As a public expert on nuclear and radiological risks, IRSN assesses the safety of nuclear facilities – reactors, fuel cycle plants, laboratories, research or radioactive waste disposal facilities – at each stage of their life cycle, from design to decommissioning. The results of its research programs and studies, the analysis of feedback from events occurring in facilities and transport, and the lessons learned from previous safety assessments feed into its expertise work.
In 2022, IRSN worked on several major expertise files, such as identifying the main challenges of the 10-year nuclear safety assessment, the Flamanville EPR reactor, following up the generic periodic review for 900 MWe reactors, the EPR2 project, fuel cycle facilities and dismantling, R85 transportation packaging, and feedback on fuel behavior in reactor over the past decade. Yet the most important files remain, one, the periodic safety review of the nuclear fleet – at the generic review stage for the 1,300 MWe reactors (RP4-1,300) and the tenyearly inspection for the 900 MWe series reactors (VD4-900) – and, two, work related to the analysis of stress corrosion damage to pipes connected to the main primary circuit of several EDF reactors; a phenomenon which has led to the prolonged shutdown of around a dozen of them.
In 2022, IRSN published its safety expertise strategy for the next 10 years. The Institute recently dealt with several major safety dossiers relating to nuclear reactors (4th safety review of the 900 MWe reactors, commissioning dossier for the Flamanville 3 EPR), fuel cycle facilities (future EDF centralized spent fuel pool), research laboratories, and the transportation of nuclear materials. In a rapidly changing context, IRSN now faces new challenges: aging of facilities, relaunch of nuclear power, climate change, etc. At this pivotal time, it was important to review the previous safety expertise strategy and prioritize the issues. This new strategy, applicable to all civil nuclear facilities, is broken down into four main areas.
The first area involves improving operational safety, with regard for example to training field operators in the proper use of safety mechanisms, or improving the reliability of interventions. This includes in-depth analyses of how well operating standards are assimilated and applied as well as feedback on operating experience.
The second area involves improving the design safety of existing facilities, based on a global vision of safety. This requires the stabilization of safety standards for existing facilities and monitoring implementation in the field, while taking into account consequences of climate change, and analyzing the conditions for keeping older facilities in operation. Encouraging operators to dispose of old waste and rapidly dismantle shut-down facilities is also part of this priority area.
The third area concerns future facilities. In particular, this involves taking a position on the safety objectives and requirements to be adopted, taking into account best practices and doctrines at international level, and taking onboard feedback acquired on the most recent projects, implementing an approach consistent with the stakes. In addition to EPR2, IRSN is preparing expertise for new reactor concepts, such as small modular reactors (SMR) which implement innovative technologies.
Finally, the last, more general area involves being able to adapt and anticipate. Faced with ongoing digitalization for operators, the possibilities offered by artificial intelligence technologies, innovative study methods, as well as the need for more global approaches to safety – including a comprehensive understanding of the socio-technical system and organizations –, the business of safety expertise will have changed markedly by 2030. IRSN is busy preparing for this.
489
TECHNICAL OPINIONS
AND REPORTS
TO THE NUCLEAR
SAFETY AUTHORITY
After the generic review of all reactors in the 900 MWe series (RP4-900), the ten-yearly inspection of each of these reactors (VD4-900) was the object of a periodic review conclusion report (RCR) drawn up by EDF. In this document, the operator rules on the facility’s compliance with its safety standards and, as such, draws up a summary of any modifications made on or planned for the facility in order to correct any non-compliant findings or improve facility safety.
At the request of the ASN, IRSN examined the various themes of this periodic review, such as facility compliance, its ability to continue operating beyond 40 years, control of potential consequences linked to its aging, protection against the effects of external stresses, civil engineering, condition of the reactor vessel, qualification of materials in accident conditions, and progress in deploying “postFukushima” measures. For each report, nearly a thousand pages were analyzed to draft the technical notice submitted by the Institute to the ASN. In 2022, the Institute published the technical notices relating to the periodic reviews of the No.2 Bugey and No.2 Tricastin reactors.
