1       Framework

The debate on the retrievability of nuclear waste from a repository or deep repository is an old one, also in Switzerland. It arose in the late 1970s among the institutions responsible for waste management.[1] It is true that the concept for nuclear waste management of the Swiss electricity industry, published in 1978, was still against direct disposal of spent fuel elements because of its commitment to reprocessing.[2] However, just one year later, various Swiss bodies recognized retrievability as a fundamental strategy for dealing with the storage of radioactive waste in geological formations.[3]

In the course of the review of radioactive waste concepts, the Commission «Disposal Concept for Radioactive Waste EKRA» extended its considerations on retrievability of high-level waste and recommended to provide for facilitated retrievability of waste within the concept of controlled long-term geological disposal.[4] The Nuclear Energy Act (KEG) has followed this recommendation. Article 37 regulates the retrieval of radioactive waste until possible closure without great effort. On this basis, and given the intended progressive implementation of the deep geological repository in the Nördlich Lägern siting region, Nagra has presented an initial report for a retrieval concept, dated November 2022.[5]

2       Content of Nagra’s retrievability report

The report «Retrievability concept for a deep geological repository», dated November 2022, is part of the general licence procedure and is intended to show how the waste can be retrieved under the most difficult conditions after completion of operation of the pilot repository. The study essentially consists of 6 chapters. The first three chapters deal with the objectives of the report, its structure, the legal basis and the general conditions, and present the fundamentals of the storage concept. Chapter 4 deals with the retrieval concept and the relevant state variables. Chapter 5 presents the retrieval concept. Chapter 6 summarizes the important conclusions and the outlook for further work. In conclusion, the report takes stock of the feasibility and desirability of retrieval: «The retrieval concept shows how retrieval of radioactive waste from the deep geological repository until possible closure can be carried out without great expense (Art. 37. para. 1 let. b KEG 2003) using current technology». This is one possible view of things.

Another view, on the other hand, attempts to situate a report on waste retrieval and decommissioning in the future much more comprehensively and to identify the important processes and procedures of such operations. From this perspective, Nagra’s report reveals fundamental weaknesses that could have been well addressed from the outset. This begins with situating the work in a broader overall context.

3       Lack of overall context  

Retrieval does not consist solely in the technical implementation of the deconstruction of the deposited waste. As also shown by the remediation of the Asse experimental repository or the military sites in the USA (as well as many other examples in the field of chemo-toxic hazardous waste), waste mixtures from such repositories have to be separated, reconditioned, repackaged, temporarily stored and transported to further facilities up to a new deep repository using sometimes complex procedures. Depending on the intended consequence or subsequent use, extensive and complex on-site treatment facilities may need to be provided. For example, if spent fuel were to go to post-reprocessing reactors, infrastructures for opening storage casks and on-site reconditioning (with hot cell) would be mandatory. Therefore, the statement in the Nagra report that «retrieval of radioactive waste … from the backfilled storage chambers» occurs «and … ends in the shaft portal at the surface» definitely falls short and raises the question of why the safety authorities did not define the requirements for the submission of the general licence procedure for the deep geological repository more broadly.[6] The statement that «the necessary processes and infrastructure for the aboveground acceptance, conditioning and interim storage of the waste … are state of the art (e.g. Zwilag) and therefore, in accordance with the requirements of the ENSI 2020a» (regulators) «guideline, are not to be considered further here», must therefore be questioned at its core. Indeed, dismantling requires an examination of the entire disposal chain of a system, including the availability of all necessary facilities and logistics. In the case of dismantling a deep geological repository in Switzerland, the current ZWILAG, for example, would have been dismantled at the longest and would therefore not be available. In such a case, there would be a need for new on-site facilities as well as for ensuring transport logistics to the required treatment and disposal facilities in Switzerland or abroad. One might expect an initial report on retrieval of waste from a deep geological repository to outline, at least in outline, the fundamentals of such a disposal system, to identify the technical, risk, logistical and legal challenges and uncertainties, and to demonstrate the complexity of such an undertaking. In the planning process for retrieval of low- and intermediate-level radioactive and chemo-toxic waste from the Asse salt mine, the planning requirements for retrieval were considered as early as 2014 based on conceptual sketches. [7] The challenges of the planning process can be gauged in further technical reports. [8]

Another example illustrates the complexity, challenges, and coordination needs of such retrieval and remediation work. For example, the planned dismantling of the production facilities at the Hanford (Washington) plutonium plant, as well as the waste dumped on the site, illustrates the range of difficulties that can arise during dismantling. [9] For example, in the case of the so-called «tank farm», where most of the highly radioactive residues from the on-site bomb production in the early decades are temporarily stored. The dismantling of these mostly single-walled steel tanks has become a real nightmare for the responsible institutions.[10] Added to this are the problems of reconditioning such waste for the «Waste Isolation Pilot Plant WIPP» repository for the long-lived waste from bomb production, as revealed by the February 2014 accident at the repository. Barrels of improperly conditioned nitrate salts containing plutonium were packed at the Los Alamos laboratory and stored at the WIPP. There, one of these barrels exploded and contaminated about one-third of the galleries underground. The repository had to be closed for the duration of the cleanup (3 years), which shut down the supply chains of all waste from the U.S. military complexes (including Hanford). Hundreds of other drums conditioned in this manner remain at the facility today. There are no plans to retrieve such waste. Cost of this cleanup: US$600 million.

