reply to post by Griffo
Most coal contains uranium and thorium, as well as potassium-40, lead-210, and radium-226. The total levels are generally about the same as in other
rocks of the Earth's crust. Most emerge from a power plant in the light flyash, which is fused and chemically stable. Some 99% of flyash is typically
retained in a modern power station (only 90% in some older ones), and this is buried in an ash dam. Some is sold for making concrete.
The amounts of radionuclides involved are noteworthy. In Victoria, Australia, 65 million tonnes of brown coal is burned annually for electricity
production. This contains about 1.6 ppm uranium (U) and 3.0-3.5 ppm thorium (Th), hence about 100 tonnes of uranium and 200 tonnes of thorium is
buried in landfills each year in the Latrobe Valley. Australia exports 235 Mt/yr of coal with 1 to 2 ppm U and about 3.5 ppm Th (Dale & Lavrencic
1993) in it, hence up to 400 tonnes of uranium and about 800 tonnes of thorium could conceivably be added to published export figures.
Other coals are quoted as ranging up to 25 ppm U and 80 ppm Th. In the USA, ash from coal-fired power plants contains on average 1.3 ppm of uranium
and 3.2 ppm of thorium, giving rise to 1200 tonnes of uranium and 3000 tonnes of thorium in ash each year (for 955 million tonnes of coal used for
power generation). Applying these concentration figures to world coal consumption for power generation (7800 Mt/yr) gives 10,000 tonnes of uranium
and 25,000 tonnes of thorium per year.
It is evident that even at 1 ppm U in coal there is more energy in the contained uranium (if it were to be used in a fast breeder reactor) than in the
coal itself. At 25 ppm U and used in a conventional reactor it would be half as much as the coal.
The actual radioactivity levels are not great. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) estimated that
average concentrations in coal worldwide were 50 Bq/kg K-40 and 20 Bq/kg each U & Th, though Australia's Commonwealth Scientific and Industrial
Research Organisation (CSIRO) puts Australian figures at average 830 Bq/kg total radioactivity, related to 1.8 ppm U and 7 ppm Th in the coal,
contrasted with some 1400 Bq/kg average in the Earth's crust. The U.S. National Council on Radiation Protection (NCRP) figures give 174 Bq/kg average
total radioactivity in US coal. Cooper (2003) gives 100-600 Bq/kg range for New South Wales (NSW) coals and Misha (2004) 145 Bq/kg average in Indian
UNSCEAR (1993) gives 3645 Bq/kg average in flyash. The above US data at 15% ash give 1200 Bq/kg in flyash. Dale (1996) quotes CSIRO figures of 2630
and 3200 Bq/kg from a high-ash NSW coal. Cooper (2003) gives up to 1500 Bq/kg for flyash and up to 570 Bq/kg for bottom ash in NSW. There are obvious
implications for the use of flyash in concrete, and the data also may be compared with levels of 1.0 or 3.7 MBq/kg sometimes taken as threshold levels
for classifying material as low-level radioactive waste, or with 25 MBq/kg for uranium metal.
With increased uranium prices the uranium in ash becomes significant economically. In the 1960s and 1970s, some 1100 tU was recovered from coal ash
in USA. In 2007 China National Nuclear Corp commissioned Sparton Resources of Canada with the Beijing No.5 Testing Institute to undertake advanced
trials on leaching uranium from coal ash out of the Xiaolongtang power station in central Yunnan. It and two nearby power stations use lignite with
high ash content (20-30%) and very high uranium content, from a single open-cut mine. The coal uranium content varies from about 20 to 315 ppm and
averages about 65 ppm. The ash averages about 210 ppm U (0.021%U) - above the cut-off level for some uranium mines. The power station ash heap
contains over 1000 tU, with annual arisings of 190 tU. (Recovery of this by acid leaching is about 70%.) Sparton also has an agreement to extract
uranium from coal ash following germanium recovery in the Bangmai and Mengwang basins in Yunnan. This ash ranges from 150 to over 4000 ppm U (0.40
%U), averaging 250 ppm U (0.025%). Then Sparton was commissioned by WildHorse Energy to assess the potential for recovering uranium from European
coal ash having 80 - 135 ppm U.
