Natural airborne radioactivity

The utilization of gamma spectrometry for the quantitative determination of low level activity radionuclides in the natural environment is limited because the influence of the natural geochemical background is very strong, but the technique is often used in the study of airborne radioactivity [6, 7]. Low-level gamma spectrometry is used principally to determine the activity of nuclides such as Co, Cs, and Pb (Fig. 15.1). 

Airborne Radioactivity Area An area where the measured concentration of airborne radioactivity, above natural background concentrations, exceeds either (1) 10% of the derived air concentration (DAC) averaged over 8 hours or (2) a peak concentration of 1 DAC. DAC values are contained in the SNL RPPM. 

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

The presence of radiation in the workplace - which is an inevitable consequence of the radioactivity of uranium - requires that additional safety precautions be taken over and above those observed in other similar workplaces. There are generally three sources from which radiation exposure may occur (i) radiation emitted from uranium ore in-situ and/or during handling (ii) airborne radiation resulting from the decay of radon gas released from the ore and uranium dust and (iii) contamination by ore dust or concentrate. Radiation levels around uranium mining and milling facilities are quite low - for the most part only a few times the natural background levels - and they decrease rapidly as the distance from... 

Table 2-8 shows the mass equivalents for natural and depleted uranium for radiation levels that caused potential radiological effects in rats exposed once for 100 minutes to airborne 92.8% enriched uranium with an estimated specific activity of 51.6 pCi/g (Morris et al. 1989). These mass equivalent values for natural and depleted uranium for the minimal concentration of radioactivity that is expected to induce potential radiological effects are well above levels that would be expected to be inhaled or ingested. In addition, the mass equivalents for natural and depleted uranium for potential radiological effects are 3,600 and 76,500 times higher, respectively, than the occupational exposure limits (short-term exposure) recommended by the National Institute for Occupational Safety and Health (NIOSH 1997). Therefore, MRLs for uranium based on studies that used enriched uranium are inappropriate. 

Szabo Z, Zapecza OS. 1987. Relation between natural radionuclide activities and chemical constituents in ground water in the Newark Basin New Jersey USA. In Graves B, ed. Radon in ground water, radon, radium and other radioactivity in ground water Hydrogeologic impact and application to indoor airborne contamination Proc National Water Well Association conference, Somerset, NJ, April 7-9, 1987. Chelsea, MI Lewis Publishers, Inc., 283-308. 

Carbon-14 collection. Carbon-14 is formed in nature by cosmic-ray interactions. It is in all carbon-containing compounds that are in equilibrium with C in air at a specific activity of 0.23 Bq g carbon. Concentration measurements in carbon-containing compounds that are no longer at equilibrium with air, such as dead trees, are used to determine their age —the time period since the end of equilibrium with airborne carbon—in terms of the fractional radioactive decay. Huctuations of cosmic-ray production of C in air over the centuries must be considered in this determination (NCRP 1985a). Carbon-14 is also produced at low rates in nuclear reactors, mostly by the (n,p) reaction with and the (n,o ) reaction with O. 

This section summarizes the methods used to evaluate and quantify the consequences of operational accidents, natural phenomena events, and external events selected in Section 3.3.2.3.5, Accident Selection as DBAs. Consequences to the public and the environment stem from airborne releases of radioactive material since no liquid or solid radioactive material would be released in the selected accidents. The airborne pathway is of primary interest for releases from nonreactor nuclear facilities according to DOE-STD-1027-92 (DOE 1997). Exposure to direct or scattered radiation is a hazard only for workers due to the distance to the public. 

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