Re-evaluation of the bentonite buffer dimension in a geological repository for spent nuclear fuel under the KURT conditions

The KBS-3 type geological repository was proposed for the disposal of spent nuclear fuel around 40 years ago. The long-term safety of the repository strongly depends on an engineered barrier consisting of a copper disposal canister and a bentonite buffer. The major functions of the buffer are to protect the disposal canister against corrosion and minimize the release of radionuclides from the canister. However, the current design of a thick buffer height above a canister makes it difficult to retrieve the deposited spent nuclear fuel. In this work, we re-evaluate the dimensions of a buffer in terms of radionuclide migration and corrosion using a mathematical approach under the KURT conditions. The calculation results show that the corrosion lifetime of the canister is longer than one million years even if the buffer thickness is reduced from 0.36 m to 0.25 m. Similarly, the buffer height above a disposal canister is reduced from 2.5 m to 1.5 m. However, it is expected that more detailed further analyses such as effects of buffer uplifting and buffer erosion should be carried out to carefully assure the safety of the repository.

Automated summary

The KBS-3 type geological repository, proposed 40 years ago for nuclear waste disposal, relies on a copper disposal canister and a bentonite buffer as an engineered barrier for long-term safety. The buffer's main functions are corrosion protection and minimizing radionuclide release. However, the current design makes it challenging to retrieve the spent nuclear fuel. This study re-evaluates the buffer dimensions for radionuclide migration and corrosion resistance, finding that reducing the thickness and height of the buffer does not significantly affect the corrosion lifetime of the canister.