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Februrary 8, 2006
'No worries' concludes low-level background radiation study
By HEATHER EMMONS
The Nevada Site Office was interested in addressing ongoing public concern over the safety of low-level waste, or LLW, shipments to the NTS. The study addressed whether residents along transportation routes receive cumulative exposure from individual LLW shipments that pose a long-term health risk. While DOE and U.S. Department of Transportation (DOT) regulations ensure that radiation exposure from truck shipments is negligible, stakeholders in rural communities along transportation routes in Utah and Nevada perceive risk about cumulative exposure, particularly when "Main Street" and the routes being used by LLW trucks are one in the same. "Most studies of radiation exposure from truck transportation are based on calculations of potential exposure," said David Shafer, DRI's executive director of the Frank H. Rogers Center for Environmental Remediation and Monitoring. "The study was designed to help answer the question, 'What do the trucks really measure?'" How the study worked: The PIC arrays took gamma readings from 1,012, or nearly 47 percent of the 2,260 trucks that delivered LLW to the NTS during the test period. The Nevada Site Office could not contractually require waste generators to participate in the study, so the database is biased to voluntary participants. Drivers parked their truck in a marked "footprint" within the array and recorded shipment information, including date, time and Waste Shipment Identification Number into a logbook located at the PIC array. The PICs were positioned three and one-third feet from the truck trailer at a height of five feet to simulate conditions of a citizen standing on a sidewalk next to a LLW truck on a standard two-lane highway in the U.S., and to be representative of the exposure of chest organs. The use of four PICs, two on each side of the truck, was to investigate and account for variations in gamma radiation levels at different locations around the trucks because of differences in the radioactivity between waste packages, as well as how the waste containers were packed in the truck. In addition to the PICs, photoacoustic sensors, positioned between the PICs on each side of the array, were used to detect when a truck entered and departed the array, as LLW trucks can arrive at the NTS around the clock. Data from the PICs and photoacoustic sensors were recorded on dataloggers. Results: Of 1,012 trucks measured, about 70 percent could not be distinguished from background radiation levels or were less than 1/100,000 of the DOT shipping standard. In reality though, their percent of the DOT standard was even less. The DOT standard (10 millirems per hour) is actually established at 2 meters distance from the truck, while the truck measurements were made at 1 meter. Although the DOT standard is set at 2 meters, the PICs were placed one meter from the trucks so that measurements of the trucks could be made faster, making it easier for truck drivers to participate in the study. At 2 meters distance, the potential exposure to a person would be less because of the increased distance from the radiation source. Only 54 trucks, or 5.3 percent of the trucks in the study, had exposures greater than or equal to 10 percent of the DOT standard as measured at one meter. When cumulative exposures were considered, the few number of trucks with comparatively higher measurements could strongly influence the results. For example, in the unlikely event that a person had been standing by the road for the 42 LLW trucks that traveled through Amargosa Valley on their way to the NTS, 35 percent of the person's total exposure would have come from just one truck. No trucks measured during the study exceeded the DOT shipping standard. Background: Since 1980, more than 27 million square feet of LLW has been disposed of at the NTS by shallow land burial. Since 1988, the majority of this waste has been generated at other DOE and Department of Defense sites and facilities in the U.S. LLW is shipped in different types of containers or forms: drums, boxes, or large, bulk-type containers like concrete monoliths. The NTS has Waste Acceptance Criteria, and generators must measure the external radiation from LLW trucks before they leave their site to ensure that it is below DOE and DOT regulations for transportation. What is low-level waste? Low-level radioactive waste can best be described by what it is not. It is not spent nuclear fuel or high-level waste from reprocessing spent fuel, such as the type proposed to be disposed at Yucca Mountain, Nev. It is not transuranic wastes that have radionuclides heavier than uranium at concentrations greater than 100 nanocuries per gram. Most low-level waste is dominated by radionuclides with short half lives and includes items like construction debris, trash, soil and equipment. Shielding provided by LLW packaging ensures that workers can handle most of this waste without any special equipment or clothing. For truck transportation, any potential risk from LLW would be from gamma radiation as the containers and the walls of the trucks would shield alpha and most beta emissions. Sources of radiation: The average individual receives approximately 360 millirem of radiation per year from natural and man-made sources. Natural sources of radiation include: terrestrial sources, like rocks, soil and building materials derived from the earth's crust (like granite) and cosmic rays from outer space. In addition, about 40 millirem of the average person's total exposure emanates from within the body itself. Man-made radiation sources include x-rays and nuclear medicine procedures, as well as consumer products like smoke detectors, building materials, lawn fertilizer and even television sets. Accounting for background radiation: In determining the amount of "net exposure" from the LLW trucks, the PICs ran continuously, whether a truck was in the PIC array or not. When trucks were not present, the gamma radiation levels measured by the PICs were used to obtain background readings at the array site. The background was subtracted from the total reading to obtain the net exposure above background that was a result of the LLW. Study available to public: The study is available to the public in public reading rooms and libraries, including the Nevada State Library, UNLV and UNR libraries and the Desert Research Institute's Dina Titus Public Reading Room located at 755 E. Flamingo Road, Las Vegas, Nev. 89119. The study also will be available in the near future at the U.S. DOE's Office of Scientific and Technical Information at www.osti.gov. About DRI: A nonprofit, statewide division of the Nevada System of Higher Education, DRI pursues a full-time program of basic and applied environmental research on a local, national, and international scale. Nearly 600 full- and part-time scientists, technicians, and support staff conduct more than 300 research projects at DRI annually. DRI generates $45 million in total revenue consisting predominately of competitively won research contracts and grants. The State of Nevada provides critical funding in support of DRI's administration, operations and maintenance, through the Nevada System of Higher Education's budget. While DRI's portion of the NSHE budget is less than 1 percent, the institute leverages these funds to enhance its competitiveness. |
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