askST: How do countries deal with waste from nuclear energy?

SINGAPORE – In 2027, Singapore will be assessed by the UN nuclear watchdog on its readiness to make an informed decision on whether to deploy nuclear energy.

One of the 19 areas under review is the management of radioactive waste. The Straits Times examines how countries deal with the toxic matter.

What is nuclear waste?

Nuclear or radioactive waste is a by-product of nuclear power plants. It contains or emits radioactive particles and can remain hazardous for thousands of years. If not properly managed, it can cause serious damage to human health and the environment. 

There are three main types of nuclear waste: high-level, intermediate and low-level waste.

They are classified mainly in terms of how radioactive they are and how long they take to decay to safe levels.

Why is nuclear waste feared?

Long-lasting toxicity: High-level radioactive waste can remain hazardous for hundreds of thousands of years, and so it needs to be shielded and secured properly, preferably underground.

Accidental contamination: In 1981, technical and human error caused a plant in Tsuruga, Japan, to spill radioactive sludge, with 16 tonnes eventually ending up in Wakasa Bay. The incident, which exposed more than 50 workers to radiation, was not reported for more than a month.

Reliance on temporary storage: Globally, most used fuel is temporarily stored in protective casks, either in indoor facilities or on land. Only Finland has built a permanent storage site more than 400m underground, which is expected to start operations later in 2026.

Difficulty in siting disposal facilities: Developing a permanent site takes years because of strict geological requirements and public and political objections.

The amount of nuclear waste generated is much lower than most other forms of waste. In 2016, each person in France generated about 350kg of household waste. The equivalent figure for nuclear waste was 2kg per person.

What options do countries have in dealing with nuclear waste?

1) Manage the waste domestically

Burying it deep underground and away from people for extremely long periods is considered the gold standard and is currently the only viable solution being widely explored.

2) Nuclear operator takes it back

This practice is limited. Turkey, for instance, must return used fuel from its upcoming plant to Russia, which is building the facility.

3) Build a multinational repository

A shared underground disposal facility hosted by one country would be ideal for smaller countries or those with unsuitable geology. But no such mega facility is currently being built.

In 2016, South Australia considered hosting a shared repository, but the proposal was met with political and public objection.

How is nuclear waste disposed of?

This is the typical journey of radioactive waste, from a nuclear plant to deep beneath the rocks:

1) Submerge used fuel in deep pool

Once extracted from a reactor, extremely hot fuel rods – around 300 deg C – are submerged in deep pools with about 8m of water above them. The water shields against radiation and cools the fuel to about 50 deg C over five to eight years.

2) Store in protective casks

At least five years later, the rods are transferred to protective steel casks that are fireproof, earthquake-resistant and able to withstand plane crashes.

The casks are monitored throughout the interim storage period. They must be licensed by the authorities and be able to hold waste for up to 100 years.

Radioactive waste in liquid or sludge form is mixed with glass to prevent the waste from leaching, before being stored in casks.

3) Deep geological storage

The final resting place for nuclear waste is in a manmade network of underground tunnels within stable, non-porous rock, far from earthquake-prone areas.

A deep geological repository needs three layers of defence:

A. Copper canister

Used fuel is encapsulated in copper canisters that are resistant to corrosion from water.

B. Buffer made of clay

Copper canisters are embedded in bentonite clay in the tunnels of the repository.

The clay buffer absorbs water and swells to fill the space around the canister and any cracks in the rock. The buffer also limits radioactive substances from escaping into the surrounding rock if the canister cracks.

C. The rock

The type of rock chosen depends on the most suitable geological conditions a country can find.

In Switzerland, for example, the chosen site, north of Zurich, is made up of opalinus clay, which is impermeable to water and can bind to radioactive substances, preventing them from migrating.

4) Deep borehole (emerging alternative)

As an alternative to deep geological repositories, this method involves drilling a borehole up to 5km deep into the Earth’s crust, placing waste canisters at the bottom 2km of the borehole and sealing the upper 3km with materials such as bentonite, asphalt or concrete.

Malaysia has explored a borehole facility in Selangor.

Sources: WORLD NUCLEAR ASSOCIATION, ADEME, ZWILAG, NAGRA, SANDIA NATIONAL LABORATORIES