A computational study for an evaluation of the current turbulence models for the prediction of a thermal striping in a triple jet is performed. The tested turbulence models are the two-layer model, the shear stress transport model, and the elliptic relaxation model. These three turbulence models are applied to the prediction of a thermal striping in a triple jet in which detailed experimental data are available. The predicted time-averaged and root-mean-square values of the temperature are compared with the experimental data, and the capability of predicting the oscillatory behavior of the ensemble-averaged temperature is investigated. From these works, it is shown that only the elliptic relaxation model is capable of predicting the oscillatory behavior of the ensemble-averaged temperature. It is also shown that the elliptic relaxation model predicts best the time-averaged temperature and the root mean square of the temperature fluctuation. However, this model predicts a slower mixing at the far downstream of the jet.
For a CO 2 ingress accident into liquid sodium in a supercritical CO 2 power conversion system coupled with a sodium-cooled fast reactor, we investigated two major design issues: i) a wastage phenomenon in regard to structural damage adjacent to the leaking position, and ii) potential channel plugging due to the formation of a particulate reaction product. In order to understand the factors affecting the occurrence of these issues, two kinds of experiments were carried out: a wastage effect test and a self-plugging test. All experimental conditions were chosen to reasonably represent the normal operating conditions and realistic design parameters of the reference plant. The test results indicate the absence of wastage, which will not lead to additional tube ruptures and damage propagation. In the current experiment, the self-plugging of PCHE channels only took place under two limited conditions: i) the sodium temperature is over 500 C and ii) the equivalent diameter of the crack opening is less than 1.5 mm with a small leakage rate of far less than 1 g/s of CO 2 ingress.
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