‘Spent’ or ‘used’ fuel from a nuclear reactor is highly dangerous material.  Consider this statement:

‘If you placed a teacup-sized piece of high level (nuclear) waste (derived from spent nuclear fuel) in the middle of a football pitch, you and everyone in the stadium would be dead before you left the centre circle’. 

This came not from an alarmist anti-nuclear campaigner but from Phil Hallington, Head of Operations and Development at Sellafield, in a BBC Radio 4 interview on the 7th January 2015 ‘How to dismantle a nuclear power station

There are currently around 500 tonnes of spent nuclear fuel at Sizewell from the operation of the Pressurised Water Reactor Sizewell B. Over its lifetime, expected to be until 2036, about 1400 tonnes of spent fuel will accumulate and is likely to be required to be stored on site for decades or centuries or indefinitely, depending on how successful or otherwise is the search for a long-term deep geological repository[1].

Should Sizewell C&D ever be built, they will add a further of 3,600 tonnes of ‘high burn-up’[2] fuel.  Spent fuel from a notional Sizewell C and D is likely to be held on site for a minimum of 160 years or, more likely, indefinitely as some of the technical, scientific and ethical hurdles to long term disposal in a repository remain intractable and as the search for a ‘volunteer community’ to host such a repository remains elusive.

‘Burning’ the fuel in the reactor (i.e. the bombarding of uranium fuel rods with neutrons to accelerate the decay process) results in the fuel in its ‘spent’ state being over a million times more radioactive than fresh fuel. It is so radioactive that standing next to spent fuel will cause death in seconds. The radioactive decay of the spent fuel also produces a large amount of heat. If the fuel is not effectively cooled it can heat up to a point where the fuel rods can catch fire.  Fuel is normally cooled in ponds of water before being moved into ‘dry store’ in casks.

After the process has used up fissionable material in the fuel, the resulting ‘spent’ fuel contains close to 200 ‘daughter’ or ‘decay’ products.  Some of these radioactive elements have a very short life span or only a few seconds or minutes whereas some radionuclides such as plutonium-239 have half-lives[3] of up to 24,000 years, leading to complications for their safe long-term storage.

The intense heat generated by the spent fuel means that it has to be stored under a protective barrier of water in spent fuel ponds after it is removed from the reactor core and remotely transferred to ‘dry cask’ storage after 5 years.  These dry stores are air cooled and do not require a water supply and pumps to operate and are considered to be much safer than storage in ponds. Sizewell B spent fuel is systematically moved from the ponds to the dry store. Both the spent fuel ponds and the dry store represent targets for terrorists:  if breached in a catastrophic event, the release of even a small proportion of the radioactivity they contain could have a dramatic impact on the local community, the environment, jobs and the well-being of thousands of people in Suffolk and possibly beyond.

Unlike the reactor, the spent fuel ponds are not protected by a strong ‘containment building’ in the UK. However, in Germany such containment buildings have been compulsory since the 1970’s due to the threat of terrorist attack.

[1] See nuclear waste management section on this website.

[2] High burn up means that more electricity can be generated from the same volume of fuel making the fuel more radioactive and hotter than Sizewell B fuel.

[3] Half-life is the time it takes for radioactivity to reduce by half.  Ten ‘half-lives are required to pass before an element can be considered ‘safe’. Thus Plutonium 239 will be potentially harmful to living organisms for 240,000 years – by the mid-242,000’s AD.