Dress rehearsal for the final disposal of spent nuclear fuel

Posiva Oy, the company responsible for the final disposal of spent fuel from Finland's current nuclear power plants, has almost completed the construction of a final disposal facility and locations in Olkiluoto, Eurajoki. The project is so close to being finished that the entire operational process can be tested, from logistics to packaging and disposal to the underground facility. Last autumn, Posiva started a integrated systems test ("yhteistoimintakoe" or YTK) that takes several months to complete.

Posiva, owned by Teollisuuden Voima and Fortum, does not yet have the licence required to start the final disposal. It submitted an application for a licence for the final disposal of spent nuclear fuel to the Government at the end of 2021, and the application is still being processed by the Radiation and Nuclear Safety Authority (STUK). Posiva is carrying out the current integrated systems test without fuel and the test does not involve any other radioactive material.

The spent nuclear fuel is sealed inside a copper and cast iron canister. During the integrated systems test, Posiva intends to fill, close and dispose of several test capsules in the bedrock at a depth of approximately 400 meters as well as backfill (with bentonite clay) and close a final disposal test tunnel with a concrete plug several metres in thickness. Posiva’s aim is to demonstrate internally, and to its owners and society, that it is capable to carry out the final disposal safely and economically.

You may have noticed that the above includes no mention of STUK, even though the organisation oversees the planning and construction of the final disposal facility very closely. There is a reason for this. Regulation does not require any test like the integrated systems test to be carried out for final disposal facilities. In other words, Posiva is carrying out the test based on its own perspective and needs. However, this does not mean that STUK will not be involved in observing the test and overseeing Posiva’s operations.

Technically, YTK is a test and STUK has very few technical safety requirements that need to be met in this context. The supervision carried out by STUK’s inspectors is based on the safety requirements, which are mainly described in STUK’s YVL guides.

The scope of the safety requirements include environmental radiation exposure, the radiation protection of employees and, in Posiva's case, the manufacture of a final disposal canister and its deposition in the final disposal tunnel. That is why our inspectors record any noticesthey may have in the inspection protocols as observations, and no requirements are presented to Posiva in this context. During the YTK, STUK will have the opportunity to practise oversight practices during operation while simultaneously learning about the stages of the process that have the highest impact for our oversight. As such, this is an exercise for STUK as well as Posiva.

In addition to the technical aspects, we are also interested in overseeing Posiva’s operations. There are many related questions that we hope to find answers to. Are Posiva’s instructions clear? Do employees know what is required of them and what to do in case of problems? If and when situations arise in which it would make more sense to deviate from the instructions, does Posiva take the time to correct its operations and learn from its experiences?

Last summer, Posiva significantly renewed its organisation when it moved from the construction phase to the operational phase. STUK is interested to see if the new organisational structure works seamlessly and as planned. In other words, the way the organisation operates is a key issue we pay attention to in this context.

It would be quite surprising if everything worked without a hitch right away, but we would be just as disappointed if the problems encountered with the first test capsule were repeated with the last test capsule. This test offers an excellent point of view on Posiva's operations and its ability to critically assess its own operations. By overseeingthe experiment, we can make valuable observations about Posiva’s readiness to start using the final disposal facility.

In the use of nuclear energy, in addition to Safety, there are two other important words that start with S: Security and Safeguards . STUK oversees all three of these areas. Experts from the International Atomic Energy Agency (IAEA) and the European Commission are also involved in the oversight of Safeguards, meaning that the oversight is already international.

It is interesting to see things done for the first time. There is a great deal of curiosity involved in getting to observe the technical implementation of final disposal. However, satisfying curiosity is not a reason to spend working hours and company money on monitoring, but rather the purpose is to learn and collect observations to support STUK’s oversight during use.

Regardless of YTK, we will simultaneously assess thedocumentations in Posiva''s licence application and continue to work on writing a safety assessment. As these tasks coincide, I am looking forward to a busy but also interesting and rewarding autumn with regard to the oversight of YTK.

The writer, Ville Koskinen, is Senior Inspector at STUK's Nuclear Waste Regulation and Safeguards  Department