Abstract:One of the limiting conditions during operation of a Pressurized Water Reactor is cladding integrity in case of occurrence of any conditions I or II events. The decoupling criterion is the absence of Departure from Nucleate Boiling (DNB) during the full sequence of any of these transients. Heat transfer between the clad and the water is limited by the DNB phenomenon when local surface heat flux is greater than the so-called Critical Heat Flux (CHF). Heat production at the surface is higher than heat removal ca… Show more
“…Without actual improvement in the fuel design, the recent advancement in data treatment methodologies, the increasingly aggressive data analysis and optimization schemes, and the relaxing in requirements on rod bundle CHF experimental data have taken away more and more safety margins without proper experimental verification and supports. Similar voice was raised by Herer that "optimized correlations and advanced methodologies reduce this margin" [4]. This concern is especially valid considering the void of a totally benchmarked and fully established facility after the closing of Columbia University, Heat Transfer Research Facility (HTRF).…”
Rod bundle experiments with axially uniform and nonuniform heat fluxes are examined to explore the potential limitations of using uniform rod bundle CHF data for CHF correlation development of light water reactors with nonuniform axial power distribution (APD). The case of upstream burnout is presented as an example of unique phenomena associated with nonuniform rod bundle CHF experiments. It is a result from combined effect of axial nonuniform power shape and different interchannel mixing mechanisms. In addition, several key parameters are investigated with respect to their potential impacts on the thermal-hydraulic behaviors between rod bundles with uniform and nonuniform APDs. This type of misrepresentation cannot be amended or compensated through the use of correction factors due to the lack of critical information in the uniform rod bundle CHF testing as well as the fundamental difference in the underlining driving mechanisms. Other potential issues involved with the use of uniform rod bundle CHF data for nonuniform APD system applications also present strong evidence concerning the limitations and inadequacy of using uniform rod bundle CHF data for the correlation, prediction, and design limit calculation for safety analysis.
“…Without actual improvement in the fuel design, the recent advancement in data treatment methodologies, the increasingly aggressive data analysis and optimization schemes, and the relaxing in requirements on rod bundle CHF experimental data have taken away more and more safety margins without proper experimental verification and supports. Similar voice was raised by Herer that "optimized correlations and advanced methodologies reduce this margin" [4]. This concern is especially valid considering the void of a totally benchmarked and fully established facility after the closing of Columbia University, Heat Transfer Research Facility (HTRF).…”
Rod bundle experiments with axially uniform and nonuniform heat fluxes are examined to explore the potential limitations of using uniform rod bundle CHF data for CHF correlation development of light water reactors with nonuniform axial power distribution (APD). The case of upstream burnout is presented as an example of unique phenomena associated with nonuniform rod bundle CHF experiments. It is a result from combined effect of axial nonuniform power shape and different interchannel mixing mechanisms. In addition, several key parameters are investigated with respect to their potential impacts on the thermal-hydraulic behaviors between rod bundles with uniform and nonuniform APDs. This type of misrepresentation cannot be amended or compensated through the use of correction factors due to the lack of critical information in the uniform rod bundle CHF testing as well as the fundamental difference in the underlining driving mechanisms. Other potential issues involved with the use of uniform rod bundle CHF data for nonuniform APD system applications also present strong evidence concerning the limitations and inadequacy of using uniform rod bundle CHF data for the correlation, prediction, and design limit calculation for safety analysis.
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