Not all structural sections are pre-stressed, even in pre-stressed concrete containments. Pressurised water reactors have cylindrical containments with cupolas on top. The cylinder walls and cupola are pre-stressed, the base slab is not. Boiling water reactors, on the other hand, have flat cylindrical covers; only the cylinder walls being pre­stressed. Pre-stressing increases the containment’s serviceability, i. e. it keeps defor­mation and cracking low; but the cross-section of the concrete cannot be overpressed completely, to ensure integrity in problem areas such as transitions between structural

sections or around openings, so today’s pre-stressed concrete containments are fitted with steel liners to guarantee their integrity. One example of a pre-stressed concrete containment with a steel liner is EPR containment.

The steel liner is anchored to the concrete structure via headed studs and/or steel profiles to give a composite steel-concrete structure. To avoid affecting the pre­stressing, the steel liner is made of thin plate, t = 6 mm, for example. When verifying the structural strength of a containment, the steel liner is only taken into account if its effects are adverse.

Pre-stressing the concrete structure induces a compressive strain in the steel liner. Pre­stressing also induces a time — and stress-based concrete creep which devolves the stresses involved and puts an additional compressive strain on the steel liner. The liner also expands under the influence of dissipation of the heat of hydration and as the concrete shrinks and also under the effects of operating conditions and in incident cases. The verification of liner integrity is obtained by limiting the liner strains and the action effects of the connectors.

Pre-stressed concrete containments with steel liners can be designed using DIN 25459 [16].