Origins of the Classification System for Radiological Designation of Areas
This note gives a brief history of the development of the classification system for the radiological designation of areas and its incorporation into the Ionising Radiations Regulations.
Under The Ionising Radiations( Sealed Sources) Regulations 1969 and The Ionising Radiations( Unsealed Radioactive Substances) Radiations 1968 there were three classes of designation – exclusion areas, controlled areas and non-controlled areas – based on specified levels of surface contamination and external radiation dose. Supervised areas were introduced into the Ionising Radiations Regulations( IRRs) in 1985.
Sheila Liddle is an RPA and RWA with over 30 years ' experience in the nuclear and non-nuclear sectors.
UKAEA designated radiation controlled areas
“ Blue”, contamination controlled areas“ Red” and any type of exclusion area“ Purple”. Where a room required designation for both radiation and contamination, it was generally classified as Red( Contamination Controlled Area). Other companies such as the CEGB, Babcock and Sellafield adopted a different classification system, which is still in use today. These were Contamination Controlled Areas( Classes C1, C2, C3 and C4) and Radiation Controlled Areas( Classes R1, R2, R3 and R4). The controls required increased with increasing number, i. e. C1 and R1 = Supervised Area, C2, R2 and above = Controlled Area.
Contamination levels for control of exposure were based originally on the maximum permitted body burden( MPBB), calculated in accordance with ICRP 2. Exposure to airborne levels equivalent to the Maximum Permissible Air Concentration could give rise to a dose equivalent of 50 mSv per year, which was then the annual dose limit.
From this, maximum permissible levels of contamination were calculated for surfaces, depending on the level of toxicity and whether the nuclide was an alpha or beta emitter. These were derived from the MPBB using dose coefficients and resuspension factors measured by John Dunster. These levels were incorporated into The Ionising Radiations( Unsealed Radioactive Substances) Regulations 1968.
Maximum Permissible Levels for surface contamination specified in The Ionising Radiations( Unsealed Radioactive Substances) Regulations 1968
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