The Low Level Waste Repository (LLWR; see http://www.llwrsite.com/ for further details) is the UK’s
principal facility for the disposal of solid low-level radioactive waste. The facility is located on the
West Cumbrian coastal plain close to the village of Drigg and approximately 5 km south-east of the
Sellafield nuclear site. The LLWR receives wastes from a range of consignors including from nuclear
industry sites, defence establishments and users of radioactive materials, and from the clean-up of
historically contaminated sites. The bulk of the volume and of total radioactive inventory received
by the LLWR comes from facilities associated with the nuclear industry. Significant radiological
impacts could arise, however, from the disposal of consignments of wastes from processing and use
of naturally-occurring radionuclides, mainly 226Ra and 232Th and their progeny. These wastes consist
of mineral sands, wastes from processing such minerals and also wastes from clean up of sites at
which processing, manufacture or use of thorium and radium products took place, e.g. radium
luminising facilities. The production of radon-222 in the waste is directly proportional to the
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inventory of its parent, radium-226, which itself is due to disposed 226Ra (half-life 1600 years) plus ingrowth
from decay of disposed 234U (half-life 250,000 years) via 230Th (half-life 77,000 years).
A particular concern for the post-closure radiological environmental impact assessment is that an
excavation into the engineered cap, or into the waste itself, could give opportunities for exposures
to radon from radium-bearing wastes. The case that can give the highest dose is if it is assumed that
a dwelling is constructed either directly above the radium-bearing waste or on spoil created by
excavation of repository cover materials and waste, including radium-bearing waste. In the past, the
case of a dwelling constructed on a degraded low level radioactive waste site or on excavated spoil
was assessed making use of models that attempt to represent the entry and build up of radon within
such a dwelling taking account of radon migration processes and the possible characteristics of the
dwelling. This approach is subject to large uncertainties because the entry of radon and
accumulation in a building is highly sensitive to ground conditions, building construction and
ventilation, and because the characteristics of a future building are unknown. For the most recent
assessments of the LLWR (Sumerling, 2008), a simpler approach was adopted using an empirical
relationship between the concentration of radon in dwellings and the concentration of 226Ra in soil,
based on general data from UNSCEAR (2000).
In the UK, there are substantial data sets of measured radon in dwellings, naturally-occurring
radionuclides in soil and radon in soil gas, all related to classification of local geology. This gives the
opportunity to develop empirical relationships that are intrinsically matched to the average
characteristics of UK houses and also, by choice of the geological association, that are appropriate to
represent ground conditions more relevant to the radiological assessment cases. This paper
describes work carried out by the British Geological Survey and the Health Protection Agency to
analyse UK data and to develop empirical relationships between uranium and 226Ra in soil, radon in
soil and radon in dwellings. These relationships will assist in the post-closure assessment of radon
related to near surface radioactive waste disposal as practiced at the LLWR.