STUK co-operates with Inspecta to study capsules for final disposal of spent nuclear fuel.

Inspecta is helping The Finnish Radiation and Nuclear Safety Authority, STUK, to review the application for construction of a final repository for spent nuclear fuel in Finland. This is a critical study as the spent fuel must be stored safely for at least 100,000 years.

Finland has been looking at various solutions for storing its spent fuel and has decided to use the same concept as Sweden, KBS-3. The concept is based on encapsulating the fuel in copper canisters stored deep in bedrock underground.

Posiva has applied to, STUK, The Radiation and Nuclear Safety Authority, to plan, design and build the storage facility at the Olkiluoto nuclear power plant. STUK will now examine and audit Posiva's application and this requires extensive expertise. After an international tender for expert support in various areas of the audit, Inspecta was chosen as one of the experts commissioned by STUK. Inspecta in Finland has conducted several assignments for STUK through the years. Inspecta in Finland could therefore connect STUK.

Inspecta to examine the capsules

Peter Segle, Inspecta
Peter Segle, Inspecta
‘Our assignment is the "Structural design and mechanical integrity of the disposal canister." This means examining how the copper canisters, with their cast iron inserts, will be affected by different load situations. We are going to investigate their mechanical integrity and how various mechanical loads would affect the capsule’, says Peter Segle, specialist and senior project manager at Inspecta Nuclear.

Peter Segle has for several years worked with the Swedish Radiation Safety Authority (SSM) and examined the corresponding Swedish repository that the Swedish Nuclear Fuel and Waste Management Company (SKB) use for storage.

‘The experience and knowledge of KBS-3 is of great use now’, says Peter.

The KBS-3 concept

With KBS-3, the spent uranium fuel is placed in a cast iron insert encased in a copper capsule and embedded in a buffer layer of bentonite clay, deep down in bedrock. The tunnels are then filled with clay that swells when saturated with water. The storage should keep the spent nuclear fuel secure in the bedrock for at least 100,000 years.

‘As in the Swedish assignment, we will evaluate the risks of external pressure on the capsule, uneven swelling of bentonite clay, earthquakes and other possible scenarios’, says Peter. With his specialized expertise in this area, the canister’s structural integrity can be assessed in various scenarios and any potential for cracking and corresponding damage can be ascertained.

To help him, Peter Segle has two other Inspecta specialists on his team. Jessica Strömbro, an expert on material mechanics, and Olof Björndahl, an expert in structural dynamics.

Bentonite clay has several functions

The bentonite clay surrounding the capsule deep inside the bedrock has several functions. One of the main functions is to act as a barrier if the canisters leak. Water-saturated bentonite clay has a great ability to slow down the spread and movement of radioactive materials. Another main function is to create a favourable chemical environment for the copper canister so that corrosion is delayed. The bentonite clay also holds the capsule in place in the hole it is stored in and can enhance the mechanical load bearing qualities of the canister in different scenarios.

Working with a very long-term perspective

The repository must be able to keep the spent fuel secured for 100,000 years. In addition, a risk analysis covering a million years is being carried out. With such a long period of time, the next ice age must be taken into account in Inspecta’s assessment.

‘That is a vast amount of time, which gives an interesting perspective to the work’, says Inspecta’s Segle. The assignment for STUK is expected to last for three years.

For more information, please contact
Peter Segle, +46 8 5011 3068
Mikael Kuokkanen, +46 8 5011 3041
Ditte Erbing, +46 8 5011 3023

 

Page created: 13 May 2013