DOE OSTI2012
This report describes the methods and results of a special analysis (SA) of the Area 3 Radioactive Waste Management Site (RWMS) on the Nevada National Security Site (NNSS). The purpose of the SA is to determine if the approved performance assessment (PA) and composite analysis (CA) (Shott et al., 2001) remain valid. The Area 3 RWMS PA and CA were prepared as a single document and received conditional approval on October 6, 1999. A conditional Disposal Authorization Statement (DAS) for the Area 3 RWMS was issued on October 20, 1999. Since preparation of the approved PA and CA, new information and additional environmental monitoring data have been used to update the PA and CA. At the same time, continual advancements in computer processors and software have allowed improvement to the PA and CA models. Annual reviews of the PA and CA required by U.S. Department of Energy (DOE) Order DOE O 435.1 have documented multiple changes occurring since preparation of the PA and CA. Potentially important changes include: Development of a new and improved baseline PA and CA model implemented in the probabilistic GoldSim simulation platform. A significant increase in the waste inventory disposed at the site. Revision and updating of model parameters based on additional years of site monitoring data and new research and development results. Although changes have occurred, many important PA/CA issues remain unchanged, including the site conceptual model, important features, events, and processes, and the points of compliance. The SA is performed to document the current status of the PA/CA model and to quantitatively assess the impact of cumulative changes on the PA and CA results. The results of the SA are used to assess the validity of the approved PA/CA and make a determination if revision of the PA or CA is necessary. The SA was performed using the Area 3 RWMS, version 2.102, GoldSim model, the current baseline PA/CA model. Comparison of the maximum SA results with the PA performance objectives indicates that there continues to be a reasonable expectation of compliance. The resident exposure scenario was evaluated for compliance with the air pathway and all-pathways annual total effective dose (TED) performance objectives. The maximum mean air pathway TED, 7E-6 millisievert (mSv) at 1,000 years (y) has decreased relative to the approved PA and is significantly less than the 0.1 mSv limit. The maximum mean all-pathways annual TED, 7E-5 mSv at 1,000 y has increased but remains a small fraction of the 0.25 mSv limit. The SA maximum mean radon-222 (222Rn) flux density, 0.03 becquerel per square meter per second (Bq m-2 s-1), has increased relative to the PA results but is significantly less than the 0.74 Bq m-2 s-1 limit. The SA results continue to support a conclusion that the disposed waste inventory is protective of intruders and groundwater resources. The maximum mean intruder TED, 0.01 mSv for an acute construction scenario at the U-3ah/at disposal unit, was less than the 5 mSv performance measure. Site monitoring data and research results continue to support a conclusion that a groundwater pathway will not exist within the 1,000 y compliance period. Projected releases to the environment are a small fraction of the performance objectives. Cost-effective options for reducing releases further are unlikely to exist. Therefore, releases from the Area 3 RWMS are judged to be as low as reasonably achievable. Comparison of the maximum CA result with the 0.3 mSv CA dose constraint indicates that no action is required to reduce the dose from the Area 3 RWMS and all interacting sources of residual radioactive contamination. The SA maximum mean CA annual TED, 0.02 mSv at 1,000 y, has increased from the approved CA result but remains less than 10% of the dose constraint. The CA TED continues to be due predominantly to inhalation of plutonium-239 resuspended from soils contaminated by nuclear weapons tests conducted near the Area 3 RWMS. The SA results estimated with the Area 3 RWMS version 2.102 model indicate that changes to the PA and CA do not significantly alter the PA/CA results or conclusions. Although increases occur for the all-pathways annual TED, the 222Rn flux density, and the CA annual TED, all PA and CA results are a small fraction of the performance objectives or dose constraints. The same conclusion was reached for the approved PA and CA. The SA results continue to support a conclusion that there is a reasonable expectation of meeting all performance objectives and the CA dose constraint. There is no need to revise the DAS at this time. The SA results support a conclusion that the Area 3 RWMS PA and CA remain valid, and revision is not necessary at this time.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