Plutonium policy update and plutonium remobilisation in the Irish Sea via nuClearNews

Plutonium Policy Update
The Nuclear Decommissioning Authority (NDA) now expects the Magnox Reprocessing Plant at Sellafield to close this year (2021) – one year later than previously planned. The newer Thermal Oxide Reprocessing Plant (THORP) was shut in November 2018. Reprocessing, which has
always been unnecessary, is the chemical separation of plutonium and unused uranium from spent nuclear waste fuel. When reprocessing ends there will be around 140 tonnes of separated civil plutonium stored at
Sellafield – the world’s largest stockpile of separated civil plutonium. […]

The story so far
When reprocessing ends in 2021 there will be around 140 tonnes of separated civil plutonium stored at Sellafield. About 23 tonnes of this is foreign-owned, largely but not exclusively by Japanese utilities, and is managed under long-term contracts.


The Options
Options considered for dealing with plutonium include using it as a fuel called Mixed Oxide Fuel (MoX) in nuclear reactors (followed by storage as spent fuel pending disposal in a Geological Disposal Facility (GDF)). There was a MoX fuel fabrication plant at Sellafield which closed in 2011.


Another option would be immobilisation of the plutonium as a waste. Given the diverse nature of the inventory, a number of different approaches are being investigated so that parts or all of the inventory can be immobilised in a form suitable for ultimate disposal in a Geological Disposal Facility (GDF). Both the re-use and immobilisation options would require new expensive plants which would be very technically challenging. Any new plant would take one or two decades to plan and build before processing of material could begin, so there is no quick or inexpensive solution. (12)
Some of the plutonium wouldn’t be suitable for reuse as MOX in nuclear reactors in any case, due to its physical or chemical properties. It will need to be immobilised and treated as waste, followed by storage pending disposal in a GDF. (13)


Plutonium Remobilisation in the Irish Sea

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.


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