“Réversibilité” is the topmost maxim for nuclear waste disposal in France: the high-level waste is to be “geologically” stored with enhanced retrievability in deep geological repositories. And in Switzerland? Nagra in a state of embarrassement.
By André Lambert
The Bözberg region in the canton of Aargau was proposed by Nagra under the code name “Jura Ost” as a potential site for the deep disposal of radioactive waste in Switzerland. Since then, the local population has been following Nagra’s further activities with critical suspicion. In particular, the “Pro Bözberg” organization, an association with rights for legal objections and complaints, is uncompromisingly committed to ensuring that only criteria of the highest possible safety are applied in all questions of nuclear waste disposal; neither political nor geographical opportunities – in particular the proximity to the ZWILAG interim storage facility – are “negotiable”. This means nothing less than the consistent application of Article 30 paragraph 3 of the Nuclear Energy Act.
In order to assess the interrelationships in this complex subject area and in its own competence, the Executive Board of “Pro Bözberg” association considers it an urgent duty not only to orient itself on one-sidedly and sectorally prepared information and propagandistic messages from the implementers management and regulatory authorities, but also to actively and independently follow developments abroad and to listen to experts on site.
Against this background, a six-member delegation of the Board of the “Pro Bözberg” association visited two facilities, which are considered to be of central importance to nuclear waste management in France, at the end of May 2019. The participants organized, prepared and fully paid for the trip themselves; they will publish their conclusions in an appropriate manner.
At the core of the following article is the striking difference between the storage concepts of the French and Swiss waste producers for high-level radioactive waste, which is the main finding of the participants. For the delegation from “Pro Bözberg” association, it is clear that the French concept is orders of magnitude more convincing than the one currently propagated by Nagra. The “Agence nationale pour la gestion des déchets radioactifs” (Andra), the French waste disposal company, stands uncompromisingly for the primacy of a technically robust, implementable and on a 1:1 scale demonstrable recovery of high-level radioactive waste (HLW): This realistic, transparent and technically verifiable approach marks a beneficial counterpoint to the utopian-sounding concept of the Swiss disposal company Nagra.
Reversibility: a fundamental socio-political claim
The public and controversial debate on the long-term “safety” of deep geological disposal of high-level waste is dominated by questions such as control, monitoring and retrievability. In contrast, there is a widespread scepticism and a deep mistrust about irreversible disposal. With good reason: Worldwide, there are too many examples of disastrous landfills of nuclear and/or chemotoxic waste that cannot, or can only hardly be remediated, and that were originally propagated as “safe” (!). A long-term process of the wide span of a definite high-level waste repository can never be “controllable”. Therefore, it makes sense (at least one would have to think so) that in a construction and storage process that will necessarily extend over more than a century, new findings must obviously be incorporated.
Monitoring and retrievability will be a valid standard in every waste disposal project in the future. At the latest, since the Swiss Expert Group on Disposal Concepts for Radioactive Waste (EKRA) published their reports, no nuclear disposal project in Switzerland is conceivable without these central requirements. Consequently, essential articles in the Nuclear Energy Act (2003) are based on the EKRA concept. This applies in particular to the facilitated retrieval of radioactive waste as a “sine qua non” condition for the granting of an operating license for deep geological repositories (Nuclear energy act Art. 37 b).
Significantly such considerations precisely prompted our French neighbors to align their storage concept (for HLW) on such standards – as consistently as prominently. In a rock laboratory, storage and retrieval tests are carried out “at depth” on a scale of 1:1 (though still without radioactive waste). The technology will be tested and optimized, and everyone will be able to see for themselves on site. And the term “réversibilité” already dominates the headline in all relevant Andra public brochures.
Pleasant willingness to self-criticism and to deal with open questions in a relaxed manner
The high-level radioactive waste (HLW) from spent fuel elements of the 58 French nuclear power plants is to be stored in a clay rock layer with a thickness of around 140 meters at a depth of almost 500 meters. With regard to the implementation of this project, Andra near Bure is operating a deep geological laboratory on the north-eastern edge of the tectonically stable Paris Basin. Here, the basic feasibility and safety of geological storage in clay rock at a depth of around 450 m are tested and verified. It is therefore an actual site-specific “stress test” for a locally adjacent geological repository for high-level waste to be realized in this rock layer – provided that it is suitable – on an area of presumably around 30 square kilometers.
The Board delegation of the “Pro Bözberg” association was impressed by the high professionalism of the application-oriented researchers and their communicative openness right from the start of their visit to the Bure Rock Laboratory. After the 10-minute drive in the shaft basket to “the bottom” (approx. 450 m below the earth’s surface), the tour followed through the extensive tunnel system of the underground experimental facilities. The participants benefited from the scientific and technical competence of the French experts accompanying them on site: a site geologist, a rock geotechnical engineer and a nuclide geochemist. These top experts presented a coherent picture of the partly complex experimental investigation processes as well as the previous results from this purposefully and farsightedly designed research facility in such a vivid and sympathetic way. These scientists showed themselves to be thoroughly and pleasantly self-critical, both in conversation and in answering questions from the group of participants. This exchange of experience with local experts was and is particularly valuable, as Swiss Nagra is also considering disposal of high-level radioactive waste in a clay rock similar to that in France.
