Some thermal hydraulic challenges in sodium cooled fast reactors

Natural convection test in Phenix reactor and associated CATHARE calculation

CFD analysis of the flow in the MICAS experimental facility, a water model of the hot pool of a sodium cooled fast reactor

The IAEA has coordinated a benchmark project on natural convection phenomena in the upper plenum of the MONJU reactor. JAEA has provided both detailed geometrical data of the plant and complete thermalhydraulic boundary conditions describing a pump trip transient, accomplished during the start-up experiments of the reactor. For the initial conditions of the pump trip transient, extensive sensitivity analyses have been made with the CFD code Trio_U. These calculations show a high sensitivity of the global flow pattern in the MONJU upper plenum depending on the initial order of the numerical scheme and the modelling of the geometrically complex upper core structure. During the pump trip, the formation of a thermal stratification within the plenum has been observed which persists for almost two hours. All calculations have shown a homogenization of the temperature in the plenum after about 15 minutes. A slight reduction of the mixing in the upper plenum could have been achieved by modifying the form of the flow holes in the inner barrel (fillets instead of sharp edges) in order to reduce their axial pressure loss.

/pdf/analysis-of-the-natural-convection-flow-in-the-upper-plenum-40vm9vtzv5.pdf

Analysis of the Natural Convection Flow in the Upper Plenum of the MONJU Reactor with Trio_U

https://scholarworks.unist.ac.kr/bitstream/201301/47844/1/000553761000009.pdf

Experimental validation of simulating natural circulation of liquid metal using water

This paper reports, to examine the function of the safety-related SNR-2 decay heat removal concept, natural convection experiments performed in two-and three-dimensional water models, scaled 1:20, under conditions of symmetric and nonsymmetric loads of the immersed coolers installed in the upper plenum at 180-deg positions with respect to each other. The temperature and velocity distributions were measured and the flow patterns recorded for different configurations of the instrumented plug. For symmetric load conditions, symmetric temperature and flow distributions were measured in two- and three-dimensional models. Nonsymmetric load conditions produce remarkable temperature differences between the two separated plenums of the two-dimensional model if fluid circulation is suppressed by a closed plug. An open plug allows fluid to pass through and shows lower temperature differences. In contrast, in the three-dimensional experiment, azimuthal fluid flow inside the plenum prevails even with the plug closed, and identical temperature distributions are measured. The calculations using the COMMIX-1B code are generally in good agreement with the measurements.

Kurt Dres

Papers

Thermohydraulic Investigations of Decay Heat Removal Systems by Natural Convection for Liquid-Metal Fast Breeder Reactors