4.107. The ice condenser containment is divided into three main compart­ments: a lower section, an upper section and the ice condenser chambers. After a high energy pipe rupture, a flow path from the lower compartment to the upper compartment through the ice condenser is established. When the high pressure steam-air mixture flows between the columns of borated ice, the steam condenses on the surface ice. If the flow of steam continues for an extended period of time, a complete meltdown of the ice will occur. Long term energy management should then be performed by some other means, for example by containment spray systems.

4.108. The design of the ice condenser system should be such as to ensure that:

— The rate of heat transfer from the steam to the ice columns is sufficient in all postulated accident conditions (i. e. that the ice loading is sufficient).

— The structures of the ice condensers maintain their geometry under any accident loading.

— The vent doors open reliably.

4.109. The heat transfer correlations used in the calculations for the ice condenser system should be based on representative tests.

4.110. The ice condenser should be designed to permit periodic maintenance, inspection and testing. The important features of the ice condenser that should be maintained during operation are the ice temperature, the total amount of ice, the uniformity of distribution of the ice, the adequacy of the flow passages between the ice columns and the operability of the vent doors. The long term behaviour of the containment systems should be considered in the design. In the course of an accident, air and non-condensable gases will flow into the upper compartment while the lower compartment becomes filled with steam. Thus the containment spray, if injected into the upper compartment only, will not reduce the pressure below a certain limit, which will depend on the ratio of the volumes of the compartments. If equipment is installed for direct energy management for the lower compartment, a vacuum relief system of an appropriate design to eliminate pressure differentials between the two compartments should be included.