Dade W. Moeller

Effective removal of airborne 222Rn decay products inside buildings.

Comparisons were made of the effectiveness of various indoor air treatment methods in reducing the lung dose due to inhalation of 222Rn decay products. The comparisons were based upon measurements of the total steady-state concentrations of 218Po, 214Pb and 214Bi, and the concentrations of these nuclides not attached to particles. These measurements, which were made inside a 78-m3 room before and after air treatment, were used along with a state-of-the art lung dose model to predict reductions in the dose to the radiosensitive bronchial tissues. Results suggest that flow-through air-cleaning methods, such as filtration and electrostatic precipitation, although effective in reducing total potential alpha energy concentration, cause a greater quantity of airborne potential alpha energy to be unattached to particles. This may result in a substantial increase in the dose to bronchial tissues. The optimal form of air treatment appears to be a combination of nonuniform positive space charge generated by an ion generator and enhanced convection from a fan. This combination of air treatment gave reductions in the mean dose to the bronchial tissues of up to 87%.

The Advisory Committee on Reactor Safeguards.

For over 25 yr, the Advisory Committee on Reactor Safeguards has had primary responsibility for conducting independent reviews and evaluations of the health and safety aspects of nuclear power reactors, chemical processing plants, and associated activities within the nuclear fuel cycle. Through the support of its Subcommittees and Working Groups, the Committee currently issues summary reports on 25-30 nuclear facilities and safety related questions each year. Topics discussed in this paper include the views and thoughts of the Committee with respect to emergency core cooling systems, fuel densification, anticipated transients without scram, reactor pressure vessel failure, turbine missiles, steamline breaks, environmental monitoring, waste management and seismicity. As will be noted, major portions of the activities, interests and responsibilities of the Committee are of direct importance to health physicists and the radiation protection profession.

Comparison of natural background dose rates for residents of the Amargosa Valley, NV, to those in Leadville, CO, and the states of Colorado and Nevada.

In the latter half of 2005, the U.S. Environmental Protection Agency (U.S. EPA) published a Proposed Rule (40 CFR Part 197) for establishing a dose rate standard for limiting radionuclide releases from the proposed Yucca Mountain high-level radioactive waste repository during the time period from 104 to 106 years after closure. The proposed standard was based on the difference in the estimated dose rate from natural background in the Amargosa Valley and the “average annual background radiation” for the State of Colorado. As defined by the U.S. EPA, “natural background radiation consists of external exposures from cosmic and terrestrial sources, and internal exposures from indoor exposures to naturally-occurring radon.” On the basis of its assessments, the U.S. EPA estimated that the difference in the dose rate in the two identified areas was 3.5 mSv y−1. The purpose of this paper is to provide an independent evaluation and review of this estimate. One of the first observations was that, because site-specific dose rate measurements for the Amargosa Valley “were not available,” the dose rates for various sources of natural background in that area, used by the U.S. EPA in its assessment, were based on modifications of the average values for the State of Nevada. A second observation was that the conversion coefficient applied in estimating the dose rates due to exposures to indoor radon and its decay products was a factor of >2 higher than the currently internationally accepted value. Further review revealed that site-specific data for many natural background sources in the Amargosa Valley were available. One particularly important observation was that about 91% of the residents of that area live in mobile homes which, due to their construction and design, have indoor radon concentrations comparable to, or less than, those outdoors. For that reason, alone, the U.S. EPA estimate of the average dose rate for residents of the Amargosa Valley, due to exposures to indoor radon, was not valid. For purposes of the comparisons in this paper, site-specific dose rates were estimated for all major natural background sources of exposure to residents of the Amargosa Valley, and those in Leadville, CO. The latter community was selected for comparison because of its altitude (3,200 m) and accompanying relatively high cosmic radiation dose rate, and the fact the size of its population is comparable to that of the Amargosa Valley. Another reason for this selection was that a comparison of the average natural background dose rate in the Amargosa Valley to that for the State of Colorado is not suitable because it fails to consider those locations within the State that have dose rates that are higher than the average. Nonetheless, for completeness, and to provide a number that could be compared to the U.S. EPA estimated difference, similar comparisons of the estimated dose rate in the Amargosa Valley to those for average residents of the States of Colorado and Nevada were included in the assessments that follow. The outcome showed that the estimated dose rates in Leadville, the State of Colorado, and the State of Nevada, were higher than those in the Amargosa Valley by 3.94 ± 1.09, 2.54 ± 2.18, and 0.95 ± 0.82 mSv y−1, respectively. Associated uncertainties were highest for the estimated dose rates due to exposures to radon and its decay products. Had the systematic errors in the radon dose conversion coefficient and the random distribution in radon concentrations been included, the overall uncertainty in the total dose rate estimates could have been as high as 150%.

Limitations on upper bound dose to adults due to intake of 129I in drinking water and a total diet-implications relative to the proposed Yucca Mountain high level radioactive waste repository.

