The most significant high-level waste from a nuclear reactor is the used nuclear fuel left after it has spent about three years in the reactor generating heat for electricity. Low-level waste is made up of lightly-contaminated items like tools and work clothing from power plant operation and makes up the bulk of radioactive wastes. Items disposed of as intermediate-level wastes might include used filters, steel components from within the reactor and some effluents from reprocessing.

Generating enough electricity for one person produces just 30 grams of used fuel each year.

High-level wastes make just 3% of the total volume of waste arising from nuclear generation, but they contain 95% of the radioactivity arising from nuclear power. Low-level wastes represent 90% of the total volume of radioactive wastes, but contain only 1% of the radioactivity.

Managing used fuel

Used nuclear fuel is very hot and radioactive. Handling and storing it safely can be done as long as it is cooled and plant workers are shielded from the radiation it produces by a dense material like concrete or steel, or by a few metres of water. Water can conveniently provide both cooling and shielding, so a typical reactor will have its fuel removed underwater and transferred to a storage pool. After about five years it can be transferred into dry ventilated concrete containers, but otherwise it can safely remain in the pool indefinitely – usually for up to 50 years.

Near Oskarshamn nuclear power plant in Sweden is a facility called CLAB (foreground). It stores all the used fuel from Swedish nuclear power plants that have provided over 40% of the country’s electricity (SKB).

Currently, the majority of used fuel is not recycled, But reprocessing used fuel to recover uranium and plutonium avoids the wastage of a valuable resource. Most of the used fuel – about 96% – is uranium, and up to 1% is plutonium, with the remaining 3% being high-level waste. Both reprocessed uranium and plutonium have been recycled into new fuel. Plutonium mixed with uranium in their oxide forms is known as mixed oxide fuel (MOX).

The high-level wastes (whether as used fuel after 50 years cooling, or the separated 3% of reprocessed fuel) will be disposed of deep underground in geological repositories.

Intermediate and low-level wastes

Intermediate- and low-level wastes are disposed of closer to the surface, in many established repositories. Low-level waste disposal sites are purpose built, but are not much different from
normal municipal waste sites. Nuclear power is not the only industry that creates radioactive wastes. Other industries include medicine, particle and space research, oil and gas, and mining – to name just a few. Some of these materials are not produced inside a reactor, but rather are concentrated forms of naturally occurring radioactive material.
Civil nuclear wastes from nuclear power plants have never caused any harm, nor posed an environmental hazard, in over 50 years of the nuclear power industry. Their management and eventual disposal is straightforward.

One characteristic of all radioactive wastes which distinguishes them from the very much larger amount of other toxic industrial wastes is that their radioactivity progressively decays and diminishes. For instance, after 40 years, the used fuel removed from a reactor has only one thousandth of its initial radioactivity remaining, making it very much easier to handle and dispose of.

Disposal

The categorization – high, intermediate, low – helps determine how wastes are treated and where they end up. High-level wastes require shielding and cooling, low-level wastes can be handled easily without shielding.

All radioactive waste facilities are designed with numerous layers of protection to make sure that people remain protected for as long as it takes for radioactivity to reduce to background levels. Low-level and intermediate wastes are buried close to the surface. For low-level wastes disposal is not much different from a normal municipal landfill. High-level wastes can remain highly radioactive for thousands of years. They need to be disposed of deep underground in engineered facilities built in stable geological formations. While no such facilities for high-level wastes currently operate, their feasibility has been demonstrated and there are several countries now in the process of designing and constructing them.