CONCLUSIONS

It is clear that the Radiation Assessments Corporation has developed a scientific document that can also be used by the Centers for Disease Control and Prevention to determine whether the estimated population doses were sufficient to proceed with an epidemiologic study in the area surrounding the Fernald Feed Materials Production Center. The document contains models and techniques that, although not widely accepted as conventional, show ingenuity in concept and application that might ultimately be important, for example, with respect to decontamination, decommissioning, dose reconstruction, and aerosol physics.

The National Research Council committee believes that the dose-reconstruction approach used provides reasonable estimates of environmental releases of uranium. However, there appears to have been some overestimation of radon releases. Radon is the radionuclide found to be the main contributor to the dose to the lung, the most important organ in this study, so the potential overestimation of the dose is of concern. Assumptions made in estimating risk such as dose-conversion factors and age and sex effects tend, in the committee's view, to overestimate the risk of lung cancer. The overestimates provide the public with information on only the highest possible exposures which would lead to the highest possible risk. Although it is difficult to determine the precise extent of overestimation, it might be by a factor of 4 to 6 and needs to be corrected. The calculations of radon releases, dose conversions, and age and sex weighting factors need to be reevaluated so as to arrive at more-realistic risk estimates.

The project has shown that the most-important combination of source and pathway for radiation exposure is through airborne radon released from the K-65 storage silos, rather than to uranium releases, as was previously believed. Airborne-radon exposures decreased markedly after 1979, the year that the silo vents were sealed; thus, the most-important source of exposure to radioactive materials has now been controlled. Uranium releases to off-site areas account for a smaller contribution to historical dose estimates; this was not previously understood.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 26
A REVIEW OF THE RADIOLOGICAL ASSESSMENTS CORPORATION'S FERNALD DOSE RECONSTRUCTION REPORT CONCLUSIONS It is clear that the Radiation Assessments Corporation has developed a scientific document that can also be used by the Centers for Disease Control and Prevention to determine whether the estimated population doses were sufficient to proceed with an epidemiologic study in the area surrounding the Fernald Feed Materials Production Center. The document contains models and techniques that, although not widely accepted as conventional, show ingenuity in concept and application that might ultimately be important, for example, with respect to decontamination, decommissioning, dose reconstruction, and aerosol physics. The National Research Council committee believes that the dose-reconstruction approach used provides reasonable estimates of environmental releases of uranium. However, there appears to have been some overestimation of radon releases. Radon is the radionuclide found to be the main contributor to the dose to the lung, the most important organ in this study, so the potential overestimation of the dose is of concern. Assumptions made in estimating risk such as dose-conversion factors and age and sex effects tend, in the committee's view, to overestimate the risk of lung cancer. The overestimates provide the public with information on only the highest possible exposures which would lead to the highest possible risk. Although it is difficult to determine the precise extent of overestimation, it might be by a factor of 4 to 6 and needs to be corrected. The calculations of radon releases, dose conversions, and age and sex weighting factors need to be reevaluated so as to arrive at more-realistic risk estimates. The project has shown that the most-important combination of source and pathway for radiation exposure is through airborne radon released from the K-65 storage silos, rather than to uranium releases, as was previously believed. Airborne-radon exposures decreased markedly after 1979, the year that the silo vents were sealed; thus, the most-important source of exposure to radioactive materials has now been controlled. Uranium releases to off-site areas account for a smaller contribution to historical dose estimates; this was not previously understood.

OCR for page 26
A REVIEW OF THE RADIOLOGICAL ASSESSMENTS CORPORATION'S FERNALD DOSE RECONSTRUCTION REPORT The project team has made substantial progress in developing final population dose estimates that could facilitate making decisions on the efficacy of an epidemiologic or health-effects study in the populations living near Fernald. The likely doses that residents around Fernald could have received were developed, with public input, for 9 scenarios that were thought to be generally typical of longer-term, younger residents, although hundreds of scenarios are possible. The dose scenarios are not specific nor do they provide a likely distribution of individual doses; but they might yield an upper-bound estimate for a potential epidemiologic study. The methods developed for these 9 scenarios could also be used to estimate individual doses, but they were not intended to be and were not so applied, because the necessary information for such determinations is expected to be developed in the context of an epidemiologic study. In the final analysis, errors in the input data will add considerable variability to individual risk estimates derived for real, as opposed to hypothetical, people. This should be made clear in the RAC report. Given the complexity of individual circumstances, not all individuals would fit into any of the selected 9 scenarios. It might be useful to individuals and the community as a whole to make available a questionnaire that could yield more relevant estimates of individual doses. Dose modeling for individuals requires such inputs as date of birth, place(s) of residence and calendar years lived there, locations of schooling and work, dietary habits (percentage of local produce and so on), and amounts and types of outdoor activities. Doses to individuals and the geographic-demographic distributions of residents would permit an estimate of the distribution of doses to the population. If the results of this dose reconstruction or the data from future dose reconstructions are to be used to determine whether an epidemiologic study should be undertaken, 5 recommendations seem warranted: Develop and clearly articulate the objectives of the dose-reconstruction effort. The objectives might include development of dose distributions to evaluate the feasibility of an epidemiologic study, of methods to implement the epidemiologic study, of ranges of potential doses to inform the public, and of individual-dose estimates for the members of the community.

OCR for page 26
A REVIEW OF THE RADIOLOGICAL ASSESSMENTS CORPORATION'S FERNALD DOSE RECONSTRUCTION REPORT Obtain community concurrence in the objectives of the study and develop a process for community involvement in their implementation. Design an iterative study plan for collecting the dosimetric and epidemiologic data needed to determine feasibility and desirability of proceeding. Determine early in the process the kinds of data needed to meet the articulated objectives. The study should be designed to provide all needed data. Resources should be allocated to reduce the uncertainty of the model used. Past efforts tended to evaluate some parameters in considerable detail, whereas others were based on published data that were highly uncertain and of questionable relevance. Put into place a study to evaluate and compare past dose-reconstruction efforts. The evaluation might include such issues as whether the desired information was obtained, whether it was presented in the best way (for example, in models at Hanford or exposure scenarios at the Fernald Feed Materials Production Center), and whether public involvement was appropriate.