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In it for the long haul – nuclear waste management requires precision and patience

According to research, a student’s attention span when attending a lecture is around 10 to 15 minutes before concentration starts to wane. In our increasingly impatient reality, some even say that peoples’ attention cannot hold more than eight seconds.­­­­­ The world of nuclear waste management stands in strong contrast with these views. Here, the perspective is in hundreds of thousands, even millions, of years. The waste must be kept secure so that it will not contaminate the environment while it is still radioactive. And this will take a long time.

When planning for the final disposal of the waste, patience is a virtue as there is no room for error. Safety is the main consideration in everything that is being done. This has been the guiding philosophy in the cooperation between the nuclear waste management company Posiva and the engineering company Etteplan.

Posiva’s final disposal solution and final disposal facility ONKALO® are the results of decades of multidisciplinary development efforts. Posiva handles research, development, and design work aimed at final disposal, and manages the construction and entire operating life of the encapsulation plant and final disposal facility.

Etteplan designs, among other things, the machine for the safe installation of canisters of spent nuclear fuel into their final resting place at the bedrock of Eurajoki, the home of Olkiluoto nuclear power plant.

More layers than in an onion

“We have needed to tackle several design challenges to produce a solution that will live through time. For example, to guarantee the waste's safe final disposal, several layers of protection are needed. If one barrier breaks, there will be another to guarantee that safety is not compromised,” says Jarkko Stenfors, the manager of Posiva’s Final Disposal Equipment Unit.

First safety barrier is the bedrock at Eurajoki which is stable, and the risk of earthquakes is practically non-existent. Next, the bentonite blocks around the canisters will prevent any water from entering. And the copper used in the containers of spent nuclear fuel is corrosion-free.

The machine part designed by Etteplan will place bentonite blocks into the final deposit holes that have been drilled into the bedrock in a deep underground tunnel. After this, the copper canisters which contain the spent fuel will be placed in the hole. When the bentonite clay swells, it provides a safe bed for nuclear waste to sleep peacefully for the next 200,000 or million years - whatever time it takes for the spent fuel to turn harmless.

“The bedrock has been steady for millions of years already. It will most likely stay so in the foreseeable future and beyond. In one scenario, the Earth’s magnetic poles would switch places within the next few thousand years.  Even in this case, the combination of clay and copper will dampen the effects this may cause,” Stenfors explains.

Jarkko Stenfors, Posiva & Henri Toivonen, Etteplan

Cross-industry expertise

What Posiva, Etteplan, and other contractors are doing under the soil of Eurajoki is unique. To achieve something that has not been done before, the engineers needed to adapt their knowledge from other industries into the new endeavor.

“During the design process we have had to consider, for example, what kind of protection from dust and corrosion is needed. Our team’s experience from designing actuators for the mining industry became handy when trying to find a solution for this problem,” says Etteplan’s Area Manager Juha Mäkelä.

“Another cross-industry skill needed in the project is machine vision. It is used, for instance, to measure distances and ensure that the installation machine's gripper is in the right place. There is no room for error, as the bentonite blocks must be installed within a millimeter’s tolerance. We are fortunate to have a wide variety of expertise within our company to carry out different design tasks,” Mäkelä continues.

Technology for a better world

While the technology behind the solution is impressive, the project's main goal is to provide a safe way for the final and permanent storage of spent nuclear fuel.

One of the last hurdles in nuclear energy production’s total safety has been the fuel's final storage.

“The Finnish Radiation and Nuclear Safety Authority has declared our process safe. Also, other countries have decided to start a similar undertaking. Our process can be adapted to different surroundings and environments, which may prove to be a critical factor when countries are considering options for energy production. Posiva's subsidiary Posiva Solutions will offer different kind of solutions in this matter,” Posiva’s Stenfors concludes.

Perhaps the longest-lasting Finnish success story will be nuclear safety throughout the next million years.