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Sellafield’s plutonium waste has continued to circulate in the Irish Sea

  Plutonium Remobilisation in the Irish Sea, No2Nuclear Power No 132 May 2021,  Low-level aqueous radioactive waste has been discharged from the Sellafield site into the Irish Sea for more than 50 years. Originally it was thought that soluble radionuclides discharged from Sellafield (such as caesium and tritium) would be diluted and dispersed whereas long lived, transuranic nuclides such as Plutonium, and Americium would leach out of the liquid phase and become preferentially adsorbed to the surface of sedimentary particles in the water column, sink to the seabed and remain permanently bound and immobilised in seabed deposits and therefore isolated from human populations and the environment.

Unfortunately, it has since emerged that a proportion of such sediment associated radioactivity has, and is being actively transported around the Irish Sea while the remainder is temporarily “sequestered” in the seabed but subject to any future disturbance mechanisms such as storm, wave and seismic activity. In addition, a proportion of dissolved nuclides did not necessarily remain dissolved in liquid form in the water column, but could become incorporated into organic particles and deposited into sedimentary environments where they could be temporarily sequestered, but subsequently recycled back into the environment by dredging, trawling storm and seismic activity. 

Plans by West Cumbria Mining (WCM) for an under-seabed coal mine off the coast of Cumbria near Whitehaven and the possibility of a Geological Disposal Facility, also under the seabed off the coast of Cumbria have raised concerns that transuranic radionuclides currently sequestered in Irish Sea sediments could be further remobilised as a result of these activities,

 A large proportion of the Sellafield-derived radionuclides disposed to sea have become associated with the sediment at two sites close to the waste disposal pipeline: the Irish Sea Mudpatch and the Esk Estuary. The Mudpatch is a belt of fine-grained sediments located about10 km from the waste pipeline.   

In 1999 Kershaw et al showed evidence that sediment-bound radionuclides over the previous decade were being redistributed. There was a decrease in the coastal zone around Sellafield and increases in Liverpool Bay and the western Irish Sea. Levels of dissolved 239/240Pu in the water column decreased only slowly since the peak discharge rates in the 1970s and much more slowly than the drop in Sellafield discharges. This suggests that material is moving from contaminated sediments and becoming dissolved in seawater where it is available for transport. Indeed, in the western Irish Sea, evidence has been found that 239/240Pu is being transported from the eastern Irish Sea. There is also evidence of the direct transport of contaminated sediment. (1) 

Daisy Ray et al. highlight the fact that “once mobilised, the radionuclides can be transported elsewhere in the Irish Sea … Although waste discharges are continuing to decrease from the Sellafield site, the Mudpatch may continue to supply “historic” Sellafield-derived radionuclides to other locations. Indeed, recent data from Welsh and Scottish coastal areas suggest that the Mudpatch still acts as a source of radionuclides to UK coastal areas.” (2) 

The model developed by Aldridge et al. at the Centre for Environment Fisheries and Aquaculture Science (CEFAS) in 2003 strongly suggest that the principal source of 239/240Pu in the Irish Sea was sediments in the eastern Irish Sea contaminated from past discharges, rather than new inputs from Sellafield. (3) Radionuclide re-distribution can occur by two principal mechanisms. Directly, by the transport of contaminated sediment, or indirectly via exchange and transport in dissolved form (dissolution). The latter process operates when tidal, wind or trawling activity re-suspends bed material allowing transfer of radionuclides to the water column. (4) 

Ray el al. also suggest that bioturbation – the reworking of soils and sediments by animals or plants – at the Cumbrian Mudpatch will continue to act as a source of “historic” Sellafieldderived radioactivity to the UK Coastal Environment. If this redistribution of historical discharges of radionuclides is happening by natural processes, it can be assumed that the problem could become much more serious as a result of human mining activities under the seabed, 
A recent report by Marine Consultant, Tim Deere-Jones concludes that:     

  It is evident that any subsidence within the WCM designated seabed mining zone will generate some form and degree of seabed morphological distortion. It is equally evident that any such seabed distortion will remobilise previously sequestered seabed sediments, and their associated pollutants, which will subsequently be transported and re-distributed through the regional marine and coastal environments. It is inevitable that such re-mobilisation and re-distribution will expose marine wildlife and human coastal populations and stakeholders to some degree of exposure doses to those pollutants via a number of mechanisms and pathways.” (5)


May 13, 2021 - Posted by | - plutonium, Ireland

1 Comment »

  1. Some relevant links/info to go with this report

    Comment by arclight2011part2 | June 19, 2021 | Reply

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