Contemporary Nuclear Vessel Design

In nearly all projects, the basic structural design is a cylindrical vessel with flat end slabs or a convex dome. Practically all recent nuclear structures consist typically of two shells, the inner and the outer containment. Today, the post-tensioned nuclear structures have reached an outside diameter of 50m and a height of 70m of the inner shell with a capacity of 1600MW.

Three types of BBR post-tensioning tendons are typically used the inner containment, as follows:

• Vertical tendons for wall post-tensioning
  The lower anchorage is situated in the roof of the tendon gallery and the higher anchorage is placed on the ring in the base level of the dome.
• Horizontally looped tendons (hoop tendons)
  These can accommodate a varying number of vertical buttresses (ribs) – for example, four buttresses with 180° tendon hoops or three buttresses with 240° tendon hoops.The tendons are anchored alternately in one of the vertical ribs and both anchorages are situated on opposite sides of the same rib.
• Cane shaped tendons
  These are placed in two right angled planes in the dome, which have a varying length.The lower anchorage is situated in the roof
  of the PT gallery and the upper anchorage is placed under the
  retaining ring of the dome.

During the entire lifetime of the pressure vessels, the greatest attention must be paid to the protection of the prestressing steel from corrosion. The BBR Network uses three different types of corrosion protection for nuclear tendons:

• Cement grouted tendons
  The cementitious grout surrounds the prestressing steel in an alkaline environment that inhibits corrosion. If there is a local fracture of a tendon, part of the prestressing force remains transmitted to the concrete due to the bond with the grout.
• Grease or wax grouted tendons
  For these unbonded tendons, the prestressing force is transmitted to the concrete primarily at the location of the anchorages. Corrosion is prevented by grease, corrosioninhibiting compounds or wax. The tendons can be mechanically tested in-situ and the actual prestressing force can be monitored by lift-off tests or through permanently installed equipment.They can be retensioned and they can also be removed for visual inspection and eventually replaced.
• Tendons protected with circulating dry air
  For these unbonded tendons, the same properties and advantages apply as for the grease grouted tendons.

To Top | Back