What to do with spent nuclear fuel?

Subject: Science and technology

Section: Nuclear Technology

Context

Japan has initiated the release of treated radioactive water from the Fukushima nuclear power plant into the ocean.

Nuclear Energy as a Clean Energy Alternative

Nuclear energy plays a vital role in mitigating climate change.
Approximately 10% of global electricity is generated from nuclear energy.
Countries like the U.S., India, and China are considering increased nuclear energy to achieve net-zero emissions and reduce reliance on carbon-based power.

Challenges

The safe storage and disposal of nuclear waste pose significant challenges.
The long-term persistence of nuclear waste in dangerous states necessitates a permanent solution.

Temporary Storage Techniques

Spent fuel can be stored in cooling pools until their radioactivity decreases.
Dry cask storage is another technique for temporary storage.
Burying waste in near-surface disposal facilities with protective coverings is common for low-level and intermediate-level waste.
These temporary solutions are crucial but not sufficient for managing high-level nuclear waste effectively.

Deep Geological Disposal for High-Level Waste

High-level waste, due to its higher radioactivity, requires more sophisticated disposal techniques.
Finland’s Onkalo repository showcases deep geological disposal as a promising solution.
Employs the Swedish KBS3 concept, proposing
- waste stored in copper canisters,
- wrapped in bentonite clay, and
- buried over 400 meters below ancient bedrock.
Release barriers are employed to keep the waste isolated from its surroundings.

The Future of Onkalo Repository

SKB’s KBS-3 Method for Final Disposal of Spent Nuclear Fuel

SKB (Swedish Nuclear Fuel and Waste Management Company) employs the KBS-3 method for the final disposal of spent nuclear fuel.
This method is based on three protective barriers: copper canisters, Bentonite clay, and the Swedish bedrock.

Copper Canisters

Copper canisters are five meters long with nodular cast iron inserts.
Each filled canister weighs about 25 tons.
The outer casing consists of five-centimeter-thick copper.
Canisters are designed to withstand corrosion and mechanical forces resulting from rock movements.

Buffer with Bentonite Clay

Copper canisters will be placed in the repository’s tunnels, embedded in Bentonite clay.
Bentonite clay acts as a buffer, protecting canisters from corrosion and minor rock movements.
Clay absorbs water, swells to fill spaces and cracks, and prevents water from entering cracked canisters.
The buffer prevents the release of radioactive substances into the rock.

Bedrock as the Final Barrier

The bedrock serves as the final barrier, isolating the waste.
The rock offers a stable chemical environment and protection from surface-level events.
Groundwater flows through rock fractures but can trap any escaped radioactive substances.