Natural radiation exposure

Sinnaeve, J., Olast, M. and McLaughlin, J., Natural Radiation Exposure Research in the Member States of the European Community State of the Art and Perspectives. Presented at APCA Speciality Conference on Indoor Radon Philadelphia, U.S.A. (Feb. 1986). 

The exposure to ionizing radiation from natural sources is continuous and unavoidable. For most individuals, this exposure exceeds that from all human-made sources combined (UNSCEAR 2000a). The two main contributors to natural radiation exposures are high-energy cosmic ray particles incident on the earth s atmosphere and radioactive nuclides that originate in the earth s crust and are present everywhere in the environment, including the human body itself. 

Wrixon, A.D. et al. (1988) Natural radiation exposure in UK dwellings, Report NRPB-R190. Chilton, Oxon., National Radiological Protection Board. 

In some cases, technology helps to reduce the natural radiation exposure. For example, when drinking water supplies are drawn from surface waters, the use of water-purification processes brings about a decrease in the concentration of radium and other naturally occurring radioactive elements. Another example is the burning of fossil fuel, which reduces the specific activity of C in the biosphere and therefore lowers the doses from those radionuclides. 

A wealth of new information about radiation exposure over the past decade prompted the revision of the BSS. First and foremost, a study of the biological effects of radiation doses received by the survivors of the atomic bombing of Hiroshima and Nagasaki suggested that exposure to low-level radiation was more likely to cause harm than previously estimated. Other developments—notably the nuclear accident at Three Mile Island in 1979 and that at Chernobyl in 1986, with its unprecedented transboundary contamination—had a profound effect on the public perception of the potential danger from radiation exposure. There were serious accidents with radiation sources used in medicine and industry in Mexico, Brazil, El Salvador and other countries. In addition, more has been discovered about natural radiation—such as household radon—as a cause of concern for health. Finally, natural radiation exposures of workers such as miners, who were not thought of as radiation workers, were discovered to be much higher than had been realised. 

The genetically significant radiation exposure of the population (Table 7.4) by natural sources (approximately 110 mrem/a) is roughly twice as much as the mean radiation exposure by artificial sources. The radiation load through X-ray diagnosis constitutes the major part of the artificial radiation the population is exposed to. The contribution from fallout from nuclear experiments is less than 1% of the natural radiation exposure. Exposure through nuclear facilities is assumed to be of the same magnitude. 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

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. 

For radiation doses <0.5 Sv, there is no clinically observable iacrease ia the number of cancers above those that occur naturally (57). There are two risk hypotheses the linear and the nonlinear. The former implies that as the radiation dose decreases, the risk of cancer goes down at roughly the same rate. The latter suggests that risk of cancer actually falls much faster as radiation exposure declines. Because risk of cancer and other health effects is quite low at low radiation doses, the iacidence of cancer cannot clearly be ascribed to occupational radiation exposure. Thus, the regulations have adopted the more conservative or restrictive approach, ie, the linear hypothesis. Whereas nuclear iadustry workers are allowed to receive up to 0.05 Sv/yr, the ALARA practices result ia much lower actual radiatioa exposure. 

The ineident eommander may rely on visual observation of plae-ards, labels, and manifests and information gathered during the response. Obtaining air measurements with monitoring equipment for toxie eon-eentrations of vapors, partieulates, explosive potential, and the possibility of radiation exposure is important for determining the nature, degree, and extent of the hazards [2]. 

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... 

Bosnjakovic, B., P.H. van Dijkum, M.C. O Riordan, and J. Sinnaeve, eds., Proceedings of Exposure to Enhanced Natural Radiation and Its Regulatory Implications, Sci. Total Environ., Volume 45 (1985)... 

Jacobi, W. and Paretzke H.G. 1985, Risk Assessment for Indoor Exposure to Radon Daughters, In Proceedings, Seminar on Exposure to Enhanced Natural RAdiation and Its Regulatory Implications, Maastricht, the Netherlands, March 25-27, Elsvier Science Publisher, Amsterdam. 

Castren, 0., The contribution of bored wells to respiratory radon daughter exposure in Finland. Proc. of Symposium on Natural Radiation Environment, (C0NF- 780422, vol.2.) pp. 1364-1370, Houston, Texas (1978). 

Reineking, A., Becker K.H. and Porstendorfer, J., Measurement of the Unattached Fractions of Radon Daughters in Houses, Presented to the Seminar on Exposure to Enhanced Natural Radiation and its Regulatory Implications, Maastricht, The Netherlands (1985). 

Many states in the U.S. are currently involved in large scale surveys to measure radon levels in homes in an attempt to assess the environmental risk from radon and radon daughter exposure. Radon daughters deliver the largest radiation exposure to the population and it is estimated that 0.01% of the U.S. population (23,000 persons) are exposed from natural sources to greater than those levels allowed occupationally (4 WLM/yr) (NCRP, 1984). 

The calculation of effective dose equivalent is sometimes used even when reporting values for natural radioactivity. The concept of effective dose equivalent was developed for occupational exposures so that different types of exposure to various organs could be unified in terms of cancer risk. It is highly unlikely that the general population would require summation of risks from several sources of radiation exposure. 

Chameaud, J., Masse, R. and Lafuma, J., Influence of Radon Daughter Exposure at low Doses on Occurrence of Lung Cancer in Rats, in Radiation Protection Dosimetry Indoor Exposure to Natural Radiation and Associated Risk Assessment, (Clemente, G., F. et al, eds) pp.385-388, Nuclear Technology Publishing, Anacapri (1983). 

We have previously documented the methodology (Marks et al., 1985a) and presented a summary of the technique (Marks et al., 1985b) at the Maastricht, The Netherlands, Seminar on Exposure to Enhanced Natural Radiation and Its Regulatory Implications. This paper represents a synthesis of the work we have conducted to date on risk assessment at uranium mill tailings vicinity properties. 

There is an increasing concern regarding the exposure of the general population to increased levels of radon decay products in indoor air. The exposure to the public from increased levels of natural radiation has been the subject of a conference held in Maastricht, The Netherlands, in March 1985 where a number of reports were presented showing high levels of radon in the indoor environment. Other reports in this volume also demonstrate that high levels of radon are not as uncommon as had been previously thought. 

This very long half-life (1.25x1(r years) isotope comprises 0.0117 percent of all potassium. Thus, this isotope is present in all of us and has always been so. In addition, the materials around us, including the soil and the building materials, contain both potassium and the heavy naturally occurring radioactive elements thorium and uranium that contribute to a level of radiation to which we are all continuously exposed. Thus, there is always radiation exposure to the general public and we must understand the exposure due to radon in this context. The amount of radioactivity is described in units of activity. The activity is the number of decay events per unit time and is calculated as follows... 

Exposure to natural sources of radiation is unavoidable. Externally, individuals receive cosmic rays, terrestrial X-rays, and gamma radiation. Internally, naturally occurring radionuclides of Pb, Po, Bi, Ra, Rn, K, C, H, U, and Th contribute to the natural radiation dose from inhalation and ingestion. Potassium-40 is the most abundant radionuclide in foods and in all tissues. The mean effective human dose equivalent from natural radiations is 2.4 milliSieverts (mSv). This value includes the lung dose from radon daughter products and is about 20% higher than a 1982 estimate that did not take lung dose into account (Table 32.4). 

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