After carrying out the fourth periodic review of the 900 MWe reactors (RP4-900), IRSN continued in 2022 with that of the twenty 1,300 MWe reactors (RP4-1,300) commissioned by EDF from the mid-1980s. This large-scale project, which began in 2019 with the examination of the safety guidance files prescribing the subjects of interest to be examined during the generic phase of the RP4-1,300, has continued since 2021 with the examination of the first safety dossiers submitted by EDF. This generic phase will be completed by the end of 2024 at which time the Institute will submit a technical notice to the ASN, enabling them to take an informed stance on the ability of 1,300 MWe reactors to continue operating beyond 40 years.
IRSN’s experts drew on the conclusions of the assessments carried out as part of RP4-900, submitted to the ASN at the beginning of 2021, to prioritize the subjects to be examined with regard to safety issues, taking into account the main differences in design between the 900 MWe and 1,300 MWe reactors. One of these concerns the double containment shell of the 1,300 MWe reactors, for which the Institute has launched a research program on the behavior of the leaktight liners on the underside of the reactor building in the event of a serious accident. IRSN will also examine the additional safety studies relating to the loading of six of these reactors with uranium-plutonium mixed oxide (MOX) fuel, which constitutes a major change in relation to their design baseline.
Finally, the RP4-1,300 expertise will also be an opportunity to focus on highly complex topics such as the potential impact of internal and external stresses (fire, explosion, heatwave, internal flooding, etc.) and the deployment of the latest “hard core” equipment, incorporating the lessons learned from additional safety assessments carried out on nuclear facilities following the Fukushima-Daiichi accident.
As their name suggests, the access hatches allow various pieces of equipment to enter and exit the containment of the reactor building. These hatches ensure the containment of radionuclides in the reactor building, particularly in the event of a serious accident, by compressing the seals when they are closed. IRSN studied the behavior of these seals under the combined action of irradiation, temperature, pressure, and water vapor. In the technical notice that it issued on this basis in 2022, the Institute asked EDF to complete its sealing demonstration in severe accident conditions, which has not yet been done for any of the reactor access hatch seals of the fleet in operation.
Jimmy is a high temperature calorigenic microreactor project developed by the company Jimmy SAS. At the request of the ASN, IRSN assessed in 2022 whether or not adequate information had been received to conduct an expertise of the safety options. This analysis showed that the main safety options (core, barriers, main accidents, etc.) were addressed in the dossier, but that their assessment would require additional information from the designer. IRSN’s analysis was therefore limited to the technical subjects underpinning the Jimmy concept – such as the reactor core and primary circuits – with a view to an initial assessment of the maturity and adequacy of the safety options currently proposed.
At the end of 2021, a phenomenon of stress corrosion cracking (SCC) affecting the pipes connected to the primary circuit of several EDF nuclear reactors was observed, leading to the prolonged shutdown in 2022 of around a dozen of them. This is a fairly common type of corrosion in conventional industry but less common in nuclear power, and generally results, for corrosion-prone materials, from the combined action of mechanical stress and an aggressive environment. This damage generates one or more cracks, which then spread within the material concerned. “In reactors, the main cooling circuits and connected circuits are made of stainless steel – alloys of iron, chromium and nickel. The basic corrosion mechanism observed is linked to thermally activated oxidation of the metal,” explains Olivier Dubois, deputy director of nuclear safety expertise at IRSN. “For a given mechanical load and chemical environment, the higher the temperature, the faster the cracks will spread.” Defects resulting from SCC in stainless steel piping are particularly difficult to detect by non-destructive testing (ultrasound or X-ray). “Furthermore, this is a pernicious phenomenon, insofar as regular inspections of the pipes can only identify the defect once it has become fairly deep. Lastly, the speed at which the cracks spread cannot be characterized precisely for the moment”, Mr Dubois goes on to say.
In parallel with the actions implemented by EDF, in 2022 IRSN used its simulation tools to assess the potential consequences of the rupture of the pipes concerned to evaluate the concomitant safety issues and share its findings with EDF. As EDF continues its work replacing the sections concerned and IRSN analyzes the various aspects of EDF’s files, the root causes of the damage remain uncertain: excessive mechanical stresses due to thermal stratification phenomena, welding anomalies, chemical effects in which oxygen present in the water could play a major role, or something else?
As part of its research in 2022, the Institute also continued its work, in collaboration with international partners such as the United States Nuclear Regulatory Commission (US NRC), on achieving a better understanding of the propagation of ultrasonic waves in stainless steels. The results obtained will enable IRSN to take a stance on the performance of non-destructive testing implemented today and testing methods currently under development.
