PWR Ice Condenser Containments.
The third type of PWR containments are the Ice-Condenser Containments. In this type of containments, ice baskets containing ice are provided in the upper portion of the containment (Fig. 1.6). The principal is to direct the flow of steam discharged during the postulated design basis LOCA through the ice baskets, that would suppress the steam pressure to 1/4th to 1/5th of that used in the design of large dry PWR containments. Figure 1.6 depicts a reinforced concrete ice condenser containment. It consists of a reinforced concrete hemispherical dome supported by a reinforced concrete cylinder, which, in turn, is supported by a reinforced concrete basemat. Metal liner plates are attached to the inside of the dome and the cylinder, and installed on the top of the basemat for making the containment essentially leaktight. Compared to the large dry PWR containments, the ice condenser containments have some special features required to ensure proper functioning of the suppression mechanism. At the floor below the ice baskets, there are inlet doors which, under a design basis accident, open up to allow the steam to pass through the ice baskets, which in turn, lowers the pressure in the containment. The thick RC primary shield wall surrounds the reactor pressure vessel, and supports the refueling cavity. The transfer of fuel assemblies from the reactor (through refueling cavity) to the spent fuel pool is similar to that described for other PWR containments. The crane wall supports the polar crane and surrounds the steam generators, pressurizer, and reactor coolant pumps. The operating floor, in general, is a RC slab supported by steel or concrete girders. Most of the movements of the movable equipment, replacement of equipment, and inspection and maintenance activities are performed from this floor. Also, the fuel transfer activities are mostly performed from the operating floor. Just below the ice basket floor, and between the containment liner and the crane wall, there are intermediate floors, which support the high energy pipes (main steam and feed water pipes) and are designed to withstand the pressures and temperatures generated by rupture of these pipes.
There are nine containments with ice-condenser designs in the United States — seven of them are steel containments, and two are of RC construction with the metal liner attached to the inside surfaces of the concrete containments. Figure 1.6 shows a PWR Ice condenser with RC containment. The internal ice-basket layout and the internal structures in the steel ice condenser containments are similar to that shown for the RC containment. However, the free standing steel containment is enclosed by a reinforced concrete shield wall, similar to that shown in Fig. 1.4.
Table 1A.4 of Appendix 1A of this chapter shows the plant-specific parameters of the nine PWR ice condenser containments.