Abstracts ASN Report 2019

NOTABLE EVENTS 2019 (ƺɀǣǕȇǣȇǕ z¨¨ɀ ɎȒ ƳƺƏǼ ɯǣɎǝ Ɏǝƺ ƺƏȸɎǝȷɖƏǸƺ ȸǣɀǸ 1. A paleoseismicity study consists in excavating trenches through the surface trace of an active fault in order to identify earthquakes which have in the past affected the region in question. Earthquakes form part of the natural risks that nuclear facilities must be able to withstand. Seismic protection measures are designed into the facilities and reviewed every ten years during the periodic safety reviews, to take account of changing knowledge. In France, the characterisation of the seismic risk that each Basic Nuclear Installation (BNI) must be able to withstand is based on a deterministic approach, detailed in basic safety rule 2001-01. This rule is supplemented by ASN Guide 2/01 which def ines the design provisions for the seismic protection of civil engineering structures. The hazard characterisation method consists in: Ҋ firstly, determining the “Maximum Historically Probable Earthquake” (MHPE) which corresponds to a return period of about 1,000 years. This level of earthquake can be considered as the most intense level “in human memory” identified in the region concerned; Ҋ then defining the “Safe Shutdown Earthquake” (SSE) which corresponds to an increase in the magnitude of the MHPE of 0.5 on the Richter scale. Furthermore, the SSE is positioned by convention as close as possible to the nuclear site within the seismotectonic zone to which it belongs. The SSE therefore integrates margins with respect to the historical earthquake recorded in the region in question: it is more intense and is positioned as close as possible to the nuclear site. On some sites, the consideration of paleoseismicity (1) data can supplement the movements associated with the SSEs. 0ɮƺȸɵ ׏׎ ɵƺƏȸɀً ƳɖȸǣȇǕ Ɏǝƺǣȸ ȵƺȸǣȒƳǣƬ ɀƏǔƺɎɵ ȸƺɮǣƺɯɀ Ȓǔ ǣɎɀ ǔƏƬǣǼǣɎǣƺɀً 0(I ȸƺƏɀɀƺɀɀ Ɏǝƺ ƺƏȸɎǝȷɖƏǸƺ ǣȇɎƺȇɀǣɎɵ ɎȒ ƫƺ ƬȒȇɀǣƳƺȸƺƳ ǣȇ Ɏǝƺ ɀƏǔƺɎɵ ƬƏɀƺِ Áǝǣɀ ȸƺƏɀɀƺɀɀȅƺȇɎ ǣɀ ȅƏƳƺ ǣȇ Ɏǝƺ ǼǣǕǝɎ Ȓǔ ƳƺɮƺǼȒȵȅƺȇɎɀ ǣȇ ǝǣɀɎȒȸǣƬƏǼ ǸȇȒɯǼƺƳǕƺ ƏȇƳ Əȇɵ ƺƏȸɎǝȷɖƏǸƺɀ ɎǝƏɎ ǝƏɮƺ ȒƬƬɖȸȸƺƳ ɀǣȇƬƺ Ɏǝƺ ǼƏɀɎ ȸƺɮǣƺɯِ ɀ Ə ȸƺɀɖǼɎً 0(I ȸƺǕɖǼƏȸǼɵ ȸƺǣȇǔȒȸƬƺɀ ȵƏȸɎɀ Ȓǔ ǣɎɀ ǔƏƬǣǼǣɎǣƺɀِ Without waiting for the periodic safety review, ASN may also ask that any event compromising the hypotheses used in the design of a facility be taken into consideration. ASN therefore asked EDF to determine whether the Le Teil earthquake of 11 November 2019, once it was characterised, required a reassessment of the MHPE and thus the SSE for the Cruas and Tricastin NPPs. If so, EDF must determine whether this reassessment will oblige it to reinforce its installations. ASN will review the entire process and issue a position statement on this subject. After the Fukushima NPP accident, ASN also asked EDF to check the robustness of its NPPs to an even higher earthquake level, the “Hardened Safety Core Earthquake” (HSCE), for which the main safety functions must continue to be guaranteed. The ground movements (accelerations) corresponding to the HSCE must be greater than those of the SSE plus 50%, and greater than those of earthquakes with a return period of 20,000 years. To meet this requirement, EDF has defined a “hardened safety core” of equipment (such as the ultimate backup diesel generator sets) that can withstand the HSCE and which is currently being deployed on its reactors. IN BRIEF The concept of the “hardened safety core” aims to create structures and equipment capable of withstanding events and of performing functions essential for the safety of the facilities and for management of an emergency on the site. Cruas-Meysse NPP ASN Report on the state of nuclear safety and radiation protection in France in 2019 21