Report published on the siting variants for a high-level waste (SF/HLW) encapsulation plant

Nagra has compared the advantages and disadvantages of sites for an SF/HLW encapsulation plant. The resulting report serves as a basis for discussion with the regions.

From Nagra’s point of view, the best solution would be to realise the encapsulation plant at the deep geological repository or at the interim storage facility (ZWILAG) in Würenlingen.

Most of Switzerland’s high-level waste is held in transport and storage casks at the interim storage facility in Würenlingen (ZWILAG), and a smaller percentage at the interim storage facility of the Beznau nuclear power plant (ZWIBEZ). Before its emplacement in a deep geological repository, the waste is transferred to smaller disposal canisters in an encapsulation plant. Where to locate such a plant is currently a topic of discussion.

In the reference case, the encapsulation plant is part of the surface infrastructure located at the repository site. In discussions with the siting regions, the question arose whether an encapsulation plant could also be located outside the repository site. At the end of Stage 2 of the site selection process for deep geological repositories, the Federal Council decided that, in collaboration with the regional conferences and the respective siting Canton, the waste producers could also investigate placing the encapsulation plant for radioactive waste outside the siting region. Nagra has now compiled the advantages and disadvantages of potential sites for an encapsulation plant in its report “High-level waste encapsulation plant: Advantages and disadvantages of different siting variants” (in German). This report serves as a basis for discussion for the transregional collaboration with the siting regions and Cantons that will now follow.

Aside from locating an encapsulation plant at the site of a deep geological repository, Nagra has compared variants for an external encapsulation plant at ZWILAG, ZWIBEZ and the Gösgen and Leibstadt nuclear power plants as well as on “greenfield” sites. The evaluation included the number of transport campaigns, the space requirements of the encapsulation plant, the use of existing infrastructures and existing know-how.

From Nagra’s point of view, the best solution would be to operate an encapsulation plant at the repository site or externally at the interim storage facility in Würenlingen because this would result in the greatest synergies. ZWILAG, for example, already operates a transloading cell for high-level waste. Moreover, unnecessary transports to new sites would be avoided.

Other countries are also planning to transfer their high-level waste into disposal canisters at an interim storage facility or at the repository: Finland and France have chosen the repository, Sweden the interim storage facility.


Questions and answers

In the past, it was said that the encapsulation plant should be built at the repository site. Why has Nagra now investigated alternatives?
The idea of locating an encapsulation plant outside the repository site was raised by actors in the participation process. Based on the decision of the Federal Council on Stage 2, Nagra is thus also considering locations outside the siting regions.

Why are the fuel assemblies not directly packaged into the disposal canisters at the nuclear power plants? This way, it would not be necessary to construct an encapsulation plant outside the nuclear power plants.
That would not be wise for several reasons:

  • First, the disposal canisters would have to be packaged into so-called shuttle overpack canisters for interim storage, and ZWILAG does not have enough space for this type of packaging.
  • Second, it is not advisable to already commit to a final disposal canister because emplacement will not begin until the year 2060. For this reason, Nagra will continue optimising the disposal canister until that time and can thus ensure that the canister will comply with the state-of-the-art in the year 2060.
  • And third, every nuclear power plant would have to have an encapsulation plant if the fuel assemblies are to be packaged there directly.

The report states that significantly more nuclear transports would be needed if the encapsulation plant were located externally than if it were constructed at the repository site. What would these transports mean in terms of safety?
In Switzerland, radioactive waste has been routinely transported from the power plants to ZWILAG for years. We have the know-how and can provide safe transports. From Nagra’s point of view, safety is not compromised as the strict international transport regulations have to be complied with either way.

What happens with ZWILAG when all the waste stored there has been transferred to a deep geological repository?
The ZWILAG interim storage facility can be entirely dismantled.


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