Drywell and Wetwell in BWR Containments
BWR containment buildings. Modern boiling water reactors (BWRs) have no steam generators, so that the reactor coolant system is more compact than that of pressurized water reactors (PWRs). The containment building can be correspondingly smaller. On the other hand BWRs also utilise the large heat sink inside the containment building for energy removal during reactor isolation events. This is due to the fact the excess of energy is formed by slightly radioactive steam, which cannot be released to the atmosphere. The BWR containments vary widely depending on certain reactor design.The major containment designs are the Mark I, Mark II and the Mark III. The BWR containments consist usually of the following parts:
- Drywell. A drywell houses the reactor coolant system.
- Suppression pool or wetwell. A wetwell is a suppression chamber, which stores a large body of water and therefore it is commonly called as the suppression pool.
- Containment envelope. The Mark III containment has a leak tight, cylindrical, steel containment vessel. This vessel surrounds the drywell and the suppression pool.
The purpose of the drywell and the wetwell (suppression pool) is to reduce the pressure if a LOCA or a MSLB occurs. The steam from a leak in these cases enters the drywell and is directed through submerged tubes into the water of the suppression pool (wetwell), where it condenses, and the pressure in the drywell is reduced.