“Whether evaluating the design of facilities in the planning stage or monitoring their construction, the challenges of extending the operational life of those in service, the decommissioning of those in final shutdown or the management of radioactive waste, the nuclear safety expert profession requires a system-wide view, over the long term. The simultaneous examination of next-generation projects and operation extension projects allows the expert, in particular, to acquire knowledge and skills that will enrich the Institute’s positioning on the various files.
At the beginning of the 2000s, the studies carried out into the design of the EPR-type reactors in the planning stage at that time fueled the definition of objectives for extending the operation of reactors in the fleet beyond 40 years. Similarly, ongoing appraisal and research on the design of EPR2 reactors or small modular reactors (SMR) will contribute to progress in various forms. Firstly, with respect to controlling the compliance of reactors in the context of their continued operation beyond 50 or 60 years, through the development of innovative non-destructive control means. Then by defining safety improvements, such as replacing equipment or components with more efficient equipment or components. Similarly, the feedback from operating the facilities currently in operation, including the most recent ones such as the Taishan EPRs, fuels the design choices for new projects.
This cross-functionality also applies between civilian and defense installations, with the examination of the safety standards applied to the nuclear propulsion of certain vessels of the French Navy fueling the studies conducted on SMRs. The safety analyses and recommendations of IRSN’s experts thus provide the authorities with the benefit of an overview of civil and defense nuclear installations.”
Karine Herviou
Deputy Director General,
in charge of Nuclear Safety
Against a backdrop of climate disruption and a growing demand for electricity – which RTE estimates must increase from 449 TWh to nearly 630 TWh in France by 2050 – the French government’s choice is focused on energy sobriety, energy efficiency, renewable energies and nuclear energy.
In February 2022, the President of the Republic announced France’s intention to acquire six new EPR2 type nuclear reactors and expressed its interest in developing new concepts such as small modular reactors (SMR). What strategy is IRSN implementing to prepare for the examination of the safety files that will be submitted to it as part of the construction of the EPR2 and the development of SMRs? How will its action contribute to the harmonization of nuclear safety approaches and practices at the international level? Responses…
EPRs and SMRs respond to quite different logical criteria. The first are high-power reactors (over 1,600 MWe) intended for generating electricity, which are envisaged as relays for the nuclear fleet in operation. The second are planned multi-purpose low-power reactors (less than 300 MWe), able to generate electricity or heat, or even both, in a combined manner, for example, in order to generate hydrogen.
For the renewal of the nuclear fleet, in May 2021, EDF proposed to start building three pairs of EPR2 reactors to the government. An option for four additional pairs is considered. At the end of June 2023, EDF submitted an application for authorization to build a first pair on the Penly site.
Drawing on the appraisal of the design and construction of the Flamanville (Manche) EPR – for which it is about to analyze the last start-up tests and ramp-up in 2024 – IRSN has defined an appraisal strategy aimed at completing, by the end of 2025, the review of the preliminary EPR2 safety report. This strategy is in line with the continuity of the appraisal of safety options, which the Institute presented to the Permanent Group of Experts for Reactors in 2019, and will be based on the ASN/IRSN guide no. 22 for the design of pressurized water reactors. To optimize resources, the Institute will focus on the main developments of the EPR2 compared to the EPR: transition from a double to a single containment enclosure and from four to three safety trains, better diversification of the cold source and the electrical supply… Then, it will assess the successive safety files produced by EDF following the decree establishing it, through to the authorization for commissioning announced by EDF for 2035/2037. For the different EPR2 pairs planned, particular attention will be paid to the effects of climate change as these can be anticipated over the planned operational life of these reactors, taking into account the planned installation sites.
Worldwide, nearly 70 SMR concepts have been announced, based on a large variety of sectors: pressurized water, high-temperature gas, fast-neutron (cooled by sodium, molten salts, gas, lead) reactors, etc. In France, the France 2030 “Innovative Nuclear Reactors” scheme provides support for the development of new reactors and has already announced several winners. For IRSN, such diversity required taking into consideration as early as possible the characteristics specific to the main concepts from a safety perspective. Thus, as from 2015, the Institute produced an initial appraisal report relating to the possible sectors in order to maintain a high level of safety requirements for this type of reactor. In 2024, it is preparing to assess the safety options file submitted by NUWARD (consortium comprising EDF, Technicatome, Naval Group, CEA, Framatome and Tractebel). The NUWARD SMR project comprises two compact pressurized water reactors of 170 MWe each, whose modularity is intended to enable part of the assembly operations to be carried out in the factory. At the same time, IRSN is continuing a cycle of discussions with the designers of other advanced models in order to identify with them, according to the characteristics of their concept, the priority topics to be investigated for safety. Security issues, which are very specific for this type of installation, will be the subject of dedicated appraisal in parallel.
