SBWR Power Cycle
The SBWR power cycle includes a single high-pressure turbine and a single
two-flow low-pressure turbine with 52-in. last-stage buckets. This arrangement
eliminates a low-pressure turbine rotor and shell. This in turn results in a
significantly smaller building size and a simpler condenser and piping arrangement,
without sacrificing thermal performance.
A single string of 100 percent feedwater heaters with individual bypass, compare to
the conventional design of dual string of 50 percent heater with string bypass, was
selected based on the demonstrated higher reliability of modern feedwater heaters.
This reduces the number of heaters, valves, and controls by 50 percent.
To achieve further simplification, the SBWR power cycle is a non-reheat cycle. The
large moisture-separator reheaters are replaced by compact high-velocity separators,
whose performance has been demonstrated through use in France. Without reheat,
pumping the water from the high-pressure feedwater heater drains into the
reactordosen't significntly improve the heat rate. Thus, the water from the
high-pressure drains is cscaded to the lower pressure-heater. This eliminates pumps,
valves, and electrical ans control systems.
The SBWR feedwater system has three variable-speed feed water pumps. The
capacity of each pump is 33 to 50 percent, and so the loss of a single pump during
operation will not cause a scram or reduced power output. pumps are powered by
adjustable-speed drives, eliminating the need for steam-driven turbines or constant
speed motoors with flow control valves.