Letter Report - Issues Regarding the Hanford Environmental Dose Reconstruction (HEDR) Atmospheric I-131 Pathway Models (1999) / Chapter Skim
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NRC Letter Report
NRC Letter Report
Pages 1-8
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Are the HEDR models "valid" for calculating a range of thyroid doses to representative people and real individuals for I-131 released to the atmosphere? Although the National Research Council committee has been reviewing various components of the ~DR study for some time, its previous charges have not been those specifically identified above.
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A second report prepared by Cochran entitled "Calibration of the Hanford Environmental Dose Reconstruction using Vegetation Data: A Revised Report" (dated March 2X, 19961. Those reports challenge specific aspects of the Hanford Environmental Dose Reconstruction, with particular criticism of the discrepancy between the vegetation measurements (principally sagebrush)
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Statistical methods have been proposed to provide validation of models when there is no definitive outcome measure, but rather only outcome measures with uncertainty. However, these statistical methods generally require multiple outcome measures to be available in the same experimental units (in the present context, this would mean having multiple types of exposure measures collected at the same times and locations)
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Several of the model components used in the environmental pathway models have been at least partially validated by data from studies of fallout from weapons tests, Chernobyl, and other dose reconstructions. Issue 2: Should a model be calibrated on the basis of a limited number of empirical data sets, and if so, how?
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In a fetter to Joe Wayman of the Hanford Litigation Office dated April 14, 1997, Napier notes a further error in the original calculations, namely, in the conversion factor to obtain concentrations Tom counts. Correction of this error tends to increase the measured concentrations by a factor of about 2.S.
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Nonetheless, the HEDR models have been shown to yield reasonable estimates of a range of thyroid doses to representative persons having a certain lifestyle, age, sex or physiology in exposed populations. However, these doses do not necessarily accurately represent the actual dose to a specific individual.
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Another factor that must be included in estimating specific individual risk is the uncertainty associated with thyroid cancer risk itself. The public should be made aware that even though the relative risk of developing thyroid cancer might be quite large, the absolute risk is small.
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As a minimum, the HEDR team should publish a corrected source-term report, publish a document that explains the errors made in the validation study and presents the corrected data, and produce the uncertainty report in a more serious and scientifically justified manner. ~ trust that you will not hesitate to contact me or Dr.
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