Appendix CRF - Part 3 - Northamptonshire County Council

Radiological Assessment 0820-2
Version 2
6 Radiological Capacity
6.1 Introduction
Section 5 presents the calculated doses for a range of scenarios and exposure
pathways. These are presented as specific doses, the annual dose calculated to arise
from a disposal of 1 MBq of the radionuclide concerned. The actual doses will
depend on how much radioactive waste is actually disposed of to the site. Because of
the conservative assumptions involved in the assessment model any doses received in
the future are likely to be significantly less that these calculated doses. These specific
doses do, however, provide a basis for decisions about the amount of waste that can
be disposed.
The radiological capacity is the amount that can be disposed without the calculated
doses exceeding the appropriate dose criterion. Two types of radiological capacity
can be calculated. The first is the capacity for individual radionuclides, which
represents how much of any one radionuclide could be disposed of. If radionuclides
are completely independent, then these capacities can be apportioned directly to the
radionuclides – e.g., 50% of the capacity to radionuclide A and 50% to radionuclide
B.
In practice, radionuclides are not independent and are present in waste streams in
certain ratios. In this case, the capacity cannot be directly apportioned to the
radionuclides and must take account of both the specific dose for each radionuclide
and the proportion of the radionuclide in the waste stream.
The radiological capacity for radionuclide Rni in a waste stream (RCi) is given by:
RC
i
where:
fi
SDi
f
DC
i
SD
f
i
i
is the fraction of the overall activity arising from Rni (such that fi=1)
is the specific dose from Rni
DC is the dose constraint
Radiological capacities for mixtures of waste streams can be calculated by
apportioning part of the overall capacity to each waste stream.
The following sections present radiological capacities at the ENRMF for individual
radionuclides (Section 6.2) and overall capacities based on an illustrative waste
stream from the UKAEA decommissioning programme at Harwell (see Section 2.2).
Section 5 presents specific doses for a range of scenarios and exposure pathways, but
radiological capacities have only been calculated for the principal exposure routes:
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