Accident Progression Analysis of an Offshore Floating Nuclear Power Plant Under Heaving Motion

Abstract Offshore Floating Nuclear Power (OFNP), in which a proven commercial light water reactor (LWR) is mounted on a floating structure such as an oil drilling rig has been proposed by the Massachusetts Institute of Technology. Based on this concept, the Japanese industry is conducting research and development on the feasibility of an OFNP with a boiling water reactor (BWR) on a floating structure and operating 30 km off the coast of Japan. As part of this study, safety analysis was conducted to confirm whether the heaving oscillation affects accident progression in design extension conditions during the oscillation of OFNP, which is assumed to occur in stormy weather and other high-wave conditions. Prior to the analysis, the terms including gravitational acceleration in the equations of motion of the reactor system analysis code RELAP5/MOD3.3 were modified to handle acceleration during oscillation. In addition, experiments corresponding to the oscillation were conducted under the same conditions of approximately 290°C and 7.2 MPa as the BWR core, and the experimental results were used to validate the code. After confirming that the code was able to reproduce the void fraction variations of the experiment, uncertainty analysis of accident progression, such as TQUV and ATWS, including various heaving conditions, was performed to analyze the effects of the oscillations.