Search

Abstract: We describe advances made recently at Los Alamos for ENDF/B-VII, and for future ENDF releases, of actinide cross-section evaluations. Using americium as an illustrative example, we describe recent experiments that have largely confirmed the nuclear theory predictions that were the basis for the ENDF/B-VII.0 data for these americium reactions. The goal of this paper is to highlight some of the open issues in our understanding of the actinide nuclear data – especially for fast reactor applications – and show examples of how experiment, theory, and integral data validation has advanced our understanding. We will also describe the usage of these data in MCNP and S N radiation transport simulations of various integral critical systems, for both criticality and for transmutation reaction rates. [Copyright &y& Elsevier]

This article discusses the Bayesian method for hypothesis testing as applied to internal plutonium and americium dosimetry cases at Los Alamos National Laboratory, New Mexico. The authors compare the Bayesian method where the interpretation of the measurements builds on and depends upon the prior probability distribution with classical statistical approaches. They argue that all the data should always be taken into account. They conclude that if there are many cases available, then the difference between Bayesian and classical statistics is slight, but when data are limited, the distinction becomes important.

The detection, distribution, and long-term behavior of 241 Am in the terrestrial environment at the Waste Isolation Pilot Plant (WIPP) site were assessed using historical data from an independent monitoring program conducted by the Carlsbad Environmental Monitoring & Research Center (CEMRC), and its predecessor organization the Environmental Evaluation Group (EEG). An analysis of historical data indicates frequent detections of trace levels of 241 Am in the WIPP environment. Positive detections and peaks in 241 Am concentrations in ambient air samples generally occur during the March to June timeframe, which is when strong and gusty winds in the area frequently give rise to blowing dust. A study of long-term measurements of 241 Am in the WIPP environment suggest that the resuspension of previously contaminated soils is likely the primary source of americium in the ambient air samples from WIPP and its vicinity. Furthermore, the 241 Am/ 239 + 240 Pu ratio in aerosols and soils was reasonably consistent from year to year and was in agreement with the global fallout ratios. Higher than normal activity concentrations of 241 Am and 241 Am/ 239 + 240 Pu ratios were measured in aerosol samples during 2014 as a result of February 14, 2014 radiation release event from the WIPP underground. However, after a brief spike, the activity concentrations of 241 Am have returned to the normal background levels. The long-term monitoring data suggest there is no persistent contamination and no lasting increase in radiological contaminants in the region that can be considered significant by any health-based standard.

The environmental impact of the February 14, 2014 radiation release from the nation's only deep geologic nuclear waste repository, the Waste Isolation Pilot Plant (WIPP) was assessed using monitoring data from an independent monitoring program conducted by the Carlsbad Environmental Monitoring & Research Center (CEMRC). After almost 15 years of safe and efficient operations, the WIPP had one of its waste drums rupture underground resulting in the release of moderate levels of radioactivity into the underground air. A small amount of radioactivity also escaped to the surface through the ventilation system and was detected above ground. It was the first unambiguous release from the WIPP repository. The dominant radionuclides released were americium and plutonium, in a ratio that matches the content of the breached drum. The accelerated air monitoring campaign, which began following the accident, indicates that releases were low and localized, and no radiation-related health effects among local workers or the public would be expected. The highest activity detected was 115.2 μBq/m(3) for (241)Am and 10.2 μBq/m(3) for (239+240)Pu at a sampling station located 91 m away from the underground air exhaust point and 81.4 μBq/m(3) of (241)Am and 5.8 μBq/m(3) of (239+240)Pu at a monitoring station located approximately one kilometer northwest of the WIPP facility. CEMRC's recent monitoring data show that the concentration levels of these radionuclides have returned to normal background levels and in many instances, are not even detectable, demonstrating no long-term environmental impacts of the recent radiation release event at the WIPP. This article presents an evaluation of almost one year of environmental monitoring data that informed the public that the levels of radiation that got out to the environment were very low and did not, and will not harm anyone or have any long-term environmental consequence. In terms of radiological risk at or in the vicinity of the WIPP site, the increased risk from the WIPP releases is exceedingly small, approaching zero., (Copyright © 2015 Elsevier Ltd. All rights reserved.)