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      Dessin de Nicolas Waeckel chapitre 5

      * “The Grand Carénage is a heavy worload! I agree” © Nicolas Waeckel

      The EDF Group launched a vast investment programme to extend the service life of its operational fleet beyond 40 years, with the goal of becoming a global reference in nuclear safety. This programme is exceptional due to the volume and complexity of the works involved, which is spread over more than a decade. It mobilises the sites, engineering departments and all of its industrial partners. The modifications are carried out during the fourth ten-yearly outages (VD4) of each reactor of the 900 and 1300 MWe series, and during the third ten yearly outages for the 1450 MWe series.

      In a similar manner, EDF Energy launched its Long-Term Operation (LTO) for the Sizewell B PWR, planning for its operation up to at least 2055.

      Framatome has carried out significant investment to refurbish its fuel fabrication plant at Romans-sur-Isère.

      In France, the service life of a nuclear reactor is not defined in advance. The Operator performs a periodic safety review (RP) every ten years to confirm the plant’s compliance with the applicable rules and to update the nuclear safety risk assessment. The safety review takes into account the plant’s condition, experience collected during operation, technological advances, standards and knowledge, including those concerning climate change and its effects. 60% of the modifications are completed during the ten-yearly outages (VD). To even out the workload of the VD4s, additional suites of modifications supporting the initial modifications are programmed during the following outages.

      VD4 Gravelinnes

      Lessons learned from the RP4 900

      Beyond the successes of the VD4 900 project, lessons must be learned for the other periodic safety reviews. These reviews started late for the 900 MWe series. The organisations had to be adapted to meet the deadlines for the first-in-series. The modification documents were delivered late. The very significant modification programme required integration in three phases. Between two ten-yearly outages, the teams live with constant changes to equipment and operating standards. These conditions do not give teams time to assimilate their plant, and organisations end up being saturated. The RP4 900 generated numerous technical prescriptions which could not be prepared for due to their late inclusion. Some modifications relating to the tornado risk have to be updated every few years to integrate new standards.

      Points of attention

      The VD4 900 project must now overcome several issues. In the context of a very heavy workload, the rate of implementation must be maintained across all the plants. The quality of work must not be compromised by the sustained pace of equipment delivery and the involvement of new contractors. It is also important to know how to close-out the project by rejecting modifications that may come to light too late.

      I commend the initiatives from the Nuclear Fleet Engineering, Decommissioning & Environment Division (DIPDE) to improve its work methods, like the standardisation of modification documents through the ‘NOM’ING’ project and the development of a hybrid digital mock- up. This should not, however, replace the presence of teams on site.

      In preparation for outages, 70% of the modifications are carried out with the reactor in service, which makes operations complex and increases the workload of control room operators, especially in terms of managing the many inhibited fire detectors, negatively affecting control room serenity. The number of exemptions from the technical specifications has increased. The activity schedules have become denser, and their reliability has deteriorated. The accumulation of limiting conditions complicates the planning of the instrumentation technician’s activities, who must carry out routine activities outside normal working hours. I expect that the findings of the organisational and human factors study carried out at Tricastin will be taken into account.

      la maquette numerique developpee par les equipes de la DIPDE

      The transition to the VD4 operating standards is not without impact on the fuel loading plans. The fuel reloading safety assessments require significantly more powerful calculation means and, in 25% of cases, the fuel loading plans have to be re-modelled (see Chapter 7).

      Hybrid digital mock-up (MNH)

      The MNH is a user-friendly digital tool that provides 3D layout drawings. It combines 3D scans of facilities with photos to create layout drawings in 3D with an accuracy of a tenth of a millimetre. It is available for each first-in- series for the CP0, CPY, P4, and P’4 series and is in the process of being developed for the N4 series. Used to support site surveys, it helps the DIPDE, the Electromechanical & Plant Engineering Support Department (CNEPE) and their partner design offices during the development phase of modifications. The Operations & Engineering Training Department (UFPI) and the plant Operators also use the MNH.

      Reactor unit compliance review (ECOT)

      These compliance reviews help to show that the reactor conditions correspond to their reference state. This is demonstrated through specific in situ inspections of structures and equipment, as well as the verification that the applicable standards are being deployed in the plant. Methodical and selective, this approach relies on the incorporation of regulatory requirements into the site’s standards and operating documents, and on representative sampling campaigns. The objective is to allow the Operator to engage in the compliance of their plant and to formalise this engagement through tangible and verifiable information.