Abstract— The purpose of this report is to comment on the potential annual doses due to the intake by adults of 129I, an important radionuclide in the proposed high-level radioactive waste repository at Yucca Mountain. An often overlooked, but significant, factor is that, in this case, the ground water, which would be the primary transport vehicle for any releases, contains relatively high concentrations of stable iodine (127I); in fact, the median concentration in the ground water in the vicinity of the proposed repository is 5.0 μg L−1. In comparison, the maximum concentration of 129I in the ground water, due to potential releases of 129I during the first 10,000 y following closure of the repository, is estimated to be ~3.7 × 10−7 Bq L−1 (~10−5 pCi L−1). This would result in a 127I to 129I ratio in the water of almost 90 million to one. Assuming no other sources of these two isotopes were being consumed, this would place an upper bound on the annual committed thyroid dose of 1.2 × 10−5 mSv (1.2 × 10−3 mrem), less than one thousandth of the Ground Water Protection Standard of 4 mrem y−1. When the additional intake of stable and radioactive iodine in other components of the diet is considered, the overall ratio of 127I to 129I would be more than 2 billion to one. The would place an upper bound on the annual committed effective dose of ~2.5 × 10−8 mSv (~2.5 × 10−6 mrem), less than one millionth of the Individual Protection Standard of 0.15 mSv (15 mrem).

Chemical and radioactive carcinogens in cigarettes: associated health impacts and responses of the tobacco industry, U.S. Congress, and federal regulatory agencies.

210Po and 210Pb were discovered in tobacco in 1964. This was followed by detailed assessments of the nature of their deposition, and accompanying dose rates to the lungs of cigarette smokers. Subsequent studies revealed: (1) the sources and pathways through which they gain access to tobacco; (2) the mechanisms through which they preferentially deposit in key segments of the bronchial epithelium; and (3) the fact that the accompanying alpha radiation plays a synergistic role in combination with the chemical carcinogens, to increase the fatal cancer risk coefficient in cigarette smokers by a factor of 8 to 25. Nonetheless, it was not until 2009 that Congress mandated that the Food and Drug Administration require that the cigarette industry reveal the presence of these carcinogens. In the meantime, cigarette smoking has become not only the number one source of cancer deaths in the United States, but also a major contributor to heart disease and other health impacts. If the latter effects are included, smoking is estimated to have caused an average of 443,000 deaths and 5.1 million years of potential life lost among the U.S. population each year from 2000 through 2004. The estimated associated collective dose is more than 36 times that to the workers at all the U.S. nuclear power plants, U.S. Department of Energy nuclear weapons facilities, and crews of all the vessels in the U.S. Nuclear Navy. This unnecessary source of lung cancer deaths demands the utmost attention of the radiation protection and public health professions.

Environmental health physics: 50 years of progress

Environmental health physics is an interdisciplinary field, involving study of the release, transport, and fate of radioactive material in the environment. Further, it addresses the interaction of humans with radioactive materials within the ambient (outdoor) environment and with the environments associated with modern technology and lifestyles. It also involves both naturally occurring and artificially produced radionuclides with the former generally being by far the highest source of exposure. In fact, doses from naturally occurring radionuclides are increasingly being used as a benchmark for the establishment of dose rate limits for people. Because of the pioneering work of early environmental health physicists, models exist today that can be used to assess the potential impacts of new nuclear facilities prior to their operation. In fact, these people represent the branch of the health physics profession who conducted environmental monitoring programs and performed the associated research studies that led to the identification of the principal radionuclides of interest, the major pathways and mechanisms through which they expose people, and the doses that may result from radioactive materials in the natural and technologically enhanced environments. One of their most important contributions was the identification and quantification of many of the key parameters that serve as input to such models. Monitoring of nuclear weapons development facilities used during and after World War II was the initial stimulus for the establishment of environmental health physics programs. Thereafter, these programs were expanded both nationally and globally, as a result of the atmospheric weapons testing programs of nations such as France, the People’s Republic of China, the former Soviet Union, the United Kingdom, and the United States. Additional stimuli were provided by the development of the commercial nuclear power industry. Current environmental programs, particularly within the U.S., focus on decontamination and decommissioning of dormant facilities from these earlier defense and commercial programs. The range of the environmental health physics aspects of these activities is the subject of this paper. Presented at the end of the paper is a summary of some of the more important lessons that have been learned. As will be noted, this is an exciting field that will present challenges to health physicists for years to come.

Significance of 14C and 228Ra in terms of the proposed Yucca Mountain high-level radioactive waste repository.

