Natural-circulation loops parallel channels

Natural-circulation loop and parallel channel thermal-hydraulics... 

Natural-circulation flows around loops and flows in parallel channels are both susceptible to departures from steady operation and excursions into oscillatory and, potentially, unstable states. Thus Gen IV nuclear reactor power systems combine the type of fluid flow and geometries that are known to potentially lead to undesirable states. In particular, undesirable oscillatory states under steady-state operation should be avoided. The complete system and associated operational envelope are designed to avoid unstable states. 

The RELAP5 model was used to simulate the thermal-hydraulics of the reactor vessel, the piping in all three primary coolant loops, the pressurizer, all three steam generators, and selected parts of the secondary systems. Reactor vessel nodalization, as developed by Bayless, is shown in Figure 1. As indicated, three parallel flow channels extend from the lower plenum through the core to the upper reactor vessel head. If the appropriate conditions exist, this arrangement will allow development of in-vessel natural circulation. 

---