Board members of “Pro Bözberg” association 500 meters below the surface in a gallery of the rock laboratory Bure (France). A tunnel construction and rock mechanics expert (with a white helmet) explains how the driving of the tunnels has to be oriented to the prevailing rock stresses, in order to improve the long-term stability of the storage galleries (the cavities drilled in such clay rock can deform in the long term under the enormous rock pressure). The long-term safety of a deep nuclear repository requires permanent containment capacity, i.e. the integrity of the repository rock must be as unrestricted as possible.
Irritating contrast with Nagra concepts
An important finding of the participants was the striking difference between the HLW storage concepts of the French and Swiss waste producers. For the participants in the information tour, it is clear that the French concept is – of an order of magnitude – more convincing than that one propagated by Nagra for more than three decades (!). Without going into the technical details set out in the Nagra reports (e.g. NTB 02-02), the fundamental differences between the concepts in the two countries can be summarized as follows:
- Storage concept and positioning
- CH – Nagra: Axial storage of the HLW containers one behind the other (keyword “string of beads”) in up to 900 (in words nine hundred!) meter long micro-tunnels in parallel storage tunnels with a diameter of about 3 meters (this corresponds to a 1 meter long spaghetti with a 3 mm diameter). The storage casks weighing over 20 tons with the encapsulated spent fuel elements are to be moved to their storage location on rail transporters and placed on bases made of compacted bentonite blocks. Then the remaining cavity between the container and the tunnel wall is to be filled with bentonite granulate at a specified bulk density and quality assured (!). Of course, all these highly complex mining processes in difficult rock formations and acute lethal radiation fields must necessarily be carried out remotely and completely robotized in a narrow tunnel, several hundred meters below the earth’s surface, absolutely trouble-free.
- F – Andra: From a secured main gallery (lined with concrete tubbings) and passable by vehicles, horizontal stump holes (French: “alvéoles”) of several decameters in length are drilled into the rock at right angles to the tunnel axis and at regular intervals (keyword “bark beetle”). The diameters of these stump holes depend on the dimensions of the waste containers to be stored in them. During drilling, a steel pipe with a wall thickness of a few centimeters is continuously inserted into the open cavity; the remaining aperture between the pipe and the cavity wall is then to be filled with bentonite. The pipe is used to stabilize the borehole and then to receive the waste containers.
The reversibility requirement in accordance with the EKRA concept and the Nuclear energy act (Art. 37 b.) stipulates that, if necessary, “the retrieval of radioactive waste … is possible without great effort“.
Nagra’s storage concept for the HLW, however, is diametrically opposed to this requirement. Imagine: a “bead-string” of containers weighing more than 20 tons each, in a nearly 1 km long micro-tunnel filled to bursting with bentonite, and in a clay host rock trending to ductility. And in this situation, a recovery should be possible “without great effort”? With all due respect: that borders on illusionary self-deception! The machinery required for this in accordance with the building concept (Nagra 2002) alone gives the impression of science fiction. In any case, such equipment exists only on paper for the time being (Nagra Technical Report NTB 02-02, p. 141): as a remote-controlled multitasking super-robot (piquantly equipped “with radiological sensors”!), it combines an “excavator module”, a “drilling module”, a “retrieval module” and a “rock protection module”.
When reading the retrieval procedure, it is difficult to resist the laconic findings: This bearing design, already conceived as a “bead-string” in the constructional approach, proves that the waste “good” can never ever be retrieved – and will never be! In any case, we can look forward to the demonstration of this futuristic technology – whenever and wherever, but mandatory – in real mountain use, scale 1:1.
And this is exactly what Andra is already doing! Its concept, including the equipment used, seems so comprehensible and convincing above all because, including all previous development steps, it can already be technically “demonstrated”: on site at storage depth and in the presence of the public. This is how you create trust and acceptance!
It is worth mentioning, however, that the French storage concept for the HLW differs in one respect. France operates a reprocessing plant (in La Hague, Normandy) in which recoverable uranium and plutonium are separated from the spent fuel elements. After this separation process, the remaining high-level waste – fission products and long-lived transuranics (actinides) – is calcined in a vitrification plant, melted down in borosilicate glasses and filled into 1.34 m high steel containers of 43 cm diameter. These steel containers weigh almost half a ton and are therefore easier to handle than the almost 5 m long spent fuel elements of the Scandinavian or Swiss concepts.
