4.17.
For surface contaminated items where the radioactivity is concentrated on surfaces, compliance with activity concentration clearance levels (Bq/g) might not be sufficient in all cases because there are additional considerations relating to the handling of the material. In such cases, surface contamination clearance levels could be specified, either for generic clearance (which may be specified by the regulatory body in accordance with para. 3.12 of GSR Part 3 [1]) or for specific clearance (which may be granted by the regulatory body in accordance with para. I.13 of GSR Part 3 [1]).
4.18.
Surface contamination clearance levels could be derived by the operating organization and reviewed and approved by the regulatory body. Alternatively, surface contamination clearance levels could be specified by the regulatory body as part of the regulatory framework for clearance. The operating organization should then comply with these surface contamination clearance levels, in addition to complying with the generic activity concentration clearance levels5.
4.19.
Surface contamination clearance levels are intended to limit the contamination that is directly accessible and could be mobilized during handling of the material. They also limit direct exposure by external irradiation from handling surface contaminated items. The radioactivity inside and on the surface of the cleared material has to be appropriately limited to guarantee compliance with the dose criterion of the order of 10 µSv in a year stated in para. I.11 of GSR Part 3 [1]. An example of the application of surface contamination and activity concentration clearance levels is given in Table 1 [27].
Surface contamination clearance levelsa (Bq/cm2) |
Activity concentration clearance levelsb (Bq/g) |
Recommended action |
Average is below the clearance level |
Average is below the clearance level |
No need to undertake separation and segregation prior to clearing waste. |
Average is above the clearance level |
Average is below the clearance level |
Separation and segregation should be undertaken unless a justification can be made that removal is not reasonably practicable, the expenditure (whether in time, trouble or money) is grossly disproportionate to the safety and environmental benefits gained, and the overall impact of disposal is less than of the order of 10 μSv in a year. |
Average is below the clearance level |
Average is above the clearance level |
Unless commercial considerations (e.g. recycling or reuse options) for the surface layer are sufficient to justify the safety and environmental impacts of separation and segregation, it would be expected that articles or substances in this configuration would be managed as radioactive waste in accordance with the national strategy for management of radioactive waste. |
Average is above the clearance level |
Average is above the clearance level |
Manage as radioactive waste in accordance with the national strategy for management of radioactive waste. |
a For example, paint, laminate or region of increased radionuclide concentration. |
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b For example, brick, blockwork or metal structure. |
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4.20.
A number of international studies have used models to establish a link between surface contamination and the resulting annual dose to an individual. Examples of such models are given in Annex I. References [28, 29] provide surface contamination clearance levels for metallic items both for direct reuse and for recycling by melting. Examples of surface contamination clearance levels applicable for general use are given in Annex II. In general, the derivation of these surface contamination clearance levels considers both the fixed and removable activity on the surface of items.
4.21.
The values of surface contamination clearance levels for certain radionuclides, as derived by different international studies and recommendations, can differ. The differences are due to different assumptions in the models used to derive the clearance levels (e.g. in relation to the material, the size of an item, geometry, or exposure scenarios). Therefore, application of a set of surface contamination clearance levels (derived for a specific situation) to a different situation should be done with care, taking into account the adequacy of any assumptions, the characteristics of the material or items, and the exposure scenarios used.
4.22.
If surface contamination clearance levels have not been specified, items with surface contamination might instead be considered in terms of their compliance with activity concentration clearance levels. This can be achieved by converting the total activity on the surface to an activity concentration (Bq/g), taking account of the total mass of the material below the surface (i.e. the activity concentration should not be calculated by just using the thickness of the layer of surface contamination). In doing this, considerations relating to the models used to derive the clearance levels need also be taken into account, particularly the averaging mass (see paras 4.23–4.37). For example, if a metal sheet with a thickness of 0.8 cm and a density of 7.8 g/cm3 has a surface contamination level of 0.4 Bq/cm2 of 60Co on one side, the average activity concentration is calculated as 0.064 Bq/g. The relevant clearance level (as specified in table I.2 of GSR Part 3 [1]) is 0.1 Bq/g. Consequently, the material would comply with the activity concentration clearance level; however, the clearance level would not be met if both sides of the metal sheet were contaminated at this level.