The environmental implications of a Severn Barrage, including water quality implications, were considered in detail during the 1980s as part of tripartite studies funded by the then Department of Energy, Central Electricity Generating Board and Severn Tidal Power Group. These studies are reported in “Energy paper 57: The Severn Barrage Project: General Studies (ISBN 0 11 412952 5) HMSO 1989” and associated reports, which can be found at:
The Environment Agency lists the organisations that are currently authorised under the Radioactive Substances Act 1993 to make disposals, either directly or indirectly, to the River Severn or its estuary on its website at:
http://maps.environment-agency.gov.uk/wiyby/wiybyController? extraClause=PROCESS_NAME~'RADIOACTIVE% 20SUBSTANCES'