MANAGEMENT OF NORM IN THE PETROLEUM INDUSTRY Akpojevwa Tega Naomi, october 2016 | Page 26

Radon emanation rates (the fraction of radon released) from scale typically are
around 5% (Nielson et al., 1988), primarily because the hard, solid structure of
the scale inhibits the release of radon as gaseous progeny.
2.1.2 Sludge and Scrapings
The NORM found in sludge are mainly from the uranium-238 and thorium-232.
The main isotopes found in sludge are those of Radium-226 and to a lesser
degree Radium-228, these two radium isotopes are present as both sulphates and
carbonates in the strontium, barium and calcium mineral scales that develop in
the tubular and other areas of the extraction rigs. (Wilson and Scott, 1992).
Not all radioactive molecules containing radium are in form of scale. They can
also be found in sludge (often oily), produced sands and scrapings. Other
radionuclides such as Lead-210 and Polonium-210 can also be found in
pipelines scrapings as well as sludge which in turn is commonly found in tank
bottoms, gas/ oil/ water separators, dehydration vessels, liquid natural gas
(LNG) storage tanks and in waste pits (OGP, 2008; IAEA, 2003). Activity
concentrations vary between production facilities; a list of findings is presented
in the next table.
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