Idaho National Engineering Laboratory Dose Reconstruction

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The radioactive lanthanum (RaLa) process was designed to extract Ba-140 (half-life of 12.9 days), which decays to La-140 (40.2 hours), from irradiated reactor fuel. The latter isotope, an intense source of high-energy gamma rays, was used to evaluate the implosion process of a nuclear weapon. The short half-life of Ba-140 required the design of a process in which fuel elements irradiated in a nuclear reactor were dissolved shortly after irradiation.

The RaLa process at the Idaho Chemical Processing Plant used fuel elements irradiated in the Material Testing Reactor (MTR) located on-site at INEL. A total of 36 RaLa runs took place at the ICPP between February 1957 and December 1959. Additional releases of radionuclides occurred as a result of a nuclear criticality accident on October 16, 1959.

Essentially all releases from the ICPP during the years 1957-1959 were due to RaLa process operations. Radionuclide emissions through the ICPP stack were monitored continuously during 1957-1959 by sampling of air that went out the stack. Information obtained from stack monitoring datasheets provided the basis for estimated releases of iodine and other radionuclides. Additional sources of information include official RaLa project reports, progress reports, operational logs, calculation sheets, and contemporary project letters.

Estimated releases of isotopes of iodine, bromine, krypton, and xenon are described in the following report:

Gaseous Releases from ICPP

Atmospheric releases of 115 radionuclides attached to aerosols have been treated separately as described in the following report:

Aerosol Releases from ICPP

Principal authors:
Robert P. Wichner,  Oak Ridge Center for Risk Analysis, Inc.
John-Paul Renier,  Oak Ridge Center for Risk Analysis, Inc.
A. Iulian Apostoaei, Oak Ridge Center for Risk Analysis, Inc.
Lynn Anspaugh, Oak Ridge Center for Risk Analysis, Inc.​

The purpose of the Aircraft Nuclear Propulsion (ANP) Program was to develop nuclear-powered airplanes. Twenty-six initial engine tests (IETs) were performed at INEL during late 1950s and early 1960s. Emissions from three tests (IETs #3, #4 and #10) were responsible for most of the releases during the ANP Program operations.

A rigorous analysis of releases from the IETs was hampered by the absence of original logbooks and other primary sampling data, which either no longer exist or have not yet been declassified for public use. Thus, for IETs #3, #4 and #10, only point estimates of total releases for each radionuclide were obtained on the basis of information retrieved from historical summary reports. The intent of the analysis of the selected IETs was to provide source terms that did not underestimate actual releases. A time-dependence of releases during a particular IET could not be determined. Due to the lack of detailed information, potential impacts of releases during the selected IETs in the ANP Program have only been investigated by performing screening calculations. A detailed reconstruction of doses resulting from releases during the ANP Program has not been performed at this time.

An analysis of the releases of 34 radionuclides in gaseous form or attached to particles is described in the following report:

Critical Review of Atmospheric Releases from IET/ANP

Principal authors:
Hans U. Behling, Sanford Cohen and Associates
John Mauro, Sanford Cohen and Associates

More than 130 radionuclides were released to the atmosphere during operations at the Idaho Chemical Processing Plant (ICPP) from 1957-1959, when releases of radioactive iodine due to radioactive lanthanum (RaLa) process operations were the highest. In addition, releases of 34 radionuclides were estimated for initial engine tests (IETs) in the Aircraft Nuclear Propulsion (ANP) Program. A screening analysis was performed to identify those radionuclides that could have contributed significantly to doses and risks to the public. The method for screening of radionuclides released to the atmosphere from the ICPP and IET/ANP is described in the following report:

Radionuclide Screening Method

Screening of radionuclides is based on an estimation of lifetime risk of cancer incidence for each radionuclide in question by using methods that do not underestimate the true lifetime risk. The estimated screening risks are compared with an assumed screening criterion, which for this study is a lifetime risk of cancer incidence of 10-5 (one chance in 100,000). If the calculated risk corresponding to an estimated release of a radionuclide equals or exceeds the screening criterion, that radionuclide is selected for inclusion in a dose reconstruction. The assumed screening criterion is a risk that is generally considered negligible. Thus, calculated screening risks should be considerable overestimates of actual risks to the public.

In a companion report, the method of screening described above was applied to upper confidence limits of estimated releases from the ICPP.

As a result of the screening, 13 radionuclides from ICPP operations and 23 radionuclides from the ANP Program were selected for further analysis. Selected ICPP radionuclides are: Sr-89; Sr-90; Y-91; Zr-95; Nb-95; Ru-103; I-131; I-133; Ba-140; Ce-141; Ce-144; Pr-143; and Pu-238.

Selected ANP radionuclides are: Kr-88; Sr-89; Sr-90; Sr-91; Y-91; Zr-95; Zr-97; Zr-97; Mo-99; Ru-103; Ru-103; Te-131; Te-132; I-131; I-133; I-134; I-135; Cs-137; Cs-138; Ba-140; Ce-141; Ce-143; Ce-144; Pr-143.

