Earthquake resistant hall for a nuclear boiler and its confinement chamber

A nuclear hall including a boiler and a confinement chamber capable of withstanding earthquakes, said hall comprising:

• a concrete structure comprising a substantially horizontal ground-supported concrete raft, and side walls standing substantially vertically on said raft;
• a metal confinement chamber having a vertical axis and a base, said chamber being placed in between said side walls and resting on said raft via said base having a surface area that is at least 25% less than the maximum horizontal section of said chamber;
• a nuclear boiler comprising a steam production block and auxiliary equipment, said boiler being housed inside said confinement chamber, resting on said base, and having a center of gravity which is at a greater distance above the raft than the diameter of the base;
• and means for limiting oscillations of the chamber and the boiler relative to the concrete structure, while still permitting relative thermal expansions and contractions therebetween;
• the improvement wherein the means for limiting oscillations comprise:
• an annular metal floor inside the confinement chamber surrounding the steam production block and being fixed thereto at a predetermined height above the base, internal radially-extending stiffeners evenly distributed around the axis of the confinement chamber for reinforcing said floor;
• at least one internal hydraulic jack acting radially between the outer end of each of said internal stiffeners and the inside surface of the confinement chamber and having a movable part, and an internal thrust block located between said jack movable part and the wall of the chamber and positioned in surface contact therewith;
• at least one external hydraulic jack acting radially in opposition to each of said internal jack-equipped stiffeners and being located between said side walls of the hall and said outside surface of the confinement chamber and having a movable jack part, and an external thrust block located between said external jack movable part and the wall of the chamber, with each external thrust block being disposed opposite to a corresponding one of the internal thrust blocks and in surface contact with said chamber wall;
• pressure accumulators operatively connected to said jacks, respectively, for applying a permanent fluid pressure to each of said jacks, tending to cause them to press said thrust blocks against the wall of said chamber and in opposition to each other;
• said thrust blocks being smooth so as to impart no damage to said wall surfaces in contact with the confinement chamber wall during relative movement therebetween;
• and
• non-return valve means disposed between each jack and an accumulator connected thereto to limit the flow of working fluid in the direction from the jack to the accumulator, thereby limiting the speed at which each jack movable part can move away from the wall of the chamber when a compression force is applied thereto during some phase of an earthquake, while allowing the jack movable part to return freely, during opposing phases of an earthquake fast enough to cause said thrust blocks to remain permanently pressed against the chamber wall, regardless of the motion of the chamber and the boiler, or the deformation of the floor;
• the non-return valve means of each internal jack limiting the compression movement of the jack movable part to a slow speed which is slow eough to avoid substantial energy dissipation in said internal jacks or any large displacement of the boiler relative to the chamber during an earthquake, said slow speed being nevertheless greater than the speed of relative motion caused by differential expansions and contractions of the chamber and the boiler, whereby such non-earthquake relative displacements take place substantially unhindered by the jacks.