Patent Number: 055704026
Section: summary

BACKGROUND OF INVENTION 1. Field of the Invention This invention relates to supports and, more particularly, to boiling water reactor control rod drive housing supports. Still more particularly, this invention relates to control rod drive housing supports with radiation shields. 2. Description of Prior Art In boiling water reactors the control rod drive housing supports are generally located underneath the reactor vessel near the control rod housings. The control rod drive housing supports limit the travel of and support a control rod in the event that a control rod drive housing is ruptured. The supports help prevent a loss of control as a result of a housing failure, thus protecting the fuel barrier. Typically, control rod drive housing supports consist of hanger rods that are attached and supported at their upper end at a beam structure immediately underneath the reactor pressure vessel and support bars which are bolted between the hanger rods below the control rod drives. Another grid of bars is installed on the support bars to transfer the load of a ruptured control rod drive housing to the support bars. Generally, a pair of grid bars support each control rod drive. Each pair of grid bars are held together by two grid clamps and a bolt. In this support system of the prior art, when it is necessary to change or replace a control rod drive, the grid bars must be removed. In order to remove the grid bars the operator must manually unscrew the grid clamp bolt, remove the two grid clamps and then remove the grid bars, each weighing approximately forty pounds. The number of grid bars which must be removed depends on the number of control rods which must be replaced. Furthermore, since the grid bars are interlocking, they must be removed starting from the outer peripheral row. Thus, if a large number of control rod drives must be replaced or if an inner control rod drive must be replaced, a large number of grid bars must be removed. The result is a time consuming and cumbersome process. Moreover, as the grid bars are heavy and awkward to handle, a dropped bar could result in serious injury. Further still, the persons handling the grid bars or working under the reactor pressure vessel are subject to substantial radiation doses. The more time a person must spend replacing the control rod drives, the more that person is subject to dangerous radiation doses. Thus, there is a need in the art for an apparatus to reduce and minimize the radiation exposure of a person working under the reactor pressure vessel of a boiling water nuclear reactor. SUMMARY OF THE INVENTION It is an object of the present invention to provide radiation shields to minimize the amount of radiation a person is subject to when replacing a control rod drive or working under the reactor pressure vessel. It is another object of the present invention to support a control rod drive housing in the event that a control rod housing is ruptured while allowing for quick and easy replacement of a control rod drive. It is another object of the present invention to provide a control rod drive housing support which can be removed automatically. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the appended claims. To achieve the foregoing and other objects, in accordance with the present invention, as embodied and broadly described herein, the control rod housing support system of this invention may comprise a first means for supporting a control rod drive in the case of a housing failure; a second means for supporting the control rod drive in the case of a housing failure and for shielding persons working under the reactor vessel from radiation, the second means being supported by the first supporting means, wherein the second means can be raised and lowered between a non-support position where the control rod drive is not supported and a support position where the control rod drive is supported; and a radiation shield means for shielding persons working under the reactor vessel from radiation, the shield means being provided about the control rod drive above the second supporting means. The first supporting means may comprise a plurality of support members provided in rows on opposing sides of a lower portion of a plurality of control rod drives and the second supporting means may comprise a plurality of support cups, each of the support cups receiving, and shielding a lower portion of the control rod drive and supporting the control rod drive in the case of a housing failure. Further, the radiation shield means may comprise a plurality of shield rings, each of the shield rings being disposed about a control rod drive housing and including pin means for maintaining the shield rings in position about the control rod drives when the support cups are removed. The shield rings are supported on the support cups when the cups are in their installed position. The shield rings may also include slots for accommodating seismic restraints between adjacent control rod drives. In accordance with a further aspect of the present invention, in accordance with its objects and purposes, the device hereof may also comprise a radiation shield apparatus for use in a nuclear reactor, comprising a cylindrical-shaped ring member having an inner diameter slightly larger than a control rod drive housing of the reactor, a lower abutment surface for engagement with a control rod drive support system, and a hanger means for supporting the ring member on a control rod drive when the lower abutment surface is not engaged by a support system.