Canister for disposal of hazardous radioactive waste in an earth borehole repository

Abstract

Various embodiments are disclosed of a canister for the disposal of hazardous radioactive waste in a borehole repository. The canister has a shell body containing the waste. In one embodiment, the canister is equipped with a removable lift adaptor that enables emplacement and removal of the canister in and from the borehole repository. A lid assembly at the top end of the shell body includes a shielded closure plug, a keyhole fitting to which the removable lift adaptor is attached to and detached from, a cover ring, and a threaded jam nut that secures and unsecures the cover ring and the lift adaptor to the keyhole fitting.

Description

CANISTER FOR DISPOSAL OF HAZARDOUSRADIOACTIVE WASTE IN AN EARTH BOREHOLE REPOSITORYCLAIM OF PRIORITY

[0001] This application claims priority to, and the benefit of, co-pending U.S. utility application entitled “Canister for Disposal of Hazardous Radioactive Waste in an Earth Borehole Repository" having serial no. 18 / 526,762 filed December 1 , 2023 and this application also claims priority to and the benefit of provisional application no. 63 / 531 ,450, filed August 8, 2023, the contents of which are each incorporated by reference in their entirety.FIELD OF THE INVENTION

[0002] The embodiments of the present disclosure generally relate to disposal of hazardous radioactive materials and, more particularly, to a canister for disposal of hazardous radioactive waste, such as spent nuclear fuel and / or high-level radioactive waste, in an earth borehole repository.BACKGROUND

[0003] The canister assembly in which hazardous radioactive waste is contained is the central component common to the storage, transportation, and permanent disposal of such waste. The canister maintains the waste in an inert gas environment to prevent degradation of the fuel cladding and provides the primary confinement of the used fuel assembly and the associated radioactive material and fission gases. Generally, the waste is loaded wet into the canister in a spent fuel pool at a reactor site (or repackaging facility) and the canister is drained, vacuum dried, backfilled with inert gas, and seal welded prior to being placed into dry storage and / or transported to an interim storage facility or repository. Alternatively, although much less common, used fuel can be loaded into the canister in a dry environment (e.g., hot cell). The canister is suitable for disposal in a deep borehole repository or mined geological repository.

[0004] U.S. Patent No. 10,692,618 and PCT Patent Application Serial No. PCT / US2023 / 034389, filed on October 3, 2023, which are incorporated herein byreference, describe hazardous waste canisters and systems for disposing of canisters having hazardous radioactive materials in an underground repository. The canisters have a basket for containing the hazardous radioactive materials. The canisters are placed in a borehole that is defined by a number of cylindrical steel casings that are bolted or otherwise secured together. The borehole is filled with a fluid, such as saline solution, and can be up to 5 kilometers deep in the earth, leading to extreme pressure on the canister. Moreover, the borehole may have both vertical and nonvertical (e.g., horizontal or transverse to vertical) portions.

[0005] Although the foregoing canisters and systems have significant merit, these technologies are in a state of infancy, and there remains many obstacles to practical implementation of such canisters and systems. The present disclosure focuses upon a canister design to enable easy and safe emplacement and removal of canisters in and from a borehole repository.SUMMARY OF THE INVENTION

[0006] Various embodiments are disclosed of a canister for the disposal of hazardous radioactive waste in a borehole repository.

[0007] In one embodiment, among others, the canister includes a shell body containing the waste. The canister is equipped with a removable lift adaptor that enables emplacement and removal of the canister in and from the borehole repository. A lid assembly at the top end of the shell body includes a closure plug, a keyhole fitting to which the removable lift adaptor is attached to and detached from, a cover ring, and a threaded jam nut that secures and unsecures the cover ring and the lift adaptor to the keyhole fitting.