Mineral sands, mined chiefly for titanium minerals and zircon, often have a significant proportion of monazite, a rare earth mineral containing
thorium and other elements of economic significance. The minerals in the sands are subject to gravity concentration, and some concentrates are
significantly radioactive, up to 4000 Bq/kg. Dust control in mineral sand plants is the main means of limiting radiation doses to personnel.
Radioactivity in Australian mineral sands (Bq/g)
ore 0.02-0.3 0.03-0.12
concentrate 0.3-3 0-0.8
Ilmenite, rutile 0.2-2 0-0.6
Zircon 0.6-1.2 1-4
Monazite 40-250 6-30
Tantalum ores, often derived from pegmatites, comprise a wide variety of more than one hundred minerals, some of which contain uranium and/or thorium.
Hence, the mined ore and its concentrate contain both these and their decay products in their crystal lattice. Concentration of the tantalum minerals
is generally by gravity methods (as with mineral sands), so the lattice-bound radioisotope impurities, if present, will report with the concentrate.
While this has little radiological significance in the processing plant, concentrates shipped to customers sometimes exceed the Transport Code
threshold of 10 kBq/kg, requiring declaration and some special documentation, labeling and handling procedures. Some reache 75 kBq/kg.
Phosphate rock used in the production of fertilizer is a major source of naturally-occurring radioactive materials (NORM), containing uranium and
thorium. Australian phosphate rock contains up to 900 Bq/kg and imported sources contain about twice this, yielding about 1000 Bq/kg in phosphogypsum
waste streams and up to 3000 Bq/kg in the superphosphate product. In the U.S., some 50 million tonnes per year are produced and state figures average
up to 10,000 Bq/kg of total radioactivity. Processing this sometimes gives rise to measurable doses of radioactivity to people. Phosphate rocks
containing up to 120 ppm U have been used as a source of uranium as byproduct – some 17,000 tU in USA, and are likely to be so again.
European fertilizer manufacturing gave rise to discharges of phophogypsum containing significant quantities of radium-226, lead-210 and polonium-210
into the North Sea and North Atlantic. This has been overtaken by offshore oil and natural gas production in Norwegian and UK waters releasing some 10
TBq/yr of radium-226, radium-228, and lead-210—contributing 90% of alpha-active discharges in those waters (two orders of magnitude more than the
nuclear industry, and with this NORM having higher radiotoxicity).
Oil and Gas production
In the oil and natural gas industry, radium-226 (Ra-226) and lead-210 (Pb-210) are deposited as scale in pipes and equipment. If the scale has an
activity of 30,000 Bq/kg it is 'contaminated' (Victoria, Australia regulations). This means that for Ra-226 scale (decay series of 9 progeny) the
level of Ra-226 itself is 3300 Bq/kg. For Pb-210 scale (decay series of 3) the level is 10,000 Bq/kg. These figures refer to the scale, not the
overall mass of pipes or other material (cf Recycling, below). Published data (quoted in Cooper 2003) show radionuclide concentrations in scale of up
to 300,000 Bq/kg for Pb-210, 250,000 Bq/kg for Ra-226 and 100,000 Bq/kg for Ra-228. In Cooper 2005, the latter two maxima are 100,000 and 40,000
Other solid NORM
Building materials can contain elevated levels of radionuclides including radium-226, thorium-232 and potassium-40, the last being most significant in
published Australian data, ranging up to 4000 Bq/kg in natural stone and 1600 Bq/kg in clay bricks and concrete. Bricks can also contain up to 2200
Bq/kg of Ra-226 (Cooper 2005).
