In this report, the U.S. Nuclear Waste Technical Review Board (Board) summarizes its major activities in calendar year 1999. Among the activities discussed in the report is the Board’s 1999 review of the U.S. Department of Energy's (DOE) viability assessment (VA) of the Yucca Mountain site. The Board’s evaluation of the VA concludes that Yucca Mountain continues to warrant study as the candidate site for a permanent geologic repository and that work should proceed to support a decision on whether to recommend the site for repository development. The Board suggests that the 2001 date for a decision is very ambitious, and focused study should continue on natural and engineered barriers. The Board states that a credible technical basis does not currently exist for the above-boiling repository design included in the VA. The Board recommends evaluation of alternative repository designs, including lower-temperature designs, as a potential way to help reduce the significance of uncertainties related to predictions of repository performance.