[0008] In another embodiment, among others, the canister includes a shell situated in the borehole repository. The shell has an elongated cylindrical shell body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste. A lid assembly is situated at the top end of the shell body. The lid assembly has a generally cylindrical closure plug with an elongated cylindrical body extending between a top end and a bottom end. Theclosure plug extends into the top end of the shell body within the cavity of the shell body;

[0009] Significantly, in this embodiment, the elongated body of the closure plug has a top portion with a first circular cross section and a bottom portion with a second circular cross section. The first circular cross section is larger than the second circular cross section so that a support shelf exists between the top and bottom portions. Moreover, the shell body has a top portion and a bottom portion with different circular cross sections that correspond substantially with the first and second circular cross sections of the lid assembly so that the plug of the lid assembly resides within the shell in mating engagement and the top portion of the plug imposes downward vertical force against the bottom portion of the shell body at the support shelf.

[0010] In another embodiment, among others, the canister has a shell with an elongated cylindrical shell body that extends between a top end and a bottom end. The canister defines an elongated cylindrical cavity that contains the radioactive waste. A closure plug having an elongated cylindrical body with a top end and a bottom end extends into the top end of the shell body within the cavity of the shell body. A closure lid is situated at the top end of the shell body. An annular relief pocket is defined by part of the plug and part of the shell body. Significantly, the annular relief pocket enables a K-TIG weld to secure together the closure lid and the shell body, and provides the primary containment boundary for the radioactive contents of the canister.

[0011] In another embodiment, among others, the canister includes a shell having an elongated cylindrical shell body that extends between a top end and a bottom end. The canister defines an elongated cylindrical cavity that contains the radioactive waste. A lid assembly attaches to and at the top of the shell body. The lid assembly has a circular periphery with top and bottom surfaces. The top and bottom surfaces having respective top and bottom edges. Significantly, the top edge is radiused to prevent snagging of the canister when the canister is pulled out of the borehole repository.

[0012] Other embodiments, apparatus, systems, methods, features, and advantages of the present invention will be apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional embodiments, apparatus, systems, methods, features, and advantagesbe included within this disclosure, be within the scope of the present invention, and be protected by the accompanying claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0014] FIG. 1 is a schematic view of a canister situated in a borehole repository in accordance with the present disclosure.

[0015] FIG. 2A is an expanded side view of the canister of FIG. 1 showing parts for the lid assembly of the canister of FIG. 1 .

[0016] FIG. 2B is a cross sectional view of the canister of FIG. 1.

[0017] FIG. 3A is a cross sectional view of the canister of FIG. 1 taken along line A- A of FIG. 3B, showing an enlarged view of (a) a support shelf that enhances the strength the the lid assembly and (b) a relief pocket that enables K-TIG welding.

[0018] FIG. 3B is a view of the top of the canister of FIG. 1 with keyhole fitting and cover ring and without the lift adapter and the jam nut.

[0019] FIG. 3C is a cross sectional view of the longitudinal shell body of the canister of FIG. 1 taken along line B-B of FIG. 2A.DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0020] FIG. 1 is a schematic view showing a canister 10 situated in a borehole repository 12 in the earth soil 14 in accordance with an embodiment of the present disclosure. The borehole repository 12 has an elongated cylindrical cavity for receiving one or more of the canisters 10. The borehole associated with the borehole repository 12 may have both vertical and nonvertical (e.g., horizontal or transverse to vertical) portions, but only a vertical portion is shown in FIG. 1 for simplicity.

[0021] Canister sizes are variable in length and diameter to accommodate different fuel types but share common features to facilitate operations. The canisters 10 are designed to withstand a range of loading conditions required for storage, transportation, and disposal, but the canister shell thickness is generally governed by hydrostatic pressure loading at depth for borehole disposal.

