International model validation programs

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Mathematical models are often used for predicting the environmental transport of radionuclides and other contaminants and for assessing the resulting exposures, doses, and risks that may occur or may have occurred. One of the major approaches used in recent years to address the reliability of model performance is to test model predictions against field measurements, an approach sometimes referred to as "model validation." For models of radionuclide transport in the environment, some of the most valuable model testing opportunities have come about as a result of the Chernobyl accident in April 1986. Several test exercises have been carried out over the last 20+ years under international programs sponsored by the International Atomic Energy Agency, the Swedish Radiation Protection Institute, and other agencies: the Biospheric Model Validation Study, Phases I and II (BIOMOVS and BIOMOVS II), the Co-ordinated Research Programme on Validation of Environmental Model Predictions (VAMP), the Biosphere Modelling and Assessment Methods programme (BIOMASS), and most recently the Environmental Modeling for Radiation Safety Program (EMRAS).

Dr. F. Owen Hoffman, President of Oak Ridge Center for Risk Analysis, organized and served as general chairman of the first international workshop dedicated to the evaluation of mathematical models used to assess the environmental transport of radionuclides and doses to humans. In 1985, he consulted with the Swedish Radiation Protection Institute in cofounding the BIOMOVS program. In 1988, Dr. Hoffman became Chief Scientist to the International Atomic Energy Agency for the VAMP program. He also headed the Multiple Pathways Assessment Working Group of the VAMP program and the Post Chernobyl Data Working Group of the BIOMOVS II program. Dr. Kathleen M. Thiessen, Senior Scientist for Oak Ridge Center for Risk Analysis, chaired the Dose Reconstruction Working Group of the BIOMASS program, and currently chairs the Urban Remediation Working Group of the EMRAS program.. Dr. Thiessen was also instrumental in completing the efforts of the Multiple Pathways Assessment Working Group of the VAMP program and the Post Chernobyl Data Working Group of the BIOMOVS II program. Drs. B. Gordon Blaylock and A. Iulian Apostoaei of Oak Ridge Center for Risk Analysis, have also been active participants in some of the international model validation programs. Drs. Hoffman, Thiessen, Blaylock, and Apostoaei also contributed to the IAEA's Safety Report Series, No.19, dealing with generic models for use in assessing radioactive discharges.

Oak Ridge Center for Risk Analysis has compiled data sets from a number of the international model validation projects. These are available to the scientific public through the Centers for Disease Control and Prevention, Radiation Studies Branch. A summary of the collection and the first several data sets are available in pdf format at the CDC's website: http://www.cdc.gov/nceh/radiation/brochure/profile_intl_projects.htm

Further information on the VAMP and BIOMASS programs, including the IAEA technical reports, is available at http://www-ns.iaea.org/projects/emras/

The Hanford Thyroid Disease Study (HTDS) is one of the largest and most complex epidemiologic studies of the relation between environmental exposures to I-131 and thyroid disease. The study detected no dose-response relation using a 0.05 level for statistical significance. The results for thyroid cancer appear inconsistent with those from other studies of populations with similar exposures. The absence of statistically significant dose-response relationships and the low estimates of excess risk reported for the HTDS can be explained by the high uncertainty associated with the use of mathematical models to reconstruct iodine 131 releases, environmental transport, and thyroid doses for individual cohort members. This uncertainty arises from unknown degrees of systematic overestimation of dose, as well as random measurement errors. Incomplete accounting for the full effect of these problems would result in an overestimation of statistical power and inappropriately narrow interval estimates for the excess risk of disease.

A paper published in Health Physics explores evidence that the HTDS statistical power was inadequate due to complex uncertainties associated with the mathematical models and assumptions used to reconstruct individual doses and concludes that, at the very least, the confidence intervals reported by the HTDS for thyroid cancer and other thyroid diseases are too narrow because they fail to reflect key uncertainties in the measurement-error structure.

