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Conference Spotlight
2025 ANS Winter Conference & Expo
November 9–12, 2025
Washington, DC|Washington Hilton
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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NN Asks: What did you learn from ANS’s Nuclear 101?
Mike Harkin
When ANS first announced its new Nuclear 101 certificate course, I was excited. This felt like a course tailor-made for me, a transplant into the commercial nuclear world. I enrolled for the inaugural session held in November 2024, knowing it was going to be hard (this is nuclear power, of course)—but I had been working on ramping up my knowledge base for the past year, through both my employer and at a local college.
The course was a fast-and-furious roller-coaster ride through all the key components of the nuclear power industry, in one highly challenging week. In fact, the challenges the students experienced caught even the instructors by surprise. Thankfully, the shared intellectual stretch we students all felt helped us band together to push through to the end.
We were all impressed with the quality of the instructors, who are some of the top experts in the field. We appreciated not only their knowledge base but their support whenever someone struggled to understand a concept.
W. S. Winters, Jr., H. Merte, Jr.
Nuclear Science and Engineering | Volume 69 | Number 3 | March 1979 | Pages 411-429
Technical Paper | doi.org/10.13182/NSE79-A19959
Articles are hosted by Taylor and Francis Online.
Phase equilibrium blowdown models are not valid for geometries having small characteristic lengths (volume-to-break-area ratios). For such geometries, the two-phase expansion is too rapid to permit adequate heat and mass transfer between liquid and vapor to maintain phase equilibrium. The two-phase expansions observed during the present pipe blowdown experiments with dichlorodifluoromethane (R-12) were found to exhibit pronounced nonequilibrium behavior. Decompression transients were characterized by a rapid drop in pressure from the initial value to levels well below the initial saturation pressure. The pressure recovery caused by delayed growth of the vapor in superheated liquid leveled off to pressure plateaus well below the initial saturation pressure. Long-term blowdown transients were not affected by the initial pressure level, but initial temperature and pipe geometry were observed to have a pronounced influence. Higher initial temperatures resulted in higher pressure plateaus and shorter blowdown times. The rapid phase expansions occurring in pipe geometries having small volume-to-break-area ratios resulted in greater departures from phase equilibrium, as evidenced by the lower pressure plateaus observed experimentally. Transient temperature measurements indicated substantial temperature differences between liquid and vapor during blowdown. Furthermore, the vapor was observed to be saturated with respect to the system pressure for most of the blowdown event. To describe this experimentally observed nonequilibrium behavior, a model was formulated that treats the expanding two-phase fluid as a pseudo-homogeneous mixture of uniformly distributed, heat transfer dominated, spherical vapor bubbles surrounded by superheated liquid. By adjusting two empirical parameters—discharge coefficient, Cd, and bubble density, N—to permit the model to simulate R-12 blowdown from one particular blowdown geometry and set of initial conditions, it was possible to use the model in predicting R-12 blowdown transients for other geometries and initial conditions as well as for pipe water blowdown. The nonequilibrium model predictions were considerably more accurate than those of the phase equilibrium model, although consistent discrepancies were observed in all model-data comparisons. It is believed that two-dimensional effects near the pipe exit, liquid inertia influences on bubble growth, and limitations in the choked flow model are primarily responsible for the discrepancies.
