4.196. Concrete should have characteristics of quality and performance (strength, porosity and tightness) consistent with its use. The quality of the concrete used for containment structures should be correspondingly high, consistent with the safety function of the containment. Design considerations will depend on the containment concept: a concrete containment with stressed cables usually ensures both strength and leaktightness, whereas a reinforced concrete containment structure usually ensures only strength while its steel liner ensures leaktightness.

4.197. Consideration should be given to the design capacity of the concrete to cope with the loads (pressure loads and thermal loads) and environmental conditions (of heat, moisture and radiation) generated by design basis accidents. This should lead to strict specifications for the concrete in terms of strength and leaktightness.

4.198. Concrete with appropriate rigidity, thermal expansion and resistance to compression should be used for all electrical penetrations, large penetrations such as equipment hatches and the joint with the basemat.

4.199. In prestressed containments, the concrete should remain in a prestressed condition even in accident conditions. Concrete materials that would limit creep or shrinkage over the years and with low porosity should be used. The possible loss of prestress of the containment tendons over the operating lifetime of the plant should be evaluated and considered in the design.

4.200. Sleeve-concrete interfaces should be designed to minimize leaks by avoiding direct paths through the interface.

4.201. Design and construction processes should be such as to prevent the development of cracks or high leak zones.

4.202. Ageing effects are required to be evaluated in the selection and design of types of concrete (para. 4.39 and Ref. [1], para. 5.47).

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