Conceptual model for small-volume alkali basalt petrogenesis: implications for volcanic hazards at the proposed Yucca Mountain nuclear waste repository

Today, 31 countries operate ∼ 450 nuclear power reactors supplying electric power to ∼ 1 billion people,∼ 15% of the world population. Nuclear reactors generate∼ 17% of global electric power needs and a number of industrialized countries depend on nuclear power for at least half of their electricity. In addition, ∼ 30 nuclear power reactors are presently under construction worldwide (Macfarlane and Miller, 2007). A comprehensive summary of the principles, practices, and prospects for nuclear energy may be found in Bodansky (1996). Concerns regarding energy resource availability, climate change, air quality and energy security imply a continuing demand for nuclear power in the world energy budget (Craig et al., 2001). However, to date no country has solved the problem of long-term disposal or storage of nuclear waste. Without a long-term solution, the viability of nuclear energy as an increasingly significant contributor to power generation in the long-range future remains unclear. There is broad consensus that geologic disposal is the safest feasible longterm solution to high-level waste and spent-fuel disposal. Although a number of countries have ongoing geologic repository research programs, there is presently no operational geologic repository for spent fuel or high-level waste on Earth. In theUnited States, where spent nuclear fuel and high-level waste amounts to ∼ 50 000 metric tons, ∼ 15% of the world total, implementation has proven to be challenging both technically and politically. Nuclear waste is currently stored on-site at existing nuclear power stations and at several temporary storage facilities. Permanent geologic disposal, like the siting of a nuclear power plant, requires careful site selection. For geologic disposal, lithology that can isolate radioactive waste from the surrounding environment and biosphere at geologic timescales∼ 104−106 a are a minimum requirement (Macfarlane and Ewing, 2006). Of particular importance in this regard are the nature, consequences and probabilities of volcanic hazards that can potentially compromise public, environmental and biospheric safety at long-term nuclear waste storage sites. Yucca Mountain (YM) in Nevada, USA was identified in the early 1980s as a potential geologic repository for nuclear waste. Yucca Mountain is made up of silicic volcanic tuffsrocks composed chiefly of pyroclastic flow and fall deposits. The proposedYuccaMountain Repository (YMR) lies on the western boundary of the Nevada Test Site (NTS) within the Basin and Range geologic province (Zoback et al., 1981; Thompson and Burke, 1974). This region is geologically active,with transtensional deformationmanifested by faulting, related