The natural circulation flow characteristic of the core in floating nuclear power plant in rolling motion

Abstract

In recent years, the FNPP (Floating Nuclear Power Plant) has got more and more attention and rapid development due to very wide prospect application on remote areas or islands. In general, the IPWR (Integral Pressurized Water Reactor) is adopted to meet the requirements of the limited space, the nuclear safety and the maneuverability in marine. The IPWR could depend on natural circulation operation to remove the residual heat of core under accident conditions or low load operation condition. Because the driving head is low, the natural circulation flow in many parallel channels is likely to be influenced by ocean motion and thermonuclear coupling effect. Among various kinds of ocean motions, the rolling motion will introduce the additional force pressure drop and change the gravity pressure drop with time, so the force acting on coolant in the assemblies will be more complex. In order to clarify the natural circulation flow characteristics of the core in FNPP in rolling motion, based on the modified RELAP5 code by adding the ocean motion module and spatial coordinate convert module, the neutron physics and thermal-hydraulic coupled model of IPWR was been established. The core three-dimensional distribution, the radial cross-section and axial distribution of main thermal-hydraulic parameters were obtained. The effect of the tangential force pressure drop, the centripetal force pressure drop and the gravity pressure drop on the coolant in the core in rolling motion were discussed. The results showed that the natural circulation flow rate fluctuates periodically with the rolling motion. And the time-varying gravity pressure drop is the main effect factor of fluctuation. Because of the structure of IPWR is compact, the rolling radius is relatively short, the effect of the general rolling motion on the natural circulation flow distribution of the core is not obvious. The coolant temperature and the fuel power distribution of the core periphery fluctuates slightly, and the reactivity feedback introduced by the coolant temperature and the fuel temperature fluctuation is relatively small. In consequence, the FNPP in the movable marine platform in natural circulation mode operation is safety in general rolling motion.