4.190. Penetrations (containment air locks) for access by personnel or equipment to the containment are required to have air locks equipped with doors that are interlocked to ensure that at least one of the doors is closed during reactor operations and in design basis accidents (Ref. [1], para. 6.58). In addition, they are required to be designed to prevent any undue exposure of operators to radiation in operational states of the plant.

4.191. The two air lock doors should be designed to withstand the same plant conditions as the containment. Local transient effects, such as exposure to open flames caused by hydrogen burning, need not be considered for the outer door.

4.192. The chamber between the two air lock doors should be so sized as to allow the passage of necessary maintenance equipment and a sufficient number of personnel, so as to avoid having to open the air lock too frequently during plant shutdown and maintenance.

4.193. The inner door of the air locks should be of a pressure sealing type. Double seals should be provided on each door and there should be provisions for testing the leaktightness of the doors and the inter-seal space. Low pressure alarms should be provided if inflatable seals are used.

4.194. Equipment hatches are large openings in the containment structure that are normally closed. They are usually designed with a bolted flange, whose leaktightness is ensured by means of soft elastomeric seals. Leak testable double seals should normally be provided. Loads and deformations due to temperature effects should be taken into account in the design of equipment hatches. In order to transport large components, the need may arise to open equipment hatches in certain reactor states other than full shutdown and for which the risk is sufficiently low. The containment should only be opened for such conditions if provision can be made for the rapid closure of equipment hatches, consistent with the possible kinetics of the accidents considered in the design basis for the reactor state concerned.

4.195. Containment openings (i. e. penetrations, air locks and hatches) should normally be closed in order to minimize the active measures required for containment isolation in the event of an accident. Exceptions are allowed if they are necessary for operational reasons and provided that the openings can be closed quickly and reliably to comply with established acceptance criteria that apply for the accident. Provisions for indicating the state of the containment openings should be put in place.