Patent Publication Number: US-2022223308-A1

Title: Hazardous material canister systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 17/194,564, filed on Mar. 8, 2021, which is a continuation application of, and claims priority to U.S. patent application Ser. No. 16/796,784, filed on Feb. 20, 2020, now U.S. Pat. No. 10,943,706, which claims priority under 35 U.S.C. § 119 to: U.S. Provisional Patent Application Ser. No. 62/808,594, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,516, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,591, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,570, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,571, filed on Feb. 21, 2019; and U.S. Provisional Patent Application Ser. No. 62/808,745, filed on Feb. 21, 2019. The entire contents of each of the previous applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to hazardous material canister systems and methods. 
     BACKGROUND 
     Hazardous material, such as radioactive waste, is often placed in long-term, permanent, or semi-permanent storage so as to prevent health issues among a population living near the stored waste. Such hazardous waste storage is often challenging, for example, in terms of storage location identification and surety of containment. For instance, the safe storage of nuclear waste (e.g., spent nuclear fuel, whether from commercial power reactors, test reactors, or even high-grade military waste) is considered to be one of the outstanding challenges of energy technology. Safe storage of the long-lived radioactive waste is a major impediment to the adoption of nuclear power in the United States and around the world. Conventional waste storage methods have emphasized the use of tunnels, and is exemplified by the design of the Yucca Mountain storage facility. Other techniques include boreholes, including vertical boreholes, drilled into crystalline basement rock. Other conventional techniques include forming a tunnel with boreholes emanating from the walls of the tunnel in shallow formations to allow human access. 
     SUMMARY 
     In a general implementation, a method for inspecting a weld of a nuclear waste canister includes positioning a gamma ray image detector near a nuclear waste canister that encloses nuclear waste. The nuclear waste canister includes a housing that includes a volume in which the waste is enclosed and a top connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister. The method further includes receiving, at the gamma ray image detector, gamma rays from the nuclear waste that travel through one or more voids in the weld; generating an image of the received gamma rays with the gamma ray image detector; and based on the generated image, determining an integrity of the at least one weld. 
     In an aspect combinable with the general implementation, the nuclear waste includes spent nuclear fuel. 
     In another aspect combinable with any of the previous aspects, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In another aspect combinable with any of the previous aspects, the gamma ray image detector includes a pinhole camera or an Anger camera. 
     In another aspect combinable with any of the previous aspects, at least one of the housing, the top, or a weld material includes a corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects, each of the housing, the top, and the weld material includes the corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects, the corrosion resistant alloy includes CRA 625. 
     In another aspect combinable with any of the previous aspects, the at least one weld includes a horizontal weld. 
     In another aspect combinable with any of the previous aspects, receiving the gamma rays includes receiving a plurality of gamma rays that emit from the nuclear waste and scatter through the volume of the nuclear waste container and through one or more voids in the one or more welds toward the gamma ray image detector. 
     Another aspect combinable with any of the previous aspects further includes rotating at least one of the nuclear waste canister or the gamma ray image detector during the receiving, at the gamma ray image detector, of the gamma rays from the nuclear waste that travel through the one or more voids in the weld. 
     In another aspect combinable with any of the previous aspects, the rotating includes rotating at least one of the nuclear waste canister or the gamma ray image detector for 360 degrees. 
     In another aspect combinable with any of the previous aspects, the at least one weld that connects the top to the housing includes a seal formed with a direct material deposition system. 
     In another general implementation, a system for inspecting a weld of a nuclear waste canister includes a nuclear waste canister that encloses nuclear waste, and a gamma ray image detector system positioned adjacent the nuclear waste canister. The nuclear waste canister includes a housing that includes a volume configured to enclose the nuclear waste and a top connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister. The gamma ray image detector system is configured to perform operations including receiving gamma rays from the nuclear waste that travel through one or more voids in the weld; generating an image of the received gamma rays with at least one gamma ray image detector; and based on the generated image, determining an integrity of the at least one weld. 
     In an aspect combinable with the general implementation, the nuclear waste includes spent nuclear fuel. 
     In another aspect combinable with any of the previous aspects, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In another aspect combinable with any of the previous aspects, the gamma ray image detector system includes a pinhole camera or an Anger camera. 
     In another aspect combinable with any of the previous aspects, at least one of the housing, the top, or a weld material includes a corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects, each of the housing, the top, and the weld material includes the corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects, the corrosion resistant alloy includes CRA 625. 
     In another aspect combinable with any of the previous aspects, he at least one weld includes a horizontal weld. 
     In another aspect combinable with any of the previous aspects, the gamma ray image detector system is configured to receive a plurality of gamma rays that emit from the nuclear waste and scatter through the volume of the nuclear waste container and through one or more voids in the one or more welds. 
     In another aspect combinable with any of the previous aspects, at least one of the nuclear waste canister or the gamma ray image detector system is configured to rotate during operation of the gamma ray image detector system to receive the gamma rays from the nuclear waste that travel through the one or more voids in the weld. 
     In another aspect combinable with any of the previous aspects, the at least one of the nuclear waste canister or the gamma ray image detector system is configured to rotate 360 degrees during operation of the gamma ray image detector system to receive the gamma rays from the nuclear waste that travel through the one or more voids in the weld. 
     In another aspect combinable with any of the previous aspects, the at least one weld that connects the top to the housing includes a seal formed with a direct material deposition system. 
     Implementations of a hazardous material storage repository according to the present disclosure may include one or more of the following features. For example, a hazardous material storage repository according to the present disclosure may allow for multiple levels of containment of hazardous material within a storage repository located thousands of feet underground, decoupled from any nearby mobile water. As another example, implementations of a hazardous material canister according to the present disclosure may be more easily deployed in a hazardous material storage repository, while also being less susceptible to breakage or leakage of hazardous material stored therein due to a seismic event, such as an earthquake. As another example, implementations of a hazardous material canister according to the present disclosure may be more easily and efficiently inspected, e.g., to ensure that there are no leakage paths from an inner volume of the canister to an ambient environment. For instance, implementations of a hazardous material canister that include one or more welds may be more easily and efficiently inspected to ensure that there are little to no voids in the one or more welds using gamma ray radiography that includes a radioactive source internal to the hazardous material canister. As yet another example, implementations of a hazardous material canister according to the present disclosure may be more easily and efficiently sealed through, e.g., a spin welding or direct material deposition process. 
     The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example implementation of a hazardous material storage repository that includes one or more hazardous material canisters according to the present disclosure. 
         FIG. 2  is a schematic illustration of another example implementation of a hazardous material storage repository that includes one or more hazardous material canisters according to the present disclosure. 
         FIGS. 3A-3D  are schematic illustrations of example implementations of a spherical hazardous material canister according to the present disclosure. 
         FIG. 4-8  are schematic illustrations of example implementations of a hazardous material canister according to the present disclosure. 
         FIG. 9  is a schematic illustration of a controller or control system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration of an example implementation of a hazardous material storage repository system  100 , e.g., a subterranean location for the long-term (e.g., tens, hundreds, or thousands of years or more), but retrievable, safe and secure storage of hazardous material (e.g., radioactive material, such as nuclear waste which can be spent nuclear fuel (SNF) or high level waste, as two examples). For example, this figure illustrates the example hazardous material storage repository system  100  once one or more canisters  126  of hazardous material have been deployed in a subterranean formation  118 . As illustrated, the hazardous material storage repository system  100  includes a drillhole  104  formed (e.g., drilled or otherwise) from a terranean surface  102  and through multiple subterranean layers  112 ,  114 ,  116 , and  118 . Although the terranean surface  102  is illustrated as a land surface, terranean surface  102  may be a sub-sea or other underwater surface, such as a lake or an ocean floor or other surface under a body of water. Thus, the present disclosure contemplates that the drillhole  104  may be formed under a body of water from a drilling location on or proximate the body of water. 
     The illustrated drillhole  104  is a directional drillhole in this example of hazardous material storage repository system  100 . For instance, the drillhole  104  includes a substantially vertical portion  106  coupled to a radiussed or curved portion  108 , which in turn is coupled to a substantially horizontal portion  110 . As used in the present disclosure, “substantially” in the context of a drillhole orientation, refers to drillholes that may not be exactly vertical (e.g., exactly perpendicular to the terranean surface  102 ) or exactly horizontal (e.g., exactly parallel to the terranean surface  102 ), or exactly inclined at a particular incline angle relative to the terranean surface  102 . In other words, vertical drillholes often undulate offset from a true vertical direction, that they might be drilled at an angle that deviates from true vertical, and inclined drillholes often undulate offset from a true incline angle. Further, in some aspects, an inclined drillhole may not have or exhibit an exactly uniform incline (e.g., in degrees) over a length of the drillhole. Instead, the incline of the drillhole may vary over its length (e.g., by 1-5 degrees). As illustrated in this example, the three portions of the drillhole  104 —the vertical portion  106 , the radiussed portion  108 , and the horizontal portion  110 —form a continuous drillhole  104  that extends into the Earth. As used in the present disclosure, the drillhole  104  (and drillhole portions described) may also be called wellbores. Thus, as used in the present disclosure, drillhole and wellbore are largely synonymous and refer to bores formed through one or more subterranean formations that are not suitable for human-occupancy (i.e., are too small in diameter for a human to fit therewithin). 
     The illustrated drillhole  104 , in this example, has a surface casing  120  positioned and set around the drillhole  104  from the terranean surface  102  into a particular depth in the Earth. For example, the surface casing  120  may be a relatively large-diameter tubular member (or string of members) set (e.g., cemented) around the drillhole  104  in a shallow formation. As used herein, “tubular” may refer to a member that has a circular cross-section, elliptical cross-section, or other shaped cross-section. For example, in this implementation of the hazardous material storage repository system  100 , the surface casing  120  extends from the terranean surface through a surface layer  112 . The surface layer  112 , in this example, is a geologic layer comprised of one or more layered rock formations. In some aspects, the surface layer  112  in this example may or may not include freshwater aquifers, salt water or brine sources, or other sources of mobile water (e.g., water that moves through a geologic formation). In some aspects, the surface casing  120  may isolate the drillhole  104  from such mobile water, and may also provide a hanging location for other casing strings to be installed in the drillhole  104 . Further, although not shown, a conductor casing may be set above the surface casing  120  (e.g., between the surface casing  120  and the surface  102  and within the surface layer  112 ) to prevent drilling fluids from escaping into the surface layer  112 . 
     As illustrated, a production casing  122  is positioned and set within the drillhole  104  downhole of the surface casing  120 . Although termed a “production” casing, in this example, the casing  122  may or may not have been subject to hydrocarbon production operations. Thus, the casing  122  refers to and includes any form of tubular member that is set (e.g., cemented) in the drillhole  104  downhole of the surface casing  120 . In some examples of the hazardous material storage repository system  100 , the production casing  122  may begin at an end of the radiussed portion  108  and extend throughout the horizontal portion  110 . The casing  122  could also extend into the radiussed portion  108  and into the vertical portion  106 . 
     As shown, cement  130  is positioned (e.g., pumped) around the casings  120  and  122  in an annulus between the casings  120  and  122  and the drillhole  104 . The cement  130 , for example, may secure the casings  120  and  122  (and any other casings or liners of the drillhole  104 ) through the subterranean layers under the terranean surface  102 . In some aspects, the cement  130  may be installed along the entire length of the casings (e.g., casings  120  and  122  and any other casings), or the cement  130  could be used along certain portions of the casings if adequate for a particular drillhole  104 . The cement  130  can also provide an additional layer of confinement for the hazardous material in canisters  126 . 