Some SMR developers are considering installing them close to industrial areas, or even urban areas, and ultimately building many units. These elements justify the definition of ambitious safety objectives in terms of limiting the consequences of accidents, including those adopted for generation III, EPR-type reactors. In addition, the possibility of operating similar SMRs in different countries wishing to acquire such reactors calls for international harmonization of the safety requirements in force. IRSN has been contributing to the work of the IAEA’s Small Modular Reactor Regulators’ Forum since 2014. It also participates in the SMR Expert Group within the NEA Nuclear Facilities Safety Committee to identify the need for knowledge related to SMRs and, under the impetus of Jean-Christophe Niel, Chairman of this committee, it has published a roadmap entitled “Research Recommendations to Support the Safe Deployment of Small Modular Reactors”. Regarding NUWARD SMR, the Institute participated in the first phase of the Joint Evaluation Review of the concept, alongside the French, Finnish and Czech nuclear safety authorities, and will be involved in the second phase of this evaluation extended to a greater number of countries.
While NUWARD SMR is a pressurized water reactor whose fuel is similar to that of the fleet in operation, the implementation of a fast-neutron or gas-cooled SMR would require the development of a fuel cycle suitable for manufacturing fuel elements and managing the waste produced. These aspects raise many specific questions in terms of nuclear safety and security.
Small modular reactors, such as NUWARD SMR, use passive systems to ensure their safety. Research projects with which IRSN is associated aim to verify that the safety functions of these passive systems will be ensured in an accident situation.
[1] France 2030 – ANR-22-PAST-0001.
While the appraisal of the “hard core” type provisions, intended to strengthen the robustness of nuclear reactors against extreme hazards following the accident at the Fukushima-Daiichi power plant and those associated with the “Grand Carénage” carried out by EDF, is still ongoing, IRSN is preparing for the new challenges, with regard to safety, of extending the operating time of the French nuclear power plant fleet: a more efficient fleet, operated for longer and more resilient to climate hazards.
The 5th periodic safety review of the 900 MWe reactors (RP5-900), which will be launched shortly after the completion of the 4th review (RP4-900), will address quite different challenges. Inclusion of the feedback from the Fukushima-Daiichi accident, and the safety objectives defined by the ASN for the operation of reactors beyond 40 years, had led to the resumption of a large number of studies, numerous modifications and major changes to the general rules of operation.
With regard to RP5-900, the main challenges are to stabilize the safety rule set of the reactors concerned and to focus on operational safety, seeking simplifications if possible; then to ensure that the facilities comply with this rule set; and finally to take into account climate change and its consequences in the long term on the damage that the facilities may be subjected to.
EDF is preparing major developments that will have an impact on IRSN’s future appraisal activities. Thus, EDF wants to deploy multi-annual programs on its sites to verify that equipment complies with their safety rule set, supplementing current operating practices, and field visits, in addition to the investigation programs already planned in the framework of periodic reviews.
In order to increase the availability of its reactor fleet in service, the operator is also considering a new MOX fuel management with increased operating times between shutdowns. The Institute will analyze the safety demonstration studies rerun by EDF to take into account this new fuel management.
In the longer term, EDF is considering a simplification of the general operating rules, by which it intends to facilitate the work of operators and limit the duration of certain shutdowns that it considers to be linked in particular to the complexity of the current safety rule set. In this area, IRSN and ASN have initiated a preliminary dialog with EDF aimed, in the first instance, at identifying the issues raised and defining a strategy.
EDF is considering other performance levers for the fleet, such as increasing the electrical power of certain reactors, including through an increase in the nuclear power capacity. This would have an impact on the margins of the safety studies, which must be anticipated sufficiently in advance.
In order to restore margins with respect to safety criteria, material changes are envisaged. For example, with the introduction of new more accident-tolerant fuels (ATF), it would be possible to limit the phenomena of oxidation and deformation of the claddings in the event of a cooling loss accident and to ensure better retention of the fission products. The results of future test campaigns and the data from the research programs conducted will enable IRSN to develop and validate specific models for simulating the behavior of these future fuels.