As part of the expertise of this periodic review, in 2022 IRSN presented to the Permanent Group of Experts for Laboratories and Plants (GPU), working closely with the ASN, the conclusions of its assessment of the supplements relating to the NPH workshop, focusing on this workshop’s behavioral studies in the event of natural hazards (earthquake, wind, etc.). The Institute underlined the extent of the reinforcement and deconstruction work that the operator has engaged to carry out, considered that the compensatory measures put in place by Orano as part of the periodic review of the UP2-800 plant had to be maintained until the work is completed, and stressed that this work should enable compliance with the safety requirements currently defined for this INB.
The decommissioning of a nuclear facility is a complex operation, raising questions about multiple issues relating to safety, radiation protection, and waste management. As part of its expertise missions, IRSN assesses, at the request of the ASN, the safety provisions proposed by operators in the file attached to the decommissioning decree request. In 2022, the Institute commissioned the assessment of the decommissioning file for the Fessenheim power plant (Haut-Rhin) whose two reactors were shut down in 2020. These two 900 MWe reactors will be the 2nd and 3rd PWR reactors to be decommissioned in France, following that of Chooz A (Ardennes).
The law of 2015 on Energy transition for green growth (TECV law) provides for the principle of immediate decommissioning to avoid foisting on future generations the burden of the related operations; it implies having timely access to the necessary provisions, reliable technical solutions, and industrial channels for radioactive waste management. In terms of safety, this principle has many advantages, such as rapid evacuation of the most radioactive substances, better knowledge of the state of the facility to be decommissioned, internal availability of human resources and skills, and fewer effects of aging. More generally, this approach reduces risks to the public and the environment at the earliest possible stage.
Spread over several years, the management of a decommissioning project begins by characterizing the initial condition of the facility concerned and precisely defining the target condition. From there, the actual reactor decommissioning is organized into four main stages: evacuation of materials and waste present, in particular in the reactor building; dismantling of the equipment present (reactor vessel, steam generators, primary and secondary circuits, etc.); clean-up of the premises (monitoring of their rehabilitation or complete deconstruction) and, finally, soil decontamination. At present, in France, several nuclear facilities – fuel cycle plants, laboratories, research reactors, etc. – are in the course of being decommissioned and dismantled. As such, they provide useful feedback on the safety of these operations, which require specific safety planning and analyses, paying particular attention to the risks of dispersion of radioactive materials due to internal factors such as fire or to co-activity, taking into account organizational and human factors.
In the case of the Fessenheim power plant, IRSN has already taken a stance on the removal operations for equipment no longer necessary for facility safety due to the fuel’s removal. Operations prior to the start of the actual decommissioning (planned for 2025) – such as decontamination of the primary circuit or evacuation of the different parts of the old steam generators stored on site – are in progress, scheduled or already completed.
Alongside these operations, the Fessenheim power plant provides an opportunity for in vivo studies of the effects of aging phenomena, particularly on equipment or materials inaccessible during regular operations or whose controls are limited. For IRSN, samples of materials and components should therefore be planned, in order to conserve them for future research and development programs, before they are altered by the dismantling operations.
In 2022, the Institute examined the seismic movements defined by EDF for the reactors in the 1,300 MWe reactor series based on historical earthquakes. In its technical notice, the Institute considers the seismic hazard satisfactory for all sites, with the exception of Cattenom and Saint-Alban. Furthermore, it considers that the new method proposed by EDF for determining the magnitude/depth pairings of historical earthquakes presents several positive developments. Nevertheless, IRSN needs additional information to verify the validity of certain choices and assumptions used by EDF in the calibration and application phases of this method.
In 2022, IRSN produced around twenty technical notices dealing with the prospective commissioning of the Flamanville 3 EPR. Several of them concern EDF’s processing of anomalies affecting pipe welding. Overall, the corresponding information was considered acceptable by IRSN. Regarding the reactor systems that are important for safety, the expertise conducted on the pressurizer valves revealed, despite constructive modifications, a need for reinforced monitoring in operation. The assessment on “recirculation”, i.e.: the possibility of cooling the core long-term following an accident, shows that this subject continues to require attention; demonstration tests are still underway. Finally, during the operation of the first EPRs commissioned worldwide, localized fluctuations in core power and fuel failures have been observed. To address this issue, EDF has provided for solutions which, according to IRSN, are acceptable in principle. In 2023, these assessments should be concluded, and the analysis of the reactor start-up tests continued.
