WENRA Approach with Respect to Design Extension of Existing Reactors

In 2014, the Western European Nuclear Regulators Association (WENRA) published a revised version of the Safety Reference Levels (RLs) for existing reactors developed by the Reactor Harmonisation Working Group (RHWG). The objective of the revision was to take into account lessons learned of the TEPCO Fukushima Dai-ichi accident. A major update of the RLs was the revision of Issue F ''Design Extension of Existing Reactors'' introducing the concept of Design Extension Conditions (DEC). The revised RLs clearly distinguish DEC not involving a severe accident (DEC-A) and involving a severe accident (DEC-B). They clarify how DEC are to be addressed in safety analysis and provide explicit goals of DEC analysis as well as attributes of the safety analysis of the selected DEC. They address adequate qualification and operability of (mobile) equipment used to manage DEC. The revised RLs also address sites where several reactors are collocated and emphasize the safety of spent fuel storage in DEC. They require independent and diverse heat removal means, one of them being effective after events involving natural hazards more severe than the one used for design basis, and address the availability of I&C, electric power and control room to manage DEC. This conference contribution discusses WENRAs view on the DEC concept for existing reactors, including the selection process for the design extension conditions and the requirements for ensuring the safety functions, in particular with respect to heat removal and emergency power. (author)