Containment - Bird's Eye View


A key principle in the design of the nuclear plant is defense in depth. There are intended to be 3 barriers between the radioactive fission products and the public in order to reduce the likelihood of radioactive releases. These 3 barriers are - the fuel cladding, the reactor coolant piping, and the containment. An EdF figure best illustrates this concept.

The containment is a large steel building, usually with a hemispherical dome. Containments are often not visible since they are usually surrounded by a steel or concrete building that provides additional boundaries and aesthetically pleasing designs.

The containment is capable of sustaining high internal pressures. Design is in the range of 45 to 60 psig, however, much higher pressures, even exceeding 100 psig may be sustained. Ice condenser containments are usually designed for about 12 psig. In either case, the containment is designed for a double ended rupture of the largest diameter pipe in the structure. These pipes are usually 3 feet in diameter.

The containment houses the reactor, reactor cooling or recirculation system and pumps. For PWRs, the pressurizer is also in the containment.

Containments have fans or chiller units for cooling during normal conditions and in the unlikely event of an accident. To provide additional cooling and pressure suppression, several ring headers are mounted in the uppermost part of the containment. These ring headers are used to spray water (often borated) to reduce pressure.

Below the containment basement, there are sumps that can be used during accident conditions. The sumps can be routed to cooling systems so that the fluid may be recirculated and cooled. A grating system is installed over the containment sump (click for photo of sump) to prevent materials from being sucked into the cooling system, usually called the Residual Heat Removal system.

PWR Containment
This photo provides a birds-eye view from the top of a PWR containment.
Using the center of the photo as a reference:

The refueling pool is directly below. During a refueling the head is removed from the reactor and is stored within the containment. The upper internals are removed and stored underwater in the refueling pool.

The crane (orange-color) is used to move new and old fuel. Directly below is the reactor.

Steam generators can be seen in the lower right and just to the upper right from the center.

Ventilation ducts can be seen along the wall of the containment.

The reactor coolant pumps, pressurizer, and emergency core cooling accumulators are also found in the containment.

Photo (of photo at a plant) by J.A. Gonyeau

The following equipment is located within the containment. Numbers below refer to the containment diagram.


Component Name


Component Name

101 Unit Vent 114 Equipment Hatch Lifting Gear
102 Auxiliary Boiler Stack 115 Reactor Head Decontamination & Storage Area
103 Containment Spray header 116 Refueling Machine
104 Steel Liner 117 Internals Lifting Rig
105 Polar Crane 118 Pressurizer
106 Laydown Area 119 Reactor
107 Main Steam Lines 120 Reactor Cooling Pumps
108 Main Feedwater Pipes 121 Accumulators
109 Steam Generators 122 Reactor Coolant Pump Motor Oil Collection Tank
110 Hydrogen Mixing Fans 123 Incore Instrumentation
111 Control Rod Drive Mechanism Fans & Plenums 124 Upper Internals Storage Stand
112 Containment Coolers 125 Reactor Coolant Drain Tank
113 Equipment Hatch Lifting Gear 126 Pressurizer Relief Tank
BWR Containment

There are 3 types of BWR containments. These are discussed and illustrated on pages 3-15 through 3-18 of the NRC's Boiling Water Reactor Systems Manual. The designs are also nicely illustrated in the Union of Concerned Scientists' page on BWR containment overpressure, as illustrated below.

Courtesy Union of Concerned Scientists

Mark I is the traditional torus and inverted light bulb design. This was the first generation of BWR containment, as used in the BWR 1 through 4 designs. Twenty two units have this style of containment. The design includes:

Mark II containment was the second generation containment as used with late BWR-4 and BWR-5 reactors. The Mark II design is an over-under configuration. The design includes:

The Mark III containment is used with the newest BWR reactor designs. The design includes:


Containment during Refueling

The Refueling operations page links to photos and graphics showing containment activities during a refueling.

Copyright 1996-2006.  The Virtual Nuclear Tourist. All rights reserved. Revised: January 5, 2006.