ASN Report 2017

341 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants structures and which can degrade the overall operation of the steam generator. To prevent or mitigate the fouling effects described above, various solutions can be used to minimise metal deposits: preventive chemical cleaning or mechanical cleaning (using hydraulic jets), material replacement (brass by stainless steel or titanium alloy, which are more corrosion-resistant) in certain secondary system exchanger tube bundles, modification of the chemical products used for conditioning of the systems and an increase in the pH of the secondary system. Some of these operations require licensing for the discharge of the conditioning products. Some chemical cleaning processes are still being tested to demonstrate that the chemical products utilised are harmless. In particular, the identification of a corrosion risk on reactors which had undergone such cleaning in 2016 led ASN to request the implementation of specific maintenance measures. Replacement of steam generators Since the 1990s, EDF has been running a Steam Generator Replacement programme (SGR) for those SGs with the most heavily degraded tube bundles, with priority being given to those made from Inconel 600 without heat treatment (600 MA) and then those made from Inconel 600 with heat treatment (600 TT). The replacement campaign for SGs with a tube bundle made of 600 MA (26 reactors) was completed in 2015 on reactor 3 at the Le Blayais NPP. It is being pursued with the replacement of SGs with heat treated Inconel (600 TT) tube bundles. 2017 saw the replacement of SGs on Cruas-Meysse reactor 1. Replacement of the SGs for Paluel reactor 2 (see box opposite) was resumed at the end of 2017 and will continue in 2018. Monitoring methods applied to main primary and secondary system pressure equipment Article 8 of the Order of 10th November 1999 specifies that the non-destructive testing processes used for in-service monitoring of the pressure equipment of the main primary and secondary systems of nuclear power reactors must be qualified before they are used for the first time. This qualification is granted by a body comprising experts from both inside and outside EDF whose expertise and independence are verified by the French accreditation committee. Qualification is a means of guaranteeing that the non- destructive testing process actually achieves the anticipated level of performance as described in specifications drawn up beforehand. Owing to the radiological risks associated with radiographic inspection, ultrasound inspections are preferred, provided that they offer equivalent inspection performance. To date, more than 90 non-destructive test processes have been qualified for the in-service inspection programmes. New processes are currently being developed and qualified in order to meet new needs. With regard to the Flamanville EPR, virtually all of the test processes for in-service monitoring of the pressure equipment of the main primary and secondary systems was qualified ahead of the Pre-Service Inspection (VCI) of the main primary system and the main secondary systems, corresponding to more than 30 qualified processes specific to the EPR. 2.2.4 Assessment of pressure equipment in operation ASN considers that the situation of the second containment barrier represented by the main primary system remains a subject of concern in 2017, with the year being marked by the processing of irregularities detected during the review of the manufacturing files for the components produced by the Areva NP Creusot Forge plant (see box p. 337). Again in 2017, very high levels of fouling were found in certain steam generators in several reactors, which could be liable to impair their operating safety. This situation is the result of maintenance that was insufficient to guarantee satisfactory cleanness. In addition to this assessment, which is similar to that made in 2016, showing a deterioration by comparison with 2015, ASN observes that the last SG replacement operations for the 900 MWe reactors were postponed notably owing to the numerous deviations in the manufacture of this equipment. These postponements led to operations to make cracked tubes on certain steam generators safe, by plugging or sleeving, until such time as they are replaced. ASN considers that the in-service monitoring of the other equipment on the main primary system, pursuant to the Order of 10th November 1999, is carried out appropriately. The detection of a new crack on vessel bottom head penetration No. 58 on Cattenom NPP reactor 3 illustrates the risk of further deterioration owing to the ageing of the facilities and confirms the need to adapt the level of in-service monitoring accordingly and to bring forward the development of repair processes. The principles for repair of this vessel bottom head penetration will be presented to ASN in 2018. 2.3 The containments 2.3.1 Monitoring the containments The containments undergo inspections and tests to check their compliance with the safety requirements. Their mechanical performance in particular must guarantee a good degree of reactor building tightness in the event of its internal pressure exceeding atmospheric pressure, which can happen in certain types of accidents. This is why, at the end of construction and then during the ten-yearly inspections, these tests include an inner containment pressure build-up with leak rate measurement, as specified in Article 8.1.1 of the Order of 7th February 2012 which sets out the general rules for basic nuclear installations.