Nuclear safety expertise

Based in particular on an ongoing research effort and on the feedback from previous safety assessments, the expert appraisal work of IRSN is intended to shore up the positions of the authorities and government bodies in relation to all nuclear safety dossiers, whether relating to facilities that are in operation, under construction or being decommissioned, or else new concepts such as small modular reactors (SMR).
Again in 2021, the work of IRSN on safety appraisals was made possible by an effort to adapt to the requirements imposed by the Covid-19 health crisis, leading in particular to the postponement of activities, such as unit shutdowns for maintenance and core refuelling. Furthermore, in response to the ramp-up in expert appraisal activities linked to decommissioning and the recovery of old waste, IRSN has reviewed its organisation by bringing together its experts in this field within the same department, thereby enabling a cross-functional approach to the examination of dossiers from different nuclear operators and the ranking of expert assessment priorities.
While 2020 saw the publication of the summary notice of the 4th periodic review of 900 MWe reactors (RP4 900), 2021 was the year in which, one, work began on the generic phase of the 4th periodic review of the 1,300 MWe reactors (RP4 1,300) and, two, expert appraisals were conducted for the commissioning of the EPR reactor at Flamanville (Manche).

393

TECHNICAL NOTICES AND REPORTS
SUBMITTED TO THE FRENCH
NUCLEAR SAFETY AUTHORITY

353

EQUIVALENTS FULL TIME
DEVOTED TO NUCLEAR
SAFETY EXPERTISE

PREPARING FOR RP4 1,300

Built for the most part in the 1980s, the twenty 1,300 MWe French nuclear power plants are now entering the generic phase of their 4th ten-year safety review (RP4 1,300). In 2021, IRSN undertook the examination of the corresponding safety dossiers transmitted by EDF with a view to drafting – as it had done in 2020 for the 4th periodic review of the 900 MWe reactors (RP4 900) – a notice to serve as the technical basis for the ASN position on the fitness of the reactors concerned to remain in operation. This generic phase will be completed with a 10-yearly inspection of each reactor, comprising tests such as a hydraulic test of the primary circuit and inspection of the reactor vessel, along with a strength test of the double concrete enclosure surrounding the reactor building.

START-UP TESTS OF THE FLAMANVILLE EPR

IRSN has also conducted an appraisal of the results of the start-up tests conducted by EDF in the framework of the commissioning authorisation request for the Flamanville EPR reactor (EPR FLA-3), in order to ensure that the equipment and systems of the reactor operate in accordance with the study hypotheses and satisfy the set criteria in terms of performance. The Institute’s analysis shows that, despite the volume of work carried out by EDF being significant, the number of test procedures not carried out or only partially carried out is still substantial. These procedures will be rolled out in the next phase of start-up tests scheduled for the third quarter of 2022.

View, in synthetic images, of the principle of the SMR reactor
studied by the Nuward consortium © Nuward Consortium

In Brief

IRSN PUBLISHES AN INFORMATION NOTE ON THE SAFETY ISSUES OF SMALL MODULAR REACTORS

SMRs, or “small modular reactors”, are reactors with a power rating of less than 300 MWe and are characterised by a simplified design compared to the high power reactors that make up the current fleet of nuclear power plants. Among the 70 reactor concepts proposed around the world – most of them at a preliminary stage — EDF’s reactor is a pressurised water reactor (PWR) concept, designated NUWARD and designed for export. The analysis of the information available tends to demonstrate that SMRs have, in principle, favourable characteristics with regard to compliance with more demanding safety objectives than high-power reactors, in terms of limiting discharges in normal or accident situations – including serious accidents – and core meltdown frequency. In its information note, the Institute points out however that these different concepts must be examined in detail in order to take up a more advanced position on the safety level that can be attained by this type of reactor.

OPERATING REACTORS OF 1,350 MWe
IN FRANCE ENTER IN THEIR FOURTH
10-YEARLY REVIEW

1,450 MWe OPERATING REACTORS
IN FRANCE

DECOMMISSIONING OF THE BRENNILIS NUCLEAR REACTOR

In March 2021, IRSN presented to the “decommissioning” permanent group of experts of ASN the conclusions of its complete decommissioning expert appraisal of the Monts d’Arrée nuclear power plant situated at Brennilis (Finistère), closing down the 70 MWe EL4 reactor which was shut down in 1985. The Institute examined in particular the organisation defined by EDF for facilitating the liaison between its engineering and the teams assigned to the on-site operations, and the clean-up principles for the site structures and land. It determined that EDF should aim first and foremost for a clean-up level compatible with any public use of the site. In its conclusions, it underlined the emergence of technical topics that may be transposed from the decommissioning currently underway of the Chooz A reactor (Ardennes). The topics concern, for example, the capacity of EDF to decontaminate steam generators, so as to reduce the level of radioactivity of the waste and the radiological exposure of the workers, or the use of remote-controlled underwater cutting equipment in the reactor vessel.

