Safety Analysis of a 300-MW(electric) Offshore Floating Nuclear Power Plant in Marine Environment

The Offshore Floating Nuclear Plant (OFNP) integrates an advanced light water reactor into a cylindrical, double-hull, floating platform. It offers a series of potential benefits in economics and safety. The 300-MW(electric) version, named OFNP-300, uses an ocean-based direct reactor auxiliary cooling system (DRACS) to remove decay heat from the core passively and indefinitely during loss of feedwater or loss of off-site power events. In the ocean, the OFNP platform may roll during storms or even statically tilt following asymmetric flooding of underwater compartments. The effects of rolling motion and static tilt on the engineered safety systems are investigated in this paper using a RELAP5-3D (version 4.3.4) model of OFNP-300. The oscillations of the platform are described as the superposition of sinusoidal motions for the six degrees of freedom, i.e., heave, roll, pitch, yaw, sway, and surge. The plant’s thermal-hydraulic responses to two postulated accidents, i.e., loss-of-coolant accident (LOCA) and station blackout (SBO), are then studied in three scenarios: (a) a design-basis 100-yr storm, (b) a bounding scenario in which the platform is assumed to pitch and roll with an amplitude of 20 deg, and (c) a bounding scenario in which the platform experiences a static tilt of 30 deg. The results of the RELAP5 analysis show that the safety margins of OFNP-300 are not challenged in the aforementioned three postulated scenarios. From a thermal-hydraulic point of view, the pitch and roll motions affect the flow in the DRACS but have no negative effect on the temperatures in the core during LOCA and SBO. Static platform tilt is tolerable up to 45 deg, beyond which the emergency core cooling system can no longer function.