Finland’s path to nuclear waste disposal

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We look back on Posiva’s four-decade journey that led to a permit application and the construction of the world’s first deep geological repository


Posiva is an expert organization responsible for the disposal of their owners’ spent nuclear fuel in Finland. Posiva oversees the R&D work on the disposal of spent nuclear fuel and the construction and operation of the encapsulation facility and disposal facility.

In the 1980s, Teollisuuden Voima began site investigations for the housing of a deep geological repository known as the ‘Repository’. In 1994, the Finnish Parliament passed a law banning the export and import of spent nuclear fuel. Therefore, the other nuclear power plant operator in Finland, Fortum, joined the repository project and a company dedicated to nuclear waste management, Posiva Oy, was formed.

The company’s first goals were to prepare an application for a policy decision (DiP) on geological disposal of spent fuel elements and to search for a suitable location for the repository.

In Finland, according to the Nuclear Energy Act, the licensing of a nuclear installation is a step-by-step process, starting with a policy decision, moving on to a building permit and culminating in an operating permit after completion.

The site for the repository was selected in 1999 and the selection was approved by the Municipality of Eurajoki. In 2000, a DiP application was made for the construction of the repository and an encapsulation facility in Olkiluoto, whereby a so-called KBS-3 process (see below) with crystalline host rock was introduced as the disposal concept. The DiP was drawn up by the Finnish government and ratified by Parliament in 2001.

The DiP contained the requirement that the preliminary surface site investigations should be confirmed by site investigations at the actual repository depth. Therefore ONKALO®, an underground research and rock characterization facility, was built in the years 2004-2012. ONKALO® was built under the supervision of the Nuclear Safety Authority (STUK) as it was designed from the early planning stages to become part of the spent fuel disposal facility. Site confirmation studies continued until 2010 when the repository level – 420-430 m below sea level – was reached.

With the construction of ONKALO®, rock construction methods were specially developed for the repository, including a drilling and blasting excavation method and the injection of groundwater flows, in order to avoid damaging the bedrock and unnecessary disturbance of the groundwater conditions. In addition, a specific Rock Suitability Classification (RSC) method was developed and iteratively tested during construction to assess rock suitability and provide input information for repository design.

A unique technology called Posiva Flow Log for locating cracks and measuring groundwater flow in them was developed and has been used not only in Olkiluoto but by several other countries and industries for over 20 years now.

Principles of geological disposal of nuclear waste

The principle of geological disposal is to isolate nuclear waste from the biosphere until its radioactivity has fallen to an insignificant level.

The safety of the repository concept in Olkiluoto is based on the KBS-3 concept, which consists of crystalline bedrock as a natural barrier and an engineered barrier system (EBS). The RDF components are a repository container, a bentonite buffer, a bentonite filling of the disposal tunnel, a disposal tunnel plug and the closure of further underground openings in the disposal facility.

The primary barrier for containment and isolation of spent nuclear fuel from the biosphere is the copper-cast-iron canister. The buffer surrounding the canister limits the movement of groundwater from bedrock to the canister and protects it from rock movement. The backfilling and closure of the tipping adits prevent water from flowing into the adits
and the end plug holds the backfill in place.

The disposal concept was studied iteratively together with site studies and developed in detail by defining requirements for its components, testing material performance at different scales (laboratory, field scale and in ONKALO®) and manufacturing tests with several potential suppliers of the RDF components.

In 2012, Posiva applied for a building permit for a repository and for the encapsulation plant.
The application included a safety case, TURVA-2012, to address the safety of spent nuclear energy disposal
Fuel in Olkiluoto. The building permit was granted by the Finnish government in 2015.

The construction of the repository started in 2016 and the construction of the encapsulation plant in 2019.

In preparation for operation, Posiva will carry out a trial run of disposal, during which all works from interim storage of spent nuclear fuel to encapsulation and disposal will be carried out with the technology, organization and procedures that will be used in practical operations later. The only difference to actual disposal is that dummy fuel elements are used instead of spent nuclear fuel. The tunnel to carry out the trial run was completed in June 2021.

Posiva is currently building the encapsulation facility and disposal facility. Construction work is progressing well and the encapsulation plant will be ready for installation and commissioning of the systems in 2022/23. The construction of the first five disposal tunnels is also in progress in the repository.

The application for an operating permit for Finland’s deep geological repository

Posiva is the first company in the world to apply for an operating license for encapsulation and disposal. The application was submitted to the Finnish government at the end of 2021.

The Ministry of Economy and Labor examines the application for the operating license and finally forwards it to the State Council for approval. STUK carries out a safety assessment of the application and is responsible for supervising the construction and commissioning of the nuclear installation. Actual disposal activities are scheduled to begin in the mid-2020s.

According to Janne Mokka, CEO and President of Posiva, the submission of the application for an operating license is a significant milestone for the entire nuclear energy industry.

“We can all be proud of the long-term and responsible approach of the different parties to the use of nuclear energy in Finland, as Posiva is now able to start the world’s first proven safe disposal of spent fuel here in Olkiluoto. We have a solution,” says Mokka.

“Decades of work to prove long-term safety and to develop the ONKALO® repository concept for the conditions of Olkiluoto is now complete and we can focus on installing the equipment in the encapsulation plant and disposal repository, commissioning the plant and preparing for operation” , he adds.

Tiina Jalonen, senior vice president of development at Posiva, says that the future prospects are now bright.

“Besides the commitment to the safe operational implementation of disposal in the future, we are developing our concept towards a more industrial solution and supporting the vision of our subsidiary Posiva Solutions to convert the know-how gained in the project into a successful Finnish export product,” says jalonen.

About Posiva

Posiva Solutions Oy is a subsidiary of Posiva Oy and focuses on the sale of Posiva’s know-how accumulated over the last 40 years in design, research and development in the field of spent nuclear fuel disposal.

The company recently announced that it would review general criteria for Lithuania to manage its spent nuclear fuel. Under an annual contract, Posiva Solutions will “discuss the principles that will ensure the safety of spent nuclear fuel and the storage of long-lived radioactive waste in a geological repository, the methodology for the long-term safety assessment, and the methods to be used for the safety assessment, software and data.” so Ignalina.

Posiva solutions

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