Seiichi Yokobori

An experimental study on rewetting phenomena in transient conditions of bwrs

Abstract It is known that rod temperature rise after boiling transition (BT) is not excursive and that the peak cladding temperature (PCT) is suppressed by rewetting to return to nucleate boiling, even if BT occurs under severe conditions exceeding abnormal operational transients for a BWR. The purpose of this study is to develop and verify the rewetting correlation. The rewetting correlation was developed based on single rod data, as a function of quality, mass flux, pressure and heat flux. The transient thermal-hydraulic code used in the BWR design analysis (SCAT) with this rewetting correlation was compared with transient rod temperature result after the occurence of BT obtianed by the 8×8 and 4×4 rod bundle. It is concluded that the transient code with the developed rewetting correlation predicts the PCT conservatively, and the rewetting time well.

Two-phase flow natural circulation characteristics inside BWR vessels

Abstract Fundamental two-phase flow behavior under natural circulation conditions is studied both experimentally and analytically. Natural circulation characteristics for both drum-type and chimney-type reactors are experimentally investigated focusing on the flow patterns, flow rate and two-phase behavior inside the vessel. Analytical studies are performed to further understand the natural circulation characteristics of an actual plant and the mechanisms of geysering-like instabilities. Experimental and analytical results confirm that sufficient and stable flow is achievable in a natural circulation BWR.

CHARACTERISTICS OF TURBULENCE IN A CYLINDRICAL VESSEL WITH LARGE SCALE RECIRCULATING REGIONS (MEASUREMENTS OF FLOW FIELDS WITH TEMPERATURE DISTRIBUTION).

The characteristics of turbulence in the fields of velocity and temperature of the upper plenum of LMFBR have been investigated to estimate the behavior of thermal diffusion near the upper core structure (UCS). An inlet nozzle of a 1/20 scale experimental vessel provided a co-axial water jet with temperature distribution. The two component velocity measurements were carried out by 3 beam laser Doppler velocimetry, where the temperature was simultaneously measured to obtain correlations among fluctuations of velocity and temperature. The results indicated that the higher temperature jet flow did not mix with colder surroundings up to the bottom. Sufficient turbulent mixing of momentum and heat was realized after the separation at the edge of UCS bottom, since the higher temperature jet flowed slantingly to the lower temperature surrounding jet.