To address public concern about potential exposure to gamma radiation from legal-weight low-level radioactive waste truck shipments to the Nevada Test Site, a stationary, automated array of four pressurized ion chambers was established for trucks to pass through. Data were collected from 1,012 of the 2,260 trucks that transported low-level radioactive waste to the Nevada Test Site from February through December 2003. To avoid perception of biasing a potential exposure low, the maximum reading (muR per hour; muR h(-1)) from the array was assigned as the gross measurement value for each truck. [In this article, exposure measurements are reported as Roentgen (R), as this unit is consistent with the data readings of the measurement instruments and has been historically presented to public stakeholders. Subsequently, dose measurements are reported as Roentgen Equivalent Man (rem).] To calculate the "net exposure" for each truck, the average and standard deviation of the maximum background values during the corresponding 12-h period when the truck arrived were subtracted from the gross value. For 483 trucks (47.7%), calculated net exposure values were equal to or less than zero, indicating that the exposure from the truck was indistinguishable from background. An additional 206 trucks (20.4%) had calculated net exposure values ranging between 0.0 and 1.0 muR h(-1). Cumulative exposure scenarios appropriate for rural transportation routes to the Nevada Test Site were developed; however, these scenarios assumed the unlikely case that the same individual was exposed to all of the trucks on that route. Cumulative exposure values were dominated by a small percentage of the trucks with comparatively high values. In communities along transportation routes, the probability of an individual receiving a potential exposure from a single truck may be a more meaningful perspective.
EXECUTIVE SUMMARYThe United States (U.S.) Department of Energy (DOE) Nevada Test Site (NTS) is one of two regional sites where low-level radioactive waste (LLW) from approved DOE and Department of Defense generators is disposed of by shallow land burial. In fiscal year (FY) 2003, more than 91,000 m 3 (3.2 million ft 3 ) of LLW were transported by truck to the NTS. Over 85,000 m 3 (3.0 million ft 3 ) were disposed of in FY 2004, driven in part by the accelerated closure of DOE Environmental Management (EM) sites such as Mound, Fernald, and Rocky Flats. The DOE and Department of Transportation (DOT) regulations ensure that radiation exposure from truck shipments is negligible. Nevertheless, particularly in rural communities, there is perceived public risk about cumulative exposure, especially when LLW transportation routes and the main highway through towns are the same. The DOE, National Nuclear Security Administration Nevada Site Office (NNSA/NSO), which manages the NTS, has agreed with the State of Nevada to restrict transport of LLW through the Las Vegas metropolitan area. Consequently, LLW generators primarily use highways through rural parts of Nevada and western Utah to reach the NTS.The NNSA/NSO and other DOE offices have provided information on potential exposure to members of the public from LLW trucks as part of public outreach activities. However, based on literature searches and discussion with other researchers in the transportation field, nearly all of the information is based on calculated versus measured exposures, although measurements of trucks are made with portable, hand-held instruments when drivers arrive at such facilities as the Area 5 Radioactive Waste Management Complex (RWMC) or the Area 3 Radioactive Waste Management Site (RWMS) on the NTS. To help better address public concerns about potential exposure from LLW trucks, a stationary and automated array of four pressurized ion chambers (PICs) was established for LLW trucks to pass through just before they reached the NTS. The PICs were positioned 1.0 m (3.3 ft) from the truck trailer at a height of 1.5 m (5.0 ft) 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 for a "Reference Man" using the Snyder-Fisher model of an adult human. The use of four PICs (two on each side of a truck) was to investigate, account, and correct for nonuniformity where gamma radiation levels from waste packages varied from side to side, and from front to back in the truck trailer. 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. Data from the PICs and photoacoustic sensors were recorded on dataloggers. All instruments were solar powered. Automating the array provided an objective and consistent means to measure and calculate exposure to gamma radiation.Each PIC was calibrated by collecting readings from exposure to ...
As part of a program to characterize and baseline environmental parameters, ambient radon-222 (Rn) monitoring was conducted in the rural community of Amargosa Valley, NV, the closest community to Yucca Mountain. Passive integrating and continuous Rn monitoring instruments were deployed adjacent to the Community Environmental Monitoring Program (CEMP) station in Amargosa Valley. The CEMP station provided real-time ambient gamma exposure and meteorological data used to correct the integrated Rn measurements, verified the meteorological data collected by the continuous Rn monitoring instrument, and for provided instrumentation for evaluating the relationships between meteorological conditions and Rn concentrations. Hourly Rn concentrations in air measured by the continuous Rn monitoring instrument (AlphaGUARD®) were compared to the average hourly values for the integrating Rn measurements (E-PERM®) by dividing the total Rn measurements by the number of hours the instruments were deployed. The results of the comparison indicated that average hourly ambient Rn concentrations as measured by both methods ranged from 0.2 to 0.4 pico-curies per liter of air. Ambient Rn values for the AlphaGUARD exhibited diurnal variations. When Rn concentrations were compared with measurements of temperature (T), barometric pressure, and relative humidity, the correlation (inversely) was highest with T, albeit weakly. iv THIS PAGE LEFT INTENTIONALLY BLANK v CONTENTS
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