Slovenia is considering options for permanent disposal: a shared repository for Krško and the TRIGA II reactor is the most cost-effective solution.

American company Deep Isolation has produced a cost assessment study for the Slovenian Nuclear Waste Agency (ARAO), which showed that it is economically far more justifiable to store spent nuclear fuel from the TRIGA II research reactor at the same site and in the same deep geological disposal system together with the fuel from Krško Nuclear Power Plant

According to the findings of this study, constructing a standalone disposal facility in deep boreholes solely for the TRIGA II reactor would cost about €65.6 million. On the other hand, integrating a small amount of fuel from this research reactor (a total of 84 fuel elements that fit into a single universal canister) into a future disposal facility for Krško Nuclear Power Plant would bring only a negligible increase in total costs. The reason lies in the fact that fixed costs of establishing the facility and infrastructure arise independently of how much waste is being disposed of.

By the way, the TRIGA II reactor began operating in the 1960s at the Jožef Stefan Institute near Ljubljana, where it is used for the production of radioisotopes for medical purposes and for training professionals, and its shutdown is planned for 2043 – when the Krško Nuclear Power Plant's extended operating life also expires.

What is the deep borehole disposal technology?

Disposal of radioactive waste in deep boreholes represents a concept of permanent geological isolation that has been considered since the 1950s, but to date it has not been commercially implemented anywhere in the world. The company Deep Isolation has developed and patented a technology that directly uses equipment and standard drilling methods from the oil and gas industry.

The concept envisions hermetically sealed, corrosion-resistant steel canisters (diameter 22–33 cm) being lowered into boreholes drilled into rock formations that are stable for hundreds of millions of years. The borehole itself begins with a vertical segment, and then, by bending, transitions into an almost horizontal 'disposal sector' up to 3.2 kilometers long, at depths from several hundred meters to as much as three kilometers below the Earth's surface. When the canisters are placed, the vertical access channel is permanently sealed with rock material, bentonite clay, and special mixtures.

This method differs from the more standard method also being considered, such as Onkalo, in which nuclear waste is disposed of in conventionally engineered mine caverns. 

Comment

Although the deep borehole disposal technology is still in the testing phase and has no commercial application in the world, this study for Slovenia emphasizes the key principle of nuclear waste management: economies of scale. Small amounts of spent fuel from research or educational reactors do not justify individual capital investments in dedicated disposal facilities. Therefore, merging inventories with large commercial power plants is the only rational and financially sustainable path. This topic carries important lessons for our region as well: every future decision on developing nuclear capacities or using research reactors must from day one count on a strategy and costs of permanent disposal of radioactive waste, where regional cooperation and pooling of resources represent the most rational model. 

But again we add: we are not sure that permanent disposal of spent nuclear fuel – by itself – is an economically smart move. Spent nuclear fuel, namely, is not actually “spent,” because it still contains the largest portion of nuclear material that could be reused through reprocessing. 

S.A.