[0022] In the preferred embodiment, as shown in FIG. 2A, the canister 10 includes a shell assembly 16 having a shell body 18 and a field-installed lid assembly 22, that together forms a canister cavity 24 in which hazardous radioactive waste 26 is placed. The hazardous radioactive waste 26 can be, for example but not limited to, chemical, biological, and / or nuclear material. In the preferred embodiment, the canister 10 stores spent nuclear fuel in the form of spent nuclear fuel rod assemblies. The hazardous radioactive waste 26, particularly, the nuclear waste may take the form of a solid, liquid, and / or gas. The shell body 18 is preferably a steel weldment, and the components of the shell assembly 16 are made from material that is highly resistant to both localized corrosion (e.g., chloride-induced stress corrosion cracking, or CISCO) and general corrosion. The canister 10 further includes drain and vent port features (shown in FIG 3A) that are use in wet-loading operations to drain water, vacuum dry, and backfill the canister cavity with a fluid or a solid, for example, an inert gas (e.g., helium).

[0023] The lid assembly 22 has a lift adaptor 28 that is removably attachable to a keyhole fitting 32 in the top end of the canister 10 and secured by a cover ring 34 and a jam nut 36 to provide a lifting interface for handling at the borehole repository surface facility and emplacement or retrieval from the borehole repository 12. The lift adaptor 22 is optional for storage and transportation operations, but is installed for borehole disposal operations, as it is used to emplace or retrieve the canister from the borehole repository 12.

[0024] More specifically, with reference to FIG. 2B, the field-installed lid assembly 22 includes a generally cylindrical shielded closure plug 38 having an elongated cylindrical body with a top end and a bottom end. The shielded closure plug 38 extends into the top end of the shell body 18 within the cavity of the shell body 18. The closure plug 38 of the lid assembly 22 is preferably a thick cylindrical steel plug that is relied upon for the primary radiation shielding during certain canister loading activities.

[0025] An annular closure ring 39, shown in FIG. 3A, secures the closure plug 38 in the shell body 18. The closure ring 39 has a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture. The closure ring 39 is preferably made of steel and is attached to the top end of the shell body 18 via a TIG welding process and secures the closure plug 38 in the shell body 18.

[0026] The keyhole fitting 32, illustrated in FIG. 3B, has a circular periphery and top and bottom surfaces. The bottom surface is situated over the top end of the shielded closure plug 38. The keyhole fitting 32 has a keyhole 42 extending through the keyhole fitting 32 between the top and bottom surfaces. The keyhole is accessible through the closure ring aperture. The keyhole fitting 32 is preferably made from steel. The integral keyhole fitting 32 facilitates handling operations. The innovative keyhole fitting 32 provides a mechanism for easy, fail-safe, remote engagement of the canister 10 using specialized tooling for pool loading and canister transfer operations to minimize radiation exposure of workers.

[0027] As shown in FIGs. 2A and 2B, the lift adaptor 28 has an elongated body with a top end and a bottom end. The bottom end of the lift adaptor 28 is removably attachable to the keyhole fitting 32. The top end of the lift adaptor 28 enables emplacement and removal of the canister 10 in and from the borehole repository 12. The lift adaptor 28 is preferably made from steel. The lift adaptor 28 has a pair of diametrically opposing, outwardly extending tabs 44 of a size and shape to enable passage through the keyhole 42 when the lift adaptor 28 is in a first rotational position. The lift adaptor 28 can then be moved to a second rotational position, which is transverse (preferably perpendicular) to the first rotational position and which enables the lift adaptor 28 to be grasped by and secured to the bottom surface of the keyhole fitting 32.

[0028] The top end of the lift adapter 28 includes both internal and external profiles to interface with standard oil and gas equipment (i.e., GS tool and flo-release overshot) used for borehole operations and provide redundant means of lifting. The internal profile 28a in FIG 2B is a stepped cylindrical pocket to interface with a standard GS tool to lift the canister. The external profile 28b in Fig 2B has a smooth cylindrical shape to interface with a standard flo-release overshot tool to lift the canister 10.

[0029] The cover ring 34 has a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture 46. When installed, the lift adaptor 28 extends through the aperture 46. The bottom surface of the cover ring 34 has a pair of downwardly extending tabs 32a of FIG 2A at opposing ends that extend into the end portions 35a, 35b of FIG. 3B of the keyhole 42 to prevent the lift adaptor 28 from rotating about its longitudinal axis from the second rotation position (secured) to the first rotational position(unsecured). The cover ring 34 is preferably made from steel. Generally, the cover ring 34 resides concentrically over the keyhole fitting 32, which in turn resides concentrically over the closure ring 39. Significantly, the circular periphery of the top surface of the cover ring 34 has a rounded, or radiused, edge 41 to prevent snagging of the canister 10 when removed from the borehole repository 12.

