Appendix CRF - Part 3 - Northamptonshire County Council

Radiological Assessment 0820-2
Version 2
groundwater and intrusion. Specific doses through at least one of these routes are
higher than the corresponding doses through irradiation, and irradiation will not
therefore determine the overall capacity. The aerosol and leachate spillage pathways
are all highly uncertain, both in terms of the possibility of occurring and duration.
The specific doses presented in Section 5 are illustrative, and might be considered in
establishing mitigation measures, but should not be used to determine overall
capacities.
The specific doses calculated as a result of off-site leachate management are based on
a generic model for a sewage treatment plant, with significant uncertainties regarding
the extent of dilution by other waste streams and the type and fat of effluents. This
model again calculates specific doses based on unit radioactivity inputs. As discussed
elsewhere, there are large uncertainties about the rate at which radionuclides would
enter the leachate at the ENRMF. Conservative assumptions have been made so that
future doses arising from releases to groundwater or accidental spillage of leachate
can be calculated. It would, however, be unreasonable to apply these same
assumptions to the routine management of leachate during the operational period.
Even if the same generic model for the sewage treatment plant is used to estimate
specific doses, it would be more appropriate to determine a permissible level of
radioactivity in leachate and then to develop authorisation conditions from these.
Monitoring of leachate would ensure compliance with these conditions and give more
control than applying conservative assumptions.
As discussed in Section 3.2.1, two dose criteria have been used to determine
radiological capacity. For exposures arising from releases to groundwater and
subsequent use of an existing borehole for irrigation purposes, a dose criterion of
20 Sv / year has been used. For exposures resulting from intrusion into the waste,
from excavation and subsequent use of waste as soil, and from consumption of
groundwater extracted from close to the site boundary, a dose criterion of 3 mSv /
year has been used.
6.2 Radionuclide-specific radiological capacities
Tables 6.1 to 6.3 present specific doses and the corresponding radionuclide-specific
capacities for the two groundwater pathways and the principal intrusion pathway
described in Sections 4 and 5.
Radionuclide
Specific
dose
(μSv y -1 per
MBq)
Radiological
capacity
(MBq)
Radionuclide
Specific
dose
(μSv y -1 per
MBq)
Radiological
capacity
(MBq)
H-3 3.66E-30 5.47E+30 Ra-226 1.56E-08 1.28E+09
C-14 2.06E-09 9.69E+09 Ac-227 5.66E-26 3.53E+26
Cl-36 6.52E-08 3.07E+08 Th-229 1.44E-08 1.39E+09
Fe-55 1.04E-43 1.92E+44 Th-230 8.24E-09 2.43E+09
Co-60 1.21E-39 1.65E+40 Th-232 4.04E-08 4.95E+08
Galson Sciences Limited 60 14 July 2009
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