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原文传递 Assessing Potential Exposure from Truck Transport of Low-level Radioactive Waste to the Nevada Test Site

题名：	Assessing Potential Exposure from Truck Transport of Low-level Radioactive Waste to the Nevada Test Site
作者：	Miller, J##Shafer, D##Gray, K##Church, B##Campbell, S##Holtz, B.
摘要：	Since 1980, over 651,558 m{sup 3} (23,000,000 ft{sup 3}) of low-level radioactive waste (LLW) have been disposed of at the Nevada Test Site (NTS) by shallow land burial. Since 1988, the majority of this waste has been generated at other United States (U.S.) Department of Energy (DOE) and Department of Defense (DoD) sites and facilities in the U.S. Between fiscal year (FY) 2002 and the publication date, the volumes of LLW being shipped by truck to the NTS increased sharply with the accelerated closure of DOE Environmental Management (EM) Program sites (DOE, 2002). The NTS is located 105 km (65 mi) northwest of Las Vegas, Nevada, in the U.S. There continue to be public concerns over the safety of LLW shipments to the NTS. They can be broadly divided into two categories: (1) the risk of accidents involving trucks traveling on public highways; and (2) whether residents along transportation routes receive cumulative exposure from individual LLW shipments that pose a long-term health risk. The DOE and U.S. Department of Transportation (DOT) regulations ensure that radiation exposure from truck shipments to members of the public is negligible. Nevertheless, particularly in rural communities along transportation routes in Utah and Nevada, there is a perceived risk from members of the public about cumulative exposure, particularly when ''Main Street'' and the routes being used by LLW trucks are one in the same. To provide an objective assessment of gamma radiation exposure to members of the public from LLW transport by truck, the Desert Research Institute (DRI) and the DOE, National Nuclear Security Administration Nevada Site Office (NNSA/NSO) established a stationary and automated array of four pressurized ion chambers (PICs) in a vehicle pullout for LLW trucks to pass through just outside the entrance to the NTS. The PICs were positioned at a distance of 1.0 m (3.3 ft) from the sides of the truck trailer and at a height of 1.5 m (5.0 ft) to simulate conditions that a member of the public (Turner, 1995) might experience if a truck were to pass while the person was on the side of the road, or if a truck were to come to a stop at a stoplight in one of the smaller towns along the transportation routes. The 1.0-m (3.3-ft) distance also allowed for comparison with gamma readings of trucks taken with portable, hand-held instruments at the two LLW disposal sites at the NTS: the Area 5 Radioactive Waste Management Complex (RWMC) and the Area 3 Radioactive Waste Management Site (RWMS). The purpose in automating the system was to provide the most objective and consistent measurement and calculation of radiation exposure from the trucks possible. The array was set up in November 2002 and equipment was tested and calibrated over the next two months. Data collection on trucks began on February 13, 2003, and continued to the end of December 2003. In all, external gamma readings were collected from 1,012 of the 2,260 trucks that delivered LLW to the NTS during this period. Because DOE could not contractually require waste generators to participate in the study, the database is biased toward voluntary participants; however, data were collected from the 10 generators that represented 92 percent of the LLW shipments to the NTS during the study period, with another eight generators accounting for the balance of the shipments. Because of the voluntary nature of the participation, the identity of the waste generators is not used in the report. Previous studies on potential exposure to the public from transporting LLW to the NTS either relied on calculated exposures (Davis et al., 2002) or was based on a small population of trucks (e.g., 88) where a relatively high-background value of 50 microRoentgens per hour ({micro}R/h) (background value measured at the LLW disposal sites) were subtracted from the gross reading of the truck trailer as measured by portable, handheld instruments (Gertz, 2001). The dataset that resulted from the DRI study is the largest collection of measurements of LLW trucks in transit of which the authors are aware.
总页数：	82
报告类型：	科技报告