[0030] The jam nut 36 of FIGs. 2A and 2B secures the cover ring 34 and the lift adaptor 28 to the keyhole fitting 32. The jam nut 36 is preferably made from steel and has female machine threads that engage male machine threads associated with the lift adaptor 28.

[0031] As illustrated in FIG. 3C, canister internals for hazardous radioactive waste 26 have a stainless steel, fuel tube 52 and four stainless steel, corrugated side supports 54a- 54d that are welded to the outer faces of the fuel tube 52 to bridge the gap between the fuel tube 52 and shell body 18. The side supports 54a-54d also transfers heat from the waste to the shell body 18.

[0032] The shielded shell body 18 and shielded closure plug 38 of the canister 10 include a significant stepped-cylinder feature that enhances the strength of the lid assembly 22. The canister 10 will be subjected to enormous pressure-induced forces, due to the borehole being filled with a fluid, such as saline solution, and having a length up to 5 kilometers deep in the earth. More specifically, as shown in FIG. 3A, the elongated body of the shielded closure plug 38 has a top portion 38a with a first circular cross section and a bottom portion 38b with a second circular cross section. The first circular cross section is larger in diameter than the second circular cross section so that a support shelf 56 exists between the top and bottom portions 38a, 38b. Furthermore, the shell body 18 has a top portion 18a and a bottom portion 18b with different diameter circular cross sections that correspond substantially with the diameters of the first and second circular cross sections of the lid assembly 22 so that the closure plug 38 of the lid assembly 22 resides within the shell 18 in mating engagement and the top portion 38a of the closure plug 38 imposes downward vertical force against the bottom portion 18b of the shell body 18 at the support shelf 56.

[0033] The stepped-cylinder feature eliminates the need for temporary lid supports that encroach on the canister cavity volume. The stepped-cylinder feature also supportsextreme external loading from hydrostatic pressure in borehole disposal, thus protecting the closure weld 62 (FIG. 3A) from excessive shear loading that could result in structural failure.

[0034] A drain port 61 with quick connect fitting is shown in enlarged part of FIG. 3A for context only. This port is used to draw water out of the canister 10. The drain port 61 is covered and sealed with an annular lid 63, which is welded as shown, preferably with a TIG welding process.

[0035] The canister 10 further includes an innovative feature to allow for an advanced welding technique to be used to perform the lid-to-shell field closure weld 62. Specifically, as illustrated in FIG.3A, an open annular relief pocket 58 enables use of K- TIG welding (TIG welding is used on the other welds shown in the figures). Preferably, the relief pocket 58 is an open groove 58 having a generally rectangular cross section and that extends in a circular manner around the top of the plug 38 and the shell 18 under the position of the closure weld 62, which attaches the closure ring 39 to the shell body 18. Generally, about half of the relief pocket 58 resides in the top portion of the plug 38 and the other half resides in the top portion of the shell body 18.

[0036] The K-TIG welding process uses an autogenous keyhole welding process, which requires no weld filler metal, to place most of the closure weld thickness and traditional tungsten inert gas TIG welding (melt-in mode) to add weld metal over the keyhole weld pass to achieve the total required weld throat. It substantially reduces the welding time and produces less weld distortion than other traditional welding techniques, such as the multi-layer TIG welding process used previously for canister field closure welds. K-TIG welding is a highly effective and efficient welding technique used for seam welds on tanks, vessels, and boxes with square butt and beveled joint preparations, but is has not been previously used for spent fuel canister field closure welds due to weld joint configuration. The innovative relief pocket 58 allows the high energy of the arc to be expelled via the back side of the weld, avoiding turbulences in the root that cause porosity in the weld. The relief pocket 58 also allows the weld to be examined using ultrasonic testing (UT) methods to provide a higher level of assurance of weld quality than methods used on other canister closure welds.