Detailed results of the screening analysis are presented in the following report:

Radionuclide Screening Results

Iodine-131 is by far the most important radionuclide released from ICPP, and it was included in a detailed analysis of doses to members of the public. A more refined analysis was also performed for the other 12 selected radionuclides released from ICPP.

Iodine-131 is also the most important radionuclide released from ANP. A rigorous analysis of releases from the IETs was hampered by the absence of original logbooks and other primary sampling data, which either no longer exist or have not yet been declassified for public use. A detailed reconstruction of doses resulting from releases during the ANP Program has not been performed at this time.

Principal author:
David C. Kocher, Oak Ridge Center for Risk Analysis, Inc.

The main exposure pathways for atmospheric releases of radionuclides include inhalation, external exposure, ingestion of food items (e.g., garden crops, milk and meat), and incidental ingestion of soil (e.g., by individuals working in dusty environments).

Exposure scenarios are defined for representative individuals in the population (i.e., hypothetical individuals chosen to provide reasonably realistic representations of exposures of the public). For the purpose of analyzing the effects of emissions from the Idaho Chemical Processing Plant (ICPP), six basic exposure scenarios were defined. The scenarios are based on site-specific information collected from detailed documents about the INEL site and surrounding regions, from individuals living in the area, and from members of the Idaho Health Effects Subcommittee (IHES). The basic scenarios include scenarios for exposure beyond the INEL site boundary or exposure at onsite locations. The off-site scenarios include estimation of doses for: a) a rural resident, b) an urban residents, and c) a migrant farm worker. The on-site exposure scenarios include: a) an on-site rancher, b) a hunter, and c) a visitor to the INEL site. These exposure scenarios are discussed at length in the following report:

Exposure Scenarios Report

Principal authors:
A. Iulian Apostoaei, Oak Ridge Center for Risk Analysis, Inc.
Elizabeth W. Reed, Oak Ridge Center for Risk Analysis, Inc.​

The concentrations of radionuclides in air at the selected offsite and onsite locations around the INEL were estimated using the CALPUFF modeling system. CALPUFF is a non-steady-state air quality modeling system developed by Sigma Research Corporation (now part of Earth Tech, Inc., of Concord, Massachusetts). The original development of the CALMET/CALPUFF models was sponsored by the California Air Resources Board and is now supported by the U.S. Environmental Protection Agency.

Local meteorological data collected at INEL and surrounding area during the years of release were used as an input to the calculations. To test the validity of estimates of airborne concentrations of radionuclides, CALPUFF was evaluated using data collected in 1999 as part of an atmospheric sulfur hexafluoride (SF6) tracer experiment. Model testing indicated that CALPUFF reproduced satisfactorily time-averaged measured concentrations.

Concentrations in air were estimated on an hourly basis and summarized as monthly averages for all major communities within a 50-mile radius of the Idaho Chemical Processing Plant. The uncertainties in the estimated concentrations in air were quantified by accounting for uncertainty in the wind field, emission rates of radionuclides and vertical wind profiles, terrain adjustment methods, and atmospheric dispersion coefficients.

The analysis of the atmospheric dispersion of radionuclides released from the ICPP is presented in the following report:

Atmospheric Dispersion Report

Principal authors:
Zivorad Radonjic, SENES Consultants Limited, Canada
Ron Stager, SENES Consultants Limited, Canada
A. Iulian Apostoaei, Oak Ridge Center for Risk Analysis, Inc.

Iodine-131 is by far the most important radionuclide released from the Idaho Chemical Processing Plant, and it was included in a detailed analysis of doses to members of the public. A more refined analysis was also performed for the other 12 radionuclides released from ICPP (Sr-89; Sr-90; Y-91; Zr-95; Nb-95; Ru-103; I-133; Ba-140; Ce-141; Ce-144; Pr-143; and Pu-238).

Estimated I-131 thyroid doses from ICPP were typically less than 4 cSv for individuals who lived at the closest locations downwind from ICPP. Thyroid doses were almost always less than 20 cSv to thyroid. More than 90% the people living around INEL received thyroid doses of less than 0.4 cSv to the thyroid.

Iodine-131 doses from ICPP are lower than doses from other nuclear operations (e.g., Hanford, Washington, or Oak Ridge, Tennessee) and also lower than doses from I-131 fallout from nuclear weapons testing at Nevada Test Site.

Other radionuclides released from ICPP produced effective doses of less than 0.1 cSv, or organ doses of less than 1 cSv. The dose to an individual from all radionuclides combined at the closest downwind location is equivalent to a thyroid dose of 2 cSv from ingestion of I-131.

Dose Assessment Report

Principal authors:
A. Iulian Apostoaei, Oak Ridge Center for Risk Analysis, Inc.
Brian A. Thomas, Oak Ridge Center for Risk Analysis, Inc.
David C. Kocher, Oak Ridge Center for Risk Analysis, Inc.
F. Owen Hoffman, Oak Ridge Center for Risk Analysis, Inc.