Feature

When MOX becomes a real danger

The introduction of mixed-oxide fuel production at Sellafield threatens public safety, says Sarah Sexton

The nuclear industry is pressing hard for the large-scale production and widespread use in nuclear reactors of mixed-oxide fuel — plutonium oxide mixed with uranium oxide, known as MOX. Britain’s Environment Agency is currently considering whether to allow British Nuclear Fuels to start MOX production at Sellafield.

Whereas uranium occurs in the ground, plutonium is produced in nuclear reactors as uranium fuel degrades. It was discovered in 1941 as part of the US Manhattan project to manufacture nuclear weapons. Since then, about 1,400 tonnes of radioactive plutonium have been produced world-wide, either specifically for nuclear weapons or as a ‘by-product’ of nuclear power reactors. As several of plutonium’s radioactive isotopes are very long-lived — 24,110 years, for instance — in effect plutonium remains permanently in the environment, even though it is decaying all the time.

Given that plutonium is an extremely efficient explosive, fears are frequently expressed about terrorist groups or governments obtaining plutonium illegally and manufacturing a crude nuclear explosive device. Only about 35 kilograms of plutonium oxide would be needed, while the technical information required to make such an explosive is easily available.

Even a small nuclear explosion would cause many hundreds, if not thousands, of deaths and injuries from the direct and indirect effects of radiation, blast or heat. There are only a few hundred burn beds in the entire NHS. The ensuing panic which follows large explosions in urban areas would be considerably exacerbated by the radioactive fall-out from a nuclear explosion.

Heat from fires would cause radioactive particles to rise, they would then be blown downwind, eventually falling to the ground under gravity at various rates and distances depending on wind speed and weather conditions. One kilogram of uniformly-distributed plutonium would contaminate about 600 km² to a radiation level of one micro-curie per m², the maximum level allowed for plutonium by international regulations. To put this in perspective, 600 km² is at least double the size of all the main urban areas in Britain (Birmingham, Glasgow, Sheffield, Bradford, Liverpool, Manchester, Edinburgh, Bristol, Coventry, Belfast and Cardiff) with the exceptions of Greater London at 1,600 km² and Leeds at about 600 km².

As significant, if not more so, however, would be a crude device containing just a few grams of reactor-grade plutonium oxide which, when detonated, did not produce a nuclear explosion but still dispersed the plutonium widely.

Plutonium delivers negligible external radiation to the body because its alpha particles do not have sufficient energy to penetrate the skin—but internal radiation is a different matter. A recent study by researchers at St Andrews University and the Medical Research Council suggests that a single alpha particle may be carcinogenic.¹

Inhaled plutonium is much more hazardous than ingested plutonium because it is more easily absorbed into the blood stream through the lungs than through the gastrointestinal tract. The long-term (chronic) health effects of internal radiation include an increased risk of cancer of the lung, gastrointestinal tract, liver and skeleton, depending on the route of plutonium intake. The cancers may take up to 25 years to appear.

Short-term (acute) effects are possible after inhalation or ingestion of larger amounts. Experiments on dogs suggest that inhaling between 10 and 20 mg of reactor-grade plutonium may cause death in humans from acute respiratory failure within a week. Inhalation of 2 to 4 mg of reactor-grade plutonium may cause death within about a month from pulmonary fibrosis or pulmonary oedema.

Estimating the impact of plutonium isotopes on human health is fraught with uncertainties; consequently many risk estimates are conservative. Nevertheless, those made by the International Commission on Radiological Protection suggest that if individuals in a population inhaled a total of 1 gram of typical reactor-grade plutonium, there would be about 20,000 extra deaths in the population; ingestion of a gram of this type of plutonium would result in nearly 400 extra deaths from cancer. To give an idea of scale, a spherical piece of plutonium oxide containing a gram of plutonium has a diameter of 5.5 mm (0.22 in)—the size of a peppercorn—and there are 1,400 tonnes of plutonium in the world.

Perhaps the most serious danger arising from the illegal acquisition of plutonium is the threat of dispersion rather than explosion. Indeed, this danger is so great that mere possession of plutonium by a terrorist group would give it vast scope for blackmail.

There have already been a few hundred known incidents of nuclear smuggling, mostly of small quantities of non-weapons-grade material — but a single gram of plutonium is more than sufficient to cause significant harm and to pose a substantial threat to human health and the environment. The potential for further thefts grows as the world produces ever greater quantities of plutonium by separating it out of spent uranium nuclear reactor fuel elements. Production of mixed-oxide fuel elements will only increase this potential.

Given that there are no economically-viable peaceful uses for plutonium, existing reprocessed plutonium should be stored or disposed of permanently. All commercial reprocessing plants should be closed down, plutonium should not be separated from spent reactor fuel elements and the production of MOX should halt.

This is an edited version of Nuclear Legacy: democracy in a plutonium economy, a briefing by Frank Barnaby. For a copy, send an A4 SAE to The Corner House, PO Box 3137, Station Road, Sturminster Newton, Dorset DT10 1YJ, UK.