     The drillhole  104  and associated casings  120  and  122  may be formed with various example dimensions and at various example depths (e.g., true vertical depth, or TVD). For instance, a conductor casing (not shown) may extend down to about 120 feet TVD, with a diameter of between about 28 in. and 60 in. The surface casing  120  may extend down to about 2500 feet TVD, with a diameter of between about 22 in. and 48 in. An intermediate casing (not shown) between the surface casing  120  and production casing  122  may extend down to about 8000 feet TVD, with a diameter of between about 16 in. and 36 in. The production casing  122  may extend inclinedly (e.g., to case the horizontal portion  110 ) with a diameter of between about 11 in. and 22 in. The foregoing dimensions are merely provided as examples and other dimensions (e.g., diameters, TVDs, lengths) are contemplated by the present disclosure. For example, diameters and TVDs may depend on the particular geological composition of one or more of the multiple subterranean layers ( 112 ,  114 ,  116 , and  118 ), particular drilling techniques, as well as a size, shape, or design of a hazardous material canister  126  that contains hazardous material to be deposited in the hazardous material storage repository system  100 . In some alternative examples, the production casing  122  (or other casing in the drillhole  104 ) could be circular in cross-section, elliptical in cross-section, or some other shape. 
     As illustrated, the vertical portion  106  of the drillhole  104  extends through subterranean layers  112 ,  114 , and  116 , and, in this example, lands in a subterranean layer  118 . As discussed above, the surface layer  112  may or may not include mobile water. In this example, a mobile water layer  114  is below the surface layer  112  (although surface layer  112  may also include one or more sources of mobile water or liquid). For instance, mobile water layer  114  may include one or more sources of mobile water, such as freshwater aquifers, salt water or brine, or other source of mobile water. In this example of hazardous material storage repository system  100 , mobile water may be water that moves through a subterranean layer based on a pressure differential across all or a part of the subterranean layer. For example, the mobile water layer  114  may be a permeable geologic formation in which water freely moves (e.g., due to pressure differences or otherwise) within the layer  114 . In some aspects, the mobile water layer  114  may be a primary source of human-consumable water in a particular geographic area. Examples of rock formations of which the mobile water layer  114  may be composed include porous sandstones and limestones, among other formations. 
     Other illustrated layers, such as the impermeable layer  116  and the storage layer  118 , may include immobile water. Immobile water, in some aspects, is water (e.g., fresh, salt, brine), that is not fit for human or animal consumption, or both. Immobile water, in some aspects, may be water that, by its motion through the layers  116  or  118  (or both), cannot reach the mobile water layer  114 , terranean surface  102 , or both, within 10,000 years or more (such as to 1,000,000 years). 
     Below the mobile water layer  114 , in this example implementation of hazardous material storage repository system  100 , is an impermeable layer  116 . The impermeable layer  116 , in this example, may not allow mobile water to pass through. Thus, relative to the mobile water layer  114 , the impermeable layer  116  may have low permeability, e.g., on the order of nanodarcy permeability. Additionally, in this example, the impermeable layer  116  may be a relatively non-ductile (i.e., brittle) geologic formation. One measure of non-ductility is brittleness, which is the ratio of compressive stress to tensile strength. In some examples, the brittleness of the impermeable layer  116  may be between about 20 MPa and 40 MPa. 
     As shown in this example, the impermeable layer  116  is shallower (e.g., closer to the terranean surface  102 ) than the storage layer  118 . In this example rock formations of which the impermeable layer  116  may be composed include, for example, certain kinds of sandstone, mudstone, clay, and slate that exhibit permeability and brittleness properties as described above. In alternative examples, the impermeable layer  116  may be deeper (e.g., further from the terranean surface  102 ) than the storage layer  118 . In such alternative examples, the impermeable layer  116  may be composed of an igneous rock, such as granite. 
     Below the impermeable layer  116  is the storage layer  118 . The storage layer  118 , in this example, may be chosen as the landing for the horizontal portion  110 , which stores the hazardous material, for several reasons. Relative to the impermeable layer  116  or other layers, the storage layer  118  may be thick, e.g., between about 100 and 200 feet of total vertical thickness. Thickness of the storage layer  118  may allow for easier landing and directional drilling, thereby allowing the horizontal portion  110  to be readily emplaced within the storage layer  118  during constructions (e.g., drilling). If formed through an approximate horizontal center of the storage layer  118 , the horizontal portion  110  may be surrounded by about 50 to 100 feet of the geologic formation that comprises the storage layer  118 . Further, the storage layer  118  may also have only immobile water, e.g., due to a very low permeability of the layer  118  (e.g., on the order of milli- or nanodarcys). In addition, the storage layer  118  may have sufficient ductility, such that a brittleness of the rock formation that comprises the layer  118  is between about 3 MPa and 10 MPa. Examples of rock formations of which the storage layer  118  may be composed include: shale and anhydrite. Further, in some aspects, hazardous material may be stored below the storage layer, even in a permeable formation such as sandstone or limestone, if the storage layer is of sufficient geologic properties to isolate the permeable layer from the mobile water layer  114 . 
     In some examples implementations of the hazardous material storage repository system  100 , the storage layer  118  (and/or the impermeable layer  116 ) is composed of shale. Shale, in some examples, may have properties that fit within those described above for the storage layer  118 . For example, shale formations may be suitable for a long-term confinement of hazardous material (e.g., in the hazardous material canisters  126 ), and for their isolation from mobile water layer  114  (e.g., aquifers) and the terranean surface  102 . Shale formations may be found relatively deep in the Earth, typically 3000 feet or greater, and placed in isolation below any fresh water aquifers. Other formations may include salt or other impermeable formation layer. 
     Shale formations (or salt or other impermeable formation layers), for instance, may include geologic properties that enhance the long-term (e.g., thousands of years) isolation of material. Such properties, for instance, have been illustrated through the long term storage (e.g., tens of millions of years) of hydrocarbon fluids (e.g., gas, liquid, mixed phase fluid) without escape of substantial fractions of such fluids into surrounding layers (e.g., mobile water layer  114 ). Indeed, shale has been shown to hold natural gas for millions of years or more, giving it a proven capability for long-term storage of hazardous material. Example shale formations (e.g., Marcellus, Eagle Ford, Barnett, and otherwise) has stratification that contains many redundant sealing layers that have been effective in preventing movement of water, oil, and gas for millions of years, lacks mobile water, and can be expected (e.g., based on geological considerations) to seal hazardous material (e.g., fluids or solids) for thousands of years after deposit. 
     In some aspects, the formation of the storage layer  118  and/or the impermeable layer  116  may form a leakage barrier, or barrier layer to fluid leakage that may be determined, at least in part, by the evidence of the storage capacity of the layer for hydrocarbons or other fluids (e.g., carbon dioxide) for hundreds of years, thousands of years, tens of thousands of years, hundreds of thousands of years, or even millions of years. For example, the barrier layer of the storage layer  118  and/or impermeable layer  116  may be defined by a time constant for leakage of the hazardous material more than 10,000 years (such as between about 10,000 years and 1,000,000 years) based on such evidence of hydrocarbon or other fluid storage. 
     Shale (or salt or other impermeable layer) formations may also be at a suitable depth, e.g., between 3000 and 12,000 feet TVD. Such depths are typically below ground water aquifer (e.g., surface layer  112  and/or mobile water layer  114 ). Further, the presence of soluble elements in shale, including salt, and the absence of these same elements in aquifer layers, demonstrates a fluid isolation between shale and the aquifer layers. 
     Another particular quality of shale that may advantageously lend itself to hazardous material storage is its clay content, which, in some aspects, provides a measure of ductility greater than that found in other, impermeable rock formations (e.g., impermeable layer  116 ). For example, shale may be stratified, made up of thinly alternating layers of clays (e.g., between about 20-30% clay by volume) and other minerals. Such a composition may make shale less brittle and, thus less susceptible to fracturing (e.g., naturally or otherwise) as compared to rock formations in the impermeable layer (e.g., dolomite or otherwise). For example, rock formations in the impermeable layer  116  may have suitable permeability for the long term storage of hazardous material, but are too brittle and commonly are fractured. Thus, such formations may not have sufficient sealing qualities (as evidenced through their geologic properties) for the long term storage of hazardous material. 
     The present disclosure contemplates that there may be many other layers between or among the illustrated subterranean layers  112 ,  114 ,  116 , and  118 . For example, there may be repeating patterns (e.g., vertically), of one or more of the mobile water layer  114 , impermeable layer  116 , and storage layer  118 . Further, in some instances, the storage layer  118  may be directly adjacent (e.g., vertically) the mobile water layer  114 , i.e., without an intervening impermeable layer  116 . In some examples, all or portions of the radiussed drillhole  108  and the horizontal drillhole  110  may be formed below the storage layer  118 , such that the storage layer  118  (e.g., shale or other geologic formation with characteristics as described herein) is vertically positioned between the horizontal drillhole  110  and the mobile water layer  114 . 
     In this example, the horizontal portion  110  of the drillhole  104  includes a storage area in a distal part of the portion  110  into which hazardous material may be retrievably placed for long-term storage. For example, a work string (e.g., tubing, coiled tubing, wireline, or otherwise) or other downhole conveyance (e.g., tractor) may be moved into the cased drillhole  104  to place one or more (three shown but there may be more or less) hazardous material canisters  126  into long term, but in some aspects, retrievable, storage in the portion  110 . 
     Each canister  126  may enclose hazardous material (shown as material  145 ). Such hazardous material, in some examples, may be biological or chemical waste or other biological or chemical hazardous material. In some examples, the hazardous material may include nuclear material, such as SNF recovered from a nuclear reactor (e.g., commercial power or test reactor) or military nuclear material. Spent nuclear fuel, in the form of nuclear fuel pellets, may be taken from the reactor and not modified. Nuclear fuel pellet are solid, although they can contain and emit a variety of radioactive gases including tritium (13 year half-life), krypton-85 (10.8 year half-life), and carbon dioxide containing C-14 (5730 year half-life). Other hazardous material  145  may include, for example, radioactive liquid, such as radioactive water from a commercial power (or other) reactor. 
     In some aspects, the storage layer  118  should be able to contain any radioactive output (e.g., gases) within the layer  118 , even if such output escapes the canisters  126 . For example, the storage layer  118  may be selected based on diffusion times of radioactive output through the layer  118 . For example, a minimum diffusion time of radioactive output escaping the storage layer  118  may be set at, for example, fifty times a half-life for any particular component of the nuclear fuel pellets. Fifty half-lives as a minimum diffusion time would reduce an amount of radioactive output by a factor of 1×10 −15 . As another example, setting a minimum diffusion time to thirty half-lives would reduce an amount of radioactive output by a factor of one billion. 
     For example, plutonium-239 is often considered a dangerous waste product in SNF because of its long half-life of 24,100 years. For this isotope, 50 half-lives would be 1.2 million years. Plutonium-239 has low solubility in water, is not volatile, and as a solid. its diffusion time is exceedingly small (e.g., many millions of years) through a matrix of the rock formation that comprises the illustrated storage layer  118  (e.g., shale or other formation). The storage layer  118 , for example comprised of shale, may offer the capability to have such isolation times (e.g., millions of years) as shown by the geological history of containing gaseous hydrocarbons (e.g., methane and otherwise) for several million years. In contrast, in conventional nuclear material storage methods, there was a danger that some plutonium might dissolve in a layer that comprised mobile ground water upon confinement escape. 
     In some aspects, the drillhole  104  may be formed for the primary purpose of long-term storage of hazardous materials. In alternative aspects, the drillhole  104  may have been previously formed for the primary purpose of hydrocarbon production (e.g., oil, gas). For example, storage layer  118  may be a hydrocarbon bearing formation from which hydrocarbons were produced into the drillhole  104  and to the terranean surface  102 . In some aspects, the storage layer  118  may have been hydraulically fractured prior to hydrocarbon production. Further in some aspects, the production casing  122  may have been perforated prior to hydraulic fracturing. In such aspects, the production casing  122  may be patched (e.g., cemented) to repair any holes made from the perforating process prior to a deposit operation of hazardous material. In addition, any cracks or openings in the cement between the casing and the drillhole can also be filled at that time. 
