“While the approach of integrating research and nuclear safety appraisal is far from being a new reality for IRSN, the progressive maturity of the dialog between these two missions – thanks to a cross-functional coordination that has succeeded in creating a real chain of complementary skills – now makes it possible to ensure its coherence and stability, as stressed by the High Council for the Evaluation of Research and Higher Education (Hcéres). Research programs must therefore meet the needs of the appraisal while maintaining the necessary distance to avoid putting the control system under strain as a result of a too direct transfer of research results into the appraisal. The introduction of cognitive technologies to both research and appraisal is also part of this maturing process.
Providing quality appraisal, in addition to being based on state-of-the-art knowledge, also requires an assessment by the Institute’s experts of the implications of their work on operational safety. In order to meet increased safety requirements, particularly following the Fukushima-Daiichi accident, nuclear facilities have seen their rule set, equipment and operating rules become more complex. It is now important for our experts to draw on feedback to ensure that the gain in safety expected from their recommendations is not called into question by the complexity of the installations.”
Karine Herviou
Deputy Director General,
in charge of Nuclear Safety
With a view to the start-up and commissioning of the Flamanville (Manche) EPR in 2024, IRSN has completed the appraisal of the major files and continued the analysis of the reactor’s assembly tests.
In 2023, IRSN completed the appraisal of the safety report and the general operating rules sent by EDF in support of the EPR commissioning request. Among the various opinions issued by the Institute in this context, three relate more specifically to the design of the pressurizer safety valves, the water filtration system of the internal tank of the reactor building (see inserts), as well as incorporating the feedback from the commissioning of the first EPRs. At the same time, the Institute continued to assess the results of the reactor start-up tests, highlighting the need to perform some of them again – in particular some hot tests – during the assembly qualification phase of the facility.
IRSN will examine the results of the post-start-up tests and the ramp-up of the EPR with a view to industrial commissioning in 2024.
In the event of a break in the primary circuit, the EPR is equipped with a safety injection system to compensate for the water loss resulting from the break and to keep the reactor core under water. As debris is likely to be carried by the water as a result of the circuit break and disturb the operation of the safety injection circuit, the latter is equipped with filters. They were subjected to qualification tests in EPR configuration in the Viktoria loop (located in Levice, Slovakia), which IRSN made use of in its analysis.
The EPR is equipped with a pressurizer to regulate the pressure and prevent an excessive pressure rise in the reactor primary circuit. The tests carried out on the pressurizer valves, actuated by pilots directly connected to it, showed that their behavior was sensitive to the temperature of the pilots, and a risk of leaks on the pilots. In its appraisal, IRSN recommended carrying out tests to corroborate the justifications provided by EDF in this regard. In the meantime, strengthened operational arrangements are implemented to ensure that the valves operate correctly under load.
Snow, storms, marine submersions, floods, earthquakes, etc. - nuclear installations are potentially exposed to natural hazards that must be assessed in order to take the appropriate protective measures. IRSN continued this work in 2023, in particular as part of international collaborations.
A multidisciplinary working group, attached to ASN and led by IRSN, investigated the damage potentially caused by wind or snow to structures and equipment important for the safety of nuclear facilities. In their report, which will provide the knowledge base for a future ASN guide, the experts showed that this damage can result not only from mechanical stresses induced by wind pressure or the weight of snow on structures, but also from indirect effects such as projectile impact, clogging of air intakes or the loss of resources external to the site.
In addition, as part of its safety assessments of nuclear sites located at the sea coast and their protection against the risk of submersion, IRSN conducted research into the estimation of extreme sea levels and developed a fully public database listing more than 800 events that have occurred since the beginning of the seventeenth century.
Lastly, in the seismic field, experts from the Institute took part in observation missions following earthquakes in the regions of Kahramanmaraş (Turkey) and La Laigne (France). The field experience acquired during these missions enhances IRSN’s insight into earthquake resistance simulation tools and the work execution plans, and contributes to the increase in skills of its experts, in particular the youngest ones.
