IMPROVEMENTS ON FRENCH NUCLEAR POWER PLANTS FOLLOWING FUKUSHIMA ACCIDENTS AND CONSISTENCY WITH NEW WENRA SAFETY REFERENCE LEVELS

摘要

From the beginning of their operation, the safety of each French Nuclear Power Plant (NPP) has been reassessed during periodic safety reviews (PSR), every ten years. As EDF is committed to continuous improvement of nuclear safety, numerous modifications have been progressively decided and implemented on its fleet of reactors, in particular to take into account operational experience feedback and to consider events at the plant or reported by other plants (sharing relevant good practices or considering appropriate corrective actions from normal or abnormal operation and other important safety-related information). The accidents which occurred at the nuclear power plants in Fukushima-Dailchi in 2011 resulted in France, as in Europe, in a complementary safety assessment (so called stress-tests) intended to confirm the compliance with their design bases and to evaluate their behavior beyond it. These evaluations have shown that nuclear facilities have a satisfactory level of safety as a result of the continuous improvements implemented on the plants in the framework of PSR, but that it was necessary to improve their robustness to be able to cope with rare and severe hazards, beyond the safety margins they already have. Planned improvements include several aspects, of which the main ones are the implementation of a hardened safety core of components intended for the management of rare and severe hazards resulting from a beyond design basis hazard and the deployment of a nuclear rapid response force (FARN as a French Acronym). The hardened safety core aims to avoid massive releases and lasting effects in the environment. To do this, it relies on existing and new equipment and on organizational provisions. Its functions include the evacuation of the residual heat, the control of reactivity, the prevention of the fuel assembly uncovery in the fuel building or in the reactor building in shutdown modes, the limitation of the major releases in the event of a core melt accident. It also includes provisions allowing the operator to ensure crisis management, including a crisis centre, means of communication, and dose and radiological measurement in the environment. Components belonging to the hardened core should be robust against hazards significantly exceeding the design basis. A site evaluation process has led to the definition of a "rare and severe earthquake " and a "rare and severe flood" for each NPP site. Other rare and severe hazards such as lightning, hail or tornadoes are also taken into account. The FARN is intended to complement the hardened safety core and the existing crisis organization to bring on site sufficient human and equipment resources within 24 hours after the occurrence of the postulated situation. The paper presents how the improvements being implemented to French NPPs after Fukushima accidents contribute to consistency with the new WENRA Safety Reference Levels (SRL), issued in September 2014, to take into account the lessons learned from TEPCO Fukushima Dailchi nuclear accidents.