Another lever is a less conservative simulation of physical phenomena occurring during incident or accident situations studied, which requires increased efforts for validating the software used. In this respect, IRSN will examine the results of the experiments carried out, for example, in the framework of the CEA’s METERO project (experimental platform allowing the study of complex and varied flows), to simulate these phenomena, compare them with those of the CATHARE software and ensure that all physical phenomena have been taken into account.
With a view to extending the operating time of the reactors beyond 60 years, IRSN has participated in defining, with ASN and EDF, the outline of a feasibility file that the operator must establish in 2024 and 2025. The Institute will assess this file starting in 2025 in order to present its conclusions to the ASN’s Permanent Groups of Security Experts in 2026. The aging of equipment and facilities will be central to this appraisal, with a particular challenge: assessing the ability of the non-replaceable equipment to ensure, for a period much longer provided for in the design, the safety functions assigned to it. This concerns three main types of equipment:
To determine climate hazards, EDF relies on a watch, reviewed every five years, which aims to anticipate the consequences of climate changes on compliance with safety objectives and must lead to in-depth analyses in the event of a “major climate event”. This process and its results are assessed by IRSN, which has its own calculation capabilities based on statistics of the extremes.
As part of the appraisal concerning the extension to the service life of existing reactors beyond 60 years, it is planned that EDF will produce a document at the end of 2024 presenting “an inventory of the provisions for adapting to climate change on an international level, and innovative solutions resulting from R&D work”. For its part, IRSN has undertaken, together with Météo France and the Pierre-Simon Laplace Institute, research through two doctoral theses to assess long-term changes in weather-related hazards.
The processing of spent fuels, recycling, storage, etc. The fuel cycle is confronted with major industrial policy challenges associated with nuclear safety issues, which will result in an increasing volume of appraisal activities for IRSN in the coming years.
Operated by ORANO in the municipality of Chusclan (Gard), the Melox plant produces fuel assemblies based on uranium-plutonium mixed oxide (MOX). The manufacturing difficulties experienced by the facility from 2018 onwards have generated increasing volumes of rejects sent to the plants in La Hague (Manche). In 2022 and 2023, IRSN published expert opinions on the safety files transmitted by ORANO for the creation of new storage capacities to accommodate them. In addition, ORANO has undertaken projects to modify this plant for which IRSN will have to carry out appraisals.
More information (in French only)In addition to these rejects, there is a problem in La Hague with the storage of plutonium from the processing of spent fuels, whose evacuation to the Melox plant is delayed. Another challenge is the storage of spent fuel assemblies in the pools in La Hague. ORANO has submitted an authorization application file, which IRSN will examine in 2024, for the densification of fuel pool storage, pending the commissioning by EDF, after 2030, of a new spent fuel storage pool on the La Hague site. At the same time, ORANO is exploring the dry storage of spent fuels in Eagle TN-type packaging.
Finally, the storage at La Hague of high-level or long-lived intermediate-level waste, in the form of glass or compacted, pending the entry into service of permanent disposal, has led ORANO to create additional storage capacities on the La Hague site.
IRSN will report its conclusions on the 2nd safety review of the Melox plant in 2024. In addition to production difficulties resulting in particular from a change in uranium supply, IRSN examines the problems of maintaining a facility in service for almost 30 years and the increase in collective dosimetry linked to these operations.
In La Hague, whether UP3 (INB no. 116) or UP2-800 (INB no. 117), the main challenges are those of reassessing the behavior of structures and equipment in service for more than 30 years in the face of natural hazards (earthquakes, snow, wind, tornadoes, etc.) and analyzing aging phenomena that influence the service life of key equipment such as the dissolver in the shearing-dissolution workshop or the evaporators in the fission product concentration workshop.
In addition, the challenge is to anticipate, for the post-2040 period (the current multi-year energy program retaining the choice of spent fuel processing until at least this deadline), an industrial solution – satisfactory from a safety point of view – either for the processing, or ultimately for the final disposal of spent fuel assemblies.
More information (in French only)
New models are being developed for transport packaging, which is essential for the fuel cycle operation. This is the case for the new TNG3 and TN112 packaging, developed by ORANO NPS for spent fuels, or the Eagle TN for their transport and dry storage. Their appraisal by IRSN has highlighted certain safety improvements.
Spread over decades, the decommissioning of nuclear facilities and the management of the resulting waste pose, par excellence, safety issues linked to the long-term management, among other things in terms of monitoring the facilities concerned and resistance to both aging and hazards, in particular climatic hazards.
