Types of Containment Buildings
- Full pressure dry containment (PWR). Dry containment envelope is a steel shell or a concrete building (cylindrical or spherical) that surrounds the NSSS (Nuclear Steam Supply System). During normal operation a prescribed negative pressure is maintained by a fan cooler system. During accidents the pressure-suppression and the heat sink can be accomplished by a fan cooler system or by a containment water spray system.
- Full pressure double wall containment (PWR). This containment usually consist of a primary containment shell (a steel or concrete shell, basically cylindrical or spherical in shape) and a secondary confinement building (a concrete shell surrounding the primary containment). The principle of the primary containment is similar to that of the full pressure dry containment. The secondary confinement building protects the systems and components against external postulated initiating events and captures leakage from the primary containment.
- Bubbling condenser containment building (PWR). The bubbling condenser containment system uses a concept for the suppression pool or suppression pools in which the high pressure steam following a LOCA or a MSLB conditions is directed through submerged tubes into pools of water. In this pools the steam is condensed and this acts against the pressure increase.
- Ice condenser containment building. The ice condenser containment system uses a concept of ice chambers in which the high pressure steam following a LOCA or a MSLB conditions is directed into chambers containing baskets filled with ice. In this chambers the steam is condensed and this acts against the pressure increase.
- 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.
- Pressurized containments in heavy water reactors. In comparison with LWR containments, most of the HWR containment buildings are accessible, therefore a ventilation is needed for maintaining working conditions. Some units use a single unit suppression, which consist of:
- A containment envelope comprising a prestressed, post-tensioned concrete reactor building.
- A large dousing tank, which is elevated around the building dome and a powerful spray system.
- A long term containment cooling system
Some units use a multi-unit vacuum building, where more containment envelopes (more units) are connected to a common vacuum building with powerful energy and pressure suppression system.