THE foreshore next to the Dounreay nuclear site in Scotland is still being seriously contaminated with radioactive particles 15 years after pollution was first detected. According to a confidential report by the site鈥檚 operators, the UK Atomic Energy Authority (UKAEA), scientists have no idea how the particles of nuclear waste are leaking into the environment. Radiation doses from some of them could breach international safety limits.
Concerned by the persistence of the pollution, the government鈥檚 Committee on the Medical Aspects of Radiation in the Environment (COMARE) and the Radioactive Waste Management Advisory Committee (RWMAC) have launched special investigations into the source, extent and potential health risks of the contamination. Members of both committees are planning a joint visit to Dounreay early in the new year.
The plant鈥檚 own 鈥渢ask force鈥�, set up earlier this year by the new director, John Baxter, produced a 20-page interim report at the end of last month. The report was sent to COMARE and RWMAC by the Scottish Office鈥檚 HM Industrial Pollution Inspectorate with apologies for the UKAEA鈥檚 鈥渄elay鈥� in compiling it.
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The confidential report reveals that radiation monitoring on the Dounreay foreshore has detected 136 鈥渕etallic particles鈥� between 1 and 3 millimetres across since 1979. After systematic surveys of the foreshore were introduced in 1984 an average of a dozen particles have been discovered every year, including 12 in 1993 and 6 so far this year, all of which have been removed. Most of the particle have been 鈥渄ominated鈥� by caesium-137, although four were composed mainly of cobalt-60. Monitoring also uncovered an unspecified number of tiny radioactive steel fragments and a 鈥渓arge number鈥� of 鈥渁gglomerates bound by black tarry substances鈥�, which are of low activity.
None of the grey and sometime sharp-edged metallic particles has yet been subject to a complete radiochemical analysis. But the UKAEA has calculated that one 20-year-old particle contained plutonium, americium and strontium, as well as caesium. Most of the particles date back to the early 1960s and are thought to come from fuel elements used in Dounreay鈥檚 old Material Testing Reactor (MTR).
All but one of the particles were found beneath several centimetres of sand on the foreshore directly between the plant and the sea, an area to which the report says public access is 鈥渄ifficult though not impossible鈥�. One particle was found in 1984 on Sandside beach, an attractive public bay west of Dounreay. Around the same time, the so-called tarry agglomerates were also found on the beach and in a rocky inlet to the east of the site known as Oigin鈥檚 Geo.
The report points out that anyone known to have been on the foreshore is carefully monitored. When the fishing boat Arnisdale was wrecked on rocks off the plant in April, its crew of four had to be rescued via the foreshore. According to their captain, David Addison, they had to take off their clothes to have them checked for contamination by UKAEA staff.
鈥淭he dose rates from the particles are substantial and surface dose rates in excess of 50 millisieverts per hour are obtained from some of the particles: continued precautions will be taken to ensure there is no possibility of a particle being carried off the foreshore,鈥� says the report. There is a 鈥渧ery remote鈥� possibility that a child could ingest a particle, it claims, although only a small proportion would be expected to dissolve on its way through the digestive system.
But David Sanderson, from the Scottish Universities Research and Reactor Centre at East Kilbride, points out that people would not need to be exposed to such particles at close range for long before they would be likely to exceed the maximum dose recommended for members of the public by the International Commission for Radiological Protection, which is currently 1 millisievert per year. The recommended maximum for radiation workers is 20 millisieverts a year, and the particles could only be handled legally in a specially controlled laboratory.
The report suggests that many of the particles came from the swarf generated by pre-1967 milling operations to remove the aluminium cladding from fuel elements in the MTR. It then speculates about twelve possible routes by which they could have found their way onto the foreshore, including leakages from drains, cooling ponds, waste pits, effluent tanks and an unlined waste shaft.
Three specific incidents could have spread the particles: a spillage in 1965 caused by a lorry breaking a temporary pipeline carrying cooling water from the MTR; an explosion in the waste shaft in 1977 which could have blown particles onto the foreshore; and leakages following the clearing of blocked effluent pipes in 1983 by 鈥渉igh pressure waste jetting鈥�.
The report says, however, that these incidents would probably have released a finite number of particles which should now be found in decreasing numbers. 鈥淓xperience has, however, shown that the rate of finds has remained fairly constant and other possible sources which involve a continuing movement of particles into the environment must be considered,鈥� it says.
The report concludes that 鈥渋t has not proved possible to define how these particles have reached the foreshore area鈥�. But it adds: 鈥淎 programme of work to enable a more definitive statement on the route by which the particles have reached the environment has been established. Once the route has been established it will be possible to identify the measures required to prevent further incidences of radioactive metallic particles reaching the foreshore.鈥�
In a statement last week, Baxter insisted that the contamination 鈥渄oes not pose a hazard to the staff on site, the people off site or the environment鈥�. But Peter Peacock, the vice-convenor of Highland Regional Council, says the leaked report poses 鈥渇undamental questions鈥� about Dounreay鈥檚 waste management practices.