[0037] Finally, it should be emphasized that the above-described embodiments, particularly any “preferred” embodiments, of the present invention are merely possible nonlimiting examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present disclosure.

Claims

CLAIMSAt least the following is claimed:1 . A system for disposal of hazardous radioactive waste, the system comprising: a borehole repository having an elongated cylindrical cavity extending into the earth; a canister in the borehole repository, the canister having an elongated cylindrical shell body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste; and a lift adaptor having an elongated body with a top end and a bottom end, the lift bottom end of the lift adaptor attached to the top end of the canister, the top end of the lift adaptor enabling emplacement and removal of the canister in and from the borehole. a lid assembly situated at the top end of the shell body, the lid assembly having: a generally cylindrical closure plug having an elongated cylindrical body with a top end and a bottom end, the closure plug extending into the top end of the shell body within the cavity of the shell body; a keyhole fitting having a circular periphery and top and bottom surfaces, the bottom surface situated over the top end of the closure plug, the keyhole fitting having a keyhole extending through the keyhole fitting between the top and bottom surfaces; a lift adaptor having an elongated body with a top end and a bottom end, the bottom end of the lift adaptor attached to the keyhole fitting, the top end of the lift adaptor enabling emplacement and removal of the canister in and from the borehole, the lift adaptor having outwardly extending tabs of a size and shape to enable passage through the keyhole when the lift adaptor is in a first rotational position and to grasp the bottom surface of the keyhole fitting when the lift adaptor is in a second rotational position, the first and second rotational positions being transverse, and wherein the lift adaptor is in the second rotational position;a cover ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the lift adaptor extending through the aperture, the bottom surface having downwardly extending tabs that extend into and through the keyhole to prevent the lift adaptor from rotating about its longitudinal axis from the second rotation position to the first rotational position; and a jam nut that secures the cover ring and the lift adaptor to the keyhole fitting, the jam nut having threads that engage threads associated with the lift adaptor.

2. The system of claim 1 , further comprising a stepped-cylinder feature wherein: the elongated body of the closure plug has a top portion with a first circular cross section and a bottom portion with a second circular cross section, the first circular cross section being larger than the second circular cross section so that a support shelf exists between the top and bottom portions; and the shell body has a top portion and a bottom portion with different circular cross sections that correspond substantially with the first and second circular cross sections of the lid assembly so that the plug of the lid assembly resides within the shell in mating engagement and the top portion of the plug imposes downward vertical force against the bottom portion of the shell body at the support shelf.

3. The system of claim 1 , wherein the lid assembly further comprises: an annular closure ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the closure ring attached to the top end of the shell body and securing the plug in the shell body, the keyhole being accessible through the closure ring aperture; an annular relief pocket defined in the top portion of the plug; and a K-TIG weld over the annular relief pocket that secures the closure plug to the shell body.

4. The system of claim 3, wherein annular relief pocket has a square rectangular cross section and wherein generally a half of the relief resides in the top portion of the plug and another half of the relief resides in the top portion of the shell body.

5. The system of claim 1 , wherein the circular periphery of the top surface of the cover ring has a rounded edge to prevent snagging of the canister when removed from the borehole repository.

6. The system of claim 1 , further comprising a fuel tube having an elongated body with four sides extending between a top end and a bottom end, the fuel tube having a substantially square cross section, the fuel tube containing the radioactive waste, and further comprising four elongated corrugated side supports, each side support designed to bridge a gap between the shell body and a respective side of the fuel tube.

