The transfer of radionuclides from sea to land in sea spray

• Main Author: Nelis, Patrick M.
• Published: University of Edinburgh 1990
• Subjects: 530.0724
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659914

This thesis reports on an investigation into the transport inland in sea spray of radionuclides discharged into the Irish Sea from the nuclear plant at Scllafield in Cumbria. The work was carried out in response to a concern about the increased incidence of childhood leukaemia in the vicinity of Britain's nuclear reprocessing facilities. It is proposed that the sea spray transfer is an important pathway of discharged radioactivity into the human environment. The inland transfer of contaminated sea spray was investigated on the beach at Drigg, between 6 and 10 km south of the BNFL Scllafield marine discharge pipeline, through which significant levels of radionuclides have been flushed since 1952. The radionuclide concentrations of coastal marram grass vegetation and collected on exposed muslin screen passive droplet collectors are reported. The method used to determine the mass of sea-salt collected by the exposed screens is described and the results of these measurements presented. The collection of the natural atmospheric radionuclide 7Bc on the exposed muslin screens was used to extract the effects of the changing wind flow on the collection of the spray droplets at different distances inland. This allowed an elucidation of the true reduction in the radionuclide air concentrations with distance from the sea. The Sellafield-produced radionuclides present on the exposed screens were found to decrease with distance inland at the same rate as the collected sea-salt, implicating the sea spray droplets as the carriers of the radioactivity. A model of the inland transfer of sea spray droplets produced in the turf zone along the shoreline is described. The collection of the contaminated spray in coastal soil, vegetation and muslin screen collectors is simulated. This model gives results which fit the measured reduction in radionuclide air concentrations with distance from the sea. A successful application to datasets of the inland transfer of spray and radioactivity reported elsewhere is also illustrated. The analysis of the changing surface air concentration with distance inland illustrated that the initially rapid reduction measured here and elsewhere is due more to the spray droplets being mixed to higher altitudes than their deposition to the ground. An analysis of a sea spray collection event in which very high radionuclide air concentrations were measured calculates that under certain conditions 1 km of coastline can produce 1.54xl05Bq of 239+240pu and 1.10xl05Bq of 241Am per hour. This material is thought to be efficiently transported inland in sea spray, and 60% of it is calculated to be still airborne 1 km from the coast. It is concluded that the sea spray transport of marine discharged radioactivity transfers significant levels of long-lived radionuclides to the land, much of it in the respirable size range, and that this material can be carried to large distances from the sea. This pathway merits further investigation as the causes of the increased leukaemia incidence in West Cumbria are sought.