Publication Abstract

Transport of Plutonium (239/240 Pu) and Caesium (137Cs) in the Irish Sea: Comparison between observations and results from sediment and contaminant transport modelling

Transport of Plutonium (^{239/240 Pu}) and Caesium (^137Cs) in the Irish Sea: Comparison between observations and results from sediment and contaminant transport modelling

J.N Aldridge, P Kershaw, J. Brown, D. McCubbin, K.S. Leonard and E.F. Young

A model for radionuclide transport in the marine environment is described and applied to the movement of Sellafield derived radionuclides ¹³⁷Cs and ^239/240 Pu in the Irish Sea. The model resolves processes operating on tidal time scales whilst being able to run over decadal time periods. Modelled processes include transport in the water column, exchange of contaminants between dissolved and particulate phases, wave-current sediment resuspension, sediment transport and mixing of material within the seabed. Transport in the water column is by a combination of tide, wind and density driven flows. Sediment transport is based on the erosion, advection and deposition of three sediment classes representing sand, flocculated mud/silt and fine background components. Transfer of radionuclides between the dissolved and sediment phases is described using rate equations. A layered seabed is incorporated with mixing between layers representing biological and physical mixing processes. Results demonstrate that the model is able to reproduce observed concentrations of radionuclides in the water column, the buildup of material in the sea bed over a thirty year time span and the recent changes in seabed distribution. The model is used to identify and quantify the mechanisms responsible for the recent redistribution of radionuclides in the region. The results suggest that while sediment transport plays an important role in redistributing contaminated sediment in the eastern Irish Sea, desorbtion, followed by transport in the dissolved phase and reabsorbtion onto particle is the primary mechanism for re-distribution of sea bed inventories of ^239/240Pu over longer distances.

Reference:

J.N Aldridge, P Kershaw, J. Brown, D. McCubbin, K.S. Leonard and E.F. Young, 2003. Transport of Plutonium (^239/240 Pu) and Caesium (¹³⁷Cs) in the Irish Sea: Comparison between observations and results from sediment and contaminant transport modelling. Continental Shelf Research 23 (9)869-899.

J.N Aldridge*, P Kershaw*, J. Brown*, D. McCubbin*, K.S. Leonard* and E.F. Young*

Continental Shelf Research, 23(9): 869-899