Patent Application
20130077729
1. Field
This invention relates generally to the storage, transportation and/or disposal of highly radioactive components, and more particularly, to a method for maximizing the loading of such components in storage and transportation casks.
2. Related Art
One type of commonly used boiling water nuclear reactor employs a nuclear fuel assembly comprised of fuel rods surrounded by a fuel channel. Each fuel channel of a boiling water reactor fuel assembly typically consists of a hollow, linear, elongated, four-sided channel of integral construction, which, except for its rounded corner edges, has a substantially square cross section. Commonly, each channel is roughly 14 feet (4.27 meters) long by five inches (12.7 cms.) square and laterally encloses a plurality of elongated fuel elements. The fuel elements are arranged to allow for the insertion of a cruciform shaped control rod, which, during reactor operation, is movable vertically to control the nuclear reaction. The control rods typically include an upper portion having a handle and four upper rollers for guiding the control rod as it moves vertically and a lower portion comprising a lower casting and lower ball rollers. The main body structure includes four blades or panels which extend radially from a central spline. Preferably, the blades extend longitudinally to a height that substantially equals the height of the fuel elements, which is approximately 12 feet (3.66 meters). The width of the control rods at the blade section is approximately twice the width of the panels, which is in the order of ten inches (25.4 cms.) and the blades are approximately 2.8 in. (7 mm) thick.
Following functional service, boiling water reactor control rod blades, fuel channels, low power range monitors and/or other irradiated components (hereinafter severally and collectively referred to as “irradiated hardware”) are difficult to store and dispose of because of their size, configuration, embrittled condition and radiological activity. Heretofore, within the United States, in-pool storage of certain irradiated hardware has been extremely space inefficient and with regard to all irradiated hardware, dry cask storage is not currently readily available. Accordingly, boiling water reactor operators necessarily dispose of irradiated hardware as soon as reasonably practical.
Irradiated hardware is typically Class C low level radioactive waste as defined and determined pursuant to 10 CFR §61 and related regulatory guidance, e.g., NRC's Branched Technical Position on Concentration Averaging and Encapsulation. Since Jul. 1, 2008, low level radioactive waste generators within the United States that are located outside the Atlantic Compact (Connecticut, New Jersey and South Carolina) have not had access to Class B or Class C, low level radioactive waste disposal capacity. Lack of disposal capacity has caused boiling water reactor operators considerable spent fuel pool overcrowding. Though currently very uncertain and subject to numerous regulatory and commercial challenges, Class B and Class C low level radioactive waste disposal capacity for the remainder of the United States low level radioactive waste generators is anticipated in the relatively near future. Even when waste disposal sites become available much of the irradiated hardware will be difficult and expensive to ship because of their size and configuration unless their volume can be significantly reduced and tightly compacted into licensed shipping casks.
Accordingly, it is an object of this invention to provide a method of segmenting and packaging irradiated hardware that will safely and compactly load the irradiated hardware into licensed shipping casks for transport or storage.
Furthermore, it is an object of this invention to provide such a method that will satisfy all licensing restrictions and requirements of the disposal site.
These and other objects are achieved by an improved method of segmenting and packaging an irradiated component for storage or shipment. The method includes the step of mapping a radiological and/or a physical characteristic of the irradiated hardware over a surface thereof. The method determines any radiological and physical licensing restrictions on the characteristic associated with a cask in which the irradiate hardware is to be placed for storage or shipment. The method then determines a segmenting plan and a loading plan that sets forth where over the surface of the component the component is to be segmented from the map obtained from the mapping step and the licensing restrictions, so that the cask receives a substantially maximum load that the cask can safely handle without violating the licensing restrictions. The irradiated hardware is then segmented in accordance with the segmenting plan and the cask is loaded with the segments in accordance with the loading plan. Preferably, the radiological characteristic is one or more of isotopic content and radiation levels and the physical characteristic is one or more of size, shape, metallurgy and weight. In one embodiment, the mapping step is performed by scanning a sensor over the surface of the irradiated hardware and recording and characterizing the sensor output. Preferably, the segmenting plan and the loading plan are determined together to maximize the load in the cask. In addition, the licensing restrictions may include an acceptance criteria of the waste disposal facility that the cask will be transported to.
