Patent Publication Number: US-2023154632-A1

Title: Target irradiation systems for the production of radioisotopes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Division of U.S. Pat. Application No. 16/548,952 filed Aug. 23, 2019, now U.S. Pat. No. 11,551,821, which claims the benefit of U.S. Provisional Pat. Application No. 62/723,328 filed Aug. 27, 2018, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The presently-disclosed invention relates generally to systems for irradiating radioisotope targets in nuclear reactors and, more specifically, to systems for irradiating radioisotope targets in heavy water-moderated fission-type nuclear reactors. 
     BACKGROUND 
     Technetium-99m (Tc-99m) is the most commonly used radioisotope in nuclear medicine (e.g., medical diagnostic imaging). Tc-99m (m is metastable) is typically injected into a patient and, when used with certain equipment, is used to image the patient’s internal organs. However, Tc-99m has a half-life of only six (6) hours. As such, readily available sources of Tc-99m are of particular interest and/or need in at least the nuclear medicine field. 
     Given the short half-life of Tc-99m, Tc-99m is typically obtained at the location and/or time of need (e.g., at a pharmacy, hospital, etc.) via a Mo-99/Tc-99m generator. Mo-99/Tc-99m generators are devices used to extract the metastable isotope of technetium (i.e., Tc-99m) from a source of decaying molybdenum-99 (Mo-99) by passing saline through the Mo-99 material. Mo-99 is unstable and decays with a 66-hour half-life to Tc-99m. Mo-99 is typically produced in a high-flux nuclear reactor from the irradiation of highly-enriched uranium targets (93% Uranium-235) and shipped to Mo-99/Tc-99m generator manufacturing sites after subsequent processing steps to reduce the Mo-99 to a usable form, such as titanium-molybdate-99 (Ti-Mo99). Mo-99/Tc-99m generators are then distributed from these centralized locations to hospitals and pharmacies throughout the country. Since Mo-99 has a short half-life and the number of existing production sites are limited, it is desirable both to minimize the amount of time needed to reduce the irradiated Mo-99 material to a useable form and to increase the number of sites at which the irradiation process can occur. 
     There at least remains a need, therefore, for a system and a process for producing a titanium-molybdate-99 material suitable for use in Tc-99m generators in a timely manner. 
     SUMMARY OF INVENTION 
     One embodiment of the present disclosure provides a target irradiation system for irradiating a radioisotope target in a vessel penetration of a fission reactor, the system including a target delivery assembly including a body defining a central bore, a basket that is slidably receivable within the central bore of the body, and a winch that is connected to the basket by a cable, the target delivery assembly being affixed to the vessel penetration of the reactor, and a target passage that is in fluid communication with the target delivery assembly, wherein the basket is configured to receive the radioisotope target therein via the target passage and be lowered into the vessel penetration of the reactor when irradiating the radioisotope target, and the target delivery system forms a portion of the pressure boundary of the reactor when in fluid communication with the reactor. 
     Another embodiment of the present disclosure provides a target irradiation system for irradiating a radioisotope target in a vessel penetration of a fission reactor, the system including a target delivery assembly including an outer tube and an inner tube disposed therein so that an annulus is formed therebetween, at least one flow channel extending between a bottom end of the outer tube and a bottom end of the inner tube, and an elevation piston slidably disposed within the inner tube, the elevation piston including a one-way check valve allowing flow in a downward direction and preventing flow in an upward direction. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. 
