plutonium discharges unaccounted for "Now you see
New Scientist, 24 April 1999
By Rob Edwards
MORE THAN A THIRD of the plutonium discharged
into the sea from the Sellafield nuclear plant in Cumbria has gone astray,
according to British government scientists. Some of it may be buried
in sand, and more than previously thought could have been carried by
currents out of the Irish Sea.
Between 1952 and 1995, Sellafield dumped 182 kilograms of plutonium
down a pipeline into the Irish Sea. This amounts to 717 terabecquerels
(TBq) of radioactivity--about half the fallout of plutonium in the entire
North Atlantic from 520 atmospheric bomb tests in the 1960s.
But Peter Kershaw and his colleagues at the Ministry of Agriculture,
Fisheries and Food's Centre for Environment, Fisheries and Aquaculture
Science at Lowestoft say there is a "significant shortfall" between
this and the amount detected by monitoring. They carried out a detailed
audit and conclude that 36 per cent (257 TBq) of the plutonium is unaccounted
for, along with up to 40 per cent (387 TBq) of plutonium's daughter
These discrepancies are described as "disappointing and surprising"
by Murdoch Baxter, the recently retired director of the International
Atomic Energy Agency's Marine Environment Laboratory in Monaco. "Having
made these excessive releases into the nearshore environment of a populated
area and having monitored it extensively, they claimed for decades that
almost all of the plutonium had remained in the Irish Sea sediments,"
he says. "Now, after all that effort and time, they say they don't know
where 40 per cent of it is."
But British Nuclear Fuels, the state-owned company that runs Sellafield,
says: "Given the period of time over which discharges have occurred
that sort of correlation is not bad."
In a study published in a special Irish Sea issue
of the Journal of Environmental Radioactivity (Vol 44, p.191), edited
by Baxter, Kershaw suggests the missing radioactivity might be concealed
in coarse-grained sand deeper than the 25 centimetres sampled in most
surveys, such as the intertidal stretch on the Sellafield shore. He
also says that the amount carried north out of the Irish Sea to Scotland
and Scandinavia could have been underestimated (New Scientist, 27 February,
Either way, Kershaw argues that the contamination is becoming less
hazardous as it is being diluted. The bulk of the plutonium and americium
that has been found is in a large mud bank at the bottom of the Irish
Sea, with the rest spread along the coast or dissolved in water.
But Dudley Goodhead, director of the Medical Research Council's radiation
and genome stability unit at Harwell in Oxfordshire, is not reassured.
Plutonium and americium are dangerous in very small doses, he says.
"By diluting them, all one is doing is spreading the risk more widely."