Switzerland’s National Cooperative for the Disposal of Radioactive Waste (Nagra) has compared the advantages and disadvantages of sites for a used fuel/high-level waste encapsulation plant. The resulting report, “High-level waste encapsulation plant: Advantages and disadvantages of different siting variants”, will serve as a basis for discussion with the regions, Nagra said.

Most of Switzerland’s high-level waste (HLW) 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 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.  

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 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,” Nagra said.

Nagra noted that 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.

Nagra said it would not be wise for fuel assemblies to be directly packaged into the disposal canisters at nuclear power plants because the disposal canisters would have to be packaged into shuttle overpack canisters for interim storage, and Zwilag does not have enough space for this type of packaging. In addition, it is not advisable to already commit to a final disposal canister because emplacement will not begin until 2060. Nagra will until then continue optimising the disposal canister to ensure it complies with the state-of-the-art in the year 2060.

Furthermore, 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.

“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. Finally, when all the waste stored at Zwilag is eventually transferred to a deep geological repository, the interim storage facility can be entirely dismantled."

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