How is nuclear waste actually dealt with?

In three steps. Spent fuel sits in a water-filled cooling pool for five to ten years, then moves into dry casks cooled passively by natural air convection, and is ultimately destined for deep geological disposal. Only Finland has reached step three: ONKALO, 450 metres down in granite, entered operation in 2025 as the world's first licensed permanent repository.

Start with what nuclear waste actually is. After about three years in the core, fuel becomes spent fuel, of which roughly 95.6% is still unreacted uranium oxide. The real challenge is the remaining 4.4%, which generates 99% of the fuel's radioactivity. About 3.4% is fission products such as caesium-137 and strontium-90 — intensely radioactive but with half-lives near 30 years, decaying 99.9% within a few centuries. The last 1% is long-lived transuranic actinides: plutonium-239 has a half-life of 24,400 years and needs roughly 250,000 years to reach safe levels. France responds with a closed fuel cycle: the La Hague plant in Normandy dissolves fuel rods in boiling nitric acid, extracts uranium and plutonium, and vitrifies the high-level liquid waste in molten glass, cutting high-level waste volume fivefold and long-term radioactivity by 90%, with the recovered plutonium made into MOX fuel that powers more than 20 French reactors.

The first stop in storage is the spent fuel pool: a steel-lined concrete basin inside the reactor building filled with about 12 metres of treated water. The water absorbs decay heat and doubles as radiation shielding — a few metres are enough to block almost all radiation from the blue-glowing assemblies below, so standing at the edge is entirely safe. Its weakness is that it requires active power: if the circulation pumps lose electricity the water evaporates and the fuel can overheat and catch fire, one of the most feared scenarios of the Fukushima crisis. After five to ten years decay heat has fallen far enough for natural air convection to handle it, and the fuel moves into dry cask storage — multi-layer cylinders about 5.2 metres tall and 2.7 metres wide, with a pressurised-helium stainless steel canister inside and feet of reinforced concrete outside, tested against locomotive impacts and drops without leaking.

The volume is manageable; the timescale is not. The United States adds about 2,000 tonnes of spent fuel a year and has accumulated more than 88,000 tonnes, while the global inventory approaches 400,000 tonnes. Stacked together, all US spent fuel rods to date would cover a standard football field to a depth of 17 metres — and dry casks are only designed to last 60 to 120 years. The scientific consensus is that the only exit is deep geological disposal. Finland's ONKALO, on Olkiluoto island 450 metres inside two-billion-year-old crystalline granite, entered service in 2025 as the world's first licensed permanent repository, a success that was as much democratic as geological: decades of engagement with the host community, including a municipal veto. The counter-example is Yucca Mountain, designated by Congress in 1982, which absorbed over US$15 billion of federal spending plus US$30 billion levied on nuclear utilities and was still killed in 2014 by political opposition in Nevada — leaving waste at more than 70 US sites and the government paying utilities billions a year in compensation. In the nuclear age, a project's social half-life matters as much as its radioactive one.

For countries with no reactors of their own, waste is still not an abstract issue. Singapore has 730 km² and no hinterland to evacuate to, so it sets its defence line at the regional level. Its Ambient Radiation Monitoring Network (ARMNet), commissioned in 2020, consists of 40 fixed stations and 5 mobile units running 24-hour real-time monitoring from the coastal waters of the Singapore Strait to the rooftops of public housing blocks, against a baseline of 0.1 microsieverts per hour, with any cross-border anomaly triggering a national alert. Singapore also leads within ASEANTOM, the ASEAN Network of Regulatory Bodies on Atomic Energy, which links more than 80 monitoring stations across Southeast Asia into a regional early warning network.

A dry cask is designed to last 60 to 120 years. The half-life of plutonium-239 is 24,400 years. Between the two lies an enormous blank that no engineering document has yet filled in.

This question is covered in depth in The Full Spectrum Every Energy Source Explained — A Singapore Perspective，第六章 6.3、6.11–6.13 与新加坡本地上下文