OPERATION OF 1,450 MWe REACTORS

At the request of the ASN, IRSN has examined the possibility, in safety terms, of operating the 1,450 MWe reactors (N4 series) concerned by a phenomenon of accelerated corrosion of the M5 alloy fuel ducts, attributed mainly to nucleate boiling and to the low iron content of the material batches used for manufacturing these ducts. This accelerated corrosion phenomenon also affects, to a lesser degree, certain 1,300 MWe and 900 MWe reactors, due to the lesser thermohydraulic stresses. Although this phenomenon has not yet been encountered in France, it has already been observed abroad on reactors operated in Germany and Brazil. EDF has undertaken to pursue investigations in order to improve the detailed understanding of the mechanisms at the origin of this phenomenon, and also envisages compensatory measures on the four reactors of the N4 series in order to reduce the probability of occurrence and the potential consequences. IRSN has deemed satisfactory the provisions tabled by EDF, the efficacy of which will be verified by means of a monitoring programme.

INCIDENT OF UNCONTROLLED DRAINAGE OF THE MAIN PRIMARY CIRCUIT OF A REACTOR AT GOLFECH

Classed as level 2 on the international INES scale on account of its potential consequences for the safety of the Golfech nuclear power plant (Tarn-et-Garonne), the uncontrolled evacuation of the main primary circuit of reactor 2 when it was being drained, on 8 October 2019, was subject to an in-depth analysis by IRSN in 2020 and 2021. This analysis brought to light a number of factors, strongly interlinked, that had weakened several lines of defense: technical, human and organisational. Following the appraisal by IRSN, the management of the EDF nuclear facilities and the Golfech nuclear power plant undertook to implement diverse technical and organisational actions for making sensitive transitions more robust, and in particular those involving the draining of the main primary circuit.

In Brief

EXPERTS INTERACTING WITH CITIZENS

In the framework of its transparency and openness to society policy, IRSN contributed in 2021 to various initiatives aimed at associating civil society with its expert appraisal work. In parallel, it continued to pursue its training initiatives on nuclear safety with representatives of Local information commissions (CLIs) and, more generally, engaged in exchanges on the technical issues surrounding nuclear safety. The Institute also organised, in conjunction with the ANCCLI, a day of exchanges on 22 June 2021 on the subject of continued operation of 900 MWe reactor vessels “beyond 40 years”. This day was an opportunity explore in detail the expert appraisals carried out, to specify what conclusions had been made, and to answer the questions that had been gathered. With the ANCCLI and the CLIS de Bure, IRSN held discussion meetings on 3 February and 30 March on HLW/ILW-LL waste management. It also took part in a public meeting organised by the French Ministry of Ecological Transition on 8 March on the topic of the initial lessons from the public post-debate consultation on the 5th National plan for the management of radioactive materials and waste.

EUROSAFE 2021 FORUM

Organised by IRSN under the aegis of the ETSON network of European TSOs, on 22 and 23 November, the EUROSAFE 2021 Forum brought together in Paris some 250 participants from around 20 countries to discuss the topic: “Fukushima-Daiichi accident, Covid-19 and threats linked to climate change: nuclear and radiological safety in a disruptive world ”.

ELEMENTS OF NUCLEAR SAFETY PRESSURISED WATER REACTORS

A new version of the publication entitled “Elements of nuclear safety ”, coordinated and drafted mainly by Jean Couturier in an IRSN collection, the initial version of which had been published in 1996, this new edition can be downloaded from the IRSN website. It presents the state of play in the field of nuclear safety knowledge over its 40 chapters, providing additional insights, such as the history of the technical and regulatory changes, the progress made in safety through R&D, lessons learned from feedback, etc.

PERIODIC REVIEW OF THE HIGH FLUX REACTOR OF THE LAUE-LANGEVIN INSTITUTE

A nuclear reactor designed for scientific research in various domains, such as materials physics or molecular biology, the high flux reactor (RHF) operated in Grenoble by the Laue-Langevin Institute (ILL) underwent a periodic review. After appraisal of the corresponding dossier, IRSN highlighted the major work carried out by the ILL on verifying the conformity of the installation with the applicable requirements and on reassessing its safety, involving in particular provisions constituting the “post-Fukushima hardened core” of the reactor in the event of extreme hazards. IRSN did nevertheless point to the need for additional safety improvements, in particular reinforcing the polar crane of the reactor building and managing the consequences of any fire that might break out in this building.

DENSIFICATION PROJECT FOR POOLS C, D AND E AT LA HAGUE

While pending the commissioning by EDF of its future spent fuel assemblies storage pool, Orano is planning to increase the operational capacity of three spent nuclear fuel storage pools that it operates on its site at La Hague (Manche), by reducing the size of the storage equipment used (densification). At the request of the ASN, IRSN conducted an appraisal in 2021 of the safety options dossier for this project and issued a notice, available in commented version on its website. In its conclusions, the Institute considers that the safety options chosen for this densification are globally suitable. It identified, moreover, matters that should be taken into account in the dossier provided, in support of the future authorisation request. These concern in particular the design of the new storage facilities and the efficiency of the pool water cooling systems.