5.19. Periodic structural tests should be conducted to demonstrate that the containment structure continues to perform as intended in the design. The test pressure should be the same as in the pre-operational test and as required by the applicable design codes. In the design, attention should be paid to the additional stresses imposed by the tests, and margins should be included to prevent the tests from causing any degradation of the containment structure. A leak test should be performed during any structural integrity test. Additional guidance is provided in Ref. [5].[12]

5.20. The design should provide the capability for periodic in-service testing of the leak rate to prove that the leak rate assumed in the safety analysis is maintained throughout the operating lifetime of the plant. The in-service leak rate tests may be made at either:

(a) A pressure that permits a sufficiently accurate extrapolation of the measured leak rate to the leak rates at the accident pressures considered in the safety analysis; or

(b) The containment design pressure.

5.21. There are also methods available to provide a continuous estimate of the overall containment leak rate during plant operation and to derive rough indications of containment leak rates in accident conditions. Such approaches are generally based on variations in the containment pressure or the mass balance during normal operation of the plant. In some cases, the use of these methods together with extensive local leak rate tests during shutdown for refuelling may justify a reduction in the frequency of the global tests.

5.22. The design should permit leak tests of isolation devices, air locks, penetra­tions and containment extensions (para. 5.12).

5.23. The design should facilitate local testing by providing access to penetra­tions and incorporating necessary connections and isolation valves.

5.24. To permit greater precision in measuring the leak rate and to improve the detection of leaking valves, a capability for testing individual valves should be provided. This may require the provision of additional isolation valves.

5.25. Design provisions should be made to permit testing of the secondary confinement envelope (the secondary containment and the surrounding building). Local leak tests of isolation devices, air locks and penetrations should also be considered.

5.26. In containments with a pressure suppression pool, features should be provided for periodically assessing any leakage that might lead to bypassing of the pool, so as to ensure that the bypass rate of the pool is consistent with the value considered in the safety analysis.

5.27. The design should permit the functional testing of the equipment in containment systems during normal plant operation.