South Korea Wrestles With the Headache of Disposing of Nuclear Waste

Nuclear power plants generate electricity from steam generators heated by nuclear fission. Raw uranium consists of more than 99 percent U-238 and some 0.7 percent U-235. It’s the latter uranium isotope that’s capable of nuclear fission and chain reaction. In most cases of nuclear power, uranium is enriched until U-235 reaches somewhere between 2 and 5 percent of the mass. Chemical treatment then turns it into powdery uranium dioxide which is sintered, or solidified, and then packaged into tubes, or nuclear rods. These are in turn bundled together for complete nuclear fuel.

This enriched uranium needs replacing about every three years, since its utility plummets after that point. The nuclear rods are taken out, becoming “spent fuel,” or high-level radioactive waste. They are infernally hot to the touch due to the energy released by radioactive decay. They also emit such intense, penetrating, radiation that even a brief exposure can kill a human. Worse, they have a ridiculously long half-life, meaning it takes tens of thousands of years for nuclear spent fuel to lose its harmful potency through radioactive decay and breaking down.

Needlessly to say, how to handle the spent fuel has hectored humanity for decades.

Beginning in 1978, when South Korea first turned on its nuclear reactors, it has accumulated some 18,000 tons of high-level radioactive waste. Most of it is simmering in cooling pools within nuclear power plants’ temporary on-site facilities. There are 25 nuclear reactors active today in South Korea, all of which spew some 700 tons of spent fuel every year.

In 2023, around 31 percent of South Korea’s electricity came from nuclear energy. The government wants the proportion to exceed 40 percent by the late 2030s, revealing a plan earlier this year to construct three more reactors.

More high-level nuclear waste is on the way, but South Korean reactors will be reaching their temporary storage capacity one by one from 2031 onward. (In 2021, overall capacity reached 98 percent. The government expanded one of the temporary facilities, earning some breathing room.) South Korea badly needs a permanent disposal site.

With that in mind, Seoul has paid close attention to Finland’s Onkalo geological repository buried underneath Olkiluoto, an island in the southwestern part of Finland. It’s the world’s first permanent disposal site for high-level nuclear waste. The trial run began in September 2024.

A warren of tunnels was excavated into the granite bedrock under Olkiluoto. An access tunnel in the shape of a rectangular spiral staircase winds down until a level nodal area conjoining vertical shafts, galleries, and technical rooms. Some tunnels reach as far down as 450 meters.

Fuel rods are packed into cast-iron canisters covered in copper capsules. In between these two metal layers is argon, an inert gas that hardly reacts to other substances. These canisters are welded shut using more copper, ready for lowering to its final destination some 430 meters underground via vertical shafts equipped with lifts. At this level, there’s a main access gallery leading to a few 70-meter-long horizontal disposal tunnels. Sprouting downward from each tunnel are some 30 deposition holes reaching 8 meters down. (Imagine a hair comb with its main spine and tinier spokes.)

Each hole is lined with bentonite, an absorbent clay. Once filled with the canisters, the holes and tunnels are then backfilled with more bentonite – the clay retains moisture, preventing corrosion of the copper and offering some level of shielding from radiation. The entrances to these dark caverns are then rendered off-limits by reinforced concrete caps. Over a few generations, about a hundred more of these tunnels are expected to be added. It will take about 100,000 years for the radioactivity to sieve through all the bedrock and man-made layers of steel, clay, and concrete. By then, it will have returned to the same level of radiation as the ore the fuel came from.

South Korea is hoping to replicate this geological sequestration. In 2023, the Korea Atomic Energy Research Institute set up a research lab to devise and test a miniature barrier system for spent fuel. Its concept and materials are very much akin to the Finnish one. The authorities hope to construct an underground research facility in 2032, where they can test the thermo-hydrodynamics of their paraphernalia in real-life underground settings.

