Energy and the Environment

Radioactive Waste Management

Radiation

Radiation can be harmful to living things and some radioactive substances stay radioactive for huge spans of time. Care and caution are required on all aspects of the use and safekeeping of radioactive substances.

People exposed to too much radiation are putting their health at risk. Having an X-ray is one way in which we can be subjected to radiation, and the number and duration of X-rays is under strict control by hospitals. But it is the effects of radiation from radioactive waste which causes the greatest public concern.

Radiation can cure people of cancer when it is used in hospitals, but it can also cause cancers when people are not properly protected from it by the nuclear industry.

Less than one thousandth of the average person's radiation dose in the UK comes from the nuclear industry. 87% comes from natural sources in the Earth and the atmosphere.

Radioactive Waste

Radioactive waste comes from nuclear power stations and the recycling of used nuclear fuel. It also comes from laboratories, and industry.

The amounts of radioactive waste discharged by nuclear power stations are strictly controlled with Government guidelines, as is the treatment and disposal of all other forms of nuclear waste.

Radioactive waste is put into one of three categories, according to how radioactive it is.

Low-level waste

Low-level waste includes materials which are only slightly contaminated - gloves, overalls, laboratory equipment, etc. It can be handled and transported quite easily. About 80% of radioactive waste is low-level.¹

In the UK, solid low-level radioactive waste is disposed of at a 300-acre site at Drigg in Cumbria, which is owned by the Nuclear Decommissioning Authority and operated by LLW Repository Ltd. Most low-level waste is packed into 200 litre steel drums and stored in a concrete vault. Low-level waste is compacted to a fraction of its original volume before it is disposed of at Drigg.

Low-level waste can also be in liquid form, for example, the water in which used nuclear fuel is stored and cooled. When it has been properly treated to reduce its radioactive content this waste can be discharged safely into the sea through a pipeline which extends one and a half miles from shore.

Intermediate-level waste

Intermediate-level waste is more radioactive and needs special handling. It includes the metal casings from irradiated (used) nuclear fuel, fuel debris and various sludges which result from the treatment of nuclear fuel. About 19% of radioactive waste is intermediate level.¹

This waste is encapsulated in cement inside stainless steel drums. In the short term these drums will be stored at Sellafield, but they will eventually be stored in a specially designed repository deep underground.

High-level waste

High-level waste is the most radioactive and arises from the reprocessing of irradiated nuclear fuel. Even though high-level waste represents only 1% of the total volume of waste arising from reprocessing, it contains about 99% of the radioactivity in the irradiated fuel.¹ Over the last 30 years, the quantity produced would fill 12 double decker buses.

High-level liquid waste is converted into a powder by evaporation. Then it is mixed and heated with other materials to turn it into molten glass which is poured into stainless containers. When the glass has cooled, a lid is welded to each container. This 'vitrification' process reduces the volume of highly active waste to one third of its original volume. The solidified glass is very radioactive and will be stored for at least 50 years to allow the radioactivity to decrease before being finally disposed of.

Storing Radioactive Waste

It is essential that any storage solution, for the short term or long term, should keep radioactive waste safely. This means protecting people from direct radiation, and stopping radioactive material entering the atmosphere, the water supply or the food chain.

The UK has not made a final decision about where to store high-level waste permanently. However, the current proposal for low and intermediate-level waste is to bury it in a safe site underground (a 'repository').

Finding a Safe Storage Site

To select a safe site, scientists must investigate all the possible ways in which the waste could move or radiation escape from the repository. One of the most important points to consider is that the waste could eventually be dissolved in the groundwater which is present in the tiny pores and cracks in natural rock.

The solution is to contain the waste within a series of barriers - both man-made and natural. In the case of intermediate level waste, the radioactive material would have to escape from the cement block, through the stainless steel container, and through the concrete encasing the containers.

Protective layer of concrete can stop most gamma rays - one of the most penetrating forms of radiation. Concrete is alkaline, and any water which comes into contact with it underground will also become alkaline. This is an additional barrier, as many radioactive elements become less soluble as the pH rises.

In any underground repository, the man-made barriers will be reinforced by the natural barrier of rock.

Any chosen site must be geologically stable, with no risk of earthquakes or volcanic eruptions, for example.

In America, detailed studies are also being made into the type of site required for a repository. Scientists have studied not only the things which are likely to happen on such a site, but also the things which we could only imagine happening.

Once the final storage site is selected, the waste will have to remain there for many years. Eventually the radioactivity will have decayed away and it will be no more radioactive than the uranium ore from which it came.