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What’s the most difficult question you’ve been asked as a maintenance instructor?
Blye Widmar
"Where are the prints?!"
This was the final question in an onslaught of verbal feedback, comments, and critiques I received from my students back in 2019. I had two years of instructor experience and was teaching a class that had been meticulously rehearsed in preparation for an accreditation visit. I knew the training material well and transferred that knowledge effectively enough for all the students to pass the class. As we wrapped up, I asked the students how they felt about my first big system-level class, and they did not hold back.
“Why was the exam from memory when we don’t work from memory in the plant?” “Why didn’t we refer to the vendor documents?” “Why didn’t we practice more on the mock-up?” And so on.
R. Jain, M. L. Corradini
Nuclear Technology | Volume 155 | Number 3 | September 2006 | Pages 312-323
Technical Paper | Thermal Hydraulics | doi.org/10.13182/NT06-A3764
Articles are hosted by Taylor and Francis Online.
Experiments were conducted in a rectangular supercritical carbon dioxide (SCCO2) natural-circulation loop at Argonne National Laboratory (ANL) in order to verify the stability margin as suggested by some previous investigators. Although a one-dimensional transient computational model developed at University of Wisconsin, Madison, predicted the development of instabilities for the SCCO2 loop, which had good agreement with some previous work, the experiments conducted at the ANL SCCO2 loop exhibited stable behavior under similar conditions. In order to bridge the gap between the numerical predictions and experimental results by distinguishing between the numerical effects and physical effects, a linear stability approach is adopted in the present study. The linear stability analysis has been conducted for three model natural-circulation loop geometries employing water or carbon dioxide as the working fluid. The results for the supercritical water loops displayed flow stability for a more accurate equation of state (EOS); however, the analysis indicated the presence of instabilities for a less accurate EOS. Furthermore, this analysis still predicts the presence of instabilities for the SCCO2 loop similar to our transient numerical predictions. We additionally note that the stability margin for both water loops and the SCCO2 loop does not correspond with proposed stability criteria from a previous analysis. These two final points suggest the phenomenon is a more complex function of both fluid properties and loop geometry.
