Patent Number: 043269206
Section: summary

The present invention relates generally to nuclear reactors which include a vertically extending reactor vessel containing a number of reactor components and positioned within a cavity located under a reactor deck arrangement and defined by a circumferential cavity wall assembly. As will be seen hereinafter, the present invention is particularly directed to the reactor vessel itself which is separate and distinct from either the deck arrangement or cavity wall assembly and the way in which the vessel is interlocked between the deck arrangement and wall assembly. As just stated, the present invention is directed generally to nuclear reactors of the type including a deck arrangement, a reactor vessel located within a cavity under the deck arrangement and a wall assembly defining this cavity. One such nuclear reactor is a pool type liquid metal fast breeder reactor in which the vessel body is constructed of stainless steel. In the past, this vessel body which is extremely large, for example on the order of 70 feet in diameter, has been provided as a joined part of the deck arrangement itself. However, the belief has been that it is not necessary nor economical to provide a stainless steel deck and, hence, the deck is preferably constructed for the most part of carbon steel. However, in order to interconnect the vessel body with the deck, a bimetallic (stainless steel to carbon steel) weld between the two is necessary. This rather large vessel is to be contrasted with the smaller reactor vessels in a loop type nuclear reactor, e.g., those on the order of 25 feet in diameter, which have been made independent of other components, but which have been supported on their underside by support feet. One drawback in utilizing a bimetallic weld of the type recited relates to the way in which the reactor vessel is inspected for cracks. More specifically, because the vessel body is constructed of stainless steel, present code requirements allow it to be inspected visually which means that simple camera equipment can be utilized for in-service inspections. On the other hand, carbon steel and the carbon steel/stainless steel weld require either ultrasonic or x-ray inspection for cracks. X-ray detection is difficult in the presence of radioactivity and ultrasonic detection is not entirely reliable. However, as will be seen hereinafter, the present invention eliminates the problem by eliminating the bimetallic weld in a manner that is uncomplicated and economical. In view of the foregoing, one object of the present invention is to provide a nuclear reactor of the general type described above but one which includes a reactor vessel separate and distinct from the rest of the components making up the reactor and particularly its deck arrangement. Another object of the present invention is to provide a reactor vessel designed without a bimetallic weld, specifically a vessel constructed in its entirety of stainless steel in a preferred embodiment. Still another object of the present invention is to provide a reactor vessel having a support flange mechanically interlocked with the reactor's deck arrangement and its cavity wall assembly in a way which accomodates thermal displacement and resists seismic forces. As will be discussed in more detail hereinafter, the reactor vessel which is designed in accordance with the present invention for use in a pool-type reactor but which in a smaller size may be used in a loop type reactor includes a main body located within the cavity defined by its cavity wall assembly and an upper circumferential rim forming a support flange located and interlocked between the deck arrangement and an upper section of the reactor's wall assembly, whereby to support the vessel body in place. In a preferred embodiment, the vessel body and its support flange are formed with one another (welded together) and constructed of stainless steel, thereby eliminating the previously recited bimetallic weld. In addition, the support flange and both the deck arrangement and cavity wall assembly provide cooperating shoulders such that the cavity wall assembly supports the reactor vessel and the support flange at the top of the vessel supports the deck arrangement. At the same time, means are provided for allowing thermal displacement and resisting seismic forces between these components.