On April 24 and 25, 2024, IRSN presented to the Advisory Committee of Experts on Waste (GPD) the conclusions of its technical review of the basic data used to assess the safety of the Cigéo project, a deep geological repository for radioactive waste. This technical review is part of the examination of the construction licence application for the Cigéo project submitted in 2023 by the French national radioactive waste management agency (Andra).

Cigéo is the French project for the reversible deep geological disposal of high-level (HLW) and long-lived intermediate-level radioactive waste (ILW-LL). Located on the border between the Meuse and Haute-Marne regions of France, Cigéo is designed to dispose of this waste 500 meters below the surface in a layer of clay rock. The construction license application is a major milestone in the creation of Cigéo.

Conclusions of IRSN's assessment

IRSN considers that the knowledge developed by Andra in the areas of waste packages, Meuse/Haute-Marne site, Callovo-Oxfordian formation and cementitious materials is based on sufficient data for the safety assessment of Cigéo at the construction licence application stage. This knowledge is based on detailed hydrogeological and geotechnical characterisations, an appropriate assessment of meteorological hazards and an adequate understanding of the properties of the host rock, cementitious materials and waste packages, as well as their evolution under the effect of transient thermal, water, mechanical and chemical disturbances.

Regarding the reference and reserve inventories, the data collected by Andra is generally relevant, both for the Cigéo safety demonstration and for the adaptability studies considering the chosen prospective industrial scenarios. Some uncertainties remain, however, including uncertainties relating to the reference inventory that may impact the number of disposal cells and the disposal chronologies; these will have to be addressed through the flexibility of Cigéo while in operation. In addition, considering the possibility of a future fleet (eight additional EPR 2, SMR, RNR, etc.), the capacity of the facility to dispose of more waste will have to be assessed on the basis of further adaptability studies, considering time horizons that can be defined once the decisions relating to the future fleet have been taken.

At this stage of the construction licence application review (GP1), IRSN has identified two topics that require particular attention, respectively relating to HLW cells and to sealing structures, which refer to the pilot phase. Regarding HLW cells, it is important to provide the supporting evidence for the design basis of metal components before the first HLW cell is excavated, and to resolve the uncertainty regarding the possibility of flexures affecting the host rock at the location of the future HLW disposal zone. For sealing structures, which are still at the stage of design principles , efforts must be made to minimise damage to the rock while excavating the facility's shafts in areas that are subsequently to be sealed. Particular attention must also be paid to the definition of these structures and the in situ demonstration of their operability.

The present review will be supplemented by the Cigéo operational and post-closure safety demonstration reviews, carried out for the GP2 and GP3 technical reviews respectively and currently underway.

Involvement of civil society in the Cigéo assessment process

In addition to its assessment of Andra's construction licence application, IRSN established a technical dialogue with the National Association of Local Information Committees and Commissions (Association nationale des comités et commissions locales d’information - ANCCLI), and the Local Committee for Information and Follow-up of the Bure Laboratory (Comité local d’information et de suivi du laboratoire de Bure - CLIS de Bure). This dialogue is a continuation of the initiatives of openness to civil society on HL and IL-LL waste carried out since 2012.

It was conducted in the form of plenary meetings and thematic workshops with the dual aim of taking the concerns of civil society into consideration in order to make IRSN's review more robust, and of allowing civil society to form its own opinion and therefore to participate in the process leading up to the public decision.

The main subjects of interest to participants in connection with GP1 assessment were the so-called "reference" and "reserve" waste inventories, the site characteristics (in particular the evolution of faults, water circulation, the potential geothermal resource, the properties of the host layer), and the pilot phase.

Download :

• IRSN Opinion n°2024-00051 of 12 April 2024: Cigéo project construction licence application – “GP1” - Evaluation of the basic data adopted for the Safety Assessment (English version)

Note: The English version of IRSN's opinion is provided for information only. Only the original document in French is authoritative.

