Patent Number: 046474234
Section: summary

BACKGROUND OF THE INVENTION The present invention relates generally to nuclear reactors and more particularly to an improved fuel handling apparatus for a nuclear reactor. Certain types of nuclear reactors, such as high temperature, gas-cooled reactors (HTGR), typically employ an array of fuel elements which form a core within the interior of the reactor. The core is enclosed within a reactor vessel. It is desirable to remove fuel elements from the reactor core periodically and replace them with new fuel elements. It may also be desirable to shift fuel elements to different positions within the reactor core. Elongated fuel elements of hexagonal cross-section are commonly stacked upright to form the core. This general type of core construction is described in U.S. Pat. No. 3,383,286 to Paget, which is incorporated herein by reference. It is known for a device for manipulating fuel elements within a reactor vessel to access the reactor core through an opening in the top of the vessel. In some relatively recently developed reactors, it has been found desirable to utilize the space above the reactor core for heat exchange apparatus and the like, without leaving space for access to the core from above by fuel handling apparatus. With this type of arrangement, it is desirable to access the core through an opening in the side of the reactor vessel. The various fuel elements are distributed in predetermined locations and typically abut one another at their sides. Accurate placement is necessary in order to position the elements in their locations. Accordingly, it is desirable that fuel handling apparatus be capable of operating with a high degree of precision. In addition, it is desirable that the apparatus lift and lower the elements along vertical paths to avoid excessive friction with adjacent elements. Friction with adjacent elements may require downward forces in excess of the gravitational force exerted on the element to bring the element to a desired elevational location. Accordingly, the fuel element handling apparatus should be capable of exerting downward force onto the elements as well as upward force. The vessel herein may be required to support a relatively high pressure differential between its interior and its exterior. To lessen interference with the structure of the vessel, it is desirable that a single penetration of relatively small diameter be sufficient to provide access to the entire core for the fuel handling apparatus. Accordingly, the fuel handling apparatus should fit through a relatively small penetration and include means for accessing fuel elements at various locations within the vessel, and should be capable of carrying a fuel element through a relatively small penetration. In addition, it is desirable that the fuel handling apparatus be capable of transporting fuel elements over relatively long distances both laterally and vertically so that both removal of spent fuel elements from the vessel to a desired remote location and, transportation of new fuel elements from a desired remote location to the interior of the vessel may be accomplished. It is further desirable that the fuel handling apparatus be adequately sealed to the vessel so that escape of radioactive material from the vessel is avoided or minimized during operation of the apparatus. The radioactive environment within the vessel excludes certain types of mechanisms from use within the vessel. Hydraulic systems, for example, may not be suitable due to breakdown of hydraulic fluids in the radioactive environment. There is a need for a fuel handling apparatus which is acceptable for use in a reactor having its refueling port located on the side of the vessel rather than in the top. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided fuel handling apparatus which is extendable through a refueling port or penetration in the side of a reactor vessel. The apparatus includes a housing defining a longitudinal axis extending through the penetration, reversible lifting means for raising and lowering fuel elements, first and second pivot arms for enabling manipulation of the lifting means, a movable support member for supporting the first and second arms, and lateral transport means for moving the support member axially of the housing. In the illustrated embodiment, a grapple head of known design for releasably supporting a fuel element from above the fuel element is supported by the lifting means. The lifting means is rigidly mounted on the second arm, which is pivotal about a horizontal axis through the first arm, so that it may be pivoted between a first position enabling lifting and lowering of the fuel elements and a second position for enabling a fuel element to be transported through the penetration. The first arm pivots about a vertical axis through the support member to enable the fuel handling apparatus to access various locations in the array of fuel elements within the reactor vessel by permitting horizontal movement of the lifting means transversely of the direction of motion of the lateral transport means. The preferred lateral transport means comprises a telescoping member and means for extending or retracting the telescoping member. Accordingly, it is a general object of the present invention to provide fuel handling apparatus which is extendable for operation through a penetration in the side of a nuclear reactor vessel. It is a further object of the present invention to provide fuel handling apparatus which enables lifting means to be inserted through a relatively small opening and to be positioned above any of a plurality of fuel elements making up the core of the reactor. It is an additional object of the present invention to provide fuel handling apparatus including lifting means which apply either upward or downward force to a fuel element and which may pass through a relatively small penetration in the side of a reactor vessel while supporting a fuel element. It is an additional object of the present invention to provide fuel handling apparatus for transporting fuel elements both laterally and vertically over relatively long distances.