The first was a workshop organized by the OECD Nuclear Energy Agency (NEA) on the consideration of natural hazards at IRSN and the second, organized by the Institute, focused on the magnitude 6.3 earthquake that hit the Petrinja region (Croatia) in 2020.
Launched jointly by IRSN, Anccli and ASN with the participation of EDF, in December 2022, in parallel with the appraisal, the technical dialog conducted as part of the 4th periodic review of the 1,300 MWe reactors (RP4-1300) continued in 2023 with the organization of three meetings (in May, June and October) at which IRSN presented technical elements on ten topics. These sessions made it possible to gather questions and expectations from civil society, which IRSN will take into account in its appraisal.
Publication of IRSN’s first safety appraisals in the framework of RP4-1300
The four opinions published by the Institute in 2023 respectively concern the change to steam generators, the new rule set for the study of primary coolant loss accidents, the post-Fukushima hard core and the assessment of the core’s reactivity following an automatic shutdown of the reactor.
Under certain conditions, reactions between products present in the spent fuel processing process can lead to the formation of unstable compounds, called red oils, generating a risk of explosion which must be prevented. At ASN’s request, IRSN examined the modification of the safety barriers associated with the ORANO Recyclage safety demonstration.
The T2 workshop of the UP3-A plant in La Hague (Manche) separates the fission products, uranium and plutonium. The resulting fission product solutions are concentrated by evaporation and then stored in workshop tanks prior to vitrification. The extraction process implemented uses an organic solvent that can, under certain conditions, form unstable nitrate compounds, called red oils, likely to decompose violently and generate a large amount of explosive gases.
Based on the documents examined at ASN’s request, IRSN considered as acceptable the modification of part of the lines of defense involved in preventing the formation of red oils in the evaporators of the new fission product concentration unit of the T2 workshop.
EDF’s discovery of thermal fatigue cracks on the Penly (Seine-Maritime) reactor no. 2 and Cattenom (Mosel) reactor no. 3, both with a unit power of 1,300 MWe, led IRSN to examine, at ASN’s request, possible changes in the periodic inspection strategy carried out by the operator.
In March 2023, EDF announced the discovery of a deep crack (23 mm with a total thickness of 27 mm) of stress corrosion cracking on a weld of the safety injection circuit connected to the primary circuit of reactor no. 1 of the Penly nuclear power station. Subsequently, when searching for any other defects, the operator detected thermal fatigue cracks on the Penly reactor no. 2 and Cattenom reactor no. 3. Thermal fatigue is a known cause of damage to nuclear reactor circuits resulting from repetitive temperature variations, which can lead to the appearance of cracks. The main method of prevention is the design of the circuits or the precautions taken in operation, in order to prevent the pipes from being subjected to cyclic temperature variations.
The fatigue cracks of the Penly reactor no. 2 and Cattenom reactor no. 3 were not discovered on the welds examined as part of the periodic inspection program, but thanks to the additional checks intended to search for stress corrosion defects. The results of these additional checks will be incorporated in the further appraisal of the kinetics of corrosion crack propagation. In the longer term, the Institute considers that EDF’s control programs with regard to these two causes of damage will have to be adapted to new knowledge and has initiated a review in this respect.
IRSN examined the safety files related to the decommissioning of various nuclear facilities such as the two reactors in Fessenheim (Haut-Rhin) and two solid waste management facilities located in Cadarache (Bouches-du-Rhône) and Fontenay-aux-Roses (Hauts-de-Seine). The Institute concluded that the submitted files were technically acceptable and made recommendations.
After analyzing the safety file for the decommissioning of the Fessenheim power plant, IRSN formulated recommendations in two areas – firstly, controlling risks during tank cutting operations, and secondly, the provisions for monitoring contamination outside certain worksite airlocks – and considered satisfactory the commitments made by EDF in terms of organizational and human factors, studying possible accident situations, waste management and impact studies.
