Abstracts ASN Report 2019

ĶłŁņŇŅňĶŇļłŁ ĴŇ ĿĴŀĴŁʼnļĿĿĸё ŇĻĸ ʼnĸņņĸĿ ļņ ӄӈŀ ĻļĺĻё ӇєӌӃŀ ļŁ ķļĴŀĸŇĸŅё ӅӈĶŀ ŇĻļĶľ ĴŁķ ŊĸļĺĻņ ӈӄӃׇŇłŁŁĸņє In normal operating conditions, the vessel is entirely filled with ŊĴŇĸŅё ĴŇ Ĵ ŃŅĸņņňŅĸ łĹ ӄӈӈׇĵĴŅ ĴŁķ Ĵ ŇĸŀŃĸŅĴŇňŅĸ łĹ ӆӃӃխ є Ň ļņ made of ferritic steel, with a stainless steel inner liner. Regular inspection of the condition of the vessel is essential for two reasons: ҄ The vessel is a component for which replacement is not envisaged, owing to both technical feasibility and cost. ҄ Monitoring contributes to the break preclusion approach adopted for this equipment. This approach is based on particularly stringent design, manufacturing and in-service inspection provisions in order to guarantee its strength throughout the life of the reactor, including in the event of an accident. During operation, the vessel’s metal slowly becomes brittle, under the effect of the neutrons from the fission reaction in the core. This embrittlement more particularly makes the vessel more susceptible to thermal shocks under pressure, or to sudden pressure rises when cold. This susceptibility is aggravated by the presence of technological flaws, which is the case for some vessels with manufacturing defects under their stainless steel liner. ASN regularly examines the evidence to substantiate the ļŁіņĸŅʼnļĶĸ ŅĸņļņŇĴŁĶĸ łĹ ŇĻĸ ʼnĸņņĸĿņ ŇŅĴŁņŀļŇŇĸķ ĵŌ ё Ňł ĸŁņňŅĸ that it is sufficiently conservative. • xƏǣȇɎƺȇƏȇƬƺ ƏȇƳ ȸƺȵǼƏƬƺȅƺȇɎ Ȓǔ ³ɎƺƏȅ JƺȇƺȸƏɎȒȸɀ The SGs comprise two parts, one of which is a part of the primary system and the other a part of the secondary system. The integrity of the main components of the SGs is monitored, more specifically the tubes making up the tube bundle. This is because any damage to the tube bundle (corrosion, wear, cracking, etc.) can lead to a primary system leak to the secondary system. Rupture of one of the tube bundles would lead to bypassing of the reactor containment, which is the third containment barrier. The SGs are the subject of a specific in-service monitoring programme, ķĸĹļŁĸķ ĵŌ ĴŁķ ŃĸŅļłķļĶĴĿĿŌ Ņĸʼnļņĸķ ĴŁķ ĸŋĴŀļŁĸķ ĵŌ є łĿĿłŊļŁĺ ŇĻĸ ļŁņŃĸĶŇļłŁņё ŇĻłņĸ Ňňĵĸņ ŊĻļĶĻ ĴŅĸ Ňłł ĵĴķĿŌ damaged are plugged, to remove them from service. ³z ǣȇ ٮ ƳƺȵɎǝ ǣȇɀȵƺƬɎǣȒȇ ƏɎ Ɏǝƺ JȸƏɮƺǼǣȇƺɀ z¨¨ ٫ ³ɎƺƏȅ JƺȇƺȸƏɎȒȸ ٫ xƏɵ א ׎׏ ז ªɖƏǼǣˡƬƏɎǣȒȇ ƳƺǔƺƬɎ ǣȇ Ə ɀɎȸƺɀɀ ٮ ȸƺǼǣƺɮǣȇǕ ǝƺƏɎ ɎȸƺƏɎȅƺȇɎ ȵȸȒƬƺɀɀ ƳɖȸǣȇǕ ȅƏȇɖǔƏƬɎɖȸƺ Ȓǔ Ɏǝƺ IȸƏȅƏɎȒȅƺ ³ɎƺƏȅ JƺȇƺȸƏɎȒȸɀ In 2019, Framatome revealed that the stress-relieving heat treatment conditions for some of the assembly welds made on SG components in the past did not meet the heating uniformity and temperature range requirements. This deviation in the stress-relieving heat treatment conditions can lead to changes in the metallurgical characteristics of the materials with respect to the hypotheses considered in the design files, or insufficient relief of the mechanical stresses induced by welding. EDF justified maintaining the integrity of the relevant equipment in service, by drawing on the results of tests performed on a representative mock-up, on material test coupons and on numerical temperature uniformity prediction models. During each reactor outage and before restart, the welds concerned are specifically checked (thickness measurements and defect search). At the same time, EDF set up a detailed characterisation programme using mock-ups and material tests. ASN called on the expertise of IRSN with regard to EDF’s models and test programmes. This deviation also affects the equipment currently being manufactured for various projects, such as the replacement SGs and the Flamanville EPR reactor. Finally, ASN asked EDF and Framatome to carry out a review of the various processes used to determine the possible extension of this problem. This review is under way. In 2019, ASN carried out three inspections since this deviation was reported in September 2019. These inspections confirmed the efforts made by EDF and Framatome. They found that the process was not correctly managed. Requests were made regarding strategies to characterise the behaviour of the materials and the representativeness of the hypotheses used in the safety cases. Final joint Heat treatment by muffles equipped with electrical resistors Joint between shells Head/ Plate joint 284 ASN Report on the state of nuclear safety and radiation protection in France in 2019 ׏׎ ٲ THE EDF NUCLEAR POWER PLANTS