Radioactive substances legislation - scope: guidance

Technical considerations

Discounting of ‘normal’ background

The ‘out of scope’ levels and the exemption levels are based on the calculated values after removing background. It is the responsibility of the authorised person^[7] to either:

• Use the total assessed value of any substance, or
• Be able to demonstrate how the background has been calculated and why that is appropriate.

Separate processes, giving rise to separate solid waste streams, can be treated on their own for the purposes of the above paragraphs. A ‘separate process’ can be defined as one in which optimisation can be achieved without compromising any optimisation steps for another process.

A substance or article is not regarded as radioactive material or radioactive waste unless the concentration of any artificial radionuclide is above the levels ‘found normally in such a substance’^[8].

The purpose of this provision is to remove materials and wastes containing radionuclides which are not amenable to controls because of their ubiquitous presence in the earth, its waters or atmosphere from the need for regulation. The concept applies to artificial radionuclides found in naturally occurring materials. For instance, due to historical atmospheric weapons tests and the Chernobyl accident, certain fission products are in global circulation. Obviously, such radioactivity is not amenable to control. Neither is the radioactivity in rainwater arising from the presence of these artificial radionuclides in the atmosphere.

Practical considerations of assessment also need to be taken into account. Authorised persons are expected to use good practice to determine the radiochemical assay of the waste, but where the difference between the level ‘found normally in such a substance’ and the increment due to additional contamination genuinely cannot be separated or reasonably measured, then the entire material can be considered as ‘out of scope’.

‘Head of chain’ calculations

For the purposes of calculating the total activity in wastes, the head of the chain may be taken to already include all radionuclides in a decay chain (in the case of radionuclides followed by the term ‘sec’), or all the listed radionuclides (in the case of the term ‘+’).

‘sec’ where it appears after a radionuclide means that, for the purpose of calculations, all radionuclides in the decay chain in secular equilibrium have been taken into account for the purposes of radiological impact assessment.

‘+’ where it appears after a radionuclide means that, for the purpose of calculations, the radionuclide includes such of its daughter radionuclides in the decay chain that are relevant for the purposes of radiological impact assessment; these radionuclides are listed in Table 4 for out of scope material.

Technical considerations

Calculations using ‘head of chain’ values can be applied to:

• Calculations of ‘out of scope’ levels for industrial activities in Table 2.
• Calculations of ‘out of scope’ levels for practices in Table 3.