J.G. HUNT
Institute of Radiation Protection and Dosimetry, Rio de Janeiro, Brazil
Email: [email protected] Abstract
Industries and other human activities that process NORM give rise to occupational and public exposures.
To help estimate the average and collective annual effective doses due to these activities, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) published in 2008 the results of literature reviews and expert group reports on the sources and effects of radiation, including NORM sources. It turns out that for occupationally exposed workers the average annual dose in NORM industries and activities is around 3 mSv and the annual collective dose is around 40 000 man Sv. The information on public exposure from these activities is sparser, but maximum annual doses can exceed 1 mSv.
1. INTRODUCTION
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has periodically compiled data and trends on occupational and public exposure due to industrial and other activities involving NORM. This paper summarizes the information available in UNSCEAR up to the present date. The information is based on the 2008 UNSCEAR report Sources and Effects of Ionizing Radiation [1]. UNSCEAR envisages compiling exposure information in due course for an update to the 2008 sources report after completing a highly pertinent re-evaluation of the risks of lung cancer due to exposure to radon. The IAEA also has a number of publications available on radiation protection and NORM [2]
2. OCCUPATIONAL EXPOSURE
The data up to 2002 summarized in Fig. 1 shows clearly that, although an occupationally exposed worker in an industry or activity exposed to natural radiation receives an average annual effective dose of around 3 mSv, owing to the large number of workers so exposed the annual collective dose for these workers is considerably higher than that from the sum of all other occupationally exposed workers. The majority of this annual collective dose comes from mining activities (other than uranium mining and ore processing), as can be seen from Table 1.
The number of mine workers occupationally exposed depends on the economic activity in this area and it is expected that this annual collective dose will increase as new information on occupational exposure becomes available from mining operations where individual monitoring had not previously been carried out and effective dose estimation was not available.
Other major sources of occupational exposure to NORM are found in the oil and gas sector, phosphate fertilizer production, zircon milling, rare earth and titanium processing industries.
Apart from mining and ore processing, other activities that result in occupational NORM exposure are shown in Table 2.
The factors that affect uncertainties in NORM exposure data are the reliability of individual monitoring methods and data recording, evaluation of anomalies, such as unexpectedly high or low values, subtraction of background doses, the choice as to who should be monitored and whether or not internal exposures are included in the effective dose estimate.
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FIG. 1. Summary of number of monitored persons and the annual collective and average effective doses to occupationally exposed workers from 1975 to 2002.
133 TABLE 1. ANNUAL DOSES RECEIVED BY COAL MINE WORKERS IN CHINA
Type of coal mine Average annual effective dose (mSv) Collective dose (man Sv)
Large sized 0.28 280
Medium sized 0.55 550
Small-sized 3.3 13 200
Bone coal 10.9 545
Average 2.4 14 600
TABLE 2. OCCUPATIONAL RADIATION PROTECTION DATA FROM GERMANY FOR RADON INHALATION IN WORKPLACES OTHER THAN MINES
Workplace Period
No. of workers Annual collective effective dose
(man Sv)
Average annual effective dose (mSv)
Monitored Measurably exposed
Monitored workers
Measurably exposed workers
Spas 1995–1999 2 2 0.01 4.77 4.77
2000–2002 4 2 0.01 4.09 4.47
Waterworks 1995–1999 128 75 0.24 1.85 3.12
2000–2002 81 47 0.11 1.39 2.50
Tourist caves and visitor mines
1995–1999 135 101 0.31 2.26 3.01
2000–2002 135 87 0.23 1.76 2.63
3. PUBLIC EXPOSURE TO NORM
The public is exposed to NORM through uranium mining and ore processing, non-uranium metal mining and smelting, the phosphate industry, coal mines and power generation from coal, oil and gas extraction, rare earth and titanium oxide industries, zirconium and ceramic industries, applications using natural radionuclides (typically radium and thorium) and the disposal of building material. For public exposure the data are very sparse and site-specific.
The main exposure pathways are through the inhalation of dust and radon, contamination of groundwater with radium isotopes and external exposure to slag with high thorium content.
For uranium mining and ore processing, the most relevant sources of exposure are (i) radon and its progeny released from open pits and underground mines, (ii) in situ leaching operations and (iii) process tailings. The release of 226Ra to liquid pathways is also relevant and careful consideration must be given to the use of contaminated land for building. For the phosphate industry, the processing of phosphate rock may generate emissions of 238U and 226Ra.
Phosphogypsum stacks, the use of phosphate fertilizer and the use of phosphogypsum in building materials are also possible sources of exposure to radon. Table 3 shows estimated doses to the public due to industrial releases of NORM in the United Kingdom.
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TABLE 3. DOSES TO THE PUBLIC DUE TO INDUSTRIAL RELEASE OF NORM IN THE UNITED KINGDOM
Industry Discharge route Pathway Annual dose (μSv)
Critical group General public Coal-fired power
station
Atmospheric release via stack
All 1.5 0.1
Building material made from ash
Radon inhalation External
600 900 Oil and gas
extraction
Authorized discharges to sea, and scales
Ingestion of seafood and external exposure due to fishing gear
<30
Gas-fired power station
Atmospheric releases via stack
All 0.75 0.032
Steel production Atmospheric releases via stack
All <100 <2
Building material made from slag
Radon inhalation External
550 800 Zircon sands Atmospheric
releases via stack
Inhalation <1 <1
4. SUMMARY OF OCCUPATIONAL AND PUBLIC EXPOSURES
For occupational exposures the collective dose is around 40 000 man Sv annually (2008), with around 17 000 man Sv from coal mining, 14 000 man Sv from other mining and 6 000 man Sv from radon in other workplaces. The average individual dose in these activities is about 3 mSv (2008). There are wide variations depending on local circumstances; some mines give rise to annual effective doses of tens of millisieverts, depending on the type of mine, geology and working conditions.
Public exposure is normally low, but considerable numbers of people can be exposed.
Doses of up to a few millisieverts annually can be measured for a few scenarios, e.g. use of sludge from water treatment as fertilizer, use of waste products for building material. There is at present no consistent approach to make a reliable global assessment of inventories and exposures. There is a diversity of ores with low levels of radionuclides from the uranium and thorium chains concentrated in products, by-products and waste and conventional mining that leads to huge volumes of material with enhanced concentrations of radionuclides of natural origin, making a challenge for disposal operations and site restoration.
REFERENCES
[1] UNITED NATIONS SCIENTIFIC COMMITTEE ON THE EFFECTS OF ATOMIC RADIATION, Sources and Effects of Ionizing Radiation, UNSCEAR 2008 Report to the General Assembly, Vol. I, Annex B: Exposures of the public and workers, United Nations, New York (2010).
[2] INTERNATIONAL ATOMIC ENERGY AGENCY, Publications on Exposure to Radiation from Natural Sources, https://www-ns.iaea.org/publications/norm-publications.asp.
135 Poster Presentation