Study on the natural circulation characteristics of a marine reactor during rolling motion

A series of natural circulation tests with a physical model of a marine reactor mounted on a rolling apparatus were performed in order to clarify the natural circulation characteristics during rolling motion. Prior to the test, two types of preliminary tests were conducted to investigate two factors, natural circulation driving force and cyclic acceleration change derived from rolling motion, which affect on the thermohydraulic behavior of the natural circulation during rolling motion. It was observed that the flow rates at hot legs and cold legs fluctuate with the change of rolling angle. The manners of these flow rate fluctuations change with the rolling period. It was found that the loop flow rate fluctuations are mainly caused by the acceleration change due to rolling motion. The core flow rate does not change with time, while it changes with the rolling period. Its change is well correlated with the Reynolds number for rolling motion. A simple analytical model was proposed, and the numerical calculation was performed. The computed result agrees well with the experimental result, and it was verified that the change of the core flow rate with rolling period is induced by the change of the natural circulation driving force and flow resistance due to rolling motion. (author)