Containment spray systems

4.90. The energy management function of the spray system is to remove thermal energy from the containment atmosphere in order to limit both the maximum values and the time durations of the high pressures and tempera­tures within the containment envelope following a design basis accident.

4.91. Containment spray systems should be designed so that a major fraction of the free volume of the containment envelope into which the steam may escape in an accident can be sprayed with water after a LOCA. For ice condenser containments, consideration should be given to installing spray systems in both the upper and the lower compartments (para. 4.110).

4.92. The spray headers and nozzles should be designed to provide an even distribution of water droplets, which should be small enough to reach thermal equilibrium with the containment atmosphere quickly during their fall.

4.93. The initial source of water for the containment spray system after a pipe rupture is usually a large storage tank. Later the spray system may operate in a recirculation mode and take water from appropriate collection points in the containment sump or the suppression pool. In determining the necessary capacity of these collection points, the need to protect equipment important to safety by preventing its submergence or by ensuring its operability despite its submergence should be taken into account in the design. Where this is not feasible the equipment should be relocated.

4.94. When the spray system is designed to operate in a recirculation mode, the spray nozzles should be designed against clogging by the largest postulated pieces of debris that can reach them through the intake screens. In the same way, the spray pumps should be designed to cope with cavitation or failure due to debris in the pump suction lines.

4.95. The pressure limiting effect of spray systems may depend on the time necessary for spray to be delivered after a LOCA. The delay time for spray delivery should therefore be determined for use in analyses of containment pressure and temperature transients. The actuation times of components and the time necessary to fill the spray piping, headers and nozzles should be taken into account in the analyses.

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