With a view to examining the safety files that will be submitted to it, IRSN develops its own studies, for example for the characterization of climatic hazards and the analysis of the aging of materials such as elastomers. The Institute has already conducted a reflection on the decommissioning strategies of the major operators (EDF, CEA, ORANO), in particular examining the necessary conditions to successfully complete all decommissioning projects, taking into account their specific features (radiological inventory, location, type of waste that will be generated, etc.). In fact, in the coming years, this will involve assessing files relating to the decommissioning of a variety of reactors (UNGG in Chinon, Saint-Laurent-des-Eaux and Bugey, PWR in Fessenheim, etc.) and nuclear fuel cycle facilities (former fuel processing facilities in La Hague, etc.).
The decommissioning operations underway at Chooz and the preparatory operations for the Fessenheim decommissioning provide, in particular thanks to the standardization of reactors for each power level, feedback that enables a certain degree of confidence in the possibility of decommissioning the nuclear fleet under satisfactory conditions. However, since parameters such as the availability of storage facilities for the waste generated may constrain the progress of decommissioning operations, IRSN is paying particular attention, as part of its appraisal of the CEA, EDF and ORANO strategies, to the chaining of the different decommissioning projects and the associated waste management.
The decommissioning of nuclear facilities and the evolution of the reactor fleet, in particular the spent fuel reprocessing strategy, will change the nature and volumes of waste to be handled, leading IRSN to prepare for the acquisition of new knowledge in view of the appraisal of future safety dossiers. The development of new reactor sectors such as SMRs has therefore stimulated reflections led by IRSN, for example, as part of the European Joint Program for the Management of Radioactive Waste (EURAD) or the international SITEX Network.
In addition, the decommissioning of nuclear facilities will generate large volumes of long-lived intermediate-level waste, requiring dedicated facilities such as ICEDA pending the entry into service of CIGEO. The same situation applies to very low-level waste, for which the imminent saturation of the current disposal capacity requires the development of new management options. Lastly, the same applies to the graphite waste (long-lived low-level) resulting from the decommissioning of UNGG-type reactors, for which the management sector is currently being defined, or bituminous waste which requires additional research relating to the safety of their management.
The creation of the CIGEO geological disposal facility, if decided, will require safety appraisal support, in particular during its pilot phase with a limited inventory aimed at qualifying some of its components and the methods adapted to its industrial operation, then during the ramp-up of the facility. It should be noted that the evolution of the French nuclear power plant fleet, with the planned commissioning of six new EPRs, raises the issue of the capacities required to accommodate the additional volumes of waste generated, in terms of operational safety and after closure of disposal.
Monitoring the aging of dry packages is also a safety issue for which IRSN has launched, in its Tournemire underground research laboratory, a research program called PALLAS, in addition to those already in progress in this laboratory.
Faced with the increasing complexity of appraisal issues and new digital capabilities linked to the evolution of cognitive technologies, IRSN is innovating to meet the future challenges of nuclear safety appraisal.
The Institute’s initiatives encompass various areas – from expert systems to tools incorporating artificial intelligence – in order to develop a set of information processing or digital modeling methods capable of facilitating the identification of items of concern in terms of safety or radiation protection and providing support for technical positions.
In order to coordinate these initiatives, the Enhanced Appraisal program has been put in place, with an organizational structure based on agile governance, integration of IRSN’s rule sets and giving priority to the design of tools to assist appraisal and to the development of knowledge that can be mobilized thanks to the intersection of the data available to the Institute.
The functional objectives of the Enhanced Appraisal program aim to facilitate the expression of needs, pool resources and strengthen knowledge and skills on these new technologies. In addition, current issues concern the impact of artificial intelligence on nuclear risk management, on the explainability and trust in the models and, more generally, on the sharing of data in the context of appraisals. These prospective reflections are carried out in collaboration with ASN – in particular on a project to develop a nuclear safety data hub – with operators (EDF, CEA, etc.) and, internationally, with German and American partners of the Institute, GRS and the US NRC. The aim is to prepare for methodological and technological developments that may have an impact on safety and, by extension, on its appraisal and on the expert’s own profession.
In an innovation laboratory approach to citizen participation in nuclear safety and radiation protection, IRSN is developing new ways of opening up to society:
With this in mind, IRSN is working on creating a metric to assess the impact of its actions, which it will share in 2024 with its counterparts that are signatories of the openness to society charter. It is also the winner of the ANR’s Science with and for society call for projects, which will enable it to conduct participatory research actions in the Dunkirk area in partnership with the Université du Littoral Côte d’Opale.
