ASN Report 2018

2.4.5  –  Preventing the effects of internal and external hazards • Fire risks In the same way as the other BNIs, NPPs are subject to ASN resolution 2014-DC-0417 of 28 January 2014 on rules applicable to BNIs for the control of fire risks. Controlling the fire risk in nuclear power plants is built around the principle of defence in depth, based on three levels: facility design, prevention and fire-fighting. Design rules must prevent a fire from spreading and mitigate its consequences; they are based primarily on “fire zoning”. This involves dividing the facility into sectors and containment areas designed to keep the fire within a given perimeter bounded by items (doors, walls and fire dampers) offering a specific fire resistance duration. The main purpose is to prevent a fire from spreading to two redundant equipment items performing a fundamental safety function. Prevention primarily consists of the following: ∙ ∙ ensuring that the nature and quantity of combustible material present in the premises remain below that of the scenarios used for zoning; ∙ ∙ identifying and analysing the fire risks in order to take steps to avoid them. In particular, a “fire permit” must be issued and protective measures must be taken for all work liable to cause a fire. Finally, fire detection and fire-fighting procedures should enable a fire to be tackled, brought under control, and extinguished within a time compatible with the fire resistance duration of the zoning elements. ASN checks that the fire risk is taken into account in the NPPs, notably through an analysis of the licensee’s baseline safety requirements, monitoring of significant events notified by the licensee and inspections performed on the sites. The important risks associated with fire have been the subject of numerous ASN requests since 2003 and ASN thus reminded EDF in 2016 that, for the purposes of the fourth periodic safety review of the 900 MWe reactors, it expected a well-structured and robust safety case based on a defence in depth approach. ASN is examining the justification methods produced by EDF. These will be submitted to the GPR for its opinion in 2019. • Explosion risks An explosion can damage elements that are essential for maintaining safety or may lead to failure of the containment with the release of radioactive materials into the facility, or even into the environment. Steps must therefore be taken by the licensee to protect the sensitive parts of the facility against explosions. ASN checks these prevention and monitoring measures, paying particular attention to ensuring that the explosion risk is included in EDF’s baseline safety requirements and organisation. ASN also ensures compliance with the “Explosive Atmospheres” (ATEX) regulations with respect to worker protection. • Internal flooding risks An internal flood, in other words which comes from within the facility, may lead to failure of equipment necessary for reactor shutdown, fuel cooling and containment of radioactive products. Steps are therefore taken to prevent internal flooding (maintenance of piping carrying water, etc.), or mitigate its consequences (presence of floor drains and water extraction pumps, installation of sills or leaktight doors to prevent the flood from spreading, etc.). These measures are regularly inspected by ASN. ASN remains vigilant with regard to the risks of internal flooding as a result of an earthquake, as well as with regard to the integration of operating experience feedback, in particular the processing of deviations affecting certain internal flooding protection measures. • External flooding risks The partial flooding of the Le Blayais NPP in December 1999 led the licensees, under the supervision of ASN, to reassess the safety of their facilities with respect to this risk in more severe conditions than previously and to make a number of safety improvements, with a schedule proportionate to the potential consequences. In accordance with the ASN requirements, EDF completed the required work on all its nuclear power reactors in 2014. At the same time, to ensure more exhaustive and more robust integration of the flooding risk, as of the facilities design stage, ASN published Guide No. 13 in 2013 concerning BNI protection against external flooding. For the existing facilities, ASN asked EDF in 2014 to take account of the recommendations of the Guide on all its reactors. ∙ ∙ for the 1,300 MWe reactors, ASN asked EDF to do this as a priority during the third periodic safety review; ∙ ∙ for the other reactors in service, EDF will do this as a priority during the next periodic safety reviews (fourth reviews for the 900 MWe reactors and second reviews for the 1,450 MWe reactors). Following the stress tests performed in the wake of the Fukushima Daiichi accident, ASN considered that, with regard to protection against flooding, the requirements arising from the complete reassessment performed after the flooding of the Le Blayais NPP in 1999 provided the nuclear power plants with a high level of protection against the risk of external flooding. However, in June 2012, ASN issued several resolutions to ask the licensees: ∙ ∙ to reinforce NPP protection against certain hazards, such as intense rainfall and earthquake-induced flooding; ∙ ∙ to define and implement a “hardened safety core” of material and organisational measures to control the fundamental safety functions in extreme situations and in particular in the case of flooding beyond the design-basis safety requirements (see point 2.9). 288  ASN report on the state of nuclear safety and radiation protection in France in 2018 10 – EDF NUCLEAR POWER PLANTS