In smelting iron ore, lead-210 and polonium-210 accumulate in dust from smelter and sinter plant operations, in the latter case to 34,000 Bq/kg at
Port Kembla, Australia.
Granite, widely used as a cladding on city buildings and also architecturally in homes, contains an average of 3 ppm (40 Bq/kg) uranium and 17 ppm (70
Bq/kg) thorium. Radiation measurements on granite surfaces can show levels similar to those from low-grade uranium mine tailings.
Radium-226 is one of the decay products of uranium-238, a uranium isotope widespread in most rocks and soils. When this radium decays it produces
radon-222, an inert gas with a half-life of almost 4 days. Radium-224 is a decay product of thorium, and it decays to radon-220, also known as thoron,
with a 54-second half-life. Because radon is so short-lived, and alpha-decays to a number of daughter products which are solid and very short-lived,
there is a high probability of its decay when breathed in, or when radon daughter products in dust are breathed in. This is a problem because alpha
particles in the lung are hazardous to human health.
Radon levels in the air range from about 4 to 20 Bq/m3. Indoor radon levels have attracted a lot of interest since the 1970s. In the US they average
about 55 Bq/m3, with an EPA action level of 150 Bq/m3. Levels in Scandinavian homes are about double the US average, and those in Australian homes
average one-fifth of those in US. Levels up to 100,000 Bq/m3 have been measured in US homes. In caves open to the public, levels of up to 25,000 Bq/m3
have been measured.
Radon also occurs in natural gas at up to 37,000 Bq/m3, but by the time the product reaches consumers, the radon has largely decayed. However, the
solid decay products then contaminate gas processing plants, and this manifestation of NORM is an occupational health issue.
Recycling and NORM
Scrap steel from gas plants may be recycled if it has less than 500,000 Bq/kg (0.5 MBq/kg) radioactivity (the exemption level). This level, however,
is one thousand times higher than the clearance level for recycled material (both seel and concrete) from the nuclear industry. Anything above 500
Bq/kg may not be cleared from regulatory control for recycling.
Decommissioning experts are increasingly concerned about double standards developing in Europe, where 30 times the dose rate from non-nuclear recycled
materials than from those out of the nuclear industry is allowed. Norway and Holland are the only countries with consistent standards. Elsewhere, a
0.3 to 1.0 mSv/yr individual dose constraint is applied to oil and natual gas recyclables, and 0.01 mSv/yr for release of materials with the same kind
of radiation from the nuclear industry.
The main radionuclide in scrap from the oil and gas industry is radium-226 (Ra-226), with a half-life of 1600 years as it decays to radon. Those in
nuclear industry scrap are cobalt-60 and caesium-137, with much shorter half-lives. Application of a 0.3 mSv/yr dose limit results in a clearance
level for Ra-226 of 500 Bq/kg, compared with 10 Bq/kg for nuclear material.
The concern arises because of the very large amounts of Tenorm (technologically-enhanced NORM) needing recycling or disposal from many sources. The
largest Tenorm waste stream is coal ash, with 280 million tonnes arising globally each year, and carrying uranium-238 and all its non-gaseous decay
products, as well as thorium-232 and its progeny. This waste is usually just buried; however, the double standard means that the same radionuclide, at
the same concentration, can either be sent to deep disposal or released for use in building materials, depending on where it comes from. The 0.3
mSv/yr dose limit is still only one-tenth of most natural background levels, and two orders of magnitude lower than those experienced naturally by
many people, who suffer no apparent ill effects
however there is no mention of man made radoactive materil including plutonium which causes many human cancers also coal ash tends to be burried where
as the release of radiation from nuclear plant accidents become air bourne and therfore more widly distributed
ps its uranium 236 which is more reactive which is being released at the japanese plant allong with plutonium which is extremly detrimental to humans
and easly absorbed through the resparitory system os please forgive my spelling i am slightly dislexic