A look back at Posiva’s four-decade journey to applying for a mining license and building the world’s first deep geological repository

Posiva is an expert organization responsible for the final disposal of its owners’ spent nuclear fuel in Finland. Posiva oversees the R&D work for the final disposal of spent nuclear fuel, as well as the construction and operation of the encapsulation plant and the storage depot.

Site studies to accommodate a deep geological repository, known as a “disposal facility”, were initiated in the 1980s by Teollisuuden Voima. In 1994, the Finnish Parliament passed a law prohibiting the export and import of spent nuclear fuel. Thus, the other nuclear power plant operator in Finland, Fortum, joined the disposal project and a company dedicated to the management of nuclear waste, Posiva Oy, was created.

The company’s first objectives were to prepare a request for a political decision-in-principle (DiP) for the geological disposal of spent nuclear fuel and to find a suitable site for the disposal facility.

In Finland, the licensing of a nuclear installation is done in accordance with the Nuclear Energy Act through a step-by-step process starting with a decision in principle, continuing with a construction license and culminating in a permit. operating after completion.

The site for the disposal facility was selected in 1999 and the selection was approved by the municipality of Eurajoki. An application was filed in 2000 for a DiP to build the final storage facility and an encapsulation plant at Olkiluoto, introducing a so-called KBS-3 method (see below) with crystalline host rock as the storage concept . The DiP was developed by the Finnish government and ratified by Parliament in 2001.

The DiP included a requirement that preliminary site surveys carried out above ground should be confirmed by site surveys at the actual depth of immersion. Thus ONKALO®, an underground rock research and characterization facility, was built in 2004-2012. ONKALO® was built under the supervision of the Nuclear Safety Authority (STUK), because from the initial planning phase, it was designed to be part of the final disposal facility for spent fuel. Site confirmation studies continued until the repository level – 420-430 m below sea level – was reached in 2010.

During the construction of ONKALO®, rock construction methods, including a drill-and-blast excavation method and the injection of groundwater flows, were developed specifically for the disposal facility. to avoid damaging bedrock and unnecessarily disturbing groundwater conditions. In addition, a specific Rock Suitability Classification (RSC) method was developed and iteratively tested during construction works to assess rock suitability and provide input information for the design of the facility. final storage facility.

A unique technology called Posiva Flow Log for locating fractures and measuring groundwater flows in them has been developed and has now been used for more than 20 years not only in Olkiluoto, but by several other countries and industries.

Principles of geological disposal of nuclear waste

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

The security of the final storage concept at Olkiluoto is based on the KBS-3 concept, which consists of crystalline bedrock as a natural barrier and an engineered barrier system (EBS). The components of the EBS are a disposal container, a bentonite pad, a bentonite backfill of the disposal tunnels, a tunnel plug and the closure of other underground openings in the disposal facility.

The primary barrier for containing and isolating spent nuclear fuel from the biosphere is the copper-cast canister. The pad surrounding the canister limits the movement of groundwater from bedrock to the canister and protects it from rock movement. Backfilling and closing of disposal tunnels prevents water from flowing into the tunnels
and the end cap holds the backfill in place.

The storage concept was studied iteratively alongside site studies and developed in detail by defining the requirements for its components, testing the performance of the materials at different scales (laboratory, field and in ONKALO®) and carrying out tests of manufacturing with several potential suppliers of EBS components.

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

Construction of the final disposal center began in 2016 and that of the encapsulation plant in 2019.

To prepare for operation, Posiva will carry out a disposal test campaign during which all operations, from interim storage of spent nuclear fuel to encapsulation and disposal, will be carried out with the technology, the organization and procedures that will be used in real operational conditions later. The only difference from real final storage is that instead of spent nuclear fuel, dummy fuel elements will be used. The tunnel to perform the test was completed in June 2021.

Posiva is currently constructing the encapsulation plant and final disposal facility. The construction work has gone well and the encapsulation plant will be ready for installation and commissioning of the systems in 2022/23. Construction of the first five disposal tunnels is also underway in the disposal facility.

Finland Deep Geological Repository Operating License Application

Posiva is the first company in the world to apply for a business license for encapsulation and a final disposal facility. The request was submitted to the Finnish government at the end of 2021.

The Ministry of Economy and Employment will examine the application for operating authorization and will, if necessary, forward it to the Council of State for approval. STUK will carry out a safety assessment of the application and is in charge of supervising the construction and commissioning of the nuclear installation. Actual disposal activities are expected to start in the mid-2020s.

According to Posiva’s CEO and President, Janne Mokka, the submission of the operating license application is an important milestone for the entire nuclear energy sector.

“We can all be proud of the long-term and responsible approach of the various parties in the use of nuclear energy in Finland, with Posiva now having the capacity to launch here the first disposal operation for spent fuel whose safety has been demonstrated in Olkiluoto. We have a solution,” says Mokka.

“The work carried out over several decades to demonstrate the long-term safety and develop the ONKALO® disposal concept adapted to the conditions of Olkiluoto is now finalized and we can concentrate on installing the equipment for the encapsulation plant. and final storage. storage, commissioning of the installation and preparation for operational activities,” he adds.

Tiina Jalonen, senior vice president of development at Posiva, says the outlook for the future is now bright.

“In addition to committing to the safe operational implementation of terminal disposal in the future, we are further developing our concept towards a more industrial solution and supporting the vision of our subsidiary Posiva Solutions to transform the expertise acquired during of the project into a successful Finnish export product,” says Jalonen.

About Posiva

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

Recently, the company announced that it would study general criteria for Lithuania to get rid of its spent nuclear fuel. Under a one-year contract, Posiva Solutions will “discuss the principles that will ensure the safe storage of spent nuclear fuel and long-lived radioactive waste in a geological repository, from safety assessment methodology to term, methods to be used for safety assessment, software and data,” according to Ignalina.

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