14C and 228Ra are two of the radionuclides that have either been identified as being potentially significant in terms of releases from the proposed Yucca Mountain high-level radioactive waste repository, or are specifically cited for consideration and evaluation in the regulations promulgated by the U.S. Nuclear Regulatory Commission. The purpose of this study was to estimate the concentrations and associated doses for these two radionuclides, if released under conditions of a scenario assumed to apply to a repository containing some of the features of the one proposed at Yucca Mountain, NV, and to compare these estimates to the regulatory limits for that facility. For 14C, the postulated condition was that an annual fractional release of 10−5 of its total remaining inventory occurs beginning at 10,000 y after repository closure. For 228Ra, the same fractional release rate was assumed, but in this case it was presumed to occur when the 228Ra inventory was projected to reach a maximum at more than 108 y after repository closure. The estimated concentrations and doses were, in turn, compared to the concentration limit, specified in the Ground Water Protection Standards (GWPSs) in the case of 228Ra, or derived, in the case of 14C, on the basis of the regulatory dose rate limit. Due to the small inventory of 14C in the waste, and its short half-life relative to the performance period evaluated, its estimated concentration in the ground water would be slightly more than 4% of the derived GWPS. Due to the relatively small initial inventory of 232Th, the precursor of 228Ra, and the correspondingly small quantities of higher atomic number actinides that could, through decay, produce additional quantities of 232Th, its estimated concentration in the ground water would be less than 3% of the GWPS, leaving the remaining portion of the limit for potential contributions from 226Ra. At the same time, however, it must be recognized that, in this case, the regulations require that any contributions of naturally occurring 226Ra and 228Ra already present in the ground water must be included in the determination of compliance. If this is done, the total concentration of 228Ra, combined with the naturally occurring concentration of 226Ra, would be about 10.5% of the limit. In a similar manner, the committed doses due to the annual consumption of each of these two radionuclides in ground water and food, produced in the local biosphere, were evaluated in terms of the Individual Protection Standard (IPS). Based on these analyses, the estimated effective dose for 14C, using the coefficients in Federal Guidance Report (FGR) No. 13, was 4.15 &mgr;Sv y−1, less than 3% of the IPS. For 228Ra, the comparable estimate at the time of maximum inventory, excluding in this case the contributions from naturally occurring 226Ra and 228Ra, was 7.39 &mgr;Sv y−1, representing about 5% of the IPS. Based on the value assumed for the fractional release rate (10−5 y−1), it was concluded that neither 14C nor 228Ra will be significant in terms of either the applicable GWPS or the IPS. While it was recognized that, due to the time spans involved, these analyses were primarily an academic exercise, it is believed that the perspectives and accompanying insights are useful.

Application of the Supreme Court's Daubert criteria in radiation litigation.

In 1993, the U.S. Supreme Court set forth the standard for determining the admissibility of expert scientific evidence in litigation. This standard is known as the Daubert criteria, named after the pertinent case, Daubert v. Merrell Dow Pharmaceuticals, Inc. The Daubert criteria require the courts to determine whether an expert’s testimony reflects scientific knowledge, whether his/her findings are derived by the scientific method, and whether the work product is based on good science. The Daubert criteria are especially important in radiation litigation because issues involving radiation doses and effects are often complex and thus a jury will typically rely heavily on the analysis and opinions of experts. According to the Daubert criteria, scientific opinions must be based on a methodology that has a valid, testable hypothesis; has been subject to peer review; and is generally accepted in the scientific community. Additionally, the expert must be qualified to present opinions based on the methodology. Although the application of the Daubert criteria in radiation litigation is highly dependent on the specific court and judge presiding over the case, there have been recent high-profile cases in which application of the criteria has resulted in the dismissal of analysis and opinions offered by scientific experts. Reasons for the dismissals have included basic scientific errors such as failure of the expert to consider all possible explanations for an observed phenomenon, the selective use of data by the expert, and the failure to acknowledge and resolve inconsistencies between the expert’s results and those of other investigators. This paper reviews the Daubert criteria as they apply to radiation litigation and provides examples of the application of the criteria from recent judgments involving the Three Mile Island and Hanford Downwinders cases.

Optimization of filtration for the reduction of lung dose from Rn decay products: Part II--Experimental.

Research was performed to determine the validity of a model developed to theoretically predict the optimal characteristics of a recirculating filter system for minimizing the lung dose to a person breathing airborne Rn progeny. Four designs, each with different filter thicknesses, solidities, and fiber diameters, were tested to evaluate the accuracy of the model over a range of parameters. Increasing thicknesses were then tested for the most effective filter design to provide a more definitive comparison of experimental data and model predictions for this key parameter. The experimental data supported the conclusion that the most effective design was a thin filter of low solidity composed of coarse fibers. Although the maximum reduction in the dose-equivalent rate observed in these experiments was 50%, this was largely due to constraints on the experimental arrangements. With properly constructed filter units, much better removal efficiencies can undoubtedly be achieved.

Optimization of filtration for reduction of lung dose from Rn decay products: Part I--Theoretical.

A theoretical model was developed for the optimization of filter characteristics that would minimize the dose from the inhalation of Rn decay products. Modified forms of the Jacobi-Porstendorfer room model and the Jacobi-Eisfeld lung dose model were chosen for use in the mathematical simulation. Optimized parameters of the filter were the thickness, solidity, and fiber diameter. For purposes of the calculations, the room dimensions, air exchange rate, particle-size distribution and concentration, and the Rn concentration were specified. The resulting computer-aided optimal design was a thin filter (the minimum thickness used in the computer model was 0.1 mm) having low solidity (the minimum solidity used was 0.5%) and large diameter fibers (the maximum diameter used was 100 microns). The simulation implies that a significant reduction in the dose rate can be achieved using a well-designed recirculating filter system. The theoretical model, using the assumption of ideal mixing, predicts an 80% reduction in the dose rate, although inherent in this assumption is the movement of 230 room volumes per hour through the fan.