Investigation of Fundamental Thermal-Hydraulic Phenomena in Advanced Gas-Cooled Reactors

Abstract

INL LDRD funded research was conducted at MIT in collaboration with INL personnel to experimentally characterize mixed convection heat transfer in gascooled fast reactor (GFR) core channels. The gas-cooled fast reactor (GFR) for Generation IV has generated considerable interest and is under development in the U.S., France, and Japan. One of the key candidates is a block-core configuration first proposed by MIT, has the potential to operate in Deteriorated Turbulent Heat Transfer (DTHT) regime or in the transition between the DTHT and normal forced or laminar convection regime during post-loss-of-coolant accident (LOCA) conditions. The DTHT regime is defined as a regime where the turbulent heat transfer deteriorates due to either a streamwise flow acceleration effect or a high buoyancy effect. This is contrary to most industrial applications where operation is in a well-defined and well-known turbulent forced convection regime. As a result, important new need emerged to develop heat transfer correlations that make possible rigorous and accurate predictions of Decay Heat Removal (DHR) during post LOCA in these regimes.Extensive literature review on these regimes was performed and a number of the available correlations was collected in: (1) forced laminar, (2) forced turbulent, (3) mixed convection laminar, (4) buoyancy driven DTHT and (5) acceleration driven DTHT regimes. Preliminary analysis on the GFR DHR system was performed and using the literature review results and GFR conditions. It confirmed that the GFR block type core has a potential to operate in the DTHT regime. Further, a newly proposed approach proved that gas, liquid and super critical fluids all behave differently in single channel under DTHT regime conditions, thus making it questionable to extrapolate liquid or supercritical fluid data to gas flow heat transfer.Suggested upgrades for the experimental facility from the 2 nd annual report were successfully installed and the control and data reduction software for facility operation was developed and tested. An extensive development of programming and controlling techniques were introduced for the software development that allowed substantial speed up of data collection and analysis process.Experimental data were collected for three different gases (nitrogen, helium and carbon dioxide) in various heat transfer regimes under a fully developed flow and reasonably uniform wall heat flux conditions. The following ranges of non-dimensional numbers, were covered in the experiment: (1) Reynolds number from 1,800 to 42,700 (2) Jackson' buoyancy parameter up to 5 10 (3) Acceleration parameter up to 6 5 10 and (4) wall to bulk temperature ratio up to 1.88. The data were obtained at various pressures up to 1MPa.Each gas unveiled different physical phenomena. All data basically covered the forced turbulent heat transfer regime, nitrogen data covered the acceleration driven DTHT and buoyancy driven DTHT, helium data covered the mixed convection laminar, acceleration 3 driven DTHT and the laminar to turbu...