Boiling Water Reactor (BWR)

BWRs are cooled and moderated by water. The main difference to the PWR is that the water in the Reactor Cooling System (RCS) is boiling and the steam produced in the core is directly conducted to the turbine. The core is similar to a PWR core and is also confined in a vessel. In the upper part of Reactor Pressure Vessel (RPV), steam separator and drier ise located. Only a small part of the coolant is converted to steam. The remainder is circulated by pumps in the bottom part of RPV.

Because the upper part of reactor pressure vessel is filled with the steam separator, the control rods have to be inserted from the bottom. Whereas PWR containments are generally designed to withstand the full pressure generated by a large LOCA, BWR containments depend on pressure suppression systems: The steam escaping e.g. after a pipe rupture is conducted into a heat sink (a water pool).