     As further shown in  FIG. 1 , a backfill material  140  may be positioned or circulated into the drillhole  104 . In this example, the backfill material  140  surrounds the canisters  126  and may have a level that extends uphole to at or near a drillhole seal  134  (e.g., permanent packer, plug, or other seal). In some aspects, the backfill material  140  may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material  140  may have a relatively low thermal conductivity, thereby acting as an insulator between the canisters  126  and the casings. 
     As further shown in  FIG. 1 , another backfill material  150  may be positioned or placed within one or more of the canisters  126  to surround the hazardous material  145 . In some aspects, the backfill material  150  may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material  150  may have a relatively low thermal conductivity, thereby acting as an insulator between the hazardous material  145  and the canister  126 . In some aspects, the backfill material  150  may also provide a stiffening attribute to the canister  126 , e.g., reducing crushability, deformation, or other damage to the canister  126 . 
     In some aspects, one or more of the previously described components of the system  100  may combine to form an engineered barrier of the hazardous waste material repository  100 . For example, in some aspects, the engineered barrier is comprised of one, some, or all of the following components: the storage layer  118 , the casing  122 , the backfill material  140 , the canister  126 , the backfill material  150 , the seal  134 , and the hazardous material  145 , itself. In some aspects, one or more of the engineered barrier components may act (or be engineered to act) to: prevent or reduce corrosion in the drillhole  104 , prevent or reduce escape of the hazardous material  145 ; reduce or prevent thermal degradation of one or more of the other components; and other safety measures to ensure that the hazardous material  145  does not reach the mobile water layer  114  (or surface layer  112 , including the terranean surface  102 ). 
       FIG. 2  is a schematic illustration of an example implementation of a hazardous material storage repository system  200 , e.g., a subterranean location for the long-term (e.g., tens, hundreds, or thousands of years or more), but retrievable, safe and secure storage of hazardous material. In some aspects, one or more components of repository  200  may be similar to components described in reference to the hazardous material repository  100  (shown with like reference numbers). For example, this figure illustrates the example hazardous material storage repository system  200  once one or more canisters  226  of hazardous material have been deployed in a subterranean formation  118 . In this example implementation, at least one of the canisters deployed in the subterranean formation comprises a spherical hazardous material canister  226  (three shown in this example). 
     Each canister  226  may enclose hazardous material (shown as material  245 ). Such hazardous material, in some examples, may be biological or chemical waste or other biological or chemical hazardous material. In some examples, the hazardous material may include nuclear material, such as SNF recovered from a nuclear reactor (e.g., commercial power or test reactor) or military nuclear material. Spent nuclear fuel, in the form of nuclear fuel pellets, may be taken from the reactor and not modified. Nuclear fuel pellet are solid, although they can contain and emit a variety of radioactive gases including tritium (13 year half-life), krypton-85 (10.8 year half-life), and carbon dioxide containing C-14 (5730 year half-life). Other hazardous material  245  may include, for example, radioactive liquid, such as radioactive water from a commercial power (or other) reactor. 
     As further shown in  FIG. 1 , a backfill material  140  may be positioned or circulated into the drillhole  104 . In this example, the backfill material  140  surrounds the canisters  126  and may have a level that extends uphole to at or near a drillhole seal  134  (e.g., permanent packer, plug, or other seal). In some aspects, the backfill material  140  may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material  140  may have a relatively low thermal conductivity, thereby acting as an insulator between the canisters  126  and the casings. 
     As further shown in  FIG. 2 , another backfill material  250  may be positioned or placed within one or more of the canisters  226  to surround the hazardous material  245 . In some aspects, the backfill material  250  may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material  250  may have a relatively low thermal conductivity, thereby acting as an insulator between the hazardous material  245  and the canister  226 . In some aspects, the backfill material  250  may also provide a stiffening attribute to the canister  226 , e.g., reducing crushability, deformation, or other damage to the canister  226 . 
     In some aspects, one or more of the previously described components of the system  200  may combine to form an engineered barrier of the hazardous waste material repository  200 . For example, in some aspects, the engineered barrier is comprised of one, some, or all of the following components: the storage layer  118 , the casing  122 , the backfill material  140 , the canister  226 , the backfill material  250 , the seal  134 , and the hazardous material  245 , itself. In some aspects, one or more of the engineered barrier components may act (or be engineered to act) to: prevent or reduce corrosion in the drillhole  104 , prevent or reduce escape of the hazardous material  245 ; reduce or prevent thermal degradation of one or more of the other components; and other safety measures to ensure that the hazardous material  245  does not reach the mobile water layer  114  (or surface layer  112 , including the terranean surface  102 ). 
     Although described as a spherical canister  226 , the canister  226  may be substantially spherical (e.g., not exactly spherical in exterior shape but close to spherical). For example, in some aspects, the spherical canister  226  may have one or more flat or substantially flat portions (e.g., at opposite poles, such as a globe). In some aspects, the canister  226  may be exactly spherical. 
     The spherical canister  226  may be deployed into the drillhole  104  by, for example, a downhole conveyance (e.g., a tubular conveyance or wireline conveyance). In alternative aspects, the spherical canister  226  may be deployed into the drillhole  104  by a downhole tractor. In some aspects, due to the spherical (or substantially spherical) shape of the exterior housing of the canister  226 , deployment of the canister  226  into the drillhole  104  may also include rolling the canister  226  through one or more portions of the drillhole  104 . In some aspects, due to the spherical (or substantially spherical) shape of the exterior housing of the canister  226 , at least a portion of the drillhole  104  (e.g., some or all of the substantially horizontal portion  110 ) may be angled vertically away from the terranean surface  102  so that the canister  226  does not move (e.g., by force of gravity) from the portion  110  toward the substantially vertical portion  106  after deployment. 
       FIGS. 3A-3D  are schematic illustrations of example implementations of a spherical hazardous material canister, such as the spherical hazardous material canister  226  shown in  FIG. 2 .  FIG. 3A  shows an example implementation of a spherical canister  300 , while  FIG. 3B  shows another example implementation of a spherical canister  350 . Each of canisters  300  and  350  may store hazardous material, such as radioactive waste. In some aspects, the radioactive waste may comprise SNF (e.g., SNF pellets are at least a portion of a SNF assembly) or high level radioactive waste. In some aspects, one or both of spherical canisters  300  and  350  may be utilized as a spherical hazardous waste canister  226  as shown in the hazardous waste repository  200  in  FIG. 2 . 
     Spherical canister  300  is shown in  FIG. 3A  and includes a spherical (or substantially spherical) housing  302  comprised of a top portion  308  (or cap  308 ) and a bottom portion  306 . Each portion  308  and  306  are at least partially hollow such that, when joined, an interior volume  304  (represented in dashed line) is defined within the housing  302 . The bottom portion  306  includes an edge  314  that has a dimension (e.g., circumference) that is substantially similar, if not identical to, a dimension (e.g., circumference) of an edge  312  of the top portion  308 . As shown in  FIG. 3A , hazardous material  310  in the form of SNF (i.e., nuclear or radioactive waste) is positioned in the interior volume  304  of the bottom portion  306  of the housing  302 . In some aspects, one or both of the edges  312  and  314  may be beveled or angled in order to more sealingly mate with the other of the edges. 
     In example implementations, the canister  300  may be from 4 to 12 inches in diameter, and made of a corrosion-resistant alloy, such as Alloy-625. In the example of the hazardous material  310  being SNF pellets, the SNF pellets (which, in an assembly for commercial nuclear fuel are cylindrical in shape) are typically 1 cm in diameter, and 1 cm in length. The SNF pellets are comprised primarily of UO 2  ceramic with a density of 10 g/cm 3 . As shown in  FIG. 3A , the housing  302  of the spherical canister  300  generally is made of two hemispheres: top portion  308  and bottom portion  306 . In this example, the bottom portion  306  may be filled with stacked SNF rods (or portions of such rods). These rods consist of small pipes that hold the SNF pellets. Longer fuel rods are used in commercial and defense fuel assemblies and typically made of an alloy of zirconium; however, these rods can be made of a different material. That material could be a corrosion-resistant alloy and/or it could contain a neutron absorber such as boron to reduce the likelihood of the fuel configuration reaching criticality. The rods could be stacked in a hexagonal close-packed array. 
     In an assembly operation of the spherical canister  300 , when the bottom portion  306  of the housing  302  is filled with fuel pellets (i.e., the volume  304  is filled), then the top portion  308  (e.g., the lid) would be placed on the bottom portion  306 , and the two hemispheres joined or sealed (e.g., threadingly, by welding, by adhesive, by mechanical fasteners, or otherwise) by joining or sealing the edges  312  and  314  together. One method for welding might be spin-welding (friction welding). The edges  312  and  314  that are welded together could be radial in direction, or they could be canted to provide greater surface area and to facilitate placement and centering. In an example implementation, the spherical housing  302  is a 4-inch inner diameter sphere that would have volume of 108 cm 3  and might hold 80 SNF pellets (allowing for imperfect packing and the volume of the rods). An 8 inch diameter sphere housing  300  could hold about eight times as many SNF pellets. 
       FIG. 3B  shows a spherical canister  350 . Spherical canister  350  includes a spherical (or substantially spherical) housing  352  comprised of a lid  358  and a bottom portion  356 . In contrast to the canister  300 , the bottom portion  356  of the canister  350  defines all or most of an interior volume  354 , while the lid  358  simply seals a small portion of the housing  352 . Thus, the canister  350 , instead of having two hemispherical portions of substantially similar size, includes a lid  358  that is smaller (and possibly much smaller) than the bottom portion  356 . When joined, the interior volume  354  (represented in dashed line) is defined within the housing  352 . The bottom portion  356  includes an edge  360  formed in a surface of the bottom portion  356  that has a dimension (e.g., circumference) that is substantially similar, if not identical to, a dimension (e.g., circumference) of an edge  362  of the lid  358 . Although not specifically shown in  FIG. 3B , hazardous material (such as material  310 ) in the form of SNF (i.e., nuclear or radioactive waste) is positionable in the interior volume  354  of the bottom portion  356  of the housing  352 . In some aspects, one or both of the edges  360  and  362  may be beveled or angled in order to more sealingly mate with the other of the edges. 
     In example implementations, the canister  350  may be from 4 to 12 inches in diameter, and made of a corrosion-resistant alloy, such as Alloy-625. In the example of the hazardous material being SNF pellets, the SNF pellets (which, in an assembly for commercial nuclear fuel are cylindrical in shape) are typically 1 cm in diameter, and 1 cm in length. The SNF pellets are comprised primarily of UO 2  ceramic with a density of 10 g/cm 3 . In this example, the bottom portion  356  may be filled with stacked SNF rods (or portions of such rods). These rods consist of small pipes that hold the SNF pellets. Longer fuel rods are used in commercial and defense fuel assemblies and typically made of an alloy of zirconium; however, these rods can be made of a different material. That material could be a corrosion-resistant alloy and/or it could contain a neutron absorber such as boron to reduce the likelihood of the fuel configuration reaching criticality. The rods could be stacked in a hexagonal close-packed array. 
     In an assembly operation of the spherical canister  350 , when the bottom portion  356  of the housing  302 , and therefore the interior volume  354 , is filled with fuel pellets, then the lid  358  is placed on the bottom portion  356 . The lid  358  is then joined or sealed (e.g., threadingly, by welding, by adhesive, by mechanical fasteners, or otherwise) to the bottom portion  356  by joining or sealing the edges  360  and  362  together. One method for welding might be spin-welding (friction welding). The edges  360  and  362  that are welded together could be radial in direction, or they could be canted to provide greater surface area and to facilitate placement and centering. In an example implementation, the spherical housing  352  is a 4-inch inner diameter sphere that would have volume of 108 cm 3  and might hold 80 SNF pellets (allowing for imperfect packing and the volume of the rods). An 8 inch diameter sphere housing  350  could hold about eight times as many SNF pellets. 
