Reconstructing the history of 14C discharges from Sellafield: Part 1 -: atmospheric discharges

C-14 specific activities, above ambient background levels, were determined in individual tree-rings (corresponding to the years 1950-1999) sectioned from an oak tree that was felled in autumn 1999, from a location 1.5 km cast of the Sellafield nuclear fuel reprocessing plant in Cumbria, north-west England. The data were used to produce a new, improved, reconstruction of Sellafield's annual atmospheric C-14 discharges between 1951 and 1999, using the most reliable discharge data set (1994-1999) as the primary basis for the determination of a new calibration factor that relates excess C-14 activity in individual tree rings to the annual discharge during the corresponding year. The results indicate that the current British Nuclear Fuels plc (BNFL) estimate of total C-14 discharges to the atmosphere prior to 1978 is significantly overestimated, while the current estimate of total C-14 discharges after 1978 is very similar to that determined in this study. In this study, the total activity of C-14 discharged to the atmosphere from Sellafield between 1951 and 1999 is estimated to be 259 +/- 63 TBq (at 2 std. dev.). The BNFL current estimate is 360 TBq. (C) 2002 Elsevier Science Ltd. All rights reserved.