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ENVIRONMENT REPORT
2015
page 12
Naturally Occurring Radioactive Materials (NORM) in Produced Water
Discharges of NORM are controlled through permits issued under the Radioactive Substances Act (RSA) 1993
8
.
Radium and many other radionuclides occur naturally in seawater and have done so for millions of years. Marine
organisms have evolved to thrive with this background radioactivity, but significant bio-accumulation of radium
would be of concern in the context of human consumption of fish.
The UKCS rock strata contains radionuclides of the Uranium and Thorium decay series and some of these dissolve
into the water present in the reservoir. The most abundant NORM element in produced water is Radium (Ra)
9
,
and in particular the Ra
226
isotope, which has a half-life of 1,620 years and emits alpha particles. As the water is
brought to the surface, the reduced pressure and temperature results in the dissolved nuclides co-precipitating
with barium sulphates
10
to form a scale on the inside of the process equipment. This NORM scale complex of
barium, radium and sulphate is insoluble in seawater. Similarly, any radionuclides discharged in solution will form
precipitates with sulphate rich seawater. These solids are not readily bio-accumulated in marine organisms and do
not have a significant impact on the marine environment or human health.
Permits for offshore reinjection or discharge of produced water are approved on the condition that the
operator notifies the relevant environment agency if the concentration of Ra
226
is greater than 0.1 Bequerel per
millilitre (Bq/ml)
11
.
8
The RSA 1993 is available to view at
www.legislation.gov.uk/ukpga/1993/12/contents9
Environmental Impacts of Produced Water and Drilling Waste Discharges from the Norwegian Offshore Petroleum Industry
Bakke, T., Klungsøyr, J., Sanni S. (2013)
www.sciencedirect.com/science/article/pii/S014111361300162110
Reservoir water is rich in barium and seawater is rich in sulphate, and so barium sulphate is formed when they meet.
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The Strategy for the Management of Naturally Occurring Radioactive Material (NORM) Waste in the United Kingdom
is
available for download a
t www.gov.scot/Resource/0045/00455971.pdf