         FIG.  1    is a perspective view of a target irradiation system, in accordance with an embodiment of the present disclosure, installed on a CANDU (CANada Deuterium Uranium) reactor; 
         FIGS.  2 A and  2 B  are perspective and cross-sectional views, respectively, of a target capsule of the target irradiation system shown in  FIG.  1   ; 
         FIG.  3    includes cross-sectional views of a hydraulic target well of the target irradiation system shown in  FIG.  1   ; 
         FIGS.  4 A and  4 B  are cross-sectional views of portions of the hydraulic target well shown in  FIG.  3   ; 
         FIGS.  5 A and  5 B  are perspective and cross-sectional views, respectively, of an elevation piston of the hydraulic target well shown in  FIG.  3   ; 
         FIGS.  6 A and  6 B  are cross-sectional views of the hydraulic target well shown in  FIG.  3   ; 
         FIGS.  7 A,  7 B, and  7 C  are perspective views of the airlock station of the target irradiation system shown in  FIG.  1   ; 
         FIGS.  8 A and  8 B  are schematic views of the piping systems in the vicinity of the hydraulic target well and the airlock station, respectively; 
         FIG.  9    is a cross-sectional view of the flask loader of the target irradiation system shown in  FIG.  1   ; 
         FIG.  10    is a perspective view of a target magazine of the target irradiation system shown in  FIG.  1   ; 
         FIG.  11    is an alternate embodiment of a target irradiation system in accordance with the present invention; 
         FIG.  12    is an alternate embodiment of a target irradiation system in accordance with the present invention; 
         FIGS.  13 A and  13 B  are perspective views of a target basket of the target irradiation systems shown in  FIGS.  11  and  12   ; 
         FIGS.  14 A and  14 B  are perspective views of the target irradiation system shown in  FIG.  11   ; 
         FIG.  15    is a top view of the target irradiation system shown in  FIG.  11    installed on a reactivity mechanism deck of a CANDU reactor; 
         FIG.  16    is a perspective view of a mechanical cable drive assembly of the target irradiation systems shown in  FIGS.  11  and  12   ; 
         FIG.  17    is a perspective view of a seeding drawer and a corresponding string of target capsules; 
         FIG.  18    is a schematic diagram of the piping system of the target irradiation system shown in  FIGS.  11  and  12   ; 
         FIG.  19    is a cross-sectional view of an alternate embodiment of a target irradiation system in accordance with the present invention; 
         FIG.  20    is a cross-sectional view of a body portion of the target irradiation system shown in  FIG.  19   ; 
         FIG.  21    is a top view of the target irradiation system shown in  FIG.  19    installed on the reactivity mechanism deck of a CANDU reactor; and 
         FIG.  22    is a side view of the target irradiation system shown in  FIG.  19    installed on the reactivity mechanism deck of a CANDU reactor. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention according to the disclosure. 
     DETAILED DESCRIPTION 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms “a”, “an”, “the”, include plural referents unless the context clearly dictates otherwise. 
     The present target irradiation system includes both elements that will be exposed to reactor neutron flux within the core of the reactor, preferably a CANDU (CANada Deuterium Uranium) reactor, and elements that will be affixed to the CANDU reactor civil structures outside of the reactor core. The system also includes a target capsule  12  ( FIGS.  2 A and  2 B ) that is designed to interface with the other system elements. There are several components which work together to form the system,  FIG.  1    illustrating the system installed on a CANDU reactor. 
     As shown in the figures, the in-core target irradiation system is comprised of a hydraulic target well  14  ( FIGS.  4 A and  4 B ), an elevation piston  16  ( FIGS.  5 A and  5 B ), a singulation device  18  ( FIG.  3   ), and a suspension (dwell) station  20  ( FIGS.  3 ,  6 A and  6 B ). These components are designed to support the target capsule  12  while it is in neutron flux. 
     As part of the system that will be insert into the CANDU core, a hydraulic target well ( FIG.  3   ) composed of zirconium alloy-3 and stainless steel is vertically inserted into an existing penetration on the reactor’s reactivity management deck (RMD)  22  ( FIG.  1   ). The existing penetration for which the system is currently intended for installation is an out-of-service adjuster absorber (AA) port. However, this system is not limited to installation in this location and can be installed in other penetration that meet the specifications for installation. 
