9906a4BAThomas

4. Health Risks from Radionuclides Released into the Clinch River

"Beginning in 1944 and continuing until the present time, the Oak Ridge National Laboratory (ORNL), located in Oak Ridge, Tennessee, has released liquid radioactive wastes into White Oak Creek, which empties into the Clinch River. The radioactive wastes came from the direct operations of the graphite reactor and the chemical separation plant as well as other ORNL operations and other nuclear facilities throughout the southern region. This facility was originally designed to operate only 1 yr as a pilot plant for the Hanford, Washington, operations. The radioactive wastes generated from the plant were intended to be stored in large tanks. The original intent was changed, and in 1944 the first radioactive effluents were released to White Oak Creek and flowed into White Oak Lake, which acted as a final settling basin for the released contaminants. The radionuclides remaining in the water column were released over White Oak Dam, which is located 1 km upstream from the Clinch River.

"The purpose of this work is to estimate off-site radiation doses and health risks (with uncertainties) associated with the release of radionuclides from the X-10 site. Following an initial screening analysis, the exposure pathways of interest included fish ingestion, drinking water ingestion, the ingestion of milk and meat, and external exposure from shoreline sediment. Four representative locations along the Clinch River, from the White Oak Creek Embayment to the city of Kingston, were chosen. The demography of the lower Clinch River supplied information dealing with land use that aided in the determination of sites on which to focus efforts. The locations that proved to be the most significant included Jones Island at Clinch River Mile (CRM) 20.5, Grassy Creek and K-25 (CRM 14), Kingston Steam Plant (CRM3.5), and the city of Kingston (CRM 0). These areas of interest have historically been and are still primarily agricultural and residential areas. Reference individuals were determined with respect to the pathways involved.

"The primary radionuclides of interest released from the X-10 facility into the Clinch River via White Oak Creek were identified in the initial screening analysis as ¹³⁷Cs, ⁹⁰Sr, ⁶⁰Co, ¹⁰⁶Ru, ¹⁴⁴Ce, ¹³¹I, ⁹⁵Zr, and ⁹⁵Nb. Of these radionuclides, ¹³⁷Cs, ⁶⁰Co, ¹⁰⁶Ru, ⁹⁰Sr, and ¹³¹I were evaluated for their contribution to internal exposure pathways, while ¹³⁷Cs, ⁶⁰Co, ¹⁰⁶Ru, ⁹⁰Sr, ¹⁴⁴Ce, ⁹⁵Zr, and ⁹⁵Nb were evaluated for their contribution to the external exposure pathway.

"This study utilized an object-oriented modeling software package that provides an alternative to the spreadsheet, providing graphical influence diagrams to show qualitative structure of models, hierarchical models to organize complicated models into manageable modules, and intelligent arrays with the power to scale up simple models to handle large problems. This software has the capability of handling multidimensional arrays of data, as opposed to the two-dimensional restriction in spreadsheets. What this means is that an equation need be keyed in only once. The operation will be performed for every entry in a given dimension of the array. This simplification of effort allows for a straightforward method for checking the equations used in the model.

"The doses and risks estimated in this study for individuals consuming fish exceeded dose and risk estimates for all other pathways. Individuals with the highest consumption rate of fish (1 to 2.5 meals/week) from the nearest location (CRM 20.5) received the highest doses. The central values of the cumulative doses for 1944 through 1991 for specific organs ranged from 0.31cSv (skin) to 0.81cSv(bone) for males. The excess lifetime risk of cancer incidence was estimated based on cancer incidence data from Japanese atomic bomb survivors and the background incidence of cancer for East Tennessee. For males, the highest risk is to the red bone marrow (central value of 3.7 x10^-5); for females, the highest risks are for the breast and red bone marrow (central values of 5.5 x10^-5 and 2.8 x10^-5, respectively). For a given individual, the organ that received the highest dose had a dose ~2 to 4 times higher than the organ that received the lowest dose. However, the organ that received the highest risk had a risk ~70 to 80 times higher than the organ that received the lowest risk. This situation illustrates the great difference in organ sensitivities to radiation-induced cancer and emphasizes the importance of calculating risks as well as doses because the organ with the highest dose may not be the organ at greatest risk.

"For individuals with the highest consumption rate, the 95% uncertainty range of the total excess lifetime risk of cancer incidence for all radionuclides and organs was 3.6 x10^-5 to 3.5 x10^-3 (2.8 x10^-3 central value) for males and 2.9 x10^-5 to 2.8 x10^-3 (2.3 x10^-4 central value) for females. The variation in results for fish ingestion across genders reflects primarily the difference in ingestion rates. For both males and females, the largest contribution to the total risk was from ¹³⁷Cs (~90%).

"The doses and risks estimated in this study are not significant enough to cause a detectable increase in health effects in the population. In most cases, the organ doses are well below the limits of epidemiological detection (1 to 30cSv) for radiation-induced health outcomes. Therefore, it is unlikely that exposure to radionuclides released from the X-10 site is responsible for an increased number of cancers to populations utilizing the Clinch River after 1944."