Patent Number: 047325275
Section: summary

In a nuclear plant, areas containing hazardous materials are separated by thick walls and slabs from areas where personnel may be present. The hazardous area is generally termed the active region of the plant. The radioactive products which may be present in this zone include gamma-emitters, which justify the thick containment walls, and/or alpha and beta emitters, considered to be contaminants. All equipment leaving an active region is considered contaminated and must be placed behind a thick wall (to protect against gamma rays) and within a sealed enclosure (to avoid spreading the contamination). When equipment in the active region must be replaced or taken out and transferred to a maintenance cell, or conversely, when it is desired to return same to its working location, full confinement must be maintained throughout the transfer procedure to avoid spreading the contamination. It is also crucial to maintain a sufficient wall thickness as a biological shield between said equipment and the plant personnel as the equipment is transferred to the maintenance or repair cell. This invention concerns such a procedure for transferring an "object" such as a piece of equipment, a machine component, a waste drum and the like from the active region or containment to the clean region, for transporting or conveying said object within the clean region and transferring it back from the clean region to the active region without ever departing from containment and biological safety requirements. A first feature of the invention consists in using, for the purpose of maintaining confinement, a two-part device including a stationary pre-enclosure and a movable "transfer" enclosure. The pre-enclosure is kept in place throughout the time required to extract an object, remove it to a cell and either bring back another object or return the same object after repair to the active region or containment. The invention will be described in terms of an active cell accessible through its top, with transfer operations carried out vertically (over-the-wall handling). However, the same procedure applies to all geometrical arrangements such as through-the-wall transfer or through-the-floor. This description will thus concern an active cell the ceiling whereof is a horizontal slab with a plug therein. The top surface of the plug is clean and must be kept clean. The inside face of the plug is within the active region and is considered contaminated and contaminating. The object, at least at the time of transfer, is suspended from the plug. The object's dimensions are assumed to be such that, on lifting the plug, said object can be removed through the unplugged opening.