[1] Yucca Mountain is a potential repository site for highlevel radioactive waste. We examine claims that the frequency of future basaltic dike intersection could be 1 Â 10 À6 /yr or higher (i.e., on average, one penetration every million yrs). These claims fail simple tests at four time scales. Spatial-temporal models that predict intrusion frequencies >2 Â 10 À7 /yr are overly pessimistic because no dikes have been found in the 13 Myr-old potential repository footprint. More realistic models are developed by considering this non-detection of dikes and by applying probabilistic hazard assessments based on known patterns of Pleistocene volcanism. Using a hazard assessment code, we estimate the frequency of dike intersection at 5.4 Â 10 À8 /yr with an upper 95% confidence bound of 9.8 Â 10 À8 /yr.
This study examines the past and future impact of nuclear reactors on anthropogenic carbon emissions to the atmosphere. If nuclear power had never been commercially developed, what additional global carbon emissions would have occurred? More than 44 y of global nuclear power have caused a lag time of at least 1.2 y in carbon emissions and CO2 concentrations through the end of 2009. This lag time incorporates the contribution of life cycle carbon emissions due to the construction and operation of nuclear plants. Cumulative global carbon emissions would have been about 13 Gt greater through 2009, and the mean annual CO2 concentration at Mauna Loa would have been ~2.7 ppm greater than without nuclear power. This study finds that an additional 14–17 Gt of atmospheric carbon emissions could be averted by the global use of nuclear power through 2030, for a cumulative total of 27–30 Gt averted during the period 1965–2030. This result is based on International Atomic Energy Agency projections of future growth in nuclear power from 2009–2030, modified by the recent loss or permanent shutdown of 14 reactors in Japan and Germany
The double-ended-guillotine break (DEGB) criterion of the largest primary piping system in the plant, which generally provides the limiting condition for the emergency core cooling system requirements, is widely recognized as an extremely unlikely event. As a result, US Nuclear Regulatory Commission (NRC) staff are currently considering a risk-informed revision of the design-basis break size requirements for commercial nuclear power plants. In support of this effort, loss-of-coolant accident (LOCA) frequency estimates have been developed using an expert elicitation process by consolidating service history data and insights from probabilistic fracture mechanics (PFM) studies with knowledge of plant design, operation, and material performance. Baseline LOCA frequency estimates for the 5 th percentile, median, mean and 95 th percentile were determined from each panelist's elicitation responses. Group estimates were determined by aggregating the individual estimates using the geometric mean of the individual estimates for each frequency parameter. Group variability was estimated by calculating 95% confidence bounds for each of the group frequency parameters (i.e., median, mean, 5 th and 95 th percentiles). A number of sensitivity analyses were conducted to examine the effects on the quantitative results from varying the assumptions, structure and techniques of the baseline analysis procedure.
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