Startup thermal considerations for supercritical-pressure light water-cooled reactors

Supercritical-pressure light water-cooled reactors (SCRs) are innovative sy stems aimed at high efficiency and cost reduction. The once-through direct- cycle plant system is the leading system of fossil-fired power plants (FPPs ). Estimates of the coolability and necessary sizes of the SCR startup syst ems, sequences, and required equipment for startup are investigated with re ference to supercritical FPPs. There are two types of supercritical boilers . One is a constant pressure boiler, and the other is a variable pressure b oiler. First, startup of the constant pressure boiler is examined. The reactor sta rts at a supercritical pressure. A startup bypass system consisting of a fl ash tank and pressure-reducing valves is required. Second, startup of the v ariable pressure boiler is investigated. The reactor starts at a subcritica l pressure, and the pressure increases with the load. A steam-water separat or and a drain tank are required for startup. The results of computer calculations show that with both constant pressure and variable pressure startup, the peak cladding temperature does Plot exce ed the operating limit through startup, and both startup sequences are feas ible. The sizes of the components required for the startup systems are asse ssed. To simplify the plant system and to reduce the component size, variab le pressure startup with steam separators in the bypass line appears desira ble.