     In some aspects of spherical canister  350 , individual SNF pellets may be placed in the bottom portion  356  without being in rod form (i.e., not as a SNF rod or rod portion). The SNF pellets may fill the bottom portion, and then the lid will be placed on top and welded to the lower section. The lower section might be shaken or vibrated as the pellets fall in to improve the packing. But the SNF pellets, in this configuration, may not be necessarily arranged in an orderly fashion. 
     In some aspects, example spherical canisters  300  and  350  (either or both) may be crush-resistant. For example, the interior volumes  304  and/or  354  may be filled (all or partially, once the hazardous waste is included therein) with a fill material that is strong under compression, such as sand. The fill material may also be any solid that is strong under compression. In an example aspect, the filling material between the SNF (in rod or pellet form) is sand saturated with a gas that helps conduct heat from the radioactivity of the pellets. That gas could be helium, argon, or nitrogen (as some examples). 
     Although both canisters  300  and  350  are shown and described as being spherical or substantially spherical in external shape, other external shapes are contemplated by the present disclosure. For example, a shape of the canister  300  or  350  may be a compromise between sphere and cylinder; the shape could be elliptical or cylindrical with rounded edges. Although some of the advantages of the spherical shape may be compromised, there can be advantages in handling and filling of a canister that included an elongated external shape. 
     Turning to  FIG. 3C , this figure illustrates another example implementation of a hazardous waste storage system that includes one or more spherical canisters.  FIG. 3C  illustrates a cross-section of a hazardous material canister  375  that is deployed in a hazardous material repository (a portion of which is shown in  FIG. 3C ). As shown, the hazardous material canister  375  may be cylindrical or substantially cylindrical in shape and sized to enclose one or more spherical canisters, such as one or more spherical canisters  300  or  350 . In some aspects, canister  375  may be used as canister  126  as shown in  FIG. 1 . The spherical canisters  300  or  350 , as shown can be placed inside of the cylindrical canister  375 , e.g., to simplify handling of hazardous material. For example, a large number of spherical canisters  300  or  350  could be placed inside the canister  375 , which, in some aspects, is similar in shape to a SNF assembly (e.g., a single SNF assembly). The hazardous material canister  375  may be, e.g., 5 to 12 inches in inner diameter and 1 to 20 feet long. As shown, the canister  375  is positioned in the substantially horizontal portion  110  of the drillhole  104 . 
     In some aspects, shielding  380  may be positioned at one or both ends of the canister  375 . In some aspects, the shielding  380  may be attached to or integral with the hazardous material canister  375 . The shielding  380  may be a radiation shielding (e.g., to reduce or stop gamma radiation from escaping the canister  375 ) or contact shielding (e.g., to reduce or eliminate damage to the canister  375  due to contact from other canisters or objects), or both. In some aspects, the hazardous material canister  375  may be made of corrosion-resistant alloy or of some other material. The hazardous material canister  375  may simplify handling and placement of the hazardous material in a deep, human-unoccupiable directional drillhole. In addition, the hazardous material canister  375  may provide an additional engineered barrier to escape of hazardous material, such as radioisotopes from SNF. The hazardous material canister  375  may be designed to hold a linear array of spherical canisters  300  or  350 . Alternatively, the hazardous material canister  375  may be larger and enclose several (e.g.,  3 ) side-by-side linear arrays of spherical canisters  300  or  350 . In some aspects, multiple linear arrays may provide for more efficient use of the volume of the hazardous material canister  375  as well as drillhole. In some aspects, space within the hazardous material canister  375  that is not occupied by the one or more spherical canisters  300  or  350  may be filled with a sand-like material, a liquid, or a gas. In some aspects, the hazardous material canister  375  includes a frame mounted in its interior volume that holds the spherical canisters  300  or  350  in place inside the hazardous material canister  375 . The hazardous material canister  375 , in some aspects, may be rectangular in cross-section rather than circular. Other cross-sectional shapes, such as hexagonal, are also contemplated by the present disclosure. 
     In some aspects, implementations of a hazardous material spherical canister according to the present disclosure may provide an additional measure of protection against the unwanted release of hazardous material stored in a hazardous waste repository in a geographic area that experiences seismic events, such as earthquakes. For example, it is widely believed that underground disposal (e.g., in deep, human-unoccupiable directional drillholes) of nuclear waste (e.g., SNF or high level waste) cannot be done safely in regions in which earthquakes are likely. Since some nuclear waste is generated in regions that have large and frequent earthquakes (e.g., nuclear waste from commercial nuclear reactors in California, Taiwan, South Korea, and Japan to name a few), that assumption requires a distant location for disposal. Distant disposal can create legal issues (some countries are mandated to dispose within the country) and real or perceived risks from transportation. 
     In some aspects, the shaking caused by a nearby earthquake is not the primary danger to a hazardous material (e.g., nuclear waste) canister positioned in a hazardous waste repository of a deep directional drillhole formed in a subterranean formation. The reason is that such accelerations are typically less than 1 g (i.e., less than 980 gal, where a gal is the standard unit for acceleration, equal to 1 cm per second per second). Such accelerations present threats to surface structures, but nuclear waste canisters are designed to endure much stronger accelerations. 
     In some aspects, the greater danger from an earthquake is that a fault (created or caused or moved by the earthquake) will shear through the hazardous waste repository of the drillhole, which in turn can damage one or more nuclear waste canisters positioned in the repository (thereby causing radioactive waste to leak into water in the subterranean formation. Such canisters, for example, may have a large length to cross-section ratio (e.g., long and thin, designed to store one or more SNF assemblies). Such canister, for instance, may store nuclear waste (e.g., SNF) in unmodified fuel assemblies for placement in the deep directional drillhole. Such fuel assemblies are typically 8 to 12 inches in diameter and 14 feet long; the canister to hold an unmodified SNF assembly would be similar in diameter and length. Thus, it is the long and narrow shape of the fuel assembly canisters that may make them vulnerable to being sheared by an earthquake fault that crosses the hazardous waste repository of the drillhole. 
     As previously described and shown in  FIGS. 3A-3C , example implementations of the present disclosure include a nuclear waste canister that encloses nuclear waste (e.g., SNF or high level waste) for storage in a deep directional drillhole, where the canister includes a spherical or substantially spherical housing. Such a spherical nuclear waste canister, in some aspects, may be less susceptible to breakage or leakage in the event of an earthquake that creates a fault that shears the hazardous waste repository of the deep directional drillhole. In some aspects, the nuclear waste, such as a SNF assembly, may be repackaged to fit into the spherical nuclear waste canister. 
     The example implementations of a canister that is shaped as a small sphere may be very resistant to shear from an earthquake. The spherical shape of the housing makes the canister more resistant to crushing compared to canisters of any other shape. A torque on the spherical canister will tend to rotate it rather than to bend it, as would be the case for a canister whose length and width are unequal. 
     As also previously described, the spherical canisters can also be placed inside of a longer cylindrical canister, to simplify handling. For example, a large number of spherical canisters could be placed inside a long outer canister, one that is similar in shape to the original fuel assembly. That canister might be 5 to 12 inches in inner diameter and 1 to 20 feet long. The outer canister also provides some protection against shear from earthquakes. 
     Earthquake faults can have a range of transverse extent, from millimeters to kilometers. If the boundary is sharp, then there will be a shearing force placed across the spherical canister. Unless the narrow line of the earthquake discontinuity lies exactly in the plane of symmetry of the sphere, the shearing force will become, in part, a force along the axis of the drillhole, and will force the sphere to move in that direction, provided that there is space to move. To provide that space, gaps may be left between the spherical nuclear waste canisters (or between outer canisters such as canister  375  that encloses multiple spherical canisters and may be filled with a fluid or other material that will yield when a force is placed on it). Once the spherical canister is more on one side of the drillhole than the other, the shearing force will be greater (as it occurs across the curved part of the spherical canister) and it will continue to push the spherical canister into the drillhole. 
     This is illustrated in  FIG. 3D . For example, as shown, a fault  390  (naturally occurring or due to seismic activity) ruptures  394  an engineered barrier of a hazardous waste repository, such as, for example, the casing  120  and cement  130  installed in the horizontal portion  110  of the drillhole  104 . A force  392  acts on the spherical canister ( 300  or  350 ). The component of the force on the spherical canister  300  or  350  along the axis of the casing  120  pushes the spherical canister  300  or  350  further along in the hazardous waste repository of the deep directional drillhole and away from the fault line  390 . This movement reduces the force  392  on the spherical canister  300  or  350  and places the spherical canister  300  or  350  in a location that prevents any danger of shearing of the canister (thereby releasing hazardous material). 
     Although earthquake faults can be very narrow, as shown in  FIG. 3D , they can also be broad and filled with crushed rock or rock that was crushed when the fault moved. In such a situation, the forces on the spherical canister  300  or  350  may tend to rotate the canister. The advantage of a spherical canister  300  or  350  is that such a canister can rotate without changing an opening in the rock formation in which it is contained in the repository (e.g., formation  118 ). 
       FIG. 4-8  are schematic illustrations of example implementations of a hazardous material canister according to the present disclosure. Although the illustrated implementations of the hazardous material canisters are shown as cylindrical or substantially cylindrical in shape, other shapes, such as spherical or substantially spherical, square or rectangular in radial cross-section, or otherwise, are also contemplated by the present disclosure. Each example implementation of a hazardous material canister shown in  FIGS. 4-8  is designed to store (perhaps permanently) hazardous waste in deep, human-unoccupiable directional drillholes (e.g., wellbores). In some aspects, each example implementation of a hazardous material canister shown in  FIGS. 4-8  is designed to be retrievable from the deep, human-unoccupiable directional drillhole to a terranean surface, when needed. The hazardous material can be chemical, biological, or, in many examples, radioactive (e.g., nuclear) in nature. For example, hazardous material may be SNF or high level radioactive waste, with either type being in solid, liquid, or gaseous form as stored in the hazardous material canister. In some aspects, each example implementation of a hazardous material canister shown in  FIGS. 4-8  is part of an engineered barrier system that prevents the hazardous material from migrating to a source of ground water or other source of mobile water that can move to consumable water sources. For example, such ground water could dissolve components of the waste and transport the dissolved radioactive components to the terranean surface and contaminate human- (or animal-) consumable water. 
     The nuclear waste emits gamma and X-radiation, making the close environment of the canister dangerous for humans. However, such nuclear waste needs to be sealed within the canister, such as by welding a top or seal onto the open canister to seal the nuclear waste within a volume of the canister 
     For example,  FIG. 4  shows an example system  400  for examining and validating a weld  408  formed on a hazardous material canister  402 , e.g., to join a cap  406  of the hazardous material canister  402  to a housing  404  of the hazardous material canister  402 . Conventional methods have been used in the past to validate the quality of such welds. Certain methods are non-destructive. These include visual inspection, ultrasonics, and gamma ray radiography. Radiography typically consists of putting a source of X-rays or gamma rays near the weld and recording the transmitted rays. Any hidden gap or void in the weld would transmit gamma (and/or X-) rays at an increased level. 
     The example system  400  (and method of operating the system  400 ) utilizes gamma ray emission (shown as  412 ) of radioactive (or nuclear) waste  410  (e.g., SNF or high level waste) as the source of the radiation used to probe the weld  408 . In some aspects, the term “gamma ray” includes both gamma rays and X-rays. The gamma rays  412 , during inspection of the weld  408 , may not be viewed directly. However, gamma rays  412  are not only absorbed, but also scattered. That is, a gamma ray hitting the nucleus of an atom, or an electron, can be deflected so that it travels in a different direction. This usually involves energy loss of the gamma ray  412 , but for the present disclosure, the energy loss is small enough that the deflected ray is still considered to be a gamma ray  412 . In some aspects, these scattered gamma rays  412  may be used to examine the quality of the weld  408 , in particular, whether there are any gaps or voids  415  within the weld  408  that seals the nuclear waste  410  within a volume  413  defined within the housing  404 . 
