Improved health effects models have been developed for assessing the early effects, late somatic effects and genetic effects that might result from low-LET radiation exposures to populations following a major accident in a nuclear power plant. All the models have been developed in such a way that the dynamics of population risks can be analyzed. Estimates of life years lost and the duration of illnesses were generated and a framework recommended for summarizing health impacts. Uncertainty is addressed by providing models for upper, central and lower estimates of most effects. The models are believed to be a significant improvement over the models used in the U.S. Nuclear Regulatory Commission's Reactor Safety Study, and they can easily be modified to reflect advances in scientific understanding of the health effects of ionizing radiation.

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%.

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-In the latter half of 2005, the U.S. Environmental Protection Agency (USEPA) 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 lo4 to lo6 years after closure. The proposed standard was based on the difference in the estimated total dose rate from natural background in the Amargosa Valley and the "average annual background radiation" for the State of Colorado. As defined by the USEPA, ''natural background radiation consists of external exposures from cosmic and terrestrial sources, and internal exposures from indoor exposures to naturallyoccurring radon." On the basis of its assessments, the USEPA estimated that the difference in the dose rate in the two identified areas was 3.5 mSv y-l. The purpose of this review was 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 USEPA in its assessment, were based on modifications of the average values for the State of Nevada. A second observation was that the conversion factor 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 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 USEPA estimate of the average dose rate for residents of the Amargosa Valley, due 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 high cosmic radiation dose rate, and the fact the size of its population is comparable to that of Amargosa Valley. For completeness, similar comparisons of the estimated dose rate in the Amargosa Valley to those for residents of Leadville, CO, the States of Colorado and Nevada. The estimated dose rates in Leadville, the State of Colorado, and the State of Nevada, were higher than those in the Amargosa Valley by 4.09,2.62, and 1.01 mSv y-', respectively. Associated uncertainties were 1 highest for the estimated dose rates due to exposures to radon and its decay products. The overall uncertainty in the dose estimates, including the errors in the radon dose coefficient, could be as high as 142%.

C and Ra 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 C, the postulated condition was that an annual fractional release of 10 of its total remaining inventory occurs beginning at 10,000 y after repository closure. For Ra, the same fractional release rate was assumed, but in this case it was presumed to occur when the Ra inventory was projected to reach a maximum at more than 10 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 Ra, or derived, in the case of C, on the basis of the regulatory dose rate limit. Due to the small inventory of C 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 Th, the precursor of Ra, and the correspondingly small quantities of higher atomic number actinides that could, through decay, produce additional quantities of Th, 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 Ra. At the same time, however, it must be recognized that, in this case, the regulations require that any contributions of naturally occurring Ra and Ra already present in the ground water must be included in the determination of compliance. If this is done, the total concentration of Ra, combined with the naturally occurring concentration of Ra, 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 C, using the coefficients in Federal Guidance Report (FGR) No. 13, was 4.15 muSv y, less than 3% of the IPS. For Ra, the comparable estimate at the time of maximum inventory, excluding in this case the contributions from naturally occurring Ra and Ra, was 7.39 muSv y, representing about 5% of the IPS. Based on the value assumed for the fractional release rate (10 y), it was concluded that neither C nor Ra will be significant in terms of either the applicable GWPS or the IPS. While it was recognized that, due to the time spa...