Main Steam System
The Main Steam System used in any power plant has 1 major purpose:
- Provide steam from the source (reactor, steam generator, or steam
separator) to the turbine
The system may have several other functions
- Provide the ability to prevent overpressurization of the steam source (if
the source puts out more heat than the turbine can accept)
- Provide the ability to prevent overcooling of the reactor coolant system
(if the steam system draws off more heat than the source can provide)
The major components in most Main Steam Systems are:
- Steam Line from the Reactor (if a BWR) , Steam generator (if a PWR),
Steam Separator (if a GCR) to the turbine.
- Main Steam Isolation Valve - usually an air operated or motor operated
valve used to isolate the steam source from the turbine.
- Safety valves - large relief valves that will open if steam pressure gets
too high (same purpose as the pop valve on your hot water heater).
- Power Operated Relief Valves - large air or motor operated valves that
usually lift at a setpoint lower than the safety valves - in order to keep the steam
pressure from getting too high.
- Non-return Valve - a large valve that prevents backward steam flow in the
The sketch below illustrates the main steam system flow path.
||The orange color shows the flow path of the steam as it goes, in this
case, from the steam generator to the high pressure turbine (then leaving in blue because
there is water in the steam) then going to the moisture separator where the water is
removed, then (in orange) to the low pressure turbine.
Copyright © 1996-2005. Joseph
Gonyeau, P.E.. The Virtual Nuclear
Tourist. All rights reserved. Revised: March 15, 2001.