At the request of the ASN, IRSN assesses the studies conducted periodically by EDF on overall fuel cycle consistency. In this context, the Institute published in 2022 a technical notice on the impact of energy mix scenarios on the nuclear fuel cycle. “While these scenarios apply first and foremost to nuclear power reactors, their impact extends to all facilities in the nuclear fuel cycle, which must be adapted to changes in reactor operation,” says Igor Le Bars, IRSN’s Director of Safety Expertise. “Therefore,” adds Jean Lombard, responsible for fuel cycle operation monitoring at IRSN, “the Institute examined in particular the operating difficulties or constraints likely to impact facility capacities for processing spent fuel assemblies and manufacturing fuel assemblies based on mixed uranium and plutonium oxides (MOX), the management of MOX waste, transportation, and the overall functioning of the fuel cycle.”
In its notice, IRSN issued recommendations relating, first of all, to the monitoring of ongoing projects to prevent saturation of plutonium storage capacity (related to production difficulties at the MELOX plant for the manufacture of MOX fuel assemblies) and fuel assembly storage capacity (related to the reduction in the processing capacity of spent fuel assemblies at the Orano Recycling site in La Hague). “The Institute also recommended the implementation of a system for regularly monitoring the fuel cycle operation to better prevent or deal with hazards that may occur at a facility in operation or in the process of being built,” Mr. Le Bars goes on to say. “Finally, IRSN recommended an update to the long-term prospective analysis – carried out in 2020 – of the effects of multi-annual energy planning on fuel cycle consistency.”
In addition to publishing its technical report, available on its website at the request of HCTISN, IRSN decided to produce an illustrated and commented version of its technical notice for the general public and stakeholders in civil society (local information commissions in particular), a document which is also available on its website.
IRSN presented to the permanent group of experts for reactors at the ASN its assessment of the feedback acquired by EDF in terms of both the manufacture and the operation of fuel assemblies and control rod clusters in its reactors for the 2010 – 2019 period. Over this period, the operator used, in the 58 pressurized water reactors (split into three standardized series of 900, 1,300 and 1,450 MWe) that currently make up its nuclear fleet, different types of fuel assemblies and clusters supplied by Framatome and Westinghouse. Over time, these products have undergone design and manufacturing changes driven by the desire to improve the safety, reliability and performance of fuel cycle operation. The evolution of these products has taken into account changes to safety standards, consistency of the fuel cycle – which currently includes recycling of spent fuel in France to manufacture mixed uranium-plutonium oxide (MOX) and enriched reprocessed uranium fuels – and supply security, as well as the lessons learned from their manufacture.
In its analysis of feedback over this period, IRSN has noted the efforts of EDF and its suppliers to improve the means of identifying and processing fuel failures (such as fuel rod cladding failure) and deploy new product designs. IRSN concluded in its notice that, although the feedback is generally satisfactory, EDF must monitor fuel behavior closely and draw more lessons from feedback acquired internationally; the operator has committed to doing so.
The European Nuclear Safety Clearinghouse – set up in 2010 for the benefit of the nuclear safety authorities and technical bodies of the EU Member States, as well as international organizations and the wider nuclear community – manages a centralized database of lessons learned from the operational experience of nuclear power plants in order to improve safety. For example, it enables countries with few nuclear reactors to benefit from the feedback and experiences in countries operating large fleets, such as France.
The Clearinghouse has several functions. These involve, in particular, collecting operational feedback data from a number of international and national sources; assessing key nuclear safety events and alerting the relevant national regulatory bodies; providing summary reports of events with similar characteristics or causes; conducting studies of precursor events at all relevant nuclear facilities; and disseminating information about corrective actions taken at certain facilities in response to lessons learned.
In 2022, a consortium of experts from the German TSO (GRS), French TSO (IRSN) and Czech TSO (SÚRO) issued new recommendations relating to the protection of nuclear power plants against the effects of external hazards of natural or human origin (excluding malicious acts) in a joint report entitled TOER External Hazard-Related Events II. Based on the analysis of significant events that occurred between 2010 and 2020, and which were recorded in national databases in France, Germany, and the Czech Republic, as well as in the International Reporting System for Operating Experience (IRS) database, this report provides recommendations to the nuclear safety authorities of Clearinghouse Member States in the interest of limiting consequences on facilities from phenomena such as earthquakes, lightning, heat waves, frost, explosions, etc.
