Project report: nuclear waste disposal

Scanclimber offers a bespoke hybrid hoist and work platform for the construction of a unique nuclear waste disposal facility in Finland.

One of the landing stations for the Scanclimber SC2000.

The Onkalo nuclear waste disposal facility under construction in Olkiluoto, Finland, will be the world’s first permanent geological repository for spent fuel and high-level radioactive waste.

It is located 500 m underground near the Finnish Olkiluoto nuclear power plant in Eurajoki on the west coast of the country.

The catalyst for the project was in 1994 when the Finnish Parliament amended its Nuclear Energy Act to require all nuclear waste generated in Finland to be disposed of in the country.

Solid environment

In 2000, Olkiluoto was identified as the location for a very long-term underground storage facility because the area consists of granite rocks. The Eurajoki Municipality then issued a building permit for the facility in August 2003, and excavation work began in 2004.

The facility was called Onkalo in Finnish, which means small cave or cave. It is being built and is located about 5 km from the main nuclear power plants.

Onkalo nuclear waste disposal facility A map of the tunnels that make up the Atkal waste disposal facility Onkalo.

Construction specialist Posiva was selected to do the work ahead of the facility’s commissioning in 2023, if everything goes according to plan. Jarno Säippä is the project manager at Posiva for the shaft sections of the project, of which there are three: a staff shaft and two ventilation shafts – one for incoming air and one for outgoing air. Säippä has a background in mining and has been certified as an official radiation inspector (STUK).

As Säippä explains, the site’s shafts and main tunnels were completed in 2012. Officials issued permits to build nuclear waste disposal facilities in 2015, and construction began in 2016 with the excavation and construction of the final nuclear waste disposal tunnels.

Säippä commented on the overall project as follows: “The main challenge of this project is that we are building the world’s first plant of this type. We set an example and a standard for the rest of the world that nuclear waste can be safely and efficiently disposed of in stable bedrock. “

Long-term containment

Scanclimber hoist / work platformScanclimber offers a bespoke hybrid hoist and work platform for the construction of a unique nuclear waste disposal facility in Finland.

After completion of the facilities, the total length of the tunnels will be around 50 km and have a total volume of around 1.5 million cubic meters. According to the plans, 6,500 tons of spent fuel will be stored in the main tunnels, which required more than 3,000 copper capsules to be installed. The entire disposal process will take about 100 years, then the premises will be closed.

The four shafts in the facility are nearly 0.5 km high, and various works had to be done within these shafts and on the walls of the shafts. Säippä adds: “Building such a facility is a huge project and requires different and specific types of tools and equipment.”

Posiva uses a Scanclimber SC2000 hybrid elevator and a work platform for the assembly work in the staff shaft. The device was specially built according to Posiva’s requirements and offers both lifting and mast climbing functions. It is used to assemble the shaft’s steel frames and do HVAC work.

In addition to the challenges of building the shaft, Posiva needed a device to transport people and goods. The SC2000 was developed with its maximum climbing height of 480 m and a load capacity of 480 kg.

The lower deck of the SC2000 is based on the idea of ​​a standard elevator with sliding door and access on every floor. This section of the platform is used to provide the material handling required for the project.

The upper deck provides a platform for staff to work on and access the shaft walls to attach the shaft fittings and install the air conditioning. The rail guides for the future passenger elevator will also be installed from this position after the construction work is complete.

“Posiva will dismantle the platform around the turn of 2023 and we will install a standard passenger lift with a counterweight in the shaft,” explains Säippä.

Challenging elements

Preparation and treatment area for nuclear waste capsules.Preparation and treatment area for nuclear waste capsules.

One challenge at the beginning of the project was that the remote control signal from the platform in a shaft that is almost 500 m deep in the bedrock did not work. To solve the problem, the radio control was replaced by a cable. There have been no problems since then, says Säippä.

The main role of the work platform is to provide the base on which the workers can install the steel frames in the shaft. The frames are 10 m high, pre-assembled elements that are lowered into the shaft with cranes close to the ground. During installation, the steel elements are screwed together and attached to the shaft wall.

As the work progresses from bottom to top, the mast of the SC2000 is extended upwards. The mast sections are transported upwards from the shaft floor using the work platform and installed from there using the standard mast assembly crane arm from Scanclimber.

Posiva will then use the work platform to install other important elements in the shaft, such as: B. electrical installations, cabling, lighting, piping, safety and emergency equipment. The guide frames for the passenger elevator, which are installed after the shafts have been completed, are also attached.

Phase 1
2004-2009: excavation of the large access tunnel to a depth of 420 m.
Phase 2
2009-2011: Excavation work continued to a final depth of 520 m. Scientists are investigating the properties of the bedrock and adapting the layout of the repository.
2012: Posiva applies for a license to build the repository.
Permission granted in November 2015.
Phase 3
2015-2017: Construction of the repository.
Phase 4
To follow: The encapsulation and burial of spent fuel elements. Twelve fuel assemblies are placed in a boron steel container and enclosed in a copper capsule. Each capsule is then placed in a separate hole in the repository and overfilled with bentonite clay.

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