Photo: swisstopo.ch / W. Wildi

By Marcos Buser & Walter Wildi

The EKRA commission

From 1999 to 2001, the two authors of this article were members of the “Expert Group for Nuclear Waste Management Concepts” (EKRA, Chairman: Walter Wildi), appointed by Federal Councillor Moritz Leuenberger. This group drew up the concept of “controlled long-term geological disposal” for radioactive waste, which was incorporated into the revised Nuclear Energy Act (LENu[4]) in 2003 under the name of “deep geological disposal“[3]. One of the key features of this concept is the formalisation of the monitoring of the deep geological repository, to ensure that the waste remains retrievable.

This concept is also the basis for Nagra’s application for a general licence for a deep geological repository for all categories of radioactive waste in the “Northern Lägern” region, which was submitted in autumn 2024 (but is not yet available to the public). At this site, all categories of waste should one day be stored in a “combined repository” at a depth of around 800 m.

A quarter of a century after EKRA’s work was completed, we can see that the current concept (“our” concept) of “deep geological disposal” is outdated, at least in part and in its fundamental aspects, and that the management of nuclear waste is looking for new ways forward. Here, we would like to give a brief overview of these developments, using Switzerland as an example.

The time frame

Switzerland’s major electricity companies have been operating nuclear power plants since 1969. Nagra was founded in 1972. Its mandate, revised in 1978, was as follows[5]: to draw up a proposal for a final repository for high, intermediate and low-level radioactive waste from nuclear power plants, medicine, industry and research. In 1978, Nagra launched the “Project Guarantee” project, under which the feasibility of a final repository in Switzerland was to be demonstrated by 1985. The repositories were scheduled to go into operation in 1990, and then at the beginning of the twentieth century. For low- and intermediate-level waste, the Federal Council approved the demonstration of the feasibility of disposal in 1988, while for high-level waste, the guarantee project was finally completed in 2006 by a Federal Council decree, two decades late.

Following the entry into force of the Nuclear Energy Act, the selection of sites for waste disposal was relaunched in 2008 as part of the “sectoral plan for deep geological repositories”. After further delays, the plan now envisages the commissioning of a repository for low- and intermediate-level waste (L/ILW) between 2050 and 2064, and for high-level waste (HLW) between 2060 and 2074, i.e. around a century after the creation of Nagra.

Transmutation: developments in the treatment of high-level waste

In 2000, the EKRA report concluded that the safest long-term method for disposing of high-level waste was to confine it behind technical and geological barriers in the geological subsoil, with the repository being monitored at least initially to allow for possible recovery. The expert report (p. 47) mentions among the possible reasons for the possible recovery of waste, in addition to breakdowns and incidents, the desire to “reuse” resources, i.e. to reuse highly radioactive spent fuel elements from nuclear power plants.

The transformation of radioactive substances was also discussed at the time and tested in experiments. These included the international “Megapie“[6] project, which was successfully carried out at the Paul Scherrer Institute (PSI) from spring 2011. However, at the time, the energy and costs involved in such a transformation (“transmutation”) on an industrial scale were too high, and so were not considered for waste treatment.

Since the beginning of the 21st century, the EKRA report and the new Nuclear Energy Act, the choice of deep geological disposal sites has continued, albeit with scepticism in large sections of the public and even in specialist circles as to whether a geological subsoil can guarantee the safe isolation of waste for a million years.

The situation regarding the treatment of highly radioactive waste has changed considerably in recent years, particularly with the emergence of transmutation as a method of transforming active nuclear materials. Today, it is the proposal by Transmutex (based in Vernier, canton of Geneva) that is under discussion in Switzerland. Transmutex proposes to bombard highly radioactive materials in reactors with neutrons from a particle accelerator, thereby transforming the materials and releasing energy. This transformation process can be stopped at any time; a power excursion (accident with release) is not possible. During this process, the energy released can be used to produce heat and therefore electricity. Highly radioactive substances, such as spent fuel rods, can also be used as fuel. This transmutation also produces radioactive waste, but with a much shorter lifespan (half-life) than the substances used as fuel. It can be disposed of with other low and intermediate level waste (L&ILW). In this case, there is no need to operate a long-term repository for high-level waste (HLW).

Transmutation has not yet been implemented on an industrial scale, but it is well on the way. As mentioned above, disposal of high-level waste is planned in Switzerland in half a century’s time. We can therefore expect transmutation to emerge at that time (or even before) as a serious alternative to deep geological disposal for highly radioactive materials. In that case, Nagra’s deep geological repository should become obsolete. If we follow the principles of a circular economy, this development is very welcome.