There are a few hurdles to overcome, however. First, copper is thought to be optimal to sheathe spent fuel in, but its durability isn’t guaranteed. Unless contacted by oxygen, copper is otherwise stable – and the fissures within Olkiluoto’s underground crystalline granite are free of dissolved oxygen, hence the location for the Finnish project. South Korean scientists have also chosen copper. Yet one study found that copper does corrode, even in oxygen-free water, and suggested that copper canisters could crack in decades rather than millennia. Along with future earthquakes and bedrock shifts, compromised copper can cause severe radioactive leakage.

Second, South Korea lacks the right equipment and technology to handle high-level radioactive waste other than to store it in makeshift on-site facilities. Besides meeting the geological conditions and capsule specs the Finnish way, equally important are the preparatory steps of transporting spent fuel, packaging it, lowering it, and following a plethora of other construction and monitoring manuals. South Korea needs more expertise and technicians.

Also, some radioactive waste is just too deleterious for humans wrapped up in radiation suits and air hoses to even approach. Robots should do everything, presenting further technical obstacles. In Japan, robots dispatched into Fukushima Daiichi’s melted reactors lost their course and collapsed. Their arms were tricky to maneuver remotely; many got stuck. Some even had their circuits frazzled by the hellish radiation. Structural renovations and AI-aided maneuvering techniques would come in handy.

Luckily – or not – for South Korea, it has a long time to figure all these problems out before being able to build a permanent geological repository, which is linked to the third issue.

South Korea will be able to run a permanent disposal site only after 2060. Zeroing in on an ideal spot that ticks off all the geological, seismic, and environmental standards is tough. Finland embarked on looking for a site in 1983. It spent 18 years reviewing a hundred potential sites until settling on Olkiluoto in 2001. But this is the easy part.

Persuading the local community to host such a site requires institutional genius and patience. Finnish people have high trust in their government and their technocrats. Societal consent is more easily built on such a foundation. South Koreans don’t – not without due reason, since the South Korean government has a long history of covering up nuclear malfunctions and accidents.

South Korea’s one and only low- and intermediate-level radioactive waste site took some 20 years to overcome residents’ resistance. Recently, South Korea’s Wolseong reactors had a hard time expanding the site’s temporary facilities to accommodate high-level nuclear waste amid fierce protests from locals. Securing a permanent high-level radioactive waste disposal site will surely face a publicity firestorm and a more protracted period of winning over residents and municipalities.

The last hurdle is the law. For now, South Korea doesn’t have any legal framework for handling nuclear spent fuel. The ruling People Power Party and the opposition Democratic Party have been drafting and scrapping bill after bill. They keep failing to see eye to eye over whether to set storage capacities according to reactors’ design life or operation period. Besides, the National Assembly is mired in legal battles over forming special counsels to investigate the Yoon Suk-yeol administration’s scandals. Productive discussions over the nuclear issue were tabled in the last congressional session.

Although not in the legislators’ discourse, questions of reversibility and retrievability are something they need to deal with in the future, too. Should technologies and social attitudes change over time, can and should the authorities reverse the disposal process or retrieve radioactive waste from the ground? This is an important question that requires a sophisticated legal rubric, and public consensus and understanding.

In the meantime, South Korea has no choice but to rely on temporary measures. The easiest and cheapest way to boost temporary storage capacity is just to dunk more spent fuel into existing cooling pools. Spent fuel heats up dramatically when congealed together, so there are underwater partitions in these pools. Scientists can carefully increase the density of compartmentalization by installing more partitions.

A better way is to build more temporary depots where spent fuel is kept in cement dry-storage casks. The Wolseong reactors’ latest storage addition adopted this method. If built and monitored properly, dry storage is safer; nuclear reactors in the United States predominantly use this option.

Either way, temporary storage sites should remain only temporary, since they are more vulnerable to disasters than disposal repositories in deep rock formations. Most importantly, it’s time to break the vicious cycle of administration after administration conveniently turning a blind eye to how to dispose of spent fuel and letting the future generations agonize over how to put it away for good.