It is therefore desirable and expedient that such overall contexts be illuminated at an early stage in a deep repository project.

4        How forward-looking should laws be?

A second related fundamental problem of such reports is that the state of the art in science and technology is not incorporated à piori into such an analysis. This is also related to the fact that a project implementer relies on legal foundations and, understandably from his point of view, adheres to this framework. But laws are usually not «set in stone» for even one generation. In a technologically advanced society, where science and technology advance at seven-mile intervals, laws should be handled with more foresight and areas that can never be fully regulated in laws should be interpreted generously. This makes it easier to identify problem areas at an early stage and to consider measures to deal with them. Legislative precautions often lag decades behind the real problems, as can be seen, for example, in the legal provisions on contaminated sites, which were not established until many decades after the problem had been identified. It therefore makes perfect sense to interpret foreseeable developments with foresight and to approach analyses comprehensively. For example, Nagra’s report on retrieval only addresses the scenario of retrieval shortly before closure of the entire facility. Another scenario that might usefully have been considered would be retrieval of the HLW inventory within the next few hundred years. If reactor technology or waste treatment technologies were to make significant advances during this several hundred-year period, allowing for the use or reconditioning of spent fuel from the early days of nuclear energy use, retrieval would have to be considered under potentially significantly more difficult conditions. This refers, for example, to the various closure structures in the storage chambers, or to the condition of the original infrastructures and their availability at the time of dismantling. Or to the condition of the fuel element casings, which could have lost their load-bearing function and could be in pellet or powder form in the storage container. The cardinal question for retrievability would actually be the worst-case scenario to be assumed in the first 1000 years of the storage process, in the sense that the entire infrastructure used for emplacing the waste would no longer be functional (e.g. rail tracks, crane tracks). An initial consideration of such a quite possible development with different dismantling scenarios under aggravated conditions would have suited the report well.

5       Procedure and content statements

As already mentioned, the report reflects the dismantling of the deep repository only in certain aspects. In approach, it would have been expedient to set up the report more comprehensively and systematically. Thus, many fundamental issues of dismantling and retrieval are not addressed. It would not have been necessary to deal with these various elements and issues in detail, but rather to illuminate the breadth and depth of a dismantling project, i.e. to present as complete an analysis as possible of the retrieval system and its parts and to assess their relevance. Some of the measures proposed in the report today could probably already have been discarded, e.g., the interim storage of the hot bentonite in empty galleries during the dismantling phase. It would have to be shown what temperatures would have to be expected in the underground and how dismantling could be carried out at all under such conditions. The high temperature in the deep repository and the high radiation emitted by the HLW canisters make fully robotized dismantling mandatory. Therefore, experience in handling HLW waste or in dismantling from mines should be included in the planning at an early stage. For example, it became apparent during the dismantling of the concrete plug in the EB experiment in the Mont Terri project how difficult it was to break through a simple 1m-thick concrete wall. Unexpected challenges of this nature must be overcome in a deconstruction project, and they will be easier to overcome the earlier they are identified. Thus, the report leaves a number of fundamental questions unanswered that could have been analyzed in the beginning today. As examples can be mentioned:

• the possible reasons for retrieval or partial retrieval of waste and the time window in which such should be ensured;
• in the case of a partial retrieval of waste or of recyclables: the risks for the remaining waste or the remaining partial repositories (and their closure);
• the characterization of the condition of the deep repository and its near- and far-field prior to retrieval and the condition of the emplacement infrastructures (e.g., crane runways HLW, rail networks HLW, support structures [segments HLW, anchorages and support elements LILW repositories, etc.]) at the time of retrieval;
• the influence of the thermal field created by decades of emplacement of HLW containers and its impact on occupational safety and the ventilation situation during decommissioning;
• the sense of temporary storage of hot deconstructed bentonites in already decommissioned storage galleries;
• the requirements for monitoring the tightness of the containers or the radiation in order to define the requirements for the use of the dismantling technology;
• the requirements for monitoring gas evolution (esp. hydrogen) and potential gas risks during dismantling (ex-hazard);
• the description and analysis of possible accident situations (e.g. gas, water, radiation), e.g. also the failure of the ventilation system or the failure of robotized equipment.[11]

The authors of the report are well aware of many of these points.[12] The reference to the fact that this work should be carried out in accordance with the further stages would have required a presentation of the mentioned stages and the concrete work and activities within these stages already in this framework report.

6       Concluding remarks

The dismantling of large nuclear and non-nuclear contaminated sites is in principle possible with the techniques and equipment available today. This seems to be the main message of the Nagra report. The other aspects of decommissioning and retrieval will be discussed in greater depth and detail during the process. This is all good and laudable as far as it goes.

