Research and analysis

Derivation of liquid exclusion or exemption levels

This report (HPA-CRCE-005) describes work for a new exemption orders regime under the Radioactive Substances Act 1993 and the Environmental Permitting Regulations 2010.

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HPA-CRCE-005: derivation of liquid exclusion or exemption levels to support the RSA93 exemption order review

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The Department of Energy and Climate Change (DECC) and the Devolved Administrations have consulted on a new exemption orders regime under the Radioactive Substances Act 1993 and the Environmental Permitting regulations 2010. The overall aim is to have a simpler set of exemption orders, informed by risk, that are more easily linked to the European Basic Safety Standards. As part of the work to support the review of the exemption orders, DECC asked the HPA to calculate activity concentration values for aqueous liquids that could be used as either exclusion (unconditional clearance) levels or as exemption levels.

The Health Protection Agency (HPA) had derived activity concentration levels for aqueous liquids for around 280 radionuclides.The rounded derived levels range from 10-4 Bq l-1 to 103 Bq l-1, and 80% of the values are between 0.01 Bq l-1 and 1 Bq l-1. HPA recommends that the volume of aqueous liquid at these derived levels that can be disposed of to a sewer is restricted to 3000 m3 y-1 and hence that the derived levels are suitable for exemption rather than for exclusion.

The HPA investigated to determine whether the derived activity levels could be measured under laboratory based conditions. Based on the preliminary findings, the HPA estimated that around 35% have such short half lives that the derived activity levels would not be measurable. Of the remaining 65%, over half of the derived levels could potentially be measured in the laboratory.