With regard to the decommissioning of INB no. 56, located in Cadarache and used by the CEA since the 1960s for storing solid radioactive waste, the Institute recommended the implementation of provisions aimed at limiting the potential consequences of one of the items of waste recovery equipment falling during handling.
Lastly, with regard to INB no. 166, another CEA solid waste storage facility located in Fontenay-aux-Roses, IRSN recommended supplementing the radiological monitoring of groundwater and water courses downstream of the site.
This device, able to correct the variations in the particle size of aerosols that disrupt the measurement of activity by current continuous ambient air monitoring systems, represents a significant advance for the radiation protection of workers in nuclear facilities.
Dedicated to the manufacture of radiopharmaceuticals, INB no. 29, located in Saclay (Essonne), is operated by CIS Bio International. Following the appraisal of the periodic safety review file for this facility, IRSN recommended, in particular, improved sealing of the containment enclosures as well as the facility being laid up if the automatic fire extinguishing system is unavailable.
IRSN co-organizes PATRAM 22, a symposium dedicated to the packaging and transport of radioactive materials
This 20th symposium, organized with the support of IRSN, brought together more than 700 players involved in the transport of radioactive materials on June 11 – 15, 2023 in Juan-les-Pins (Alpes-Maritimes). It enabled them to debate a wide range of topics in this respect, such as mechanics, safety, containment, heat transfer, manufacturing, security, maintenance and quality.
The Integrated Feedback Platform (PIREX) has been deployed within IRSN for two and a half years now. A new version, which went into operation in 2023, incorporates developments coordinated with users. It was a component of the seminar bringing together IRSN, GRS and NRC at the end of the year.
Developed by IRSN in order to capitalize on all significant events reported each year by the operators of nuclear facilities or transports of radioactive substances, the Integrated Feedback Platform (PIREX) uses algorithms implementing artificial intelligence techniques (automatic language processing, machine learning, etc.) in order to extract, faster and more comprehensively than before, lessons learned from the some 47,000 significant events reported by nuclear facilities since their start-up. PIREX thus makes it possible to orient, on the one hand, IRSN’s appraisal work (identification of the issues and themes to be examined) and R&D work (identification of new knowledge needs) and, on the other hand, the support to the security authorities (support for inspections, assessments, etc.).
At their joint seminar, IRSN, GRS and NRC discussed, among others, the contribution of innovative technologies for safety appraisals, of which PIREX is a good example.
Several countries, especially in the European Union, are interested in new concepts of small modular reactors that make extensive use of passive safety systems. As part of its appraisal and research activities, IRSN participated in various discussions and technical meetings on this subject throughout 2023[1].
Speaking in April at the seminar chaired by Mariya Gabriel, European Commissioner for Research and Innovation, on the EU’s strategic autonomy and research conducted within the EURATOM framework, the Director General of IRSN presented the nuclear safety challenges linked to new technologies such as small modular reactors (SMR). The presentation of the IRSN “PASTIS” project, dedicated to passive safety systems for pressurized water reactors, illustrated the associated research needs.
On November 30, 2022, in Washington the President of the French Republic launched a Franco-American nuclear cooperation program. In this respect, the IRSN and the US NRC included in a common roadmap the aspects related to the safety of SMRs and the contribution of passive systems to it. Technical discussions made it possible to compare the safety analyses of the US NUSCALE and French NUWARD reactors. They are continuing with a view to collaborating on the use of the future PASTIS platform, located in Cadarache, which was presented in the follow-up meeting at the Elysée on November 29, 2023.
This software system makes it possible to simulate accident scenarios with a reactor core meltdown, from the initiating event to releases into the environment. Originally developed for pressurized water reactors, ASTEC has evolved to apply to other nuclear reactors and facilities such as nuclear fuel storage pools and, soon, some small modular reactors.
