Patent Number: 041558090
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to nuclear reactors, and more particularly provides a variable stiffness support system for support structure in the annular region of a condenser type reactor containment. 2. Description of the Prior Art Commercial nuclear reactors typically include a primary reactor system circulating a fluid coolant through a reactor core. The primary system is enclosed in a reactor containment building. Consistent with the stringent safety oriented attitudes of the nuclear industry, the containment is designed to withstand a pressure transient under assumed major accident conditions. A particular containment design includes a fusible material such as ice, in the solid state, supported in a lattice within an annular region surrounding the primary system to quench the pressure transient. This "condenser" type containment is more fully described in U.S. Pat. No. 3,423,286. Within the annular region are not only large quantities of the fusible material typically held in baskets supported in a lattice structure, but also cooling ducts extending vertically about sixty feet, to circulate a cooling medium, such as air, thereby maintaining the fusible material in solid form. Support of the lattice and the ducts has, in the past, been performed by massive mechanical structures which include a multitude of fasteners. This large and complex support structure resulted from stringent design limitations including (1) the need for insulating the support structure from the atmospheric temperature surrounding the primary system, (2) the large pressure loading on the outer surface of the cooling ducts under accident conditions, and (3) the large mechanical loadings transmitted to the structure under seismic or other abnormally high mechanical loadings. Also, these limitations, particularly the latter, are variable with each nuclear plant, and therefore required provision of separately designed support structure with different frequency response at each individual plant. The prior art support structures therefore include a large beam rigidly affixed to the annulus wall, heavily insulated, with numerous connections to the ducts and the lattice, both of which are supported from the beam. The beam transmits both duct and lattice loads to the concrete or steel wall of the annulus. The structure must be specifically designed for proper seismic response, including different beams for each reactor plant. It is highly advantageous to provide a support structure that minimizes the massive support structures presently designed, that is easily adjustable for plant sites with varying seismic spectrums, that minimizes the amount of fasteners, and that is compatible with existing duct and lattice structures. SUMMARY OF THE INVENTION This invention provides a structure for supporting the lattice which supports a fusible material, such as ice, in the solid state, in the annular region of a condenser-type reactor containment. The inventive support structure affixes the lattice to a wall of the annular region in a manner which not only is easily adjustable to varying seismic requirements, but which also significantly lessens the mass of the support structure and the number of fasteners required. It further allows the pressure load on the vertical cooling ducts which have a very high surface area to be transmitted under accident conditions directly to the annular region wall, and not necessarily through the lattice support structure. The lattice support structure includes a horizontal elongated support member, such as a U-shaped channel, spaced from, and rigidly affixed to, an annular wall. Within the horizontal member is a flexible member, such as a hollow rectangular tube. The horizontal support member and flexible member are affixed such that the flexibility of the flexible member is selectively adjustable. This attachment can be by joining of the two members with two bolts. Varying the position of the bolts varies the flexibility of the flexible member and the resulting bending under load. The lattice structure is movably coupled to the flexible member by a connection, such as a spherical bushing, that allows relative motion between the lattice and the flexible member. The cooling ducts can be rigidly affixed directly to the wall or to the horizontal support member so that pressure loads under accident conditions are transmitted directly from the ducts, to the support member, and to the annular wall. It will be evident that the same lattice support structure can be utilized at nuclear plants designed for different seismic loading, merely by varying the position of the bolts joining the flexible member and the support member. Under seismic or other inordinately high mechanical loading of the annular wall, the disclosed support structure assures that an improper frequency loading of the lattice is avoided.