HKNIC - Managing Nuclear Waste

Managing Nuclear Waste

Waste arising in the nuclear fuel cycle is categorised as high, medium, or low level waste according to the amount of radioactivity.

Managing Nuclear Waste
Source: World Nuclear Association

Low Level Waste (LLW) is produced at various stages of the fuel cycle, such as tailing in mining, and during maintenance activities for reactor operations. Examples of LLW from a nuclear power station are contaminated tools, waste paper and discarded protective clothing from nuclear power station maintenance. Radioactivity in LLW varies and certain LLW is no more radioactive than natural substances such as granite. Daya Bay produces typically less than 75 cubic metres of LLW per year.

Intermediate Level Waste (ILW) is produced during reprocessing and during normal reactor operation. It is sufficiently radioactive to require shielding and containment during storage and handling. Examples include sludges and resins arising from the treatment of primary cooling water of the nuclear power station. Most of the material classified as ILW makes up of the concrete shielding material of the packaging used to store radioactive waste, and Daya Bay produces typically less than 75 cubic metres of such packaged waste each year. After packaging, both LLW and ILW from a nuclear power station will be isolated from the environment for typically 300 years so that their radioactivity will reduce with time to natural levels.

High Level Waste (HLW) is a waste produced after spent fuel has been reprocessed, containing the fission products which arise from the fission of U-235 for power production, and a very small quantity of long-lived highly radioactive products formed in a process known as transmutation in which uranium 238, plutonium 239 and their transmutation products absorb neutrons produced by nuclear fission events in the reactor to become other radioactive elements. In countries such as Canada and the US that do not plan to reprocess spent fuel but dispose it directly, HLW represents spent fuel itself. From the quantity of spent fuel produced at Daya Bay, about 2.5 tonnes of HLW will be generated each year following reprocessing.

HLW is highly radioactive. After being extracted from the spent fuel, it typically needs a period of 20 to 50 years to cool down. The quantity of such waste generated worldwide is currently small and it is stored at dedicated facility. Technology has been developed to pack the waste in glass in a process known as vitrification. The packaged vitrified waste can then be stored underground in a stable geological formation to isolate it and prevent its movement for over thousands of years. Furthermore, the radioactivity will fall over time and after several thousand years it will fall to natural levels. In comparison, industrial wastes such as those containing cadmium or mercury remain hazardous indefinitely.

HLW needs to be stored only for a finite period of time and the quantity is small. So storage is technically manageable. Even if Hong Kong used only nuclear electricity, each citizen would on average over a lifetime be responsible for producing only a 6 centimetre cube of packaged HLW, about the size of a small soft drinks can, that would need storing in isolation. If Hong Kong were to use only coal to produce electricity, by contrast, the average person would be responsible for around 600 tonnes of CO2 and 20 tonnes of coal ash over a lifetime. The toxic metals in the coal ash, such as arsenic, lead, molybdenum, cadmium and chromium, would be with us forever.

There is currently no need to package and store HLW on a large scale, but work is underway to make long-term isolation of HLW a practical solution.