Environmental monitoring in the vicinity of Sellafield following deposition of radioactivity from the Chernobyl accident

British Nuclear Fuels plc carries out an extensive program of routine environmental monitoring around its operating sites. following the reactor accident at Chernobyl, USSR, in April 1986, special monitoring arrangements were implemented and expanded as the situation developed. Results from the Sellafield Site were of special significance as they showed that West Cumbria was an area of high deposition. Descriptions of the monitoring carried out around Sellafield, and the results obtained, are presented here. Analysis of these results is described in terms of assessment of radiological significance of the incident to the population of Cumbria. Additionally, the effects of the accident on Sellafield environmental monitoring results for 1986 are described and the implications for 1987 and future years considered as a supplement to the summary of annual environmental monitoring data. The major radionuclides detected were **1**3**1I, **1**3**4Cs and **1**3**7Cs. Early results for rainwater indicated concentrations of iodine and cesium more than 30 times those recorded in lakes.