GENERAL

Performance of containment systems

1.55. The performance parameters for containment systems should be established in accordance with the functions to be performed in the operational states or design basis accident conditions assumed in the design of the plant. In particular, performance in terms of structural behaviour and leaktightness should be established for the entire period of an accident, including recovery of the plant and establishment of safe shutdown conditions.

1.56. On the basis of the performance parameters, the analyses carried out for each postulated initiating event and each set of plant operating conditions should define a set of design parameters for each containment system. The strictest set of these parameters should become the design basis for each containment system. Examples of these design parameters include heat transfer rates, response times for the actuation of safety features, and the closing and opening times of valves.

1.57. Containment systems should be so designed that their instrumentation and control systems and electrical, structural and mechanical parts are compatible with each other and with other items important to safety.

1.58. Attention should be paid to accidents initiated in shutdown states (e. g. with the containment open and systems disabled for maintenance). In this condition the configuration of the containment systems may be different from their configuration under power, and attention should be paid to the redundancy levels and specific failure modes of systems and equipment. In some cases the containment may lose leaktightness because a hatch or a personnel lock has to remain open for a certain period of time. The time necessary for closure of the hatches or personnel locks should be compatible with the kinetics of the accidents postulated to occur in these conditions.