7. A canister for disposal of hazardous radioactive waste in a borehole depository, the canister comprising: a shell having an elongated cylindrical body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste; a lid assembly situated at the top end of the shell body, the lid assembly and the shell body defining the cavity in combination, the lid assembly having: a generally cylindrical closure plug having an elongated cylindrical body with a top end and a bottom end, the closure plug extending into the top end of the shell body within the cavity of the shell body; a keyhole fitting having a circular periphery and top and bottom surfaces, the bottom surface situated over the top end of the closure plug, the keyhole fitting having a keyhole extending through the keyhole fitting between the top and bottom surfaces;a lift adaptor having an elongated body with a top end and a bottom end, the bottom end of the lift adaptor attached to the keyhole fitting, the top end of the lift adaptor enabling emplacement and removal of the canister in and from the borehole, the lift adaptor having outwardly extending tabs of a size and shape to enable passage through the keyhole when the lift adaptor is in a first rotational position and to grasp the bottom surface of the keyhole fitting when the lift adaptor is in a second rotational position, the first and second rotational positions being transverse, and wherein the lift adaptor is in the second rotational position; a cover ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the lift adaptor extending through the aperture, the bottom surface having downwardly extending tabs that extend into and through the keyhole to prevent the lift adaptor from rotating about its longitudinal axis from the second rotation position to the first rotational position; a jam nut that secures the cover ring and the lift adaptor to the keyhole fitting, the jam nut having threads that engage threads associated with the lift adaptor.

8. The canister of claim 7, further comprising a stepped-cylinder feature wherein: the elongated body of the closure plug has a top portion with a first circular cross section and a bottom portion with a second circular cross section, the first circular cross section being larger than the second circular cross section so that a support shelf exists between the top and bottom portions; and the shell body has a top portion and a bottom portion with different circular cross sections that correspond substantially with the first and second circular cross sections of the lid assembly so that the plug of the lid assembly resides within the shell in mating engagement and the top portion of the plug imposes downward vertical force against the bottom portion of the shell body at the support shelf.

9. The canister of claim 8, wherein the lid assembly further comprises: an annular closure ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the closure ring attached to the top end of the shell body and welded to the closure plug and shell to cover the K-TIG closure weld, the keyhole being accessible through the closure ring aperture; an annular relief pocket defined in the top portion of the plug; and a K-TIG weld over the annular relief pocket that secures the closure plug to the shell body and provides a primary containment boundary for the radioactive wast of the canister.

10. The canister of claim 8, wherein annular relief pocket has a square rectangular cross section and wherein generally a half of the relief resides in the top portion of the plug and another half of the relief resides in the top portion of the shell body.11 . The canister of claim 7, wherein the circular periphery of the top surface of the cover ring has a rounded edge to prevent snagging of the canister when removed from the borehole repository.

12. The canister of claim 7, further comprising a fuel tube having an elongated body with four sides extending between a top end and a bottom end, the fuel tube having a substantially square cross section, the fuel tube containing the radioactive waste, and further comprising four elongated corrugated side supports, each side support designed to bridge a gap between the shell body and a respective side of the fuel tube.

13. The borehole repository comprising the canister of claim 7.

14. A method for disposing of hazardous radioactive waste, the method comprising the steps of: providing a canister having an elongated cylindrical shell body that extends between a top end and a bottom end, the shell body defining an elongated cylindrical cavity that contains the radioactive waste; positioning a keyhole fitting having a circular periphery and top and bottom surfaces over the top end of the canister, the keyhole fitting having a centrally positioned keyhole extending through the keyhole fitting between the top and bottom surfaces; providing a lift adaptor having an elongated body with a top end and a bottom end, the top end of the lift adaptor enabling emplacement and removal of the canister in and from the borehole, the body having outwardly extending tabs of a size and shape to enable passage through the keyhole when the lift adaptor is in a first rotational position and to grasp the bottom surface of the keyhole fitting when the lift adaptor is in a second rotational position, the first and second rotational positions being transverse; inserting the lift adaptor in the first rotational position into the keyhole; rotating the lift adaptor to the second rotational position; providing a cover ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the bottom surface having downwardly extending tabs; inserting the cover ring about the lifting adaptor through the aperture and then inserting the downwardly extending tabs into and through respective parts of the keyhole to prevent the lift adaptor from rotating about its longitudinal axis from the second rotation position to the first rotational position; and securing the cover ring and the lift adaptor to the keyhole fitting with a jam nut having threads that engage threads associated with the lift adaptor.