     For an example, a flat weld  408  may be formed that connects the canister housing  404  with the canister lid  406  (e.g., by spin welding).  FIG. 4  shows an example implementation of a portion of the hazardous material canister  402  in a vertical orientation. The weld  408  may be horizontal, as shown with the dashed lines in  FIG. 4 . Also, the dashed lines may show where the lid  406  of the canister  402  and the housing  404  of the canister  402  meet (i.e., at the weld  408 ). In some aspects, a cross section of the canister  402  taken at the weld  408  is circular. Thus, the weld  408  itself may be a circular weld that joins adjoining circumferential edges of the housing  404  and the lid  406  of the canister  402 . In some aspects, at least one of the housing  404 , lid  406 , or weld  408  are made of a corrosion-resistant alloy, such as Alloy 625. 
     As shown in  FIG. 4 , the highly radioactive material  410  is emplaced in the volume  413  of the canister  402  below the weld  408 . The radioactive material  410  (e.g., nuclear waste) emits gamma and X-rays (shown collectively as  412 ) in all directions. The gamma rays of interest are those that are emitted in a generally upward direction, and which paths cross the weld  408  to be examined. 
     When the source of gamma rays  412  is sufficiently high, an image of the source distribution can be obtained by using a gamma ray camera  420  that includes a shield  422  (e.g., a lead shield) with one or more openings  424 . For example, as shown, the shield  422  may have a single small opening  424  and a gamma ray detector  426  positioned behind the hole  424  (e.g., opposite the canister  402 ). For example, as shown in  FIG. 4 , the gamma ray, or “pinhole,” camera  420  is positioned so as to receive gamma rays  412  that potentially exit the sealed canister  402  through one or more voids  415  in the welded portion  408 , through the pinhole  424 , and at the gamma ray image detector  426 . 
     In an alternative aspect, the pinhole  424  may be a horizontal slit. A horizontal slit may admit more gamma rays  412 , but the slit provides no horizontal resolution, which is not needed if the goal is to validate a thin horizontal weld (such as weld  408 ). The validation of the weld  408  may include testing if the layer of the weld scatters as many gamma rays  412  as do the layers of the housing  404  and/or lid  406  (e.g., above the weld  408  or below the weld  408 ). If the scattering is the same or substantially the same, then it indicates that there are no voids  415  in the weld  408 . 
     In further alternative aspects, the gamma ray camera  420  comprises an Anger camera or a coded aperture camera. For example, as an Anger camera, the gamma ray camera  420  includes a series of holes in a gamma absorber such as lead. 
     In this example implementation, the gamma ray camera  420  operates to provide pinhole imaging of scattered radiation  412 ; the presence of a void  415  in the weld  408  creates a region in an image created by the gamma ray image detector  426  with less exposure. Thus, the pinhole camera  420  images any voids  415  as a “dark” region, i.e., one with fewer gamma rays  412  being received from the nuclear waste  410  in the canister  402 . 
     The pinhole camera  410 , as shown, for example, is used in gamma ray radiography of the hazardous material canister  402  in combination with the stored radioactive waste  410  as the source of the gamma rays  412  used to verify the integrity of the weld  408 . For example, aspects of the present disclosure include the pinhole camera  420  to measure scattered radiation (e.g., gamma rays  412 ) emitted naturally from within the canister  402  (e.g., by the enclosed nuclear waste  410 ) with no need to add an additional source. Thus, aspects of the present disclosure include a source of the gamma rays  412  used to measure or determine an integrity of the weld  408  that seals nuclear waste  410  in the canister  402  that is the nuclear waste  410 , itself. 
     In some aspects, one or both of the nuclear waste canister and the gamma ray image detector are rotated during the operation of the detector to receive scattered gamma rays and generate an image of the received gamma rays. Thus, in some aspects, the gamma ray image detector may operate to inspect a complete circumference of the weld as the detector or the canister (or both) rotates (e.g., around 360 degrees). 
     A controller, control system, or computing system (e.g., control system  900 ) may be connected to the gamma ray image detector  426  and/or the gamma ray camera  420  to receive images from the detector  426 . The images show, for example, the scattered radiation that shows the presence of any void in the weld  408 . Based on the image, the computing system  900  may determine an integrity of the weld  408 . For example, the computing system  900  may determine that the images include portions that show voids of a particular size that indicates that the weld  408  is not sufficient to seal the radioactive waste  410  in the hazardous material canister  402 . 
     Turning to  FIG. 5 , this figure illustrates an example system  500  for examining and validating a weld  510  formed on a hazardous material canister  502 , e.g., to join a cap  506  of the hazardous material canister  502  to a housing  504  of the hazardous material canister  502 . Conventional methods have been used in the past to validate the quality of such welds. Certain methods are non-destructive. These include visual inspection, ultrasonics, and gamma ray radiography. Radiography typically consists of putting a source of X-rays or gamma rays near the weld and recording the transmitted rays. Any hidden gap or void in the weld would transmit gamma (and/or X-) rays at an increased level. 
     In this example, the canister  502  includes the lid  506 , which is sealed to the housing  504  of the canister  502  by a weld  510  (e.g., by spin welding). For instance, example implementations utilize a spin welding system is used to attach the lid  506  to the housing  504  of  FIG. 5  (e.g., through the technique of spin welding). Further, in some aspects, implementations of  FIG. 5  include a shield  512  (lead or other material that absorbs gamma rays) that is placed within a volume  511  of the canister  502  to prevent gamma rays  520  from the radioactive waste  508  from reaching one or more gamma ray detectors  530 , but low enough that the shield  512  does not interfere with the imaging of the weld  510 . If the weld  510  is created through spin welding, then a region to be examined by the gamma ray detectors  530  can be no more than one or several millimeters in vertical extent. If this is the case, then the shield  512  may cover most of the canister  502 . As another example, a shield made from tungsten or tungsten carbide could be used. The shield  512  could also be made of a material such as sand (or tungsten carbide) that is packed in at the top part of the canister  502 . 
     The example system  500  (and method of operating the system  500 ) utilizes gamma ray emission (shown as  520 ) of radioactive (or nuclear) waste  508  (e.g., SNF or high level waste) as the source of the radiation used to probe the weld  510 . In some aspects, the term “gamma ray” includes both gamma rays and X-rays. 
     As shown, a flat weld  510  may be formed that connects the canister housing  504  with the canister lid  506  (e.g., by spin welding).  FIG. 5  shows an example implementation of a portion of the hazardous material canister  502  in a vertical orientation. The weld  510  may be horizontal, as shown with the dashed lines in  FIG. 5 . Also, the dashed lines may show where the lid  506  of the canister  502  and the housing  504  of the canister  502  meet (i.e., at the weld  510 ). In some aspects, a cross section of the canister  502  taken at the weld  510  is circular. Thus, the weld  510  itself may be a circular weld that joins adjoining circumferential edges of the housing  504  and the lid  506  of the canister  502 . In some aspects, at least one of the housing  504 , lid  506 , or weld  510  are made of a corrosion-resistant alloy, such as Alloy 625. 
     As shown in  FIG. 5 , the highly radioactive material  508  is emplaced in the volume  511  of the canister  502  below the weld  510 . The radioactive material  508  (e.g., nuclear waste) emits gamma and X-rays (shown collectively as  520 ) in all directions. The gamma rays of interest are those that are emitted in a generally upward direction through an aperture  514  of the shield  512  toward the scatterer  516 . 
     In this example, a scatterer is positioned near or attached to an inner surface of the cap and aligned with the small hole in the shield. In this example, gamma ray radiation is caused to scatter by the scatterer so that the radiography of the weld is essentially a shadow image. 
     In this example implementation shown in  FIG. 5 , the gamma shield  512  is placed above the nuclear material  508  but below the weld  510 . The shield  512  reduces upward gamma rays  520 , and attenuates the number of gamma rays  522  that can travel directly to the gamma ray imaging detector  530  from the nuclear material  508 . For example, gamma rays  520  emitted by the nuclear material  508  pass through the aperture  514  in the radial middle of the shield  512  and hit a point  518  of the scatterer  516 . The aperture  514  could be open or filled with any material that does not strongly absorb gamma radiation. The point  518  of the scatterer  516 , in some examples, is a small sphere or disk of material that strongly scatters gamma rays  520  (to scattered gamma rays  522 ); an example is tungsten or tungsten carbide or tungsten carbide cobalt. The gamma rays  522  scatter off the point  518  in all directions, which gives the scatterer  516  the effect of being a point source of gamma rays  522 . Some of these rays  522  pass through the weld  510  and the parts of the canister  502  near the weld  510  onto the gamma imaging detector  530  (e.g., a piece of film, as is often used for dental X-rays, or an array of gamma detectors). A shadow of the weld  510  on the imaging detector  530  reveals any gaps or discontinuities (e.g., voids) in the weld  510 . The shield  512  may also act to limit the number of gamma rays  520  that emerge from the lid  506  of the canister  502 . 
     In some aspects, the gamma shield  512  serves other additional purposes. For example, if the canister  502  is placed in an external radiation shield without a lid (as may be done when the canister  502  is sitting above a directional drillhole prior to being lowered into the hole), then a top of the external radiation shield can be open, since most of gamma rays  520  in the upward direction is absorbed by the shield  512 . Also, the shield  512  may reduce an amount of gamma radiation  520  that travels directly from the radioactive waste  508  to hit the imaging device  530 ; such direct radiation, if not attenuated, would create a background “fogging” that could obscure the shadow image. Further, due to the aperture  514  in the shield  512 , gamma rays  520  impinge on the point  518  of the scatterer  516  to provide a “point-like” source for the shadow radiography. The shield  512  also absorbs most of the upward traveling gamma rays  520 , thus providing radiation shielding in the upward direction (e.g., from the volume  511  toward the lid  506 ). 
     Continuing with  FIG. 5 , the shield  512  may also provide an internal radiation shield that may ease handling of the canister  502  and allows the weld  510  to be made with a lid  506  that does not have an external radiation shield attached. Further, the gamma shield  512  is placed below the weld  510  and is thus in a relatively low gamma ray environment, which facilities radiography of the weld  510 . Further, the shield  512  includes the aperture  514  that allows gamma rays  520  to hit the point  518  of the scatterer  516  that is positioned at the same or close to same planar location as the weld  510 . Scattering from this point  518  provides a point-like source of gamma rays  522  for the weld  510 , which then can be examined by using shadow imaging. 
     In an example operation of the system  500 , gamma rays  520  emitted by the nuclear material  508  pass through the aperture  514  in the radial middle of the shield  512  and hit the point  518  of the scatterer  516 . The gamma rays  522  scatter off the scatterer  516  in all directions, which gives the scatterer  516  the effect of being a point source of gamma rays  522 . Some of these rays  522  pass through the weld  510  onto the gamma imaging detector  530 . The shadow of the weld  510  on the imaging detector  530  will reveal any gaps or discontinuities in the weld  510 . 
     When the source of gamma rays  522  is sufficiently high, an image of the source distribution can be obtained by using a gamma ray camera (such as camera  420 ) that includes a shield (e.g., a lead shield) with one or more openings. For example, as shown for camera  420  (which can be used in system  500  and includes gamma ray detectors  530 ), the shield may have a single small opening and gamma ray detector  530  positioned behind the hole (e.g., opposite the canister  502 ). For example, much like as shown in  FIG. 4 , a gamma ray, or “pinhole,” camera is positioned so as to receive gamma rays  522  that potentially exit the sealed canister  502  through one or more voids in the welded portion  510 , through the pinhole, and at the gamma ray image detector  530 . 
     The validation of the weld  510  may include testing if the layer of the weld scatters as many gamma rays  522  as do the layers of the housing  504  and/or lid  506  (e.g., above the weld  510  or below the weld  510 ). If the scattering is the same or substantially the same, then it indicates that there are no voids in the weld  510 . 
