Patent Number: 060875461
Section: summary

FIELD OF THE INVENTION This invention relates to a nuclear reactor disposal package and to a method of decommissioning a commercial nuclear reactor by enclosing the reactor vessel in a container. BACKGROUND OF THE INVENTION At the end of the operating life of a nuclear reactor assembly, the owner is presented with three decommissioning alternatives. Entombment consists of placing the reactor vessel and other parts of the assembly in a sealed condition for an indefinite period of time to allow the ionizing radiation to decay to acceptable levels. At that time the assembly may be modified further or removed. Mothballing consists of placing and maintaining portions of the assembly in protective storage for a period of time before dismantling the assembly. Prompt Removal is the removal of all radioactive components of the assembly without the delays accompanying the entombment and mothballing alternatives. The most cost-effective alternative has been determined by the nuclear industry to be prompt removal. The nuclear reactor vessel, along with its internal components, comprise the majority of the radioactivity at a shut-down commercial nuclear power facility. The disposal of spent (used) nuclear reactor fuel in the United States is typically the responsibility of the United States Department of Energy (DOE). The reactor fuel will be transferred to the DOE, independent of the reactor vessel and internals disposal. Therefore, the nuclear reactor will not be packaged and transported with reactor fuel. In the prompt removal process, the reactor vessel internals have been segmented, removed, and packaged for transportation and disposal in small transportation containers and shielded casks. This requires the handling of components with high curie contents generating high radiation doses. This type of radioactive material must be packaged and transported to satisfy the regulations of both the United States Nuclear Regulatory Commission and the United States Department of Transportation. The packaging and transportation effort is further complicated by the weight of the reactor vessel, typically measured in the hundreds of tons. Techniques exist to segment the reactor vessel and internals in order to reduce the physical size and curie content of material loaded into licensed transportation containers. These techniques require a substantial amount of underwater cutting and material handling due to the high radiation levels associated with the components. If the vessel is removed and transported intact without segmenting it as described, risk is involved. The steel reactor vessel is subjected to neutron radiation during the operation of the reactor. This radiation causes a change in the molecular structure of the steel, making it brittle. This embrittlement is a risk to the integrity of the reactor vessel if the vessel is packaged as its own transportation container without a container outside. This invention is a package containing and protecting the vessel and provides a method of packaging the reactor vessel, with the internal components intact, into a single container, thus reducing the cost of preparation activities and exposure of workers to ionizing radiation. This package, when fitted with external impact limiters and tiedown devices, meets the transportation requirements for a Type B package as defined in Title 10 of the Code of Federal Regulations, Part 71. Additionally, it reduces the total volume of radioactive waste for disposal. This invention thus eliminates the need to segment the reactor vessel and internals for packaging and transportation, and eliminates the segmentation of portions of the reactor vessel internals into waste which is considered Greater-Than-Class-C. This type of waste is a significant problem, since it is generally not accepted for disposal in near-surface land disposal facilities, the only type of radioactive waste disposal facility currently operating within the United States. This invention reduces the concentration of Greater-then-Class-C waste by averaging the Greater-than-Class-C waste with other materials in the vessel. These reduced concentrations generally allow the package to meet acceptable criteria for burial in near-surface land disposal facilities. SUMMARY OF THE INVENTION The invention is a package comprised of a steel outer container having top and bottom heads and a continuous sidewall shell therebetween. The sidewall shell is secured thereto and extends inward therefrom a plurality of support lugs, all being at the same level and having vertical bores therethrough. Under the invention, the reactor vessel is a cup-shaped reactor shell having an upwardly facing annular lip, containing and supporting operating components. A closure head sits on the lip, the head being vertically apertured above the lip and the lip being bored and formed with internal threads in alignment with the apertures. The vessel is disposed in the outer container, the outer container and the reactor vessel defining between them a clearance space. A plurality of threaded studs engage the threaded bores in the lip respectively, and extend up through the respective apertures in the head and through the respective lugs. A plurality of threaded nuts are disposed on the respective studs above the lugs, each nut compressing the lug and the closure head against the lip of the reactor shell to secure the vessel in the outer container. A mass of concrete substantially fills the clearance space. The invention may also be expressed as a method by which this invention packages the reactor vessel and internals. The reactor vessel is lifted up into a heavy-wall steel cylinder shell and secured there. Specifically, the invention uses the existing reactor vessel/closure head/stud holes both to attach a lifting device to the reactor vessel, and to attach the reactor vessel to lugs inward from the steel cylinder shell to support the reactor vessel. As will be seen later with reference to the drawings, an open-ended steel cylinder shell is used to accomplish the objective. The shell is designed to both support the structural loads and provide the radiation shielding necessary to meet transportation regulations. It is also fitted with support lugs to support the weight of the reactor vessel. In order to trim the reactor coolant nozzles to fit within the package, the steel cylinder is floor-supported on a ring. The ring is fabricated with notches to give access to the reactor coolant nozzles. The ring provides both radiation shielding for the nozzle-cutting workers, and temporarily supports the steel cylinder during nozzle-cutting operations. Prior to lifting the reactor vessel into the steel cylinder shell, all connections to the reactor vessel are cut and the vessel is injected with a Low-density Cellular Concrete. The purpose of the Low-density Cellular Concrete is to "fix" the loose radioactive surface contamination which may be present in the reactor vessel. A lifting device is installed on the reactor vessel using the closure stud-holes as attachment points. The reactor closure head is securely attached to the reactor vessel by utilizing a plurality of the existing reactor head closure studs and nuts. The reactor vessel, with the installed internals, is lifted vertically until the reactor coolant nozzles are positioned in the notches of the steel cylinder support ring. While the reactor vessel is supported by the lifting device, the reactor coolant nozzles are trimmed to a size to fit within the steel cylinder. The reactor vessel is then lifted to its final position within the steel cylinder shell until the reactor closure head stud-holes are aligned with the steel cylinder support lugs. The reactor vessel is then securely attached to the steel cylinder shell using studs through the lugs and nuts similar to the original reactor closure head stud and nut design. With the reactor vessel securely attached to the steel cylinder, the cylinder shell is relocated and a bottom closure plate is welded in place. Subsequent to this step, the steel cylinder shell is filled with concrete of a strength required to withstand the structural forces imposed on the package during the transportation scenarios defined by the regulatory agency. Voids between the reactor vessel and transportation container are thus filled with concrete. The transportation package top wall, or upper closure plate, is installed and welded. The package is now complete. It may be placed onto a cradle assembly, secured to the assembly with tiedown devices, labeled and cushioned as required.