Safety must never be taken for granted. As ageing potentially means a decrease of the plant safety level, a reassessment of its safety must be carried out to check it is adapted to new regulations and safety and radioprotection practices. It has to be combined with the operating feedback and to take into account the future of the plant (life time, evolution of activity and materials implemented).
The objective is to identify any non-conformity with the current regulations and practices, in order to examine their acceptability, given the compensatory actions proposed by the operator. The Nuclear Safety Authority will rule on the plant's future, taking into account the acceptability of the propositions. There is a great deal at stake for the operator in such a reassessment, especially if the plant is older. Questions related to seismic behaviour are frequently a subject requiring the reinforcement of the buildings. The feasibility of this may lead the operator to decide to shut down the plant more or less in the short term.
The objective is not necessarily to eliminate the existing non-conformity, but to check that the plant's safety and radioprotection arrangements are adequate for the future operating context as defined by the operator, respecting the regulations in force.
The practice of this periodic safety reassessment enables the avoidance of any serious discrepancy between the plant's operation and the new regulations and practices, and encourages an on-going upgrading of plant safety and operating practices.
The safety reassessment of older plants represents a growing part of IRNS's activity (French Nuclear Safety Authority technical support). Such a reassessment needs to involve specialists in all the technical fields. One of the main difficulties is the assessment of the arrangements proposed by the operator to deal with the identified unsatisfactory points. This concerns particularly earthquake protection, as no general rules allow an assessment of the seismic behaviour of existing buildings. This can lead to complex and long assessments, firstly of the concerned buildings' behaviour, secondly of the adequacy of the reinforcements proposed.
An application of such a safety reassessment will be done with an older facility operated by the CEA in the nuclear center of Cadarache. This facility, built in the early 1960's, is dedicated to the study of irradiated materials and fuels.