IRSN is currently participating in the preliminary review of the safety options for the NUWARD™ project by the French (ASN), Finnish (STUK) and Czech (SUJB) safety authorities with the support of their technical safety organizations (TSO) respective ones, including IRSN for France. 

​​The NUWARD™ project is a concept of electricity production unit, supported by EDF, consisting of two pressurized water nuclear reactors of 170 MWe each. From a safety point of view, this concept has characteristics common to other SMR concepts in development abroad, in particular its low power, its compactness and the implementation of passive safety provisions. For IRSN, SMRs m​ust meet safety requirements at least equivalent to those adopted for third generation reactors, their low power and the inherent safety characteristics put forward by their designers should benefit safety.

IRSN experts have been contributing for nearly ten years to thoughts on the safety requirements and approaches for these new concepts, in particular through their involvement in various international working groups of the IAEA and the SMR Regulators' Forum. [1]

IRSN also participates in several European projects which aim to acquire knowledge on these new concepts, both in support of the safety demonstration and in the validation of simulation tools, for pressurized water reactors but also for other types of reactors, for example high temperature reactors dedicated to cogeneration. 

The evaluation of the performance of passive safety systems being a central element of the safety demonstration of SMRs, a very good understanding of the physical ​phenomena that participate to their activation, their operation and those which can prevent them is necessary. IRSN is considering the development of a specific experimental research platform (PAssive Systems Thermalhydraulic Investigations for Safety) to support its expertise. This new experimental facility will provide knowledge in particular on the operation of a passive core cooling system as well as on the passive cooling of a metal containment immersed in a water pool. ​

For more information : our information memo on Small Modular Reactors​

Notes:

1. The SMR Regulators' forum brings together the safety authorities of France, the United States, Canada, the United Kingdom, Finland, Japan, South Korea, China, Russia, the Czech Republic and South Africa

During the ten-yearly in-service inspection of reactor 1 of the Civaux nuclear power plant, which began on August 21, 2021, EDF performed ultrasonic testing of several welds in the emergency core cooling system, in accordance with the applicable preventive maintenance program. The examinations revealed the presence of faults near the welds of some pipe elbows.

The emergency core cooling system (ECCS) is a safety system that njects borated water into the reactor main coolant circuit (also called main primary circuit) to cool the core in the event of a breach affecting the main coolant circuit. The objective is thus to maintain a sufficient water level in the core to cool the fuel assemblies.

The emergency core cooling system is made up of two independent safeguard trains connected to the primary circuit via a hot leg [1] and cold leg [2] connecting pipe of each of the four loops of the primary circuit.

Ultrasonic examinations carried out on Civaux reactor No. 1 revealed the presence of faults near the welds of some pipe elbows (see figure). In accordance with the applicable preventive maintenance program, examinations were then extended by EDF to adjoining welds. In order to determine the origin of these cracks, the pipes were cut, and the welds involved have been sent to the laboratory for expertise. By metallographic and microscopic examination, EDF was thus able to determine the nature and depth of the faults detected. The origin of faults seems to be stress corrosion cracking.

Stress corrosion is a mode of damage that typically results from the combined action of mechanical stress and an aggressive environment with respect to the material. In order to better understand the factors behind the observed corrosion, EDF has undertaken a verification of the manufacturing files. At the same time, it carries out a performance review of the control procedures used. These analyzes aim to develop a verification program for welds likely to be affected by the phenomenon.

If these faults develop in the emergency core cooling system piping, it could lead to a leak or a break. If this break occurs on a pipe, this leads to a loss of coolant accident, the damaged elbows being located downstream of the isolation valves of the emergency core cooling system. The emergency core cooling system train unaffected by the breach would then ensure the injection of water into the primary circuit and the cooling of the core. If, on the other hand, this rupture or leak occurs simultaneously on several pipes, the cooling of the reactor core could potentially no longer be ensured. Events such as an earthquake (generating mechanical stresses in the involved pipes) or start-up of the emergency core cooling system (causing cold water to enter hot pipes) can simultaneously stress these circuits.