Organized on June 1, 2022 by the Nuclear Energy Agency (OECD/NEA) with the contribution of IRSN, this forum was attended by a group of experts to reflect, based on feedback from three business areas (civil aviation, healthcare facilities, and the nuclear industry), on ways to strengthen the resilience of the nuclear sector. The objective was, in particular, to review the experiences of different organizations and identify best practices to better prepare for future crises.
The English version of this reference work, published in 2020, encapsulates seven years of efforts to capitalize on nuclear safety knowledge and was supervised by Jean Couturier. This educational publication, which is unparalleled internationally, can be downloaded free of charge on the IRSN English website, in the Science and Technical Collection.
IRSN was selected in 2022 as part of two European calls for tenders launched by the Dutch safety authority ANVS (Autoriteit Nucleaire Veiligheid en Stralingsbescherming) and Norwegian safety authority DSA (Direktoratet for strålevern og atomtryggleik) which were each seeking a partner or consortium able to perform TSO functions.
Concerning ANVS, IRSN has partnered with the Belgian TSO BelV and Bureau Veritas to respond to the three lots of the tender: assessments, inspections, and recommendations for future developments. The five-year contract is renewable up to a total term of 10 years.
For the second call for tenders, launched by DSA, IRSN partnered with BelV, the Australian safety authority (ARPANSA), and a Norwegian university (NMBU). The services will focus in particular on the future decommissioning of nuclear reactors and spent fuel disposal facilities.
These two contracts will strengthen the Institute’s European positioning in terms of safety expertise and consolidate its privileged relationship with BelV.
The coastal location of many nuclear facilities makes them vulnerable to the risk of coastal flooding, which means accurate estimates of extreme sea levels are of vital importance. As part of a Franco-Quebec research team combining the National Institute for Scientific Research (INRS) and Gustave Eiffel University, IRSN participated in the development of a methodology for improving integration of historical data, which is of interest to many nuclear sites around the world as well as to other types of coastal infrastructure such as ports or bridges.
IRSN experts were asked in 2022 to make various contributions to the safe management of radioactive materials and waste, both nationally and internationally. Whether to inform political choices in this area, to provide technical support for Nuclear Safety Authority decision-making, or to develop international agreements to meet present and future challenges, the Institute mobilized its expertise throughout the year, as evidenced by the following three actions.
Fulfilling its mission of providing support to the public authorities, in accordance with regulatory provisions, IRSN submitted to the Minister of Energy a proposal for a multi-actor, multi-criteria analysis methodology concerning possible management options for certain types of radioactive materials and waste, as part of the French national management plan (PNGMDR). The objective of this methodology guide is to facilitate public decision-making assistance by identifying the criteria selected by a variety of stakeholders in order to highlight the benefits and drawbacks of each waste management option, with regard to environmental and health, safety, socio-economic, and territorial issues. The guide will enable authorities to co-construct this type of analysis in an open and transparent manner, prior to making their decisions.
IRSN analyzed the dossiers relating to the safety review of the Manche Disposal Center (CSM), a LILW-SL (Low- and Intermediate-Level Short-Lived) waste disposal facility located within the town limits of La Hague. Presented to the permanent group of experts for waste at the ASN, the Institute’s conclusions show that the safety level of the CSM, which received LILW-SL waste until 1994, is currently satisfactory and under control for the monitoring phase of several hundred years. However, the Institute points out that the solution envisaged by Andra to improve the longevity of the site’s coverage leaves residual risks in the event of intrusion into the disposal area beyond this monitoring phase; therefore, the memory of these risks must be transmitted and the opportunity to remove certain waste assessed.
Finally, IRSN also contributed to the IAEA’s activities by participating from June 27 to July 8, 2022 in the 7th meeting of the IAEA Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management in Vienna. At the request of the ASN, representing France at this Convention, the Institute analyzed some fifty reports from contracting countries. It also chaired a review group of the national programs of 11 countries that are signatories to the Convention and participated in presentations made at the review meeting.
