Reflood, analysis

ORNL small-break LOCA tests Experimental investigation of heat transfer and reflood analysis was made under conditions similar to those expected in a small-break LOCA. These tests were performed in a large, high-pressure, electrically heated test loop of the ORNL Thermal Hydraulic Test Facility. The analysis utilized a heat transfer model that accounts for forced convection and thermal radiation to steam. The results consist of a high-pressure, high-temperature database of experimental heat transfer coefficients and local fluid conditions. 

Anklam, T. M., 1981b, ORNL Small-Break LOCA Heat Transfer Test Series 1 High Pressure Reflood Analysis, NUREG/CR 2114, ORNL/NUREG/TM-446, Oak Ridge Natl. Lab., Oak Ridge, TN. (4)... 

The core water level is calculated from a detailed core thermal-hydraulic calculation. The quench front is calculated by a theoretical correlation proposed by Yamanouchi, et al. [24]. The heat transfer coefficient sharply changes by about 2 orders of magnitude in the vicinity of the quench front. In order to prevent the numerical instability caused by the abrupt change in the heat transfer coefficient, the neighboring nodes of the quench front are more finely divided into a size 1/100 of the thickness of the normal node as shown in Fig. 6.21. The flow regimes assumed in the reflood analysis are described in Fig. 6.22. Various heat transfer correlations are prepared according to the flow conditions. Table 6.9 [21] summarizes them. 

Safety analysis of the Super LWR is described in ref. [121]. The SPRAT-DOWN code for the analysis of downward flowing water rods and the SPRAT-DOWN-DP code for depressurization in an LOCA were prepared. The LOCA analysis of the Super LWR was performed in combination with SPRAT-DOWN-DP and the reflooding module of SCRELA. ATWS analysis is also described in ref. [121]. The momentum equation is included in the SPRAT-DOWN code from the ATWS analysis. The design of the two-pass core of the Super LWR and the safety analysis at subcritical pressure during startup are described in ref. [122]. 

Table 6.21 Sensitivity analysis for reflooding phase of 100% cold-leg break LOCA ...

The analysis results of the reflooding phase following the end stage of Fig. 7.107 [37] are shown in Fig. 7.111 [37]. The changes of the quench front and hottest cladding temperature in the upward flow seed channel are quite similarly to those of the Super LWR. The peak temperature is much lower than the criterion of 1,260°C. 

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