It is clear from the IAEA publication – Safety of Nuclear Power Plants: Design, SSR-2/1 (Rev. 1) that the classification of the initiating events for safety analyses is changing. New groups appear, using a new term – design extension conditions (DEC). In 2016 Bulgarian Nuclear Regulatory Agency (BNRA) substantially changed the content of “Regulation on ensuring the safety of nuclear power plants” and a new classification of the initiating events appeared too. In this document one of the sub-categories of events is postulated multiple failure events. Although the IAEA uses the term DEC analyses (without fuel melting) and the BNRA – analyses of postulated multiple failure events, the two terms essentially mean the same thing.
Keywords: analyses, DEC, safety, severe accidents.