15. The method of claim 14, further comprising the steps of: securing the plug in the shell body with an annular closure ring having a circular periphery with top and bottom surfaces and with a centrally positioned circular aperture, the keyhole being accessible through the closure ring aperture;providing an annular relief pocket defined in the top portion of the plug; andK-TIG welding the closure ring at the top end in a location adjacent to and over the annular relief pocket to secure and seal the plug in the shell body.

16. The method of claim 14, further comprising the step of providing a stepped-cylinder feature wherein: the elongated body of the closure plug has a top portion with a first circular cross section and a bottom portion with a second circular cross section, the first circular cross section being larger than the second circular cross section so that a support shelf exists between the top and bottom portions; and the shell body has a top portion and a bottom portion with different circular cross sections that correspond substantially with the first and second circular cross sections of the lid assembly so that the plug of the lid assembly resides within the shell in mating engagement and the top portion of the plug imposes downward vertical force against the bottom portion of the shell body at the support shelf.

17. The method of claim 14, further comprising the steps of: providing a rounded edge at the circular periphery of the top surface of the cover ring; and preventing snagging of the canister on borehole casing segments when the canister is removed from the borehole repository.

18. The method of claim 14, further comprising a fuel tube in the cavity of the shell, the fuel tube having an elongated body with four sides extending between a top end and a bottom end, the fuel tube having a substantially square cross section, the fuel tube containing the radioactive waste, and further comprising four elongated corrugated side supports, each side support designed to bridge a gap between the shell body and a respective side of the fuel tube.

19. The method of claim 14, further comprising the steps of: lowering the canister into a borehole repository using the lift adaptor; and removing the jam nut, cover plate, keyhole fitting, and lift adaptor from the borehole repository.

20. A canister for disposal of hazardous radioactive waste, the canister comprising: a borehole repository having an elongated cylindrical cavity extending into the earth; a shell situated in the borehole repository, the shell having an elongated cylindrical shell body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste; a lid assembly situated at the top end of the shell body, the lid assembly having a generally cylindrical closure plug with an elongated cylindrical body extending between a top end and a bottom end, the closure plug extending into the top end of the shell body within the cavity of the shell body; wherein the elongated body of the closure plug has a top portion with a first circular cross section and a bottom portion with a second circular cross section, the first circular cross section being larger than the second circular cross section so that a support shelf exists between the top and bottom portions; and wherein the shell body has a top portion and a bottom portion with different circular cross sections that correspond substantially with the first and second circular cross sections of the lid assembly so that the plug of the lid assembly resides within the shell in mating engagement and the top portion of the plug imposes downward vertical force against the bottom portion of the shell body at the support shelf.21 . A canister for disposal of hazardous radioactive waste, the canister comprising: a shell having an elongated cylindrical shell body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste; a closure plug having an elongated cylindrical body with a top end and a bottom end, the closure plug extending into the top end of the shell body within the cavity of the shell body; a closure lid situated at the top end of the shell body; an annular relief pocket defined by part of the plug and part of the shell body; and a K-TIG weld over the annular relief pocket that secures together the closure plug and the shell body and provides a primary containment boundary for the radioactive waste of the canister.

22. The canister of claim 20, further comprising a borehole repository having an elongated cylindrical cavity extending into the earth and wherein the canister is situated in the borehole repository.

23. A canister for disposal of hazardous radioactive waste, the canister comprising: a borehole repository having an elongated cylindrical cavity extending into the earth; a shell situated in the borehole repository, the shell having an elongated cylindrical shell body that extends between a top end and a bottom end, the canister defining an elongated cylindrical cavity that contains the radioactive waste; and a lid assembly attached to and at the top of the shell body, the lid assembly having a circular periphery with top and bottom surfaces, the top and bottom surfaces having respective top and bottom edges, the top edge being radiused to prevent snagging of the canister when the canister is pulled out of the borehole repository.

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