Test operation – Countdown to starting final disposal
Test operation involves testing all aspects of how the disposal facility for spent nuclear fuel operates. During test operation, non-radioactive dummy fuel elements are used instead of actual spent nuclear fuel. Test operation demonstrates the functionality of the entire final disposal process and the personnel’s readiness for industrial final disposal operations. Test operation started on 30 August 2024. It will take several months to complete.
Test operation can be divided into two parts:
The test operation of the aboveground encapsulation plant and the test operation of the underground disposal facility excavated into the bedrock.
The test operation of the encapsulation plant includes several stages:
- Arrival of fuel at the encapsulation plant
The spent fuel is brought to the disposal facility from TVO’s spent fuel interim storage, which is also known as the “KPA storage”. A special transfer cask is used for transporting the fuel. The distance for transferring the fuel is quite short as the KPA storage is also located at Olkiluoto. - Assembling the canister and taking it into the encapsulation cell
The empty final disposal canister is assembled and taken to the encapsulation cell. The canister comprises a cast-iron insert and a copper outer shell. They are joined together during assembly. The completed canister is inspected and taken to the encapsulation cell using an automated canister transfer trolley. - Placing fuel inside the canister
The loading of spent fuel into the canister takes place in the fuel handling cell. The empty canister arrives to the handling cell via the transfer corridor which runs under the handling cell. All the stages of the canister loading are performed remotely inside facilities that have robust radiation protection; the concrete walls of the handling cell are up to 1.3 m thick. At no point are fuel elements disassembled. Rather, they are placed inside the canister as they are. Once all the fuel assemblies have been dried at the drying station and placed inside the canister, the canister is filled with argon gas and sealed tightly with an inner steel lid. - Welding and machining of the canister lid
The topmost part of the canister – the copper lid – is installed in the welding cell. This is done using friction stir welding. After the welding, the integrity of the joint on the copper lid is equivalent to the integrity of the canister shell. The leak-tightness of the joint is verified with eddy current and ultrasonic inspections as well as a visual inspection. Then, the canister surfaces are smoothed out at the machining station. The welding and machining are performed fully remotely. - Moving the canister into storage and then to the canister lift
After machining, the canister is moved to the canister storage, which is located inside the overground encapsulation plant. From there, it is taken to the canister lift.
Similarly, the final disposal in the bedrock comprises several stages:
- Taking the canister down to ONKALO
The encapsulation plant is connected to the underground disposal facility via a canister lift, which transports canisters down to the final disposal level. This is a long trip, as the reception station is located 430 metres underground. The canister lift is not the speediest ride: it moves at a speed of 0.4 m per minute. It takes approximately 50 minutes for the canister to travel all the way down. - Transferring the canister into a deposition tunnel
Once the canister is ready for final disposal, it is taken from the underground reception station into a deposition tunnel using the canister transfer and installation vehicle. The underground vehicles operate fully remotely. - Installing the bentonite clay buffer
A deposition hole is 8 m deep and has a diameter of 1.75 m. At this stage, bentonite clay is installed at the bottom and on the sides of the hole. This uses the buffer installation system, which is a unique, specially designed and purpose-built piece of equipment. - Placing the canister inside the deposition hole
The canister is placed inside the deposition hole using the canister transfer and installation vehicle. Once the canister is in place, the hole is filled with bentonite clay and levelled out. - Tunnel backfill
Once the holes inside the test operation tunnel have been filled, the entire tunnel is backfilled with bentonite clay. The backfill installation system is used for this. Finally, the mouth of the tunnel is closed with a concrete plug.
Q&A for the test operation of Posiva’s facilities
What does test operation of the disposal facility mean?
Test operation involves testing all aspects of how the disposal facility operates. The facility houses many unique pieces of equipment and systems that are the result of decades of research and that are now being used together for the first time ever. Test operation demonstrates the functionality of the entire final disposal process and the personnel’s readiness for safe, industrial final disposal operations. During test operation, non-radioactive dummy fuel elements are used instead of actual spent nuclear fuel.
How significant is the test operation?
Posiva is the first company in the world to conduct test operation of a disposal facility for spent nuclear fuel. The pioneering work is highly significant because, in terms of sustainable nuclear power, final disposal has been an unanswered question. All eyes are now on us globally, from nuclear power and waste management to the regulatory authorities that oversee such operations.
Why do you not communicate more specifically about the test operation schedule?
Because we are doing many things for the first time and we do not want to cut corners. Test operation involves a number of different stages that affect one another, so we do not even have exact information about all the time frames. We will, however, regularly communicate on how the test operation progresses.
It has been said that Posiva Solutions has sold entrance tickets for the test operation to various nuclear waste organisations around the world. Is this correct?
Yes it is. Nuclear waste organisations globally are immensely interested in Posiva’s test operation. Paying for an “entrance ticket” means purchasing a great deal of knowhow, depending on the contract of course.
Does the test operation involve sections that may jeopardise nuclear safety?
The test operation uses non-radioactive dummy fuel elements instead of radioactive spent fuel. The purpose of the test operation is to train for correct and safe operation before starting the actual operations. The goal for the test operation is to ensure that everything will work as it should during actual operation.
