ASN Report 2018

In 2018 , t he appr oved o r gani s a t i ons ca r r i ed ou t 7,704 inspections on NPE design and manufacture for the NPE intended for the Flamanville EPR and 3,196 inspections for the replacement NPE intended for the NPP reactors in operation. These inspections are performed under ASN supervision. 2.2.2  –  Evaluation of the design and manufacture of NPE • Irregularities in the manufacturing plants 2017 and 2018 were marked by analysis of the consequences of the detection of irregularities in 2016, of varying scope and severity, in several NPE manufacturing plants. This was in particular the case in the Framatome Creusot Forge plant, where these practices had continued for several decades. Considering that these irregularities reveal unacceptable practices and that the industry needs to take fundamental measures to restore a high level of quality in the supply chain, ASN asked Framatome to conduct a review of the files of the components manufactured by Creusot Forge, to analyse the reasons the irregularities were not detected and to develop a quality and safety culture to guarantee the required irreproachable level of quality. At the same time, ASN asked EDF to analyse the causes of the breakdown in Framatome monitoring and to assess the steps taken by Framatome. These requests were extended to all the Areva NP plants. The fact that these requests were addressed and additional measures implemented satisfactorily by the Creusot Forge plant meant that at the end of January 2018, ASN considered that the resumption of manufacturing of components intended for French nuclear facilities could be envisaged in this plant under certain conditions, more particularly monitoring of the activities performed. In conjunction with this step and together with the organisations it approves, ASN is examining the handling of the deviations detected during the files review when evaluating the conformity of new equipment. Similar action is also carried out for the components integrated into equipment in service on the basis of analyses carried out by Framatome and EDF (see the box concerning the Creusot Forge plant). At the same time, EDF has begun work to adapt its inspection practices in order to counter the risk of fraud, more particularly by carrying out unannounced or cross-inspections. • Reinforcing justification of the design of NPE ASN has regularly observed that the justifications and demonstrations provided by the manufacturers with regard to NPE regulations, more particularly concerning the correct design of this equipment, are unsatisfactory. The industrial firms, EDF and Framatome in particular, therefore took fundamental measures as of the first half of 2015 to change their practices and bring them into line with the regulatory requirements. ASN monitored these measures, most of which were carried out within the framework of the French Association for NSSS design, construction and monitoring rules (AFCEN) and involved the majority of the profession. ASN considers that this approach is a positive one and, for most of the problems identified in 2015, considers that the AFCEN guidelines and methods published are appropriate. This approach will be repeated in the coming years so that the profession continues to make progress on certain topics and in order to learn the lessons from the initial applications of the guidelines and methods created. 2.2.3  –  Monitoring the operation of pressure equipment The reactor Main Primary and Secondary Systems (CPP and CSP) operate at high temperature and high pressure and contribute to the containment of the radioactive substances, to cooling and to controlling reactivity. The monitoring of the operation of these systems is regulated by the Order of 10 November 1999 relative to the monitoring of the operation of the Main Primary and the Main Secondary Systems of nuclear pressurised water reactors. These systems are thus monitored and periodically maintained by EDF. This monitoring is itself checked by ASN. These systems are subject to periodic re-qualification every ten years, comprising a complete inspection of the systems involving non-destructive examinations, pressurised hydrotesting and verification of the good condition and proper operation of the over-pressure protection accessories. • Nickel-based alloy areas Several parts of pressurised water reactors are made with nickel-based alloy. The use of this type of alloy is justified by its resistance to generalised or pitting corrosion. However, in reactor operating conditions, one of the alloys adopted, Inconel 600, proved to be susceptible to stress corrosion. This particular phenomenon occurs when there are high levels of mechanical stress. It can lead to the appearance of cracks, as observed on certain SG tubes in the early 1980s or, more recently in 2011, on a vessel bottom head penetration in Gravelines reactor 1 and in 2016 on a vessel bottom head penetration in Cattenom reactor 3. These cracks require that the licensee repair the zones concerned or isolate the part of the system concerned. At the request of ASN, EDF adopted an overall monitoring and maintenance approach for the areas concerned. Several parts of the main primary system made of Inconel 600 alloy are thus subject to special monitoring. For each of them, the in-service monitoring programme, defined and updated annually by the licensee, is submitted to ASN, which ensures that the performance and frequency of the checks carried out by EDF are satisfactory and able to detect the deteriorations in question. • The strength of reactor pressure vessels The reactor pressure vessel is an essential component of a pressurised water reactor and contains the reactor core and its instrumentation. For the 900 MWe reactors, the vessel is 14 m high, 4 m in diameter, 20 cm thick and weighs 330 tonnes. For the EPR, currently under construction at Flamanville, the vessel is 15 m high, 4.90 m in diameter, 25 cm thick and weighs 510 tonnes. In normal operating conditions, the vessel is entirely filled with water, at a pressure of 155 bar and a temperature of 300°C. It is made of ferritic steel, with a stainless steel inner liner. Regular monitoring of the state of the reactor pressure 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. 282  ASN report on the state of nuclear safety and radiation protection in France in 2018 10 – EDF NUCLEAR POWER PLANTS