Compliance Assessment for Greater Confinement Disposal Program
Project Description and Significance
The Department of Energy's Nevada Field Office (DOE/NV) disposed of a variety of difficult radioactive wastes, including a small quantity of transuranic (TRU) radioactive waste at the Nevada Test Site (NTS). Because shallow trench burial was not deemed appropriate for these wastes, an alternative disposal concept was implemented. Several 10-ft-diameter, 120-ft-deep boreholes were augered into the desert, and the transuranic waste was buried within them. This disposal concept was dubbed greater confinement disposal (GCD) because it provides for better isolation of radioactive waste than shallow land burial.
The federal regulation directing disposal of TRU waste is the Environmental Protection Agency's (EPA's) 40 CFR 191. In 1989, DOE/NV contracted with Sandia to perform a compliance assessment of the NTS GCD borehole disposal site relative to 40 CFR 191. In FY93, an additional study was added to Sandia's work scope, as the result of requests from DOE Headquarters. The purpose of the new study is to investigate available disposal technologies (including GCD boreholes) for use at the NTS to dispose of certain radioactive or mixed wastes that cannot be disposed of in existing or proposed disposal systems. In FY95 Sandia was asked to assess the viability of using the GCD concept for by-product material from Fernald.
Sandia's Contribution
The GCD compliance assessment process consists of iterative analyses (as described in the figure see next page) designed to assess the likelihood that the waste currently disposed of in GCD boreholes will comply with the EPA standards. Sandia has completed two iterations of the compliance assessment and is currently working on the third and final iteration.
Iterations are based on sensitivity analyses of assessment results, used to define new data-collection activities. This ensures that data-collection funds are efficiently focused on the most significant safety issues. Results from the new data-collection activities are then incorporated into the next compliance-assessment iteration. Closure is obtained when either compliance is indicated or economic considerations preclude the needed data-collection activities or no amount of additional data can make the site pass.
The compliance assessment analyses are purposefully biased to underpredict the performance of the system ( i.e., they estimate poorer performance than the existing knowledge about the system would suggest). This conservatism is decreased only if results from new data-collection activities indicate that there is a defensible basis to do so. Given this bias, the results are conservative and therefore provide a means for making a confident decision about the long-term safety of the disposal site. Furthermore, the process is also defensible because it is visible and tractable. To further facilitate decision making, it is recommended that the process be implemented in a participatory framework to address all stakeholders' concerns in a formal manner.
The GCD compliance assessment process is not specific to the GCD borehole facilities but could also be applied to other waste-disposal facilities. Therefore, this process development and its implementation tools (such as the Sandia Environmental Decision Support System see fact sheet) play an important national role in ensuring the long-term safety of the disposal of the nation's radioactive and hazardous wastes in an economically efficient manner. This process ensures prudent expenditure of funds.
Future Work
The 40 CFR 191 compliance assessment work for the TRU wastes in the GCD boreholes at the NTS will be completed as early as 2001. Sandia will also continue to support DOE/NV on special assignments. One current special assignment is to help develop a strategy for the application of probabilistic methods to performance assessments for DOE low-level wastes.
For further information, contact:
John Cochran
Sandia National Laboratories, MS-1345
Albuquerque, New Mexico 87185-1345
Phone: (505) 848-0415
e-mail: jrcochr@sandia.gov
Submitted October 1995 Layout design by Wanda Mar.
Submitted October 1995