Direct Cycle Light Water Reactor Operating at Supercritical Pressure.

The concept of a direct cycle light water reactor (LWR) operating at supercritical pressure is presented. It is attractive for improving the thermal efficiency of LWRs and for simplifying the reactor system(1). The critical pressure of water is 22.1 MPa (221 bars). The density of water changes continuously above it and the concept of boiling does not exist. The system is conceptually depicted in Fig. 1. The water coolant which flows into the core is heated up and can be directly fed to turbines. Compared with the current BWRs, the recirculation system and steam separators and dryers will be eliminated. The vessel size will be greatly reduced. This will reduce the capital cost. The thermal efficiency will be also revolutionally improved. The feasibility of the system was studied through the conceptual design of the core.The axial temperature and density distribution of the coolant in the core were calculated at 25 MPa (250 bars) using a single channel model of a fuel and coolant. The density decreases continuously from the inlet (0.725 g/cm3) to the outlet (0.137 g/cm3) and the temperature increases from 583 K (310°C) to 689 K (416°C). The heat is efficiently removed due to the high specific heat of water around 658 K (385°C). The density change is mild at 250 bars than 225 bars which is close to the critical pressure. It is desirable to choose 250 bars for the stability of the flow in the core.