EDF decided to preventively shutdown Civaux’s No. 2 reactor on November 20, in order to carry out early examinations on the welds, the ten-yearly outage of the reactor being scheduled in a few months. The first results of examinations on this reactor show the presence of defects at the same welds as on reactor No. 1. EDF therefore decided to unload the fuel assemblies from the core of reactor No. 2 to proceed to in-depth investigations and to the repairs that may prove necessary.

As a generic anomaly relating to the 1,450 MWe reactors cannot be ruled out at this stage, EDF has decided to shut down the two reactors at the Chooz B nuclear power plant in the Ardennes from December 16, which are of the same type as those of Civaux (1450 MWe reactors), in order to carry out checks.

IRSN considers that EDF's decision to shut down the two Chooz B reactors, in addition to the two Civaux reactors, is satisfactory from a safety point of view. Examinations on Chooz B's reactors will determine whether they are affected by the same defects. In-depth investigations must be carried out in order to determine the phenomena at the origin of stress corrosion crac​ks and to define the scope of the examinations to be carried out.

Specific examinations may also be necessary on other reactors in operation.

Download IRSN information report of December 16, 2021​: Detection of cracks in pipes of the emergency core cooling system of the reactors No. 1 and No. 2 of the Civaux nuclear power plant​​ (PDF)

Notes:

1. After the reactor pressure vessel outlet.
2. Before the reactor pressure vessel inlet .

As part of preparations for the public debate on the 2019-2021 French National Plan for the Management of Radioactive Materials and Waste (2019-2021 PNGMDR), the President of the National Public Debate Commi​ssion asked the French Institute for Radiological Protection and Nuclear Safety (IRSN) to carry out an assessment of the dry storage of spent nuclear fuels containing mixed uranium and plutonium oxide (MOX) or enriched reprocessed uranium oxide (ERU).

This report complements the IRSN n°2019-00181 report on concepts and safety issues related to the storage of spent nuclear fuel published in March 2019 (French issue in June 2018) in response to a request from the Parliamentary Committee of Inquiry into the Safety and Security of Nuclear Facilities in France.

IRSN examined, on the one hand the potential compatibility with dry storage of some of the MOX or ERU spent fuels currently stored underwater, and, on the other hand, the potential changes to transport and dry storage concepts in order to raise the reference residual heat values at present accepted, namely below 6 kW for transport and below 2 kW for dry storage.

In conclusion, IRSN’s assessment did not reveal any factors that would rule out storing in dry conditions some of the MOX and ERU fuels currently stored underwater. Nevertheless, the various possible options should be examined, incorporating the related safety and radiation protection requirements as well as all industrial constraints.

The French version of this report was pu​blished in April 2019, and the English version in January 2020.

Download IRSN Report 2019-00903: Assessment of dry storage possibilities for MOX or ERU spent fuels (PDF)

In the frame of the marketing of new radiation therapy devices coupling a linear electron accelerator to a magnetic resonance imaging system (MR-linac), the French Nuclear Safety Authority requested IRSN to provide a state of the art for this technology and to identify any points requiring vigilance.

IRSN's analysis relied on the expertise of the French Medical Physics Society, SFPM. The numerous observations and recommendations established by the IRSN/SFPM working group are synthesized in the advice published by the IRSN.

Download IRSN Report 2018-00232 : Request for a study on the implementation of linear accelerators coupled with a nuclear magnetic resonance imaging system in radiotherapy (MR-linacs) (PDF)

The implementation of the defence in depth principle leads applicants to define provisions to prevent accidents, including severe accidents, and to limit their consequences should they occur. Some severe accident situations potentially lead to large early radiological releases, for which it appears impossible to define realistic and demonstrable provisions to limit their consequences according to current knowledge and the techniques available: applicants shall then use the “practical elimination” approach.

IRSN publishes an orientation document which defines “practical elimination” approach and its place in safety demonstration for nuclear power plants involving pressurized water reactors.

Download the document: The practical elimination approach of accident situations for water-cooled nuclear power reactors (document updated in March 2021)