     In some aspects, one or both of the hazardous material canister  502  and the gamma ray image detector  530  are rotated during the operation of the detector  530  to receive scattered gamma rays  522  and generate an image of the received gamma rays  522 . Thus, in some aspects, the gamma ray image detector  530  may operate to inspect a complete circumference of the weld  510  as the detector  530  or the canister  502  (or both) rotates (e.g., around 360 degrees). A controller, control system, or computing system (e.g., control system  900 ) may be connected to the gamma ray image detector  530  and/or a gamma ray camera to receive images from the detector  530 . The images show, for example, the scattered radiation that shows the presence of any void in the weld  510 . Based on the image, the computing system  900  may determine an integrity of the weld  510 . For example, the computing system  900  may determine that the images include portions that show voids of a particular size that indicates that the weld  510  is not sufficient to seal the radioactive waste  508  in the hazardous material canister  502 . 
     Turning to  FIG. 6 , this figure illustrates an example system  600  for examining and validating a weld  610  formed on a hazardous material canister  602 , e.g., to join a cap  606  of the hazardous material canister  602  to a housing  604  of the hazardous material canister  602 . Conventional methods have been used in the past to validate the quality of such welds. Certain methods are non-destructive. These include visual inspection, ultrasonics, and gamma ray radiography. Radiography typically consists of putting a source of X-rays or gamma rays near the weld and recording the transmitted rays. Any hidden gap or void in the weld would transmit gamma (and/or X-) rays at an increased level. 
     In this example, the canister  602  includes the lid  606 , which is sealed to the housing  604  of the canister  602  by a weld  610  (e.g., by spin welding). For instance, example implementations utilize a spin welding system is used to attach the lid  606  to the housing  604  of  FIG. 6  (e.g., through the technique of spin welding). Further, as shown, the hazardous material canister  602  includes a gamma ray source  618  located within a volume  611  of the canister  602  to create gamma rays  622  that pass through the weld  610  in a gamma ray radiography analysis. In some aspects, the gamma ray source  618  is a radioactive material (that is in addition to the radioactive nuclear waste  608  disposed in the canister  602 ) in a particular location within the volume  611  of the canister  602 . In some aspects, the particular location of the radioactive material  618  may be centered in the inner volume  611  of the canister  602  near the lid  606  of the canister  602  (as shown in  FIG. 6 ). In some situations, having the radioactive source  618  internal to, rather than external of, the canister  602 , can have substantial handling and safety advantages. 
     In some aspects, the radioactive material  618  may be connected to a support  616  that is, in turn, connected to the lid  606  (or other part of the canister  602 ). The radioactive material  618 , in some aspects, may be americium-241 (Am-241) that can be used to generate gamma rays  622  that are then utilized to inspect and validate the quality of the weld  610  or other material (e.g., a corrosion-resistant alloy such as Alloy 625 placed by three-dimensional (3D) printing) that attaches the lid  606  to the housing  604  of the canister  602 . 
     As shown in  FIG. 6 , the radioactive material  618  may be a physically small (but, in some aspects, highly radioactive) source on a radial centerline axis of the canister  602  at the same vertical level (as shown, the is canister oriented vertically) as the lid/canister seal (i.e., the weld  610  shown by a dotted line in this figure). As noted, one example source may be americium-241, which has a half-life of 4.6 years. This relatively short half-life means that the radioactive material  618  can be small and yet emit a large rate of gamma rays  622 . Americium-241 also emits a relatively low energy 59.5 keV gamma ray. This low energy is well-matched to the need to examine a relatively thin (e.g., 0.5 cm) canister weld  610 . Many other gamma sources could be used, including Co-60, Cs-137, Ba-137, Ir-192, and Na-22. 
     An example of placement of the gamma source is shown in  FIG. 6 . In this figure, the canister  602  is shown with a radial axis of symmetry  613  (shown with a dashed line) in a vertical orientation. The small Am-241 gamma source  618  is attached (e.g., permanently) to the lid  606  of the canister  602  prior to welding (or sealing). The source  618  may be held in place by a support structure  616 . In  FIG. 6 , the support structure  616  is a narrow rod but can also be a larger cylinder or other shape. In an example implementation, the source  618  is positioned in the same radial plane of the weld  610 , although it could be at a different location. 
     In an example operation of the system  600 , gamma rays  622  emitted by the radioactive source  618  scatter in all directions. Some of these rays  622  pass through the weld  610  onto a gamma ray image detector  630  (e.g., as an array of detectors as part of a gamma ray camera) and/or a single gamma ray image detector  632  (also as part of a gamma ray camera). The shadow of the weld  610  on the imaging detector  630  will reveal any gaps or discontinuities in the weld  610 . An image of the source distribution can be obtained by using a gamma ray camera (such as camera  420 ) that includes a shield (e.g., a lead shield) with one or more openings. For example, as shown for camera  420  (which can be used in system  600  and includes gamma ray detectors  630 ), the shield may have a single small opening and gamma ray detector  630  positioned behind the hole (e.g., opposite the canister  602 ). For example, much like as shown in  FIG. 4 , a gamma ray, or “pinhole,” camera is positioned so as to receive gamma rays  622  that potentially exit the sealed canister  602  through one or more voids in the welded portion  610 , through the pinhole, and at the gamma ray image detector  630 . 
     The validation of the weld  610  may include testing if the layer of the weld scatters as many gamma rays  622  as do the layers of the housing  604  and/or lid  606  (e.g., above the weld  610  or below the weld  610 ). If the scattering is the same or substantially the same, then it indicates that there are no voids in the weld  610 . 
     In some aspects, one or both of the hazardous material canister  602  and the gamma ray image detector  630  are rotated during the operation of the detector  630  to receive gamma rays  622  and generate an image of the received gamma rays  622 . Thus, in some aspects, the gamma ray image detector  630  may operate to inspect a complete circumference of the weld  610  as the detector  630  or the canister  602  (or both) rotates (e.g., around 360 degrees). A controller, control system, or computing system (e.g., control system  900 ) may be connected to the gamma ray image detector  630  and/or a gamma ray camera to receive images from the detector  630 . The images show, for example, the scattered radiation that shows the presence of any void in the weld  610 . Based on the image, the computing system  900  may determine an integrity of the weld  610 . For example, the computing system  900  may determine that the images include portions that show voids of a particular size that indicates that the weld  610  is not sufficient to seal the radioactive waste  608  in the hazardous material canister  602 . 
     In aspects that utilize a moving gamma detector ( 630  or  632 ), the motion may be relative (i.e., not absolute). In some aspects, therefore, the canister  602  may be rotated rather than the detector  630 . If the single gamma ray detector  632  is utilized, and the radioactive source  618  acts as a point source, then only one point on the canister  602  will be imaged at any one time. If the detector  632  is extended in the horizontal direction then a horizontal section of the canister  602  can be observed. 
     In some aspects, the gamma ray detector  632  (or detectors  630 ) may determine the energy of the observed gamma rays  622 . If this is done, then extraneous gammas (from, for example, the nuclear waste  608 ) can be discriminated against. For example, while not shown in the  FIG. 6 , a shield (lead or other material that absorbs gamma rays) can be placed around the housing  604  of the canister  602  to prevent gamma rays from the nuclear waste  608  from reaching the detectors  630  (or  632 ). Any shield placed around the housing  604 , however, would be low enough such that the shield does not interfere with the imaging of the weld  610  (i.e., interfere with gamma rays  622  from the radioactive source  618 ). If the weld  610  is created through spin welding, then the region to be examined may be no more than one or several millimeters in vertical extent. If this is the case, then the shielding may cover most of the housing  604  of the canister  602 . As another example, a shield made from tungsten or tungsten carbide could be used. The shield could also be made of a material such as sand (or tungsten carbide) that is packed in at the top part of the canister  602 . 
     In an alternative implementation, the radioactive source  618  may be a flat, thin disk located at the same or similar vertical height (and radial plane) as the weld  610 . This thin disk provides a shadow with variating resolution; the highest resolution would be at the height of the weld  610 . Any void at the weld height may be observed with no need for de-blurring. This alternative configuration offers the capability of maximum resolution at the desired inspection location, while allowing a more intense (i.e., larger) radioactive source  618  to be used. 
     A controller, control system, or computing system (e.g., control system  900 ) may be connected to the gamma ray image detector  630  and/or a gamma ray camera to receive images from the detector  630 . The images show, for example, the scattered radiation that shows the presence of any void in the weld  610 . Based on the image, the computing system  900  may determine an integrity of the weld  610 . For example, the computing system  900  may determine that the images include portions that show voids of a particular size that indicates that the weld  610  is not sufficient to seal the radioactive waste  608  in the hazardous material canister  602 . 
     Turning to  FIG. 7 , this figure shows an example implementation of a system  700  for sealing a hazardous material canister  702  by welding, and more specifically, spin welding, a lid  706  of the canister  702  to a housing  704  of the canister  702 . As shown in this example implementation, radioactive waste (or material)  708 , e.g., nuclear waste  708 , is emplaced in a volume  710  of the housing  704  of the hazardous material canister  702 . The nuclear waste  708 , in some aspects, includes SNF (such as a SNF assembly or portion thereof) or high level waste. For instance, after SNF or high level waste is loaded into the hazardous material canister  702 , the canister  702  must be closed and sealed in order to prevent any potential leakage paths or radioactive waste leaks from the radioactive waste  708 . Further, possible pathways that could speed a corrosion path from the outside to the volume  710  of the canister  702  should be avoided. In some aspects, the lid  706  to the canister  702  is welded in place to seal the SNF (or high level nuclear waste) within the canister  702 . The weld should be of high quality and offer protection against corrosion that is equally as good as that of the material of the canister  702  (e.g., a corrosion resistant alloy such as CRA 625). In some aspects, welding is very difficult to achieve in a high radiation environment. The canister  702  contains radioactive material  708  that emits high fluxes of gamma rays and X rays (collectively, “gamma rays”). In some aspects, the weld must satisfy the stringent criteria of the Nuclear Regulatory Commission. The weld is inspected to assure that it has this quality. 
     The system  700  of  FIG. 7  (and methods performed by or with the system  700 ) seals the hazardous material canister  702  through the preparation of the housing  704  and the lid  706  and the application of spin (or friction) welding the lid  706  onto the housing  704  of the canister  702  into which the nuclear waste  708  is enclosed and then sealed (e.g., by the spin welding of the lid  706  onto the housing  704 ). An example implementation is shown in  FIG. 7 , which includes a cross-sectional view (vertical) of the canister housing  704 , the lid  706 , and a flywheel  722 , which may be used in some aspects to rotate or oscillate the lid  706  about an axis of rotation  724  during the welding process. The flywheel  722  and an optional shield  720  may be part of a spin welding system used to attach the lid  706  to the housing  704  of  FIG. 7 . 
     For example, in some aspects, an open edge  711  of the housing  704  (e.g., the circumferential edge  711  of the housing  704  of the canister  702  in the case of a cylindrical housing) is polished to make a flat and clean surface. A circumferential edge  707  of the lid  706  is similarly prepared. The lid  706  is then pressed onto the housing  704  (at the open edge  711 ) and rotated (or in alternative implementations, oscillated). Friction generated between the two circumferential edges  711  and  707  (of the housing  704  and the lid  706 ) creates a weld  713 . In some aspects, no additional metal needs be added to form the weld  713 . 
     In an example operation, the canister  702  is set vertically with the flat polished end  711  facing upward. The lid  706  is placed vertically above the open housing  704  of the canister  702  after the nuclear waste  708  has been inserted and held tightly by, e.g., the flywheel  722 , and made to spin. The lid  706  and flywheel  722  would then be lowered to make contact between the lid  706  and the top circumferential edge  711  of the housing  704 . The flywheel  722  could be released, so that the weight of the flywheel  722  would press the two polished surfaces  711  and  707  together. Friction causes the flywheel  722  to gradually slow its rotation, and simultaneously, the friction heats the polished flat surfaces  711  and  707  of both the housing  704  and the lid  706 , heating them to a particular welding temperature (e.g., based on the material of the housing  704  and lid  706 ). When the spin rotational rate decreases to zero, the lid  706  and the canister  702  are welded together. Then, the flywheel  722  can be removed and the weld  713  is made to sealingly enclose the nuclear waste  708  within the canister  702 . 
