Reflooding Analysis Code

The water rods are neglected which is conservative from the viewpoint of their role as a heat sink. The effect of the water rods on the quench front velocity should be assessed in a future study. The SCRELA reflood module is used in the calculation for which the flow chart is shown in Fig. 6.19. This module, also developed at the early stage of SCWR studies in the University of Tokyo like the SCRELA blowdown module, was based on the REFLA of IAEA [20, 21]. The flow chart of the calculation is shown in Fig. 6.19. The SCRELA reflood module includes the system momentum calculation, the thermal equilibrium relative velocity correlation, and the quench front velocity correlation . 

The system momentum calculation is modeled by coupling a reactor vessel part and an ADS line part as described in Fig. 6.20. The reactor vessel part is represented by momentum balance between the downcomer and the core water levels. The equation is described in terms of acceleration, pressure difference between the 

19 Flow chart of SCRELA reflood module. (Taken from ref. [6] and used with permission from Atomic EnCTgy Society of Japan) 

V Velocity A Flow area Z Height Vol Volume P Pressure g Gravity p Density Subscripts d-. Downcomer c Core 

The pumping head of the LPCI and the friction loss are neglected. The boundary conditions are the water levels and pressures in the downcomer and the core. As described in (6.20), the pressure at the core water level is obtained as the addition of the pressure in the upper plenum, the friction loss from the core water level to the upper plenum. 

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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]. 

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