Site characterization of the Yucca Mountain disposal system for spent nuclear fuel and high-level radioactive waste Rob P. Rechard a,n , Hui-Hai Liu b , Yvonne W. Tsang b , Stefan Finsterle b a Nuclear Waste Disposal Research & Analysis, Sandia National Laboratories, P.O. Box 5800, Albuquerque 87185-0747, NM, USA b Earth Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron, Berkeley 94720, CA, USA article info Available online 3 July 2013 Keywords: Site characterization High-level radioactive waste Spent nuclear fuel Radioactive waste repository Performance assessment Yucca Mountain abstract This paper summarizes the investigations conducted to characterize the geologic barrier of the Yucca Mountain disposal system. Site characterization progressed through (1) non-intrusive evaluation and borehole completions to determine stratigraphy for site identification; (2) exploration from the surface through well testing to evaluate the repository feasibility; (3) underground exploration to study coupled processes to evaluate repository suitability; and (4) reporting of experimental conclusions to support the repository compliance phase. Some of the scientific and technical challenges encountered included the evolution from a small preconstruction characterization program with much knowledge to be acquired during construction of the repository to a large characterization program with knowledge acquired prior to submission of the license application for construction authorization in June 2008 (i.e., the evolution from a preconstruction characterization program costing o$0.04  10 9 as estimated by the Nuclear Regulatory Commission in 1982 to a thorough characterization, design, and analysis program costing $11  10 9 —latter in 2010 constant dollars). Scientific understanding of unsaturated flow in fractures and seepage into an open drift in a thermally perturbed environment was initially lacking, so much site characterization expense was required to develop this knowledge. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction In 1987, Congress selected Yucca Mountain as the sole location to be characterized for a potential disposal site for high-level radioactive waste (HLW), commercial spent nuclear fuel (SNF), and SNF owned by the US Department of Energy (DOE-owned SNF or DSNF) [1]. Yucca Mountain (YM), located at the boundary between the Nellis Air Force Range and the Nevada National Security Site (formally known as the Nevada Test Site or NTS), 1 had been under consideration for a repository since 1978. In 2008, DOE submitted the Safety Analysis Report for the construction License Application (SAR/LA) to the Nuclear Regulatory Commission (NRC) (Fig. 1). DOE had spent $15  10 9 (in 2010 US dollars) since site selection began in 1983 [2, p.10]. This cost included all waste management program costs required by the Nuclear Waste Policy Act of 1982 (NWPA) [3] such as the Yucca Mountain Project (YMP) cost of $11  10 9 . Although the Obama Administration and Congress brought a de facto halt to YMP by a lack of funding in 2010 and began the process of formulating new policy, much can be learned from the past scientific challenges encountered 2 . This paper summarizes information on site characterization to provide a historical perspective on the performance assessment (PA) underlying the SAR/LA described in this special issue of Reliability Engineering and System Safety [4]. In keeping with the intended audience, this special issue devotes much to modeling and results; however, characterization of the natural barrier consumes much of the time and resources required to evaluate a geologic disposal system. Site characterization is at the heart of understanding the current behavior of components of the disposal system. Certainly, a description of the final understanding of the behavior of the Yucca Mountain disposal system is most satisfying academically, but re-examining the progression of this under- standing, although somewhat tedious, provides a means for a future repository program to perceive the technical uncertainty that will exist at various phases of the project. The uncertainty that will exist cannot be grasped solely by examining the progression of characterization conducted at Yucca Mountain, but it provides a good starting point that can be enhanced by reading companion Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ress Reliability Engineering and System Safety 0951-8320/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ress.2013.06.020 n Corresponding author. Tel.: +1 505 844 1761; fax: +1 505 844 2348. E-mail address: rprecha@sandia.gov (R.P. Rechard). 1 Because the area was known as the Nevada Test Site during most of the disposal system characterization of Yucca Mountain, this paper and companion papers use NTS rather than the current NNSS acronym. 2 At the time of submittal of the SAR/LA; DOE reported spending $13.5 x 10 9 with ~ $9.9 x 10 9 spent by YMP (in 2007 dollars) [4, Table, ES-1]. Most of the costs reported herein are for the year reported and have not been converted to a constant US dollar basis by accounting for inflation. Reliability Engineering and System Safety 122 (2014) 32–52