Radiation-induced volume changes in the fuel kernels and buffer layers of UCO-TRISO particles irradiated to an average burnup of 16.1% FIMA have been determined. Measurements of particle dimensions were made on polished cross-sections of 56 irradiated particles at several different polish planes. The data were then analyzed to compute the equivalent spherical diameters of the kernels and the various coating layers, and these were compared to the average as-fabricated values to determine changes due to irradiation. The kernel volume was found to have increased by an average of 26±6%. Buffer volume decreased by an average of 39±2% due to densification.

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Automation poses a great opportunity to increase both system and human performance. However, it is important to pay attention to the design of the collaboration between the human operator and the automated systems. If not designed correctly, the overall performance may be severely reduced. Previous research indicates that an intermediate level of automation might be the solution that minimizes the tradeoffs between manual and automated actions. However, there are still many remaining unanswered questions related to impacts on situation awareness (SA) and workload during different levels of automation (LOAs). Some of the documented issues of automation include reduced SA, complacency, and over reliance on the system automation.The Advanced Reactor Technologies Human Automation Collaboration Research Project has conducted two experimental studies investigating the effect of different LOAs on system and human performance. The results from the first experimental study were published in Oxstrand and Le Blanc (2014) and Le Blanc and Oxstrand (2015) and are summarized in this report. The second experimental study was conducted by Idaho National Laboratory researchers. This report focuses on the second experimental study and details the design of the study and results.The second experimental study aimed to investigate the effects automation has on overall human-system performance. Researchers employed a simplified process control simulation using a nested experimental design to evaluate performance differences between four LOAs (manual, intermediate, adaptable, and automatic) with varying faults and conditional changes occurring during each scenario. The effects of automation were measured by participants' ability to detect and respond to failing automation and conditional changes using a variety of metrics assessing SA, system performance, and workload. The intent of this study is to determine the optimum conditions for human automation collaboration.The results of the present study indicate that more automation led to better system performance under normal operating conditions, and poorer SA and system performance under fault conditions. The results for the two middle LOAs are not as straightforward. Consistent with the hypothesis, system performance using adaptable automation exceeded system performance when using the intermediate LOA. However, contrary to the hypotheses, SA and fault performance were not superior using the adaptable LOA than using the intermediate LOA. The results of this study indicate that although adaptable automation fulfills half if its promise (i.e., it produces system performance closer to fully automatic than intermediate LOAs), it falls short of also enhancing SA and fault performance. This study demonstrates the fundamental tradeoff associated with high LOAs: automation enhances performance during normal conditions, but increases failure (sometimes catastrophically) of the humansystem under the condition of automation failure. In contrast, although manual performance is inferior to automati...

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Analyzing initiating event rates is important because it indicates performance among plants and also provides inputs to several U.S. Nuclear Regulatory Commission (NRC) risk-informed regulatory activities. This report presents an analysis of initiating event frequencies at U.S. commercial nuclear power plants since each plant's low-power license date. The evaluation is based on the operating experience from fiscal year 1988 through 2013 as reported in licensee event reports. Engineers with nuclear power plant experience staff reviewed each event report since the last update to this report for the presence of valid scrams or reactor trips at power. To be included in the study, an event had to meet all of the following criteria: includes an unplanned reactor trip (not a scheduled reactor trip on the daily operations schedule), sequence of events starts when reactor is critical and at or above the point of adding heat, occurs at a U.S. commercial nuclear power plant (excluding Fort St. Vrain and LaCrosse), and is reported by a licensee event report. This report displays occurrence rates (baseline frequencies) for the categories of initiating events that contribute to the NRC's Industry Trends Program. Sixteen initiating event groupings are trended and displayed. Initiators are plotted separately for initiating events with different occurrence rates for boiling water reactors and pressurized water reactors. p-values are given for the possible presence of a trend over the most recent 10