Developments in the field of low-, intermediate- and high-level radioactive waste

Low- and intermediate-level radioactive waste has been produced on a daily basis since nuclear power plants began operating. It is conditioned in the plants and at ZWILAG, partly by incineration of organic matter, and then stored in the ZWILAG halls in Würenlingen. Waste from medicine, industry and research (MIF) is stored in the federal interim storage facility at the Paul Scherrer Institute in Würenlingen.

Final disposal in a deep geological repository was originally planned for the beginning of this century, but has now been delayed by several decades in several stages, as mentioned above. And this is not without consequences, not least because the watertight packaging of the waste was not designed to last for such a long time. If the waste had been stored deep underground at the beginning of this century, as originally planned, it would now be protected behind the technical and natural barriers present in the repository and would be monitored as part of the repository’s surveillance.

Radioactive waste packages containing large quantities of organic material, such as ion exchange resins from the operation of boiling water reactors, are particularly at risk. If oxygen enters the waste containers, for example through a leak caused by corrosion, the resins decompose and radioactive gases escape. Leaks have already been discovered in an interim storage facility, with the result that the waste had to be repackaged (DSN 2003, p.24) [7]. In the long term, this situation is untenable and waste containing organic materials must be thermally treated before it can be disposed of.

But let’s come back to high-level radioactive waste: if it were one day to undergo transmutation, the storage of low- and intermediate-level radioactive waste in a deep geological repository at a depth of 800 m would also lose its appeal. The cost of such a geological repository, under high rock and water pressure and at temperatures in excess of 30°C , is all the more disproportionate in this case as, for the necessary isolation period of a few thousand years, no real risk of massive release of radioactive substances into the environment can be identified. Other host rocks and sites, with suitable storage conditions, would in this case be more appropriate than the Opalinus clays of the Northern Lägern region at a depth of more than 800 m.

Consequences for the radioactive waste management programme and nuclear energy in Switzerland

The general licence procedure currently under way is hardly affected by the above statements. However, if a general licence is ever granted, the question arises as to whether it is really necessary to build a deep repository at a cost of at least CHF 20 billion, or whether it would not be more sensible to invest in the transmutation of high-level waste and plan a suitable repository for low- and intermediate-level waste.

As mentioned above, transmutation requires reactors combined with particle accelerators. If such facilities were to be built in Switzerland, the Nuclear Energy Act would have to be amended. If the law were to be amended, it would in any case have to be ensured that reactors capable of causing chain reactions and core meltdown, and which produce highly radioactive waste, were no longer authorised in future. An alternative would be to sell the high-level waste and transmute it in facilities abroad.

Transmutation using particle accelerators is not the only alternative to the current concept of deep disposal. For some years now, the transmutation of waste using high-power lasers, as proposed by the French physicist and Nobel Prize winner Gérard Mourou, has also been on the agenda. As we can see, various physical, physico-chemical and crystallographic alternatives are emerging that could eventually be considered for more sustainable disposal of this waste. Medium-term alternatives to deep geological disposal, currently under discussion, are also conceivable. Regardless of the disposal option that will one day be implemented: what should ultimately count in the choice of a new disposal route is the definitive elimination of the dangers that highly radioactive waste represents for man and the environment.

[3] CFRA, 2000: Concepts for radioactive waste management. Final report commissioned by the Department of the Environment, Transport, Energy and Communications, 31 January 2000.

[4] 732.1 Nuclear Energy Act (LENu) of 21 March 2003.

[5] The initial mandate concerned only low- and intermediate-level waste.

[6] https://www.nuklearforum.ch/fr/nouvelles/transmutation-dactinides-au-psi-experience-internationale-megapie/

[7] DSN 2003: Expert report on the application by the Paul Scherrer Institute to amend the operating licence for the federal interim storage facility. DSN 22/483.

Correction

The SPRIN-D study published at the beginning of February (https://cms.system.sprind.org/uploads/SPRIND_Studie_Beschleunigergetriebene_Neutronenquelle_d8cde0cf9d.pdf) analyses in detail the transmutation of highly radioactive waste in Germany. It argues in detail the feasibility of this method for the disposal of HLW. The above statement that “the ongoing general licence procedure is hardly affected by the above statements” is therefore no longer tenable.