      Forward planning for the VD3 N4

      The project for the VD3 N4 series was launched in 2021 with an alignment logic of ‘4-4-3’ with the VD4 900 projects and the VD4 1300 projects. The N4 series will benefit from the latest advances in nuclear safety as early as its VD3, without having to wait for its fourth periodic safety review. The first-in-series at Chooz is scheduled for 2029 and will take into account the modifications of the 1300 MWe series, which are taken as the reference. The power output of the ultimate emergency diesel generators warrants special attention.

      controle mis d une cuve reacteur de paluel
      Vercors: a reactor building mock-up

      Vercors is a mock-up of a P4-type reactor building at a one-third scale. This mock-up is used to predict changes (creep, propagation of defects, and water diffusion in concrete) in a reactor building representative of EDF reactors. Time is accelerated by a factor of 9.

      The Vercors facility currently represents a 70-year-old reactor building. The leak rate criteria of the reactor containment remain compliant. Changes in its dimensions and leak rate seem to be stabilising over time. No specific weaknesses have been detected, whether in the pre-stressing or due to the appearance of specific leakage areas such as the basemat, the top ring, penetrations or equipment hatch.

      The workload is constantly growing. The VD4 900 projects are in full swing, with a volume of activity that is decreasing more slowly than expected due to the additional work phases (lot B and lot B+). For the 1300 MWe series, even though the RP3 safety reviews have yet to be definitively closed out, the engineering programme for the fourth periodic reviews (RP4) has already been launched at full speed with modifications to be deployed from 2026. The RP3 for the 1450 MWe series and the RP5 for the 900 MWe series will soon be added. This stacking effect must be brought under control to ensure that the workload is sustainable for all stakeholders: EDF engineering, the Operator, industrial partners, the ASN and IRSN. In line with my recommendation from 2022, I advocate the development, in conjunction with the ASN, of a ‘strictly necessary’ culture, and the use of a method of ‘weighting’ safety challenges to enable prioritisation of the modifications, as well as foregoing those that contribute very little to nuclear safety margins.

      maquette vercors

      François Roussely predicted as early as 2010 that “the only reasonable logic cannot be a continuous increase in safety standards […]”, and it was necessary to “combine safety standards and economic constraints as effectively as possible, including an international or at least European vision”.

      The industrial programme for the in-service sites has intensified significantly these past few years. The volume of work of the RP4 with its cavalcade of modifications has distanced us from the historical approach of ‘leaping from one 10-yearly outage to the next’, moving instead towards a continuous stream of modifications. Sites with four or six 900 MWe reactors are constantly completing modification after modification, without being able to achieve any stability before starting the RP5. Added to this are the Covid pandemic and the stress corrosion cracking issue. The outage placement programme has reached a level of instability too great for the smooth implementation of an industrial programme of this scale. The context has become so complex that a simple refuelling outage (offering a break in maintenance activities) on a reactor with an 18-month fuel cycle can no longer be scheduled.

      I commend the joint initiatives supported by EDF and the ASN to better manage and lighten the workload of periodic safety reviews. A multi- year outlook makes it easier to identify periods with high volumes of work. Ownership between EDF and the ASN will help to moderate and make progress on safety studies. Finally, a ‘workload management’ working group has enabled optimisation of the assessment process for certain requests from the ASN. For the RP4 1300, EDF has also suggested simplifying the assessment of modification studies in a way similar to the method used for the 900 MWe series, working on the basis of expert opinions and the transposition of studies already carried out.

      cnpe de paluel tts vd4 1 300

      Heysham 1 Forty years


      The IAEA offers its Member States review missions on the safety aspects of long-term operation (SALTO): a comprehensive safety review directly addressing strategy and key elements for the safe long-term operation of nuclear power plants. The evaluation of programmes and performance is made on the basis of the IAEA’s Safety Standards and other guidance documents. These reviews are led by peers who check compliance and issue recommendations for improvements where necessary. These reviews enable plant staff to share their work practices with experts; they strengthen the public’s confidence, and provide assistance for licence renewals and plant life extension requests.

        Your opinion is important to us!

        Let us know what you think about this chapter.