Michiyuki Kobayashi

Natural circulation characteristics of a marine reactor in rolling motion and heat transfer in the core

A series of single-phase natural circulation tests in a model reactor with rolling motion was performed in order to investigate effects of the rolling motion on its thermal-hydraulic behavior. The loop flow rate in each leg changes cyclically with the rolling angle due to the inertial force of the rolling motion. As the rolling period becomes shorter, the amplitude of the loop flow rate oscillations becomes larger, and the phase lag between the rolling angle and loop flow rate oscillations becomes larger. On the other hand, the core flow rate does not oscillate, though its value changes with the rolling period. Its change correlates well with both the Reynolds number for rolling motion and the Rayleigh number, and it is considered to be caused by the change of the thermal driving head and the pressure loss through the loop. In order to simulate core flow rate change with the rolling period, a simple one-dimensional analytical model was proposed, and its verification was demonstrated. Heat transfer in the core is enhanced by the rolling motion and the enhancement is thought to be caused by the internal flow due to the rolling motion. Heat transfer coefficient in the core is well correlated with the Richardson number for rolling motion and is classified into three regimes.

GO-FLOW: A New Reliability Analysis Methodology

A reliability analysis methodology, GO-FLOW, is presented. Detailed explanations and two examples of GO-FLOW analysis are given.The GO-FLOW is a success-oriented system analysis technique. The mode...

Natural circulation characteristics of a marine reactor in rolling motion

Abstract A series of single-phase natural circulation tests in a model reactor with rolling motion was performed, in order to investigate the natural circulation characteristics of a marine reactor in a stormy weather. It was found that the loop flow rate in each leg changes cyclically with the rolling angle due to the inertial force of the rolling motion. As the rolling period becomes shorter, both the amplitude of the loop flow rate oscillations becomes larger and the phase lag between the rolling angle and loop flow rate oscillations becomes larger. On the contrary, the core flow rate does not oscillate, though its value changes with the rolling period. Its change correlates well with both the Reynolds number for rolling motion and the Rayleigh number, and it is considered to be caused by the change of the thermal driving head and pressure loss through the loop. In order to simulate core flow rate change with the rolling period, a simple one-dimensional analytical model was proposed. The calculated results agree well with the experimental results, and its verification is demonstrated.

The GO-FLOW reliability analysis methodology—analysis of common cause failures with uncertainty

Common cause failures (CCFs) have long been recognized as an important issue in the probabilistic safety assessment (PSA) for nuclear power plants. Uncertainty ranges of system failure probabilities are important information for the evaluation of system reliability. The function of CCF analysis together with uncertainty analysis has been provided to the GO-FLOW methodology. Overview of the GO-FLOW methodology, the method to treat the CCFs in the GO-FLOW, the procedure of CCF analysis together with uncertainty are described. As the sample system, PWR auxiliary feedwater system has been taken and an analysis has been performed by the proposed analysis framework.

Experimental investigation of natural convection in a core of a marine reactor in rolling motion

A series of single-phase natural circulation experiments in a simulated marine reactor mounted on a rolling bed was performed and the average Nusselt number in the core was evaluated in order to investigate effects of the rolling motion on the heat transfer in the core. Heat transfer with an upright attitude is well correlated with the Rayleigh number and is slightly lower than El-Genks correlation. Heat transfer in the core is not affected by the inclination angle because the inclination of the present experiment is not large enough to cause any remarkable changes in the flow pattern of the core. Heat transfer in the core is enhanced by the rolling motion which is thought to cause internal flow in the core. Heat transfer during the rolling motion is correlated with the Richardson number for rolling motion, R iR , and is classified into three regimes: (1) region A (0.05<R iR ≤0.3) where heat transfer is dominated by the inertial force due to the rolling motion; (2) region B (0.3<R iR ≤2) where heat transfer is affected by the combined effect of the inertial force and natural convection; and (3) region C (R iR >2) where heat transfer is affected only by the natural convection.

Pressure and Fluid Oscillations in Vent System due to Steam Condensation, (I): Experimental Results and Analysis Model for Chugging

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional ...

Natural circulation of integrated-type marine reactor at inclined attitude

A steady-state single-phase natural circulation test was performed to clarify the effect of inclination by using a model of an integrated-type marine reactor. It was found that several types of flow pattern occur in the natural circulation loop corresponding to the range of inclination angle. Stable flow rates are sustained up to near 90° because of the occurrence of a driving force arising from those sections of the facility which were horizontal before the inclination. It was found that the temperature distribution in the steam generator at inclined attitude depends essentially only on the elevation z. The applicability of a one-dimensional analytical model was examined. It was clarified that employment of detailed U-turn flow paths, their correlation, and temperature-distribution function of core is essential for improvement.