Editing Boiling water reactor (section)

=== Condensate and feedwater ===
{{Unreferenced section|date=July 2011}}
[[File:Boiling water reactor no text.svg|thumb|upright=1.60|Schematic diagram of a ''boiling water reactor'' (BWR):
{{columns-list|colwidth=30em|{{ordered list
 | Reactor pressure vessel
 | Nuclear fuel element
 | Control rods
 | Recirculation pumps
 | Control rod drives
 | Steam
 | Feedwater
 | High-pressure turbine
 | Low-pressure turbine
 | Generator
 | Exciter
 | Condenser
 | Coolant
 | Pre-heater
 | Feedwater pump
 | Cold-water pump
 | Concrete enclosure
 | Connection to electricity grid
}}}}
]]
Steam exiting the [[turbine]] flows into [[condenser (heat transfer)|condensers]] located underneath the low-pressure turbines, where the steam is cooled and returned to the liquid state (condensate). The condensate is then pumped through [[feedwater heater]]s that raise its temperature using extraction steam from various turbine stages. Feedwater from the feedwater heaters enters the [[reactor pressure vessel]] (RPV) through nozzles high on the vessel, well above the top of the [[nuclear fuel]] assemblies (these nuclear fuel assemblies constitute the "core") but below the water level.

The feedwater enters into the downcomer or annulus region and combines with water exiting the moisture separators. The feedwater subcools the saturated water from the moisture separators. This water now flows down the downcomer or annulus region, which is separated from the core by a tall shroud. The water then goes through either jet pumps or internal recirculation pumps that provide additional pumping power (hydraulic head). The water now makes a 180-degree turn and moves up through the lower core plate into the nuclear core, where the fuel elements heat the water. Water exiting the fuel channels at the top guide is saturated with a steam quality of about 15%. Typical core flow may be 45,000,000&nbsp;kg/h (100,000,000&nbsp;lb/h) with 6,500,000&nbsp;kg/h (14,500,000&nbsp;lb/h) steam flow. However, core-average [[porosity|void fraction]] is a significantly higher fraction (~40%). These sort of values may be found in each plant's publicly available Technical Specifications, Final Safety Analysis Report, or Core Operating Limits Report.

The heating from the core creates a thermal head that assists the recirculation pumps in recirculating the water inside of the RPV. A BWR can be designed with no recirculation pumps and rely entirely on the thermal head to recirculate the water inside of the RPV. The forced recirculation head from the recirculation pumps is very useful in controlling power, however, and allows achieving higher power levels that would not otherwise be possible. The thermal power level is easily varied by simply increasing or decreasing the forced recirculation flow through the recirculation pumps.

The two-phase fluid (water and steam) above the core enters the riser area, which is the upper region contained inside of the shroud. The height of this region may be increased to increase the thermal natural recirculation pumping head. At the top of the riser area is the moisture separator. By swirling the two-phase flow in cyclone separators, the steam is separated and rises upwards towards the steam dryer while the water remains behind and flows horizontally out into the downcomer or annulus region. In the downcomer or annulus region, it combines with the feedwater flow and the cycle repeats.

The saturated steam that rises above the separator is dried by a chevron dryer structure. The "wet" steam goes through a tortuous path where the water droplets are slowed and directed out into the downcomer or annulus region. The "dry" steam then exits the RPV through four main steam lines and goes to the turbine.