However, anyone who has been involved in such remediation cases knows that such projects are much more complex and unpredictable than expected. Problems such as those expected at Asse, as they occurred or are occurring during the dismantling tests of the «tank farm» at Hanford or the dismantling work for the chemo-toxic waste at the Stocamine underground storage site (Wittelsheim, F) show how important it is to think through all possible aspects of a dismantling project at an early stage: From the overarching issues of interim storage, reconditioning of retrieved waste, to re-treatment or re-storage in a deep geological repository, to the small practical day-to-day issues that can massively complicate a decommissioning operation at a site: unexpected roof breaking, decommissioning problems with a number of casks, water inflow in the repository, mishaps and accidents when using robotic equipment, and so on. Most importantly, there are also today’s knowledge deficiencies in the actual implementation of a remediation program. Demonstration objects are needed, and the earlier these are operated, the better the experience gained can be incorporated into further planning. In this sense, it should be in the interest of Nagra itself to present as soon as possible an integral report on the retrieval of radioactive waste from a deep repository in the configuration of Nördlich Lägern, covering as far as possible all planning and technical issues, including a procedural process (step-by-step plan) that defines when which issues are to be addressed and in which stages. Such a procedure would be welcome from the point of view of acceptance of the project by the affected population.

References

[1] Siehe Zusammenstellung in Buser, M., 1998. «Hüte»-Konzept versus Endlagerung radioaktiver Abfälle: Argumente, Diskurse und Ausblick. Hauptabteilung für die Sicherheit von Kernanlagen. Januar 1998. S.34.ff., https://www.ensi.ch/de/wp-content/uploads/sites/2/2014/09/huete-konzept-98-scn.pdf (25.07.23)

[2] VSE et al., 1978. Die nukleare Entsorgung der Schweiz. Verband Schweizerischer Elektrizitätswerke (VSE), Gruppe der Kernkraftwerkbetreiber und -projektanten (GKBP), Konferenz der Überlandwerke (UeW), Nationale Genossenschaft für die Lagerung radioaktiver Abfälle (Nagra). 9. Februar 1978. Kapitel 4.

[3] Buser, M., 1988. «Hüte»-Konzept versus Endlagerung radioaktiver Abfälle: Argumente, Diskurse und Ausblick. Hauptabteilung für die Sicherheit von Kernanlagen (HSK). Januar 1998. S. 34, 37-38.

[4] EKRA, 2000. Entsorgungskonzepte für radioaktive Abfälle. Schlussbericht im Auftrag des Departements für Umwelt, Verkehr, Energie und Kommunikation, 31. Januar 2000. S. 74.

[5] Nagra, 2022. Rückholungskonzept für ein geologisches Tiefenlager, Nagra Interner Bericht NIB 22-13.

[6] Nagra, 2022. S. 1.

[7] BfS, 2014. Schachtanlage Asse II. Technische Herausforderung der Rückholung. Fachtagung 13. Februar 2014. Kurzfassung der Vorträge. Bundesamt für Strahlenschutz, sowie die im Laufe der folgenden Jahre publizierten Konzeptberichte der Arbeitsgemeinschaft Konzeptplanung Rückholung (siehe Quellenverzeichnis)

[8] Arge KR, 2015a. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle der radioaktiven Abfälle von der 725- und der 750-m-Sohle – Arbeitspaket 01: Planungsgrundlagen, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung; Arge KR, 2015b. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle von der 725- und 750-m-Sohle – Arbeitspaket 02: Bearbeitungskonzept und Projektablaufplan, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung; Arge KR, 2016a. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle von der 725- und der 750-m- Sohle – Arbeitspaket 05: Verfahrensschritte – Entwurf -, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung; Arge KR, 2016b. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle von der 725- und der 750-m- Sohle – Arbeitspaket 06: Grobkonzepte – Entwurf -, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung; Arge KR, 2017. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle von der 725- und 750-m-Sohle – Arbeitspaket 04: Kriterienkatalog und Bewertungsmaßstäbe, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung; Arge KR, 20. Rückholung der radioaktiven Abfälle aus der Schachtanlage Asse II – Konzeptplanung für die Rückholung der radioaktiven Abfälle von der 750-m-Sohle, Arbeitspaket 07: Bewertung der Grobkonzepte, Gelsenkirchen, Arbeitsgemeinschaft Konzeptplanung Rückholung.

[9] ein guter Überblicksartikel erschien dazu in der New York Times, 31. May 2023. A Poisonous Cold War Legacy That Defies a Solution. https://www.nytimes.com/2023/05/31/us/nuclear-waste-cleanup.html (25.07.2023).

[10] Department of Ecology, State of Washington. Tank Waste Monitoring and Closure. https://ecology.wa.gov/Waste-Toxics/Nuclear-waste/Hanford-cleanup/Tank-waste-management/Tank-monitoring-closure (1.09.2023); Office of Environmental Management, 2023. Hanford Makes Progress Retrieving Tank Waste, Prepares for Future Transfers. April 18 2023. https://www.energy.gov/em/articles/hanford-makes-progress-retrieving-tank-waste-prepares-future-transfers (1.09.2023).

[11] Nagra, 2022. S. 55, präzisiert, dass dies zu einem späteren Zeitpunkt nachgeholt werden sollte.

[12] Nagra, 2022. S. 57.