Appendix CRF - Part 3 - Northamptonshire County Council

Radiological Assessment 0820-2
Version 2
The regulatory guidance notes that the following are events for which the dose
guidance levels for human intrusion events apply:
human intrusion directly into a disposal facility;
other human actions that damage barriers or degrade their functions, such as
removing material from a disposal facility cap. Barriers considered to be
affected by these human actions may be engineered, natural or a combination
of both.
The dose criteria used do not affect the way in which the dose assessments are
conducted, but they are important for assessing the radiological capacity of a disposal
facility. For the assessment of the ENRMF, three potential events are assessed that
are considered to fall within these definitions:
Direct excavation of waste.
Occupation and subsequent use of the site following removal of the cap or
excavation and re-distribution of waste.
Use of a borehole at the site boundary as a source of drinking water.
The first two of these events are derived from the inadvertent intrusion scenario in the
SNIFFER methodology. Although doses to those excavating the waste could be
regarded as transitory according to the regulatory guidance, and therefore subject to a
dose guidance level of up to 20 mSv/year, the lower dose criterion of 3 mSv/year has
been used in the calculation of radiological capacities.
The third event is included to provide a comparison with assessments of potential
releases of non-radiological hazardous substances. Radiological assessments are
based on calculating releases to the accessible environment and then determining
doses to members of the critical group. For future releases, the same approach is used
but a range of potentially exposed groups are considered at different release points
where contaminated resources might be exploited in the future. In order to show
compliance with the Groundwater Directive, assessments of potential releases of nonradiological
hazardous substances must show that a site does not allow the discharge
of List I substances into groundwater or the pollution of groundwater by List II
substances. Such assessments therefore use compliance points at the water table,
regardless of whether the groundwater is actually exploited at that point.
To provide a comparison between the two types of assessment, the radiological
assessment has been extended to include use of a borehole at the site boundary for
drinking water. This provides a compliance point for groundwater, although
boreholes for drinking water would not normally be permitted in such locations as
they would degrade the function of the natural barriers that are a key part of providing
long-term safety for radioactive waste disposal. In calculating the radiological
capacity of the site, it is therefore appropriate to regard such a borehole as an intrusion
event and to use the dose guidance level of 3 mSv/year.
Galson Sciences Limited 22 14 July 2009
WS010001/ENRMF/CONSAPPCRF 572