Diagnosing ocean tracer transport from Sellafield and Dounreay by equivalent diffusion and age
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A simple approach for estimating the equivalent diffusion for diagnosing tracer transport is proposed. Two different expressions are derived; one is based directly on an analytical solution of the two-dimensional advection-diffusion equation, the other uses the variance of the tracer distribution. To illustrate some features of the equivalent diffusion and possible applications thereof, idealized releases of passive tracers from the nuclear fuel reprocessing plants at Sellafield in the Irish Sea and Dounreay on the northern coast of Scotland have been simulated with a regional isopycnic co-ordinate Ocean General Circulation Model. Both continuous and pulse releases are considered; the former being representative of the actual historical discharges from the reprocessing plants, the latter resembling an accidental scenario. Age tracers are included to calculate the mean time elapsed since the tracers left their source regions. It is found that in the Nordic Seas the age of tracers from Dounreay is approximately 2 years younger than the age from Sellafield. Although tracers from both sources eventually end up along the same transport routes, significant qualitative differences regarding the dispersion properties are found. It is argued that one single parameter, the equivalent horizontal diffusion, which is estimated to be in the range of 20–56 m2 s−1 from Sellafield and 170–485 m2 s−1 from Dounreay, determines these differences.
Key wordsequivalent diffusion passive tracers age tracers sellafield dounreay
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- AMAP, 2004: Amap Assessment 2002: Radioactivity in the Arctic. Tech. Rep., Oslo, Norway, 320pp.Google Scholar
- Drange, H., R. Gerdes, Y. Gao, M. Karcher, F. Kauker, and M. Bentsen, 2005: Ocean General Circulation Modelling of the Nordic Seas. The Nordic Seas: An Integrated Perspective, AGU Monograph, 199–220.Google Scholar
- Gao, Y., H. Drange, and M. Bentsen, 2003: Effects of diapycnal and isopycnal mixing on the ventilation of CFCs in the North Atlantic in an isopycnic coordinate OGCM. Tellus, 55B, 837–854.Google Scholar
- Morse, P., and H. Feshbach, 1953: Methods of Theoretical Physics, Part I. McGraw-Hill, 177–182.Google Scholar
- Okubo, A., 1971: Oceanic diffusion diagrams. Deep-Sea Research, 8, 789–802.Google Scholar
- Orre, S., 2008: Circulation features in the northern North Atlantic Ocean inferred from simulated radioactive tracers. Ph. D. dissertation, University of Bergen, 126pp.Google Scholar