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