrum of information sources and opinions is used in the safety review and for the implementation of corrective measures. For operating NPPs in Slovakia, these sources consist mainly of safety reports that have been elaborated after ten years of operation, level 1 probabilistic safety assessments, IAEA reports on safety issues, proposals of experts taking part in missions to NPPs, and the results of various international technical projects. Standard regulatory activities, such as routine and special reviews, play an extremely important role. Even though there are many national and international sources of information, the full responsibility of operators and the regulatory body is recognized. The following basic points are considered in regulatory reviews and decision making: The aim of safety reviews is to provide a basis for safety upgrading; the present safety standards are used as a basis for safety reviews; and probabilistic and deterministic approaches are used in parallel. International involvement is welcome, regarding both accumulation of knowledge and building a higher level of confidence. Because of limited resources, safety upgrading measures should be distributed in time; priority is given to the oldest V-230 units. Utilities should first select a feasible option for safety upgrading and then apply for regulatory approval. Extensive consultations should take place between the operator and the regulatory body during the preparation of a regulatory resolution. After approval by the regulatory body of the option proposed, this becomes an obligatory requirement, which can be modified only in exceptional circumstances and when it is technically justified and approved by the regulatory body. Gradual safety upgrading during extended refuelling outages is better than long term plant shutdown; the duration of major safety upgrading is usually several years. The involvement of national companies is important to ensure sustainable progress in plant