Of the PWR plants that have been licensed for commercial operation in the United States, ^80% utilize either reinforced or prestressed concrete pri­mary containments. In meeting the same basic func­tional and performance requirements as noted for BWR containments, the concrete containments in PWR plants are of three different functional designs: subatmospheric (reinforced concrete), ice condenser (reinforced concrete), and large/dry
(reinforced and prestressed concrete). The primary differences between these containment designs relate to volume requirements, provisions for accident load — ings/pressures, and containment internal structures layout. The PWR containment structure generally consists of a concrete basemat foundation, vertical cylindrical walls, and dome. The basemat may consist of a simple mat foundation on fill, natural cut, or bedrock or may be a pile/pile cap arrangement. Most of the plants have utilized the simple mat on fill or bedrock design. Interior containment surfaces are lined with a thin carbon steel liner to prevent leakage. Exposed surfaces ofthe carbon steel liner are typically painted to protect against corrosion and to facilitate decontamination should it be required. Depending on the functional design, the concrete containments can be on the order of 40-50 m in diameter and 60-70 m high, with wall and dome thicknesses from 0.9 to 1.4 m and base slab thicknesses from 2.7 to 4.1 m. Two of the PWR plants (Bellefonte and Ginna) have rock anchor systems to which the post-tensioning tendons are attached. Figure 3 presents a cross-section for a prestressed concrete, large, dry containment.

The containment internal structures in PWR plants are typically constructed of conventionally reinforced concrete and tend to be more massive in nature than the internal structures in BWR plants, because they typically support the reactor pressure vessel, steam generators, and other large equipment and tanks. In addition, these structures provide shielding of radiation emitted by the NSSS. Some of the specific functions that these structures (typically floor slabs, walls, and columns) are required to per­form include the following:

1. provision of human accessibility;

2.

support and separation of various plant equipment;

3. resistance to emergency loading conditions;

4. transfer of containment loads to containment foundation;

5. missile protection; and

6. channeling/routing steam and air through ice condensers (PWR ice condenser containments).

PWR plants that utilize a metallic primary contain­ment (large dry and ice condenser designs) are usually contained in reinforced concrete ‘enclosures’ or ‘shield’ buildings that, in addition to withstanding environmen­tal effects, provide radiation shielding and particulate collection and ensure that the freestanding metallic primary containment is protected from the natural environment. The secondary containment consists of a vertical cylinder wall with shallow dome and is often supported by the containment basemat.

Except for differences in the spent — and new-fuel storage pools, structures that fall into the other struc­tures category are essentially the same at the PWR and BWR plants. The spent — and new-fuel storage pools for PWR plants are typically located in an auxiliary building proximate to the containment. These reinforced concrete wall and slab structures are generally massive in cross-section to support a large pool of water and the fuel elements and are lined on the water side with stainless steel. The pools are connected to the reactor/refueling cavity (inside containment) via a transfer channel that is also a safety-related structure since it must provide radia­tion shielding and support for the fuel transport mechanism and fuel.