Spectacular though Dounreay’s exploding waste shaft might have been, the centerpiece of its contamination of the surrounding ocean has been its 19-year discharge of radioactive metal fragments from its fuel rods.
Dounreay, conceived when uranium was scarce, was designed to recycle and reuse uranium reactor fuel. Between 1958 and 1996, as a first step in this process, the aluminum cladding was shaved away from the uranium core in large ponds, with the liquid protecting workers from the radiation. The shavings accumulated at the bottom of these ponds and were periodically collected and dumped into the shaft (see above) or the silo (see below). The liquid from these ponds was drained to large settling tanks to allow smaller shavings to settle out, and then the liquid was discharged into the sea.
In theory, only the liquids drained off the top of Dounreay’s settling tanks would flow down this tunnel. But the waste did not settle properly. As well as the liquid, … pieces of fuel rod were also washed out. There is now a plume of radioactive particles on the seabed to the north of Dounreay covering hundreds of square kilometres.
Two kilometres of beach outside the Dounreay nuclear plant have been closed since 1983, and fishing banned, when it was found old fuel rod fragments were being accidentally pumped into the sea. The cause was traced and corrected but particles – including plutonium specks, each capable of killing a person if swallowed – are still being washed on to this bleakly beautiful stretch of sand and cliff on mainland Britain’s northern edge.
Dounreay staff documented evidence of shavings evading their control system in the mid-60s, including a discovery in 1965 that a cracked pipe had allowed milling-pond water to enter a storm drain. The practice of dumping shavings into the shaft and silo was halted in 1969, when shavings were discovered contaminating the land routes from the milling pond to those two destinations.
Filters were not installed on liquid pumped to the settling tanks until 1984-5. This followed several instances in the 70s and early 80s where high-pressure water had to be used to force effluent through the clogged discharge lines to the sea. The first reactor fuel shavings (generally called “radioactive particles” in the news) were discovered on neighboring beaches during this time. In 1992, new discharge lines and a new diffuser were installed. In 1995, more roadside contamination was discovered.
 “Dounreay’s catalogue of idiocy is a cautionary tale of nuclear danger”, The Guardian, September 11, 2006. http://www.theguardian.com/commentisfree/2006/sep/12/comment.politics
 “Robots scour sea for atomic waste,” The Observer, May 24, 2008. http://www.theguardian.com/environment/2008/may/25/pollution.conservation