Health Physics, February 2007, Volume 92, number 2, pages 99-111

A letter to the editor of the Journal of the American Medical Association explores the same topic: JAMA, August 2, 2006 - Volume 296, No. 5

Oak Ridge Center for Risk Analysis was involved with Lawrence Berkeley National Laboratory (LBNL) as a technical liaison between LBNL and the City of Berkeley. The responsibilities of SENES included the following: 

1. A review of atmospheric dispersion models to determine the applicability to the prediction of tritium concentrations resulting from releases from the National Tritium Labeling Facility (NTLF)  
2. Evaluation of tritium releases at LBNL using a CALPUFF complex terrain methodology
3. Estimation of excess lifetime risk of cancer incidence associated with discrete routine releases of tritiated water vapor from the NTLF at LBNL  
4. Assessment of radiological dose and excess lifetime risk of cancer for specified reference individuals exposed to releases of tritiated water vapor from routine operation of the NTLF at LBNL  
5. Guidance in the placement of additional air monitoring stations for the measurement of tritium in the environment
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Since 1950, the U.S. Department of Energy has operated and tested more than 50 nuclear reactors at the Idaho National Engineering Laboratory (INEL) in southeastern Idaho. Also tested were waste-disposal, fuel processing, and fuel handling facilities. In 1992, the Radiation Studies Branch of the Centers for Disease Control and Prevention (CDC) started a dose reconstruction study at INEL. http://www.cdc.gov/nceh/radiation/brochure/profile_ineel.htm

The purpose of the INEL dose reconstruction is to identify chemicals and radioactive materials released since the site opened and to determine the potential health effects of these releases on the neighboring communities. Phase I of the dose reconstruction study included preliminary estimates of the release of radionuclides and chemicals, and was completed in 2001. The results indicated that airborne emissions from radioactive lanthanum (RaLa) process operations at the Idaho Chemical Processing Plant (ICPP) and from initial engine tests (IETs) in the Aircraft Nuclear Propulsion (ANP) Program during late 1950s and early 1960s resulted in the greatest potential for off-site exposures of the public to radionuclides and chemicals released.

Phase II of the dose reconstruction study was initiated in 2002. Oak Ridge Center for Risk Analysis [formerly SENES Oak Ridge, Inc.], and Sanford Cohen & Associates were contracted by CDC to assess the public health risks from the releases of radionuclides from the ICPP and ANP. SENES estimated the releases of radionuclides from the ICPP for the years 1957-1959 using historical source documents. These release estimates have been put through a screening procedure to select radionuclides for a detailed dose reconstruction.

The link below provides more information about each step of the Phase II INEL study and to download the reports.

Additional Information and Project Reports
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From 1994 to 1999, a team of scientists and engineers performed detailed dose reconstruction analyses focused on past releases of radioactive iodine, mercury, and polychlorinated biphenyls (PCBs) released from the U.S. government complexes on the Oak Ridge Reservation. Listed below are the tasks included in the Oak Ridge Dose Reconstruction. Oak Ridge Center for Risk Analysis [formerly SENES Oak Ridge, Inc.] was the principal investigator for Tasks 1 and 4.

Oak Ridge Dose Reconstruction Project Summary Report

Task 1: Iodine-131 Releases from X-10 Radioactive Lanthanum Processing

Task 2: Mercury Releases from Y-12 Lithium Enrichment

Task 3: Polychlorinated Biphenyls (PCBs) in the Environment near Oak Ridge

Task 4: Radionuclides Released from X-10 to the Clinch River via White Oak Creek

Task 5: Systematic Review of Historical Records of Oak Ridge Operations

Task 6: Review of Historical Uranium Effluent Monitoring Data

Task 7: Additional Screening Calculations for Materials Not Evaluated in Phase I

Prototype of Individual Risk and Dose Calculator for the Oak Ridge Region (IRAD)

An interactive individual web-based calculation of risk and dose was developed in conjunction with the ORDR by Oak Ridge Center for Risk Analysis. This calculator considers the effect of combined exposures to I-131 in fallout and from releases from the 1944-1956 operation of RALA processing at Oak Ridge. See link below:

Individual Risk and Dose Calculator for the Oak Ridge Region (IRAD)
[http://50.243.118.105/irad]

Oak Ridge Center for Risk Analysis [formerly SENES Oak Ridge, Inc.] carried out a reevaluation of dose estimates for exposures to radionuclides released from the Hanford Reservation to the Columbia River for the Agency for Toxic Substances and Disease Registry. Through examination of historical documents and recent summary reports, SENES identified potential sources of bias in the dose estimates prepared during the Hanford Environmental Dose Reconstruction Project. In addition, SENES prepared revised dose estimates and corresponding risk estimates for people consuming fish and waterfowl from the Columbia River. These results were intended for use in establishing the need for medical monitoring in potentially exposed populations.