Patent Number: 041705173
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention provides a new reactor vessel to cavity seal arrangement that forms a permanent flexible seal between the reactor vessel and the reactor cavity floor effecting a water-tight seal for the refueling canal during refueling operations while accommodating material expansions and contractions that occur during normal reactor operations, without destroying the water-tight integrity of the seal. The invention can best be understood by reference to the plan view of a reactor containment illustrated in FIG. 1 which shows a nuclear steam generating system of the pressurized water type incorporating the permanent water tight seal ring of this invention. A pressurized vessel 10 is shown which forms a pressurized container when sealed by its head assembly 12. The vessel has coolant flow inlet means 14 and coolant flow outlet means 16 formed integral with and through its cylindrical walls. As is known in the art, the vessel 10 contains a nuclear core (not shown) consisting mainly of a plurality of clad nuclear fuel elements which generate substantial amounts of heat depending primarily upon the position of control means, the pressure vessel housing 18 of which is shown. The heat generated by the reactor core is conveyed from the core by coolant flow entering through inlet means 14 and exiting through outlet means 16. The flow exiting through outlet means 16 is conveyed through hot leg conduit 20 to a heat exchange steam generator 22. The steam generator 22 is of the type wherein heated coolant flow is conveyed through tubes (not shown) which are in heat exchange relationship with water which is utilized to produce steam. The steam produced by the steam generator 22 is commonly utilized to drive a turbine (not shown) for the production of electricity. The flow is conveyed from the steam generator 22 through conduit 24 to a pump 26 from which it proceeds through cooled leg conduit 28 to inlet means 14. Thus, it can be seen that a closed recycling primary or steam generating loop is provided with coolant piping communicably coupling the vessel 10, the steam generator 22, and the pump 26. The generating system illustrated in FIG. 1 has three such closed fluid flow systems or loops. The number of such systems should be understood to vary from plant to plant, but commonly two, three or four are employed. Within the containment 42 the reactor vessel 10 and head enclosure 12 are maintained within a separate reactor cavity surrounded by a concrete wall 30. The reactor cavity is divided into a lower portion 32 which completely surrounds the vessel structure itself and an upper portion 34 which is commonly utilized as a refueling canal. In prior art designs, air flow communication was maintained between the lower reactor vessel well 32 and the refueling canal 34 to assist cooling of the concrete walls of the reactor cavity and the excore detectors embedded within the concrete walls. The air flow was facilitated by exhaust fans positioned within the containment 40 outside of the concrete barrier 30. During refueling operations, the reactor vessel flange 36 was sealed to the reactor cavity shelf 40 by a clamped gasket seal ring which prevented leakage of refueling water to the cavity space directly below the reactor vessel. Such seals, however, required considerable time be allotted for their installation and could not be fastened into place until the reactor cooled down. Furthermore, installation of the seal cut off the air path which facilitated circulation of the cooling medium around the lower portion of the vessel cavity. This invention expedites refueling procedures by providing a permanent reactor vessel to cavity seal 38 between the reactor vessel flange 36 and the cavity shelf 40 which accommodates the normal material expansions and contractions experienced during reactor operation while maintaining the water-tight integrity of the seal essential during refueling operations. In addition, a structural modification to the cavity wall around the nozzle locations 14 and 16 facilitates air flow in the lower portion of the reactor cavity, which enables cooling to occur during refueling operations as well as during reactor operations. Continuous air cooling is accomplished through the designed enlarged apertures 44 surrounding the coolant piping exiting through the cavity walls 30. The seal ring of this invention can better be appreciated by reference to FIG. 2 which shows a cross-section of the seal and its interface with the reactor cavity shelf and the reactor vessel flange. In its preferred form, the seal is constructed as a 0.25 inch thick stainless steel annular ring having a quarter-circle cross-section with an approximate eight inch radius. At one end the seal 38 is welded to the reactor vessel flange 36 and at the other end to an angle 46, covering an edge of the reactor shelf 40, which is secured by an anchor 48 embedded in the concrete of the cavity wall 30. Thus, the permanent seal 38 maintains the water-tight integrity of the refueling canal 34 and isolates the portion of the reactor vessel well 32 encompassing the vessel 10. The particular design of this invention has been shown to exhibit the flexibility and durability of accommodating over 400 cycles of expansion and contraction, far exceeding the number required to satisfy normal reactor operations and refueling requirements throughout reactor life. Thus, the containment arrangement of this invention expedites refueling operations by removing the present necessity of testing and/or replacing seal O-rings at refueling and the sealing and raising of seal plates, thus increasing the efficiency of reactor operations. Furthermore, the vessel well cooling system can be continuously operated to assure that the excore detectors and concrete cavity walls are continuously maintained below their specified temperature limits, thereby assuring the continued reliability of the containment equipment.