REMOBILIZATION OF SELLAFIELD-DERIVED RADIONUCLIDES AND TRANSPORT FROMTHE NORTHEAST IRISH SEA

Plutonium-239,240 activities in seawater from the north-east Irish Sea , collected in January 1992, were in the range of 0.17-4.30 mBq l(-1) in solution and 7.2-62.3 Bq kg(-1) in suspended particulates. The Pu-2 38:Pu-239,Pu-240 activity ratios for the soluble fraction were consist ent with those of the underlying sediments but inconsistent with conte mporary discharges from Sellafield, indicating that most of the pluton ium in solution was derived from re-dissolution from the sediment. The activity ratios for the particle associated material were more variab le, but again, on average, typical of the sediments. The annual loss o f Pu-239,Pu-240 from the north-east Irish Sea in solution was estimate d to be 1.19 TBq and that associated with suspended particulates to be 0.11 TBq. From this, a halving time of 350 years for the loss of Pu-2 39,Pu-240 activity from the sediment by dissolution was determined. A similar treatment of Cs-137 data yielded an annual loss of 86 TBq in s olution and a halving time of 23 years. Calculations using a numerical model of the Irish Sea yielded similar estimates of current loss rate s and permitted the estimation of total cumulative losses from the Iri sh Sea by advection through the North Channel of 7.9 TBq of Pu-238, 48 TBq of Pu-239,Pu-240 and 2.6 x 10(4) TBq of Cs-137. (C) 1997 Elsevier Science Limited.