A further understanding of the invention claimed hereafter can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As previously mentioned, following functional service, boiling water reactor irradiated hardware components are difficult to store and dispose of because of their size, configuration, embrittled condition and radiologic history. To make those components easier to store and package, different forms of consolidation have been proposed. For example, as described in application Ser. No. ______ [Attorney Docket No. CLS-UFS-014 UTILITY], filed concurrently herewith, and as shown in
Following compaction, the sleeve enclosure containing the fuel channel may be laterally segmented to a desired length as identified by the steps of the method claimed hereafter by use of hydraulic shears 22. As explained hereafter, the physical limitations of the storage facility and/or transport cask and the radiation levels of the incremental sections of the sleeve containing the fuel channel, will dictate the optimal location along the length of the fuel channel at which lateral segmentation is desired. The outer sleeve 12 may also have an inner sleeve 14 that extends at least the length the fuel channel 10. The inner sleeve 14 is inserted within the fuel channel and the top of the inner sleeve 14 may be drawn to the top of the outer sleeve 12 and the bottom of the inner sleeve 14 may be drawn to the bottom of the outer sleeve 12 in place of the top 16 and bottom 28 seals previously noted.
Another piece of irradiated hardware that boiling water reactor operators have difficulty storing and disposing of, because of their size, configuration, embrittled condition and radiological activity following functional service, is the control rod blade, such as the one illustrated in
The cruciform shaped main body 40 is comprised of four shaped metallic panels 42 of metallic tubes containing powdered boron carbide or other neutron absorbing material that are welded together and to the central spline 44 lengthwise at opposing angles to form the cruciform shape. Because of the radioactive nature of the control rod, it is necessary for the volume reduction process to be performed under water, most preferably in the spent fuel pool. To separate the control rod into practically transportable segments it will be necessary to laterally segment the main body portion 40. However, under water lateral segmentation of the panels 42 will rupture both the sheathing and the tubes contained with the sheathing of the panels 42, thereby exposing the spent fuel pool to unwanted debris in the form of sheathing material, tubes and boron carbide. Embrittlement of the control rod blades caused by the extended neutron exposure that they would have experienced within the reactor compounds the difficulty of the lateral segmentation process. As in the case of the reactor fuel channels, and as will be explained in more detail hereafter, both physical and radiological criterion will dictate the optimal location along the length of the panel 42 at which lateral segmentation is desired to obtain maximum density packaging for transportation or storage. In other words, the configurations of the transport casks, the intended placement of a separated segment of a panel within the transport casks, and the radiation intensity of the segment will all contribute to determine at what elevation along the panel 42 lateral segmentation should be made. Once the desired location of lateral segmentation of the panel 42 is determined, a preformed band of malleable metal will be slid along the length of the panel to that location or wrapped around the panel at that location. Two such bands 48 are shown in
In accordance with one embodiment of this invention, the irradiated hardware is characterized for cask shipment by passing a sensor, such a radiation detector, over the surface of the irradiated hardware component to determine the dose rate and isotopic content of various locations on the component. The irradiated hardware can be then characterized by using commercially available software, such as the RADMAN software available from WMG Inc., Peekskill, N.Y. or software available from DW James Consulting LLC, North Oak, Minn. Each of the components of the irradiated hardware to be packaged is then mapped into segments. For irradiated hardware that requires lateral segmentation in order to be loaded into a shipping cask 56, boundaries of the segments where cuts are to be made are determined by using a combination of physical and radiological information. The physical information comprises one or more of the size, shape and weight of each segment and those of some or all of the remaining segments to be loaded into the cask 56. The radiological information may comprise the isotopic content and radioactivity of the segments. The boundaries are determined together with the generation of a cask loading plan that will maximize the loading of a shipping cask in which the irradiated hardware is to be placed; taking into consideration, the acceptance criteria of the waste disposal facility that the cask is to be transported to or stored in, the metallurgy, isotopic content, weight and operating history of the segments and the isotopic signature of the plant. The irradiated hardware is then cut or sheared along the boundaries and loaded into the cask according to the loading plan. For example, in the most simplistic form of the method, the lateral cuts will be determined so that the segments do not exceed the weight and dimensional loading limitations of the cask and the loading plan will load the more radioactive segments towards the center of the cask. In a more sophisticated example, the mapping plan and the loading plan will be treated as a three-dimensional problem and solved as a simultaneous equation by a computer program.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
This application claims priority UNDER 35 U.S.C. §119(e) from U.S. Provisional Application Ser. No. 61/537,704, filed Sep. 22, 2011, entitled “Method of Segmenting and Packaging Retired Irradiated Hardware” and is related to patent application Ser. No. ______, entitled “Method of Segmenting Irradiated Boiling Water Reactor Control Rod Blades,” filed concurrently herewith (Attorney Docket CLS-UFS-014 UTILITY).
| Number | Date | Country | |
|---|---|---|---|
| 61537704 | Sep 2011 | US |