     In some aspects, the polished surfaces  711  and/or  707  may be configured in opposing male and female surfaces to better create a strong seal with the weld  713 . In some aspects, the polished surfaces  711  and/or  707  could be flat on average, but have an undulating up-and-down surface to better create a strong seal with the weld  713 . As another example, the shield  720  may comprise a gamma ray shield that sits on top of the lid  706  (e.g., between the lid  706  and the flywheel  722 ) to, e.g., aid in transport of the canister  702 . The shield  720  may be spun (e.g., by the flywheel  722 ) during welding or the shield  720  may be attached to the lid  706  after the lid  706  has been welded to the housing  704  of the canister  702 . 
     Although the system  700  shown in  FIG. 7  includes the flywheel  722 , alternative implementations do not include the flywheel  722 . For example, a spin welding system may force the lid  706  onto the housing  704  while causing relative motion therebetween to result in friction to enable the weld  713  without the use of the flywheel  722 . Further, as noted, spin motion (e.g., repeated 360° rotation) is also not essential. In some aspects, a back-and-forth oscillation between the lid  706  and the housing  704  may be utilized to form the weld  713 . 
     In some aspects, the described example operation of the system  700  can be done remotely without a nearby presence of humans (who would be endangered by the gamma rays). Further, in some aspects, no additional material (e.g., filler material) is used for the weld  713 ; only the material of which the canister housing  704  and lid  706  is needed to create the weld  713 . In some aspects, the lid  706  and the housing  704  may both be made of corrosion-resistant metal alloys. One such choice for an alloy would be Alloy-625 (CRA 625). As another example, such material may facilitate flat, clean surfaces that lead to high quality welds with little to no microscopic gaps and voids. As another example, a flat weld between the lid  706  and the canister housing  704  may be particularly amenable to inspection to verify that the seal is complete and there are not gaps or voids. This can be done either by using hypersonic probing or by using radiological methods (e.g., as described with reference to  FIGS. 4-6 ). 
     Turning to  FIG. 8 , this figure shows an example implementation of a system  800  for sealing a hazardous material canister  802  by sealing a housing  804  of the canister  802  to enclose radioactive waste  808  within a volume  810  of the canister  802  with a material deposition system  820 . As shown in this example implementation, radioactive waste (or material)  808 , e.g., nuclear waste  808 , is emplaced in the volume  810  of the housing  804  of the hazardous material canister  802 . The nuclear waste  808 , in some aspects, includes SNF (such as a SNF assembly or portion thereof) or high level waste. For instance, after SNF or high level waste is loaded into the hazardous material canister  802 , the canister  802  must be closed and sealed in order to prevent any potential leakage paths or radioactive waste leaks from the radioactive waste  808 . Further, possible pathways that could speed a corrosion path from the outside to the volume  810  of the canister  802  should be avoided. In some aspects, a cap  806  is formed on and sealed to the housing  804  by the 3D printing system  820  to seal the SNF (or high level nuclear waste) within the canister  802 . The seal should be of high quality and offer protection against corrosion that is equally as good as that of the material of the canister  802  (e.g., a corrosion resistant alloy such as CRA 625). In some aspects, sealing or welding is very difficult to achieve in a high radiation environment. The canister  802  contains radioactive material  808  that emits high fluxes of gamma rays and X rays (collectively, “gamma rays”). In some aspects, the seal must satisfy the stringent criteria of the Nuclear Regulatory Commission. The seal is inspected to assure that it has this quality. 
     As shown,  FIG. 8  shows the example system  800  (and methods performed by or with the system  800 ) to enclose the nuclear waste  808  in the hazardous material canister  802  by the direct material (e.g., metal) deposition system  820 , e.g., a 3D printing system. In some aspects, direct material deposition may have advantages over welding. Thus, described implementations include a method of forming and attaching a lid  806  to the housing  804  of the hazardous material canister  802  that contains radioactive (or other toxic) material  808 . In some aspects, the canister  802  (e.g., the housing  804  and/or the lid  806 ) may be made of a corrosion-resistant alloy, such as Alloy-625. Such an alloy can also be used as a material  822  for the direct material deposition system  820 . Thus, the system  800  may be used in one or more example operations for building the lid  806  for the canister  802  made in-place (through direct material deposition) once the housing  804  has been filed with the radioactive material  808 . 
     In the example system  800  shown in  FIG. 8 , a sub-lid  812  may be placed on an open end  811  of the housing  804  (through which the nuclear waste  808 , such as SNF assemblies, is inserted into the volume  810  of the canister  802 ). In this example, the sub-lid  812  is also made of Alloy-625, but it could be made of a different metal (e.g., corrosion resistant alloy or other metal). In some aspects, the sub-lid  812  may be made of a material that prevents gamma rays from passing therethrough (e.g., a gamma ray shield). In some aspects, the sub-lid  812  may not provide a seal to the housing  804  by itself, but may provide a platform on which the cap  806  is deposited by the system  820  and formed. The sub-lid  812 , in some aspects, may be relatively thin (as shown) or it could be thick (e.g., relative to a thickness of the canister housing  804  or the lid  806  formed on the canister housing  804  by the direct material deposition system  820 ). 
     In an example operation of the system  800 , the lid  806  is constructed (e.g., to a particular thickness) using the direct material deposition system  820 . In this example, the direct material deposition system  820  may be a 3D printer. For example, a print head of the 3D printer moves over a top surface of the sub-lid  812  and the open end edge  811  of the housing  804  to deposit material  822  (e.g., corrosion resistant alloy droplets (such as Alloy-625)), which may be liquid or semi-solid. As shown in  FIG. 8 , part way through the complete example operation, the lid  806  is partially formed, with a remaining portion  807  of the lid  806  shown in dashed line (to be completed). By moving the print head over these surfaces, the full lid  806  is made and sealed to the housing  804 . The lid  806 , once formed, seals the nuclear waste  808  in the volume  810  of the canister  802 . 
       FIG. 9  is a schematic illustration of an example controller  900  (or control system) according to the present disclosure. For example, the controller  900  can be used for the operations described previously, for example as or as part of a gamma ray detection system as described herein. For example, the controller  900  may be communicably coupled with, or as a part of, a gamma ray pinhole camera or gamma ray image detector as described herein. 
     The controller  900  is intended to include various forms of digital computers, such as printed circuit boards (PCB), processors, digital circuitry, or otherwise. Additionally the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device. 
     The controller  900  includes a processor  910 , a memory  920 , a storage device  930 , and an input/output device  940 . Each of the components  910 ,  920 ,  930 , and  940  are interconnected using a system bus  950 . The processor  910  is capable of processing instructions for execution within the controller  900 . The processor may be designed using any of a number of architectures. For example, the processor  910  may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor. 
     In one implementation, the processor  910  is a single-threaded processor. In another implementation, the processor  910  is a multi-threaded processor. The processor  910  is capable of processing instructions stored in the memory  920  or on the storage device  930  to display graphical information for a user interface on the input/output device  940 . 
     The memory  920  stores information within the controller  900 . In one implementation, the memory  920  is a computer-readable medium. In one implementation, the memory  920  is a volatile memory unit. In another implementation, the memory  920  is a non-volatile memory unit. 
     The storage device  930  is capable of providing mass storage for the controller  900 . In one implementation, the storage device  930  is a computer-readable medium. In various different implementations, the storage device  930  may be a floppy disk device, a hard disk device, an optical disk device, a tape device, flash memory, a solid state device (SSD), or a combination thereof. 
     The input/output device  940  provides input/output operations for the controller  900 . In one implementation, the input/output device  940  includes a keyboard and/or pointing device. In another implementation, the input/output device  940  includes a display unit for displaying graphical user interfaces. 
     The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, for example, in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. 
     Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, solid state drives (SSDs), and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) or LED (light-emitting diode) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat-panel displays and other appropriate mechanisms. 
     The features can be implemented in a control system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), peer-to-peer networks (having ad-hoc or static members), grid computing infrastructures, and the Internet. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     A first example implementation according to the present disclosure includes a nuclear waste canister that includes a spherical or substantially spherical outer housing that defines an inner volume; and a storage space defined within the inner volume of the outer housing, the storage space configured to enclose a plurality of portions of the nuclear waste. The outer housing is configured to store nuclear waste in a human-unoccupiable directional drillhole 
     In an aspect combinable with the first example implementation, the nuclear waste includes spent nuclear fuel. 
     In another aspect combinable with any of the previous aspects of the first example implementation, the portions of the nuclear waste include spent nuclear fuel pellets. 
     In another aspect combinable with any of the previous aspects of the first example implementation, the outer housing includes a corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects of the first example implementation, the corrosion resistant alloy includes CRA 625. 
     In another aspect combinable with any of the previous aspects of the first example implementation, the outer housing includes a first portion and a second portion. 
     In another aspect combinable with any of the previous aspects of the first example implementation, each of the first and second portions of the outer housing includes a hemispherical portion. 
     In another aspect combinable with any of the previous aspects of the first example implementation, herein the hemispherical portions are configured to weld together to form the outer housing. 
     In another aspect combinable with any of the previous aspects of the first example implementation, the first portion includes a semispherical portion that includes a hole and the second portion includes a lid sized to fit the hole. 
     In another aspect combinable with any of the previous aspects of the first example implementation, semispherical portion and the lid are configured to weld together to form the outer housing. 
     Another aspect combinable with any of the previous aspects of the first example implementation further includes a plurality of rods positioned in the storage space, each of the rods configured to hold a plurality of spent nuclear fuel pellets. 
     In another aspect combinable with any of the previous aspects of the first example implementation, each rod is made from a corrosion resistant material or a neutron absorbing material. 
     A second example implementation includes a method for containing nuclear waste that includes placing a plurality of portions of nuclear waste in a storage space of an inner volume of a spherical or substantially spherical outer housing of a nuclear waste canister; and sealing the nuclear waste canister to enclose the plurality of portions of nuclear waste in the inner volume. 
     An aspect combinable with the second example implementation further includes moving the sealed nuclear waste canister into a hazardous waste repository of a human-unoccupiable directional drillhole formed in a subterranean formation. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the nuclear waste includes spent nuclear fuel. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the portions of the nuclear waste include spent nuclear fuel pellets. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the outer housing includes a corrosion resistant alloy. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the corrosion resistant alloy includes CRA 625. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the outer housing includes a first portion and a second portion. 
     In another aspect combinable with any of the previous aspects of the second example implementation, each of the first and second portions of the outer housing includes a hemispherical portion. 
     Another aspect combinable with any of the previous aspects of the second example implementation further includes welding the hemispherical portions together to form the outer housing. 
     In another aspect combinable with any of the previous aspects of the second example implementation, the first portion includes a semispherical portion that includes a hole and the second portion includes a lid sized to fit the hole. 
     Another aspect combinable with any of the previous aspects of the second example implementation further includes welding the semispherical portion and the lid together to form the outer housing. 
     Another aspect combinable with any of the previous aspects of the second example implementation further includes inserting a plurality of spent nuclear fuel pellets into a plurality of rods positioned in the storage space. 
     In another aspect combinable with any of the previous aspects of the second example implementation, each rod is made from a corrosion resistant material or a neutron absorbing material. 
     A third example implementation includes a nuclear waste storage system that includes a cylindrical nuclear waste container that defines an inner space; and a plurality of nuclear waste canisters according to any of the aspects of the first example implementation positioned in the inner space of the nuclear waste container. 
     In an aspect combinable with the third example implementation, the nuclear waste container includes radiation shielding at a first proximate end and a second distal end of the container. 
     A fourth example implementation includes a method for inspecting a weld of a nuclear waste canister that includes positioning a gamma ray image detector near a nuclear waste canister that encloses nuclear waste. The nuclear waste canister includes a housing that includes a volume in which the waste is enclosed and a cap connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister. The method further includes receiving, at the gamma ray image detector, gamma rays from the nuclear waste that travel from the nuclear waste, through a hole in a gamma ray shield that is positioned in the volume to hit a scatterer positioned above the shield, scattered toward the weld, and through one or more voids in the weld; generating an image of the received gamma rays with the gamma ray image detector; and based on the generated image, determining an integrity of the at least one weld. 
