Controls on anthropogenic radionuclide distribution in the Sellafield-impacted Eastern Irish Sea

Daisy Ray,Peter Leary,Francis Livens,Neil Gray,Katherine Morris,Kathleen A Law,Adam J Fuller,Liam Abrahamsen-Mills,John Howe,Kieran Tierney,Graham Muir,Gareth T.W Law

doi:10.1016/j.scitotenv.2020.140765

Abstract

Understanding anthropogenic radionuclide biogeochemistry and mobility in natural systems is key to improving the management of radioactively contaminated environments and radioactive wastes. Here, we describe the contemporary depth distribution and phase partitioning of 137Cs, Pu, and 241Am in two sediment cores taken from the Irish Sea (Site 1: the Irish Sea Mudpatch; Site 2: the Esk Estuary). Both sites are located ~10 km from the Sellafield nuclear site. Low-level aqueous radioactive waste has been discharged from the Sellafield site into the Irish Sea for >50 y. We compare the depth distribution of the radionuclides at each site to trends in sediment and porewater redox chemistry, using trace element abundance, microbial ecology, and sequential extractions, to better understand the relative importance of sediment biogeochemistry vs. physical controls on radionuclide distribution/post-depositional mobility in the sediments. We highlight that the distribution of 137Cs, Pu, and 241Am at both sites is largely controlled by physical mixing of the sediments, physical transport processes, and sediment accumulation. Interestingly, at the Esk Estuary, microbially-mediated redox processes (considered for Pu) do not appear to offer significant controls on Pu distribution, even over decadal timescales. We also highlight that the Irish Sea Mudpatch likely still acts as a source of historical pollution to other areas in the Irish Sea, despite ever decreasing levels of waste output from the Sellafield site.

Highlights

The authorised discharge of low-level aqueous radioactive waste from the Sellafield nuclear site (Cumbria, UK) to the Eastern Irish Sea has taken place since 1952 (Kershaw et al, 1992; Gray et al, 1995)
In the Esk Estuary, the total organic matter content ranged from ~7 wt% at the sediment surface to ~4 wt% at depth (Table S2), possibly reflecting microbially-mediated oxidation of organic matter (Froelich et al, 1979)
Cesium, Pu, and 241Am-containing low-level aqueous effluent is legally discharged from the Sellafield site into the Eastern Irish Sea

Summary

Introduction

The authorised discharge of low-level aqueous radioactive waste from the Sellafield nuclear site (Cumbria, UK) to the Eastern Irish Sea has taken place since 1952 (Kershaw et al, 1992; Gray et al, 1995). Discharge activities increased throughout the 1960s due to elevated waste throughput and processing. They peaked in the mid-1970s due to increased storage times for Magnox fuels (Kershaw et al, 1992). As the site is transitioning from spent fuel reprocessing to decommissioning and post operational clean-out, the discharges should continue to decrease

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