The vitrified waste in the steel moulds is then to be placed in storage containers, closed with a lid and welded. The principle of storage according to the Andra concept can be traced via the following links, at least schematically:
Every step is clear, plausible and technically comprehensible. The waste canisters are to be shielded from radiation in a transport unit, first driven (by cable car) over a tunnel ramp then to the mouth of the intended storage gallery and pushed to the intended position in the several decameter long storage micro-tunnel with a telescopically acting hydraulic ram. The diameter of the steel pipes for receiving the containers (containing the vitrified high-level waste) in the host rock is 70 cm.
With wise foresight, the French are also planning the option of direct storage of spent fuel elements (as in Switzerland); for this purpose, the tunnels with correspondingly larger diameters (at least 1 m) must be drilled out. There is no doubt that the drilling of such storage tunnels will be technically challenging and will require a correspondingly complex test phase until operational maturity.
Since the HLW steel-containers on ceramic sliding elements within the steel tube in the storage holes basically remain freely movable, the retrieval is carried out essentially with the same equipment as were used for storage. For this purpose, a hydraulic gripping mechanism that engages on the inside of a groove provided for this purpose on the container is sufficient. This allows it to be pulled out of the storage tunnel again. Tests with containers that had been rusted-up artificially (by using acids) to the storage pipe have shown that the hydraulic pulling system has sufficient reserves of force to even master this case.
Conclusions and outlook
Andra’s storage concept for HLW (“bark beetle” configuration): already at the present stage of development, it is orders of magnitude better than Nagra’s “bead-string” model, which is actually still based on the “Stone Age” model of its failed crystalline project. It should be noted, then, that this was a long time ago, when nuclear disposal was still conceived as a final storage facility. No mention of retrieval!
Nagra could no longer resist the paradigm shift in the wake of the EKRA conclusions, albeit with the utmost restrained enthusiasm. The repository concept had to be adapted, including the question of reversibility. But if Nagra, at least since the beginning of the Sectoral Plan era, has been swaggering about monitoring, control and monitoring in a pilot storage facility, then it should be rigorously consistent to ensure that it can be retrieved “without great effort” in accordance with the Nuclear energy act. A technical recovery, which deserves that name! Whatever this is to be designed in terms of engineering and with due regard for operational safety and radiation protection, Nagra’s storage concept is almost a germination of the idea that retrieval is almost deliberately impossible. So who wonders that Nagra’s propaganda rather unwillingly addresses the issue of retrievability – as a some kind “lukewarm infusion”.
Even if the concept of the French – also undisputed by themselves! – still has a big potential for improvement and optimization and fundamental questions still await clarification, it can be regarded as a worth considering, far superior approach to the Swiss concept. Nagra, but first and foremost the technical supervisory authority Ensi, are called upon to devote serious attention to these questions. For without a concept that convincingly presents reversibility to the public, can be demonstrated on a 1:1 scale and is understood by the general public, the realization of a deep nuclear repository is illusory. The equation continues to apply:
Competence + proof of practice + credibility = acceptance.
No “fait accompli”
According to Nagra’s “claimed” strategic action plans, the storage operation is to last about 15 years (2060 -2075), followed by the closure of the main repository, with an “observation phase” of about 50 years in total. The repository-planning of the Andra moves in completely different dimensions (even if one abstracts from the almost 12 times more extensive nuclear power plant park). Here, after the construction of the accesses, the inclined shaft (“descenderie”) and various vertical supply shafts, the storage technology, which has been tried and tested up to then, is to be gradually brought to the required level of industrial-operational maturity again in a 10-year test phase while adhering to the strictest safety requirements. Thereafter, i.e. from around 2035 onwards, Andra expects storage operations to last for over a century. Over this long period, the waste already stored – which can always be retrieved – remains in its “alvéoles” shielded from massive but removable steel shutters. In this way Andra fulfills the social claim of “réversibilité” in a credible manner. The following generations have the options of an improved or alternative handling of the waste or the definitive closure of the plant – if required – thanks to technological progress. The project thus follows France’s parliamentary decision according to which (quote): “… this storage, which is intended to be permanent, must be reversible for at least 100 years in order to leave choices to subsequent generations and in particular the possibility of recovering stored waste.”
 EKRA (2000): Disposal Concepts for Radioactive Waste, Final Report, Expert Group on Disposal Concepts for Radioactive Waste, Federal Office of Energy, Bern; EKRA (2002): Beitrag zur Entsorgungsstrategie für radioaktiven Abfälle in der Schweiz, (Contribution to the disposal strategy for radioactive waste in Switzerland), Schlussbericht, Bundesamt für Energie, Bern (only German version).
 “… ce stockage, prévu pour être définitif, soit réversible pendant au moins 100 ans pour laisser des choix aux générations suivantes et notamment la possibilité de récupérer des déchets stockés.”