     In an aspect combinable with the fourth example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the gamma ray image detector includes a pinhole camera. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, at least one of the housing, the cap, or a weld material includes a corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, each of the housing, the cap, and the weld material includes the corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the corrosion resistant alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the at least one weld includes a horizontal weld. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the hole in the gamma ray shield is radially aligned with a centerline axis of the housing. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the hole in the gamma ray shield and the scatterer are radially aligned with a centerline axis of the housing. 
     An aspect combinable with any of the previous aspects of the fourth example implementation further includes rotating at least one of the nuclear waste canister or the gamma ray image detector during the receiving, at the gamma ray image detector, of the gamma rays from the nuclear waste that travel through the one or more voids in the weld. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the rotating includes rotating at least one of the nuclear waste canister or the gamma ray image detector for 360 degrees. 
     In an aspect combinable with any of the previous aspects of the fourth example implementation, the cap is spin welded to the housing. 
     A fifth example implementation includes a system for inspecting a weld of a nuclear waste canister that includes a nuclear waste canister and a gamma ray image detector system. The nuclear waste canister encloses nuclear waste and includes a housing that includes a volume configured to enclose the nuclear waste, a cap connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister, a gamma ray shield that is positioned in the volume between the nuclear waste and the cap, and a scatterer positioned above the shield. The gamma ray image detector system is positionable adjacent the nuclear waste canister and configured to receive gamma rays from the nuclear waste that travel through a hole in the gamma ray shield to hit the scatterer to scatter toward the weld and travel through one or more voids in the weld, generate an image of the received gamma rays, and based on the generated image, determine an integrity of the at least one weld. 
     In an aspect combinable with the fifth example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, wherein the gamma ray image detector includes a pinhole camera. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, at least one of the housing, the cap, or a weld material includes a corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, each of the housing, the cap, and the weld material includes the corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the corrosion resistant alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the at least one weld includes a horizontal weld. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the hole in the gamma ray shield is radially aligned with a centerline axis of the housing. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the hole in the gamma ray shield and the scatterer are radially aligned with a centerline axis of the housing. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, at least one of the nuclear waste canister or the gamma ray image detector is configured to rotate during the receiving, at the gamma ray image detector, of the gamma rays from the nuclear waste that travel through the one or more voids in the weld. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the rotation includes 360 degrees. 
     In an aspect combinable with any of the previous aspects of the fifth example implementation, the cap is spin welded to the housing. 
     A sixth example implementation includes a method for inspecting a weld of a nuclear waste canister that includes positioning a gamma ray image detector near a nuclear waste canister that encloses nuclear waste. The nuclear waste canister includes a housing that includes a volume in which the nuclear waste and a gamma ray source material are enclosed and a top connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister. The method further includes receiving, at the gamma ray image detector, gamma rays from the gamma ray source material that travel through one or more voids in the weld; generating an image of the received gamma rays with the gamma ray image detector; and based on the generated image, determining an integrity of the at least one weld. 
     In an aspect combinable with the sixth example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the gamma ray source material includes Americium-241. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the gamma ray source material is positioned at a vertical location in the volume of the canister to vertically align with the at least one weld. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the gamma ray source material is positioned at or near a radial centerline of the volume of the canister. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, each of the housing, the top, and the weld material includes the corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the corrosion resistant alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the at least one weld includes a horizontal weld. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, receiving the gamma rays includes receiving a plurality of gamma rays that emit from the gamma ray source material and scatter through the volume of the nuclear waste container and through one or more voids in the one or more welds toward the gamma ray image detector. 
     An aspect combinable with any of the previous aspects of the sixth example implementation further includes rotating at least one of the nuclear waste canister or the gamma ray image detector during the receiving, at the gamma ray image detector, of the gamma rays from the gamma ray source material that travel through the one or more voids in the weld. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the rotating includes rotating at least one of the nuclear waste canister or the gamma ray image detector for 360 degrees. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the nuclear waste canister further includes a gamma ray shield positioned in the volume and vertically between the nuclear waste and the gamma ray source material. 
     In an aspect combinable with any of the previous aspects of the sixth example implementation, the gamma ray shield is positioned vertically between the at least one weld and the nuclear waste. 
     A seventh example implementation includes a system for inspecting a weld of a nuclear waste canister that includes a nuclear waste canister that encloses nuclear waste and includes a housing that includes a volume configured to enclose the nuclear waste and a top connected to the housing with at least one weld to seal the nuclear waste in the nuclear waste canister. The system further includes a gamma ray source material positioned in the volume of the housing; and a gamma ray image detector system positionable adjacent the nuclear waste canister and configured to receive gamma rays from the gamma ray source material that travel through one or more voids in the weld, generate an image of the received gamma rays with the gamma ray image detector, and based on the generated image, determine an integrity of the at least one weld. 
     In an aspect combinable with the seventh example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the gamma ray source material includes Americium-241. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the gamma ray source material is positioned at a vertical location in the volume of the canister to vertically align with the at least one weld. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the gamma ray source material is positioned at or near a radial centerline of the volume of the canister. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, each of the housing, the top, and the weld material includes the corrosion resistant alloy. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the corrosion resistant alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the at least one weld includes a horizontal weld. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, a plurality of gamma rays emit from the gamma ray source material and scatter through the volume of the nuclear waste container and through one or more voids in the one or more welds toward the gamma ray image detector. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, at least one of the nuclear waste canister or the gamma ray image detector is rotated during the receipt, at the gamma ray image detector, of the gamma rays from the gamma ray source material that travel through the one or more voids in the weld. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, at least one of the nuclear waste canister or the gamma ray image detector is rotated for 360 degrees during the receipt, at the gamma ray image detector, of the gamma rays from the gamma ray source material that travel through the one or more voids in the weld. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the nuclear waste canister further includes a gamma ray shield positioned in the volume and vertically between the nuclear waste and the gamma ray source material. 
     In an aspect combinable with any of the previous aspects of the seventh example implementation, the gamma ray shield is positioned vertically between the at least one weld and the nuclear waste. 
     An eighth example implementation includes a method of sealing a nuclear waste canister including inserting nuclear waste into an open volume of a housing of a nuclear waste canister; preparing at least one of an edge of an open end of the housing or an edge of a lid sized to fit on the open end of the housing; attaching the edge of the open end of the housing to the edge of the lid by spin welding the lid onto the housing; and enclosing the open volume of the housing to seal the nuclear waste within the nuclear waste canister. 
     An aspect combinable with the eighth example implementation further includes attaching a flywheel to the lid; and rotating the flywheel to spin weld the lid onto the housing. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, the flywheel is attached to a gamma ray shield that is part of or mounted on the lid. 
     An aspect combinable with any of the previous aspects of the eighth example implementation further includes oscillating at least one of the housing or the lid to spin weld the lid onto the housing. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, at least one of the lid or the housing includes a corrosion-resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, the corrosion-resistant metallic alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, preparing at least one of the edge of the open end of the housing or the edge of the lid includes preparing both of the edge of the open end of the housing and the edge of the lid. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, preparing includes polishing or smoothing. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, the spin welding includes welding the lid to the housing without any filler or flux material. 
     In an aspect combinable with any of the previous aspects of the eighth example implementation, the nuclear waste includes spent nuclear fuel. 
     A ninth example implementation includes a system for sealing a nuclear waste canister that includes a nuclear waste canister and a spin welding system. The nuclear waste canister includes a housing that defines an open volume and a lid sized to fit on an open end of the housing. The open end of the housing includes an edge that mirrors an edge of the lid. The open volume of the housing is sized to enclose nuclear waste. The spin welding system is configured to attach the edge of the open end of the housing to the edge of the lid by spin welding the lid onto the housing to enclose the open volume of the housing to seal the nuclear waste within the nuclear waste canister. 
     An aspect combinable with the ninth example implementation further includes a flywheel attachable to the lid, where the spin welding system is configured to rotate the flywheel to spin weld the lid onto the housing. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the flywheel is attached to a gamma ray shield that is part of or mounted on the lid. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the spin welding system is configured to oscillate at least one of the housing or the lid to spin weld the lid onto the housing. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, at least one of the lid or the housing includes a corrosion-resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the corrosion-resistant metallic alloy includes CRA 625. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, at least one of the edge of the open end of the housing or the edge of the lid is prepared prior to attachment. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the preparation includes polishing or smoothing. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the spin welding system is configured to weld the lid to the housing without any filler or flux material. 
     In an aspect combinable with any of the previous aspects of the ninth example implementation, the nuclear waste includes spent nuclear fuel. 
     A tenth example implementation includes a method of sealing a nuclear waste canister that includes inserting nuclear waste into an open volume of a housing of a nuclear waste canister; positioning a sub-lid on top of an edge of an open end of the housing; depositing a liquid or semi-solid metal on top of at least one of the sub-lid or the edge of the open end of the housing; and sealing, with the liquid or semi-solid metal, the open volume of the housing to seal the nuclear waste within the nuclear waste canister. 
     In an aspect combinable with the tenth example implementation, at least one of the sub-lid, the liquid or semi-solid metal, or the housing includes a corrosion resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, each of the sub-lid, the liquid or semi-solid metal, and the housing includes the corrosion resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, the corrosion resistant metallic alloy includes Alloy 625. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, each of the sub-lid and the edge of the open end of the housing is circular. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, a circumference of the sub-lid is greater than an inner circumference of the edge of the open end of the housing, and the circumference of the sub-lid is less than an outer circumference of the edge of the open end of the housing. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, depositing the liquid or semi-solid metal on top of at least one of the sub-lid or the edge of the open end of the housing includes depositing the liquid or semi-solid metal to cover the sub-lid and a portion of the edge of the open end of the housing that is exposed by the sub-lid. 
     An aspect combinable with any of the previous aspects of the tenth example implementation further includes depositing an amount of the liquid or semi-solid metal to form a lid of a particular thickness on the housing of the canister. 
     In an aspect combinable with any of the previous aspects of the tenth example implementation, depositing the liquid or semi-solid metal on top of at least one of the sub-lid or the edge of the open end of the housing includes three-dimensionally (3D) printing the liquid or semi-solid metal on top of at least one of the sub-lid or the edge of the open end of the housing. 
     An eleventh example implementation includes a system for sealing a nuclear waste canister that includes a nuclear waste canister including a housing that defines an open volume and a sub-lid sized to fit on an open end of the housing, the open end of the housing including an edge, the open volume of the housing sized to enclose nuclear waste; and a direct metal deposition system configured to deposit a liquid or semi-solid metal on top of at least one of the sub-lid or the edge of the open end of the housing and seal, with the liquid or semi-solid metal, the open volume of the housing to seal the nuclear waste within the nuclear waste canister. 
     In an aspect combinable with the eleventh example implementation, at least one of the sub-lid, the liquid or semi-solid metal, or the housing includes a corrosion resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, each of the sub-lid, the liquid or semi-solid metal, and the housing includes the corrosion resistant metallic alloy. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, the corrosion resistant metallic alloy includes Alloy 625. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, the nuclear waste includes spent nuclear fuel. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, each of the sub-lid and the edge of the open end of the housing is circular. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, a circumference of the sub-lid is greater than an inner circumference of the edge of the open end of the housing, and the circumference of the sub-lid is less than an outer circumference of the edge of the open end of the housing. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, the direct metal deposition system is configured to deposit the liquid or semi-solid metal to cover the sub-lid and a portion of the edge of the open end of the housing that is exposed by the sub-lid. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, the direct metal deposition system is configured to deposit an amount of the liquid or semi-solid metal to form a lid of a particular thickness on the housing of the canister. 
     In an aspect combinable with any of the previous aspects of the eleventh example implementation, the direct metal deposition system includes a three-dimensional (3D) printer. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims.