HPA-CRCE-005 - Derivation of Liquid Exclusion or Exemption Levels to Support the RSA93 Exemption Order Review

Synopsis

As part of the better regulation initiative, 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 HPA to calculate activity concentration values for aqueous liquids that could be used as either exclusion (unconditional clearance) levels or as exemption levels. 

HPA has derived activity concentration levels for aqueous liquids for around 280 radionuclides, using a dose criterion of 10 µSv y^-1. The calculations were based on the methodology used for Generalised Derived Limits (GDL) published by HPA. 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.

HPA undertook a preliminary investigation to determine whether the derived activity levels could be measured under laboratory based conditions. Based on the preliminary findings, HPA estimates that out of around 280 radionuclides, 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.

Last reviewed: 24 August 2010