Intermediate depth disposal operations were conducted by the U.S. Department of Energy (DOE) at the DOE's Nevada Test Site (NTS) from 1984 through 1989. These operations emplaced highspecific activity low-level wastes (LLW) and limited quantities of classified, "special case" transuranic (TRU) wastes in 37 m (120-ft) deep, 3 m (10 ft) diameter Greater Confinement Disposal (GCD) boreholes.Four boreholes contain about 60,000 kg (132,000 lb.) of classified TRU waste packages, containing less than 330 curies of Plutonium-239. All of the TRU wastes emplaced in the GCD boreholes are classified for national security reasons and cannot be disposed of in the DOE's Waste Isolation Pilot Plant.The U.S. Environmental Protection Agency's (EPA's) 40 CFR 191 defines the requirements for protection of human health from disposed TRU wastes. This EPA standard sets a number of requirements, including probabilistic limits on the cumulative releases of radionuclides to the accessible environment for 10,000 years. This report presents the performance assessment (PA) that has been conducted to determine if disposal of TRU waste in the GCD boreholes complies with the EPA's 40 CFR 191 requirements.Sandia National Laboratories completed this PA using all available information and an Iterative PA Methodology, which focused work on uncertainty reduction in a cost-effective fashion that does not overestimate system performance and assured defensibility. The simplicity of the conceptual models of the GCD disposal system allowed them to be implemented in Microsoft ® Visual Basic™ macros in an Access™ database. This PA model is built from a mathematical expression for mass conservation that includes the operation of a number of transport processes, including dissolution, precipitation, reversible chemical sorption onto soil, advection, diffusion, dispersion, radioactive decay and ingrowth, plant uptake, and bioturbation. The mathematical model and implementing code was used to calculate a complementary cumulative distribution function of integrated normalized release to the accessible environment for 10,000 years and probability distributions of dose based on two exposure conditions for the 1,000 year individual protection requirements.The primary conclusions of this PA are that the disposal of TRU wastes in the GCD boreholes will, at most, result in minuscule doses to individuals, and that the GCD disposal system easily meets the EPA's 1985, 40 CFR 191 requirements for disposal of TRU waste. Further, there is a strong, reasonable expectation that actual system performance will be better than what is simulated in this PA.vi ACKNOWLEDGMENTS

NOTE 1: FCT Document Cover Sheet should be filled out and submitted with the deliverable. Or, if the PICS:NE system permits, completely enter all applicable information in the PICS:NE Deliverable Form. The requirement is to ensure that all applicable information is entered either in the PICS:NE system or by using the FCT Document Cover Sheet. NOTE 2: In some cases there may be a milestone where an item is being fabricated, maintenance is being performed on a facility, or a document is being issued through a formal document control process where it specifically calls out a formal review of the document. In these cases, documentation (e.g., inspection report, maintenance request, work planning package documentation or the documented review of the issued document through the document control process) of the completion of the activity, along with the Document Cover Sheet, is sufficient to demonstrate achieving the milestone. If QRL 1, 2, or 3 is not assigned, then the Lab / Participant QA Program (no additional FCT QA requirements) box must be checked, and the work is understood to be performed and any deliverable developed in conformance with the respective National Laboratory / Participant, DOE or NNSA-approved QA Program.

Revision History Revision Description FCRD-UFD-2015-000129 Rev. 0 Sandia programmatic review (for DOE/NE-53 policy review and possible international peer review; SNL tracking number 275569) FCRD-UFD-2015-000129 Rev. 1 Sandia formal review (SAND2015-8712 R) for unclassified, unlimited release. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. CONTEXT FOR THIS STUDY This is a technical presentation that does not take into account the contractual limitations under the Standard Contract. Under the provisions of the Standard Contract, DOE does not consider spent fuel in canisters to be an acceptable waste form, absent a mutually agreed to contract modification. DISCLAIMER This information was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S.

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