     As shown in  FIGS.  2 A and  2 B , the target capsule  12  is the delivery vehicle, which allows for the separation of materials in an inert environment designed to eliminate corrosion related degradation from exposure to environmental mediums, such as the hydraulic transfer medium, while in the core of the reactor. The target capsule  12  is preferably constructed of a commercial grade 5 titanium, which is composed of Titanium-Aluminum-Vanadium (Ti-6AI-4V), with welded endcaps  13 . The target capsule  12  is shaped to maximize flow performance through the transfer tubing  23 .  FIGS.  2 A and  2 B  show the capsule design with a target material of natural molybdenum  11  inside. In order to ensure that the target capsule  12  is secure prior to use in the reactor  15  ( FIG.  1   ) and to maintain its integrity, it preferably undergoes a comprehensive leak test and inspection process during manufacturing. The endcap  13  closure design incorporates allowances, such as side bulges  17 , for end forces that could be experienced by the capsule to ensure that the welded joint does not degrade or fail because of impact or forces during transfer. The j oint, ends and body section are preferably designed such that they will not be stretched or j ammed due to pressures experienced during operation of the system. 
     Referring to  FIG.  3   , the target well  14  is the guide and housing for the target capsule  12  from the RMD  22 , down into the Calandria  19  ( FIG.  1   ). The target capsule  12  will be positioned within this well at the bottom for a defined duration in order to be exposed to the CANDU reactor neutron flux. During operations, the target capsule  12  is transported up this well to the RMD  22  using hydraulic flow. The propellant medium contemplated by this design is independently supply heavy water (D 2 O), as this propellant minimizes the health and safety hazardous associated with being exposed to the CANDU reactors neutron flux, and further minimizes the impact on operations of the reactor. This system is not limited to using heavy water as its propellant. Operational set point adjustments would allow for other propellant mediums to be utilized to achieve the same hydraulic flow. 
     As best seen in  FIGS.  4 A and  4 B , the target well  14  is composed of an inner and outer tube  24  and  26 , respectively, with an elevation piston  16  ( FIGS.  5 A and  5 B ) and force-limiting device  25  (located within inner tube  24 ) to limit any damage to other reactor systems because of positive acceleration of the target capsule  12  beyond the operating velocity.  FIGS.  4 A,  4 B,  6 A and  6 B  depict the detailed components of the target well  14  and illustrates the flow paths, as discussed in greater detail below. 
     As shown in  FIGS.  6 A and  6 B , during the forced cooling process, flow of heavy water will flow down the annulus  28  created between the outer  26  and inner tubes  24  and then divert from the base of the inner tube  24  upward into the inner tube  24 . This flow path creates the required flow rate to elevate strings of targets  12  by utilizing the inner tube  24  and the elevation piston  16 . 
     The elevation piston  16 , depicted in  FIGS.  5 A and  5 B , includes a central check valve  32  that allows for unidirectional flow. This feature enables elevation of the target string ( FIGS.  6 A and  6 B ) while still accounting for the potential need to pass heavy water across the target capsules ( FIGS.  4 A and  4 B ) to dissipate heat generated from the irradiation of the target material within the target capsules  12 , as shown in  FIGS.  4 A and  4 B . Similarly, this feature allows for the target capsules  12  to fall, under gravity, to the bottom of the well by passively allowing the displacement of heavy water through the check valve  32 . The target capsules  12  that have been placed in the reactor and exposed to the CANDU reactor flux will have significant radiation hazards composed of short-half life (1-2 hours) isotopes, and medium-half life (4-6 hours) isotopes. Since this presents a significant hazard to the CANDU reactor station, the target well  14  has been designed with a suspension (dwell) station  20  ( FIGS.  3 ,  6 A and  6 B ). 
     The dwell station  20 , shown in  FIGS.  3 ,  6 A and  6 B , is located outside of the Calandria  19  but beneath the RMD  22 , in the concrete shield structure  29  ( FIG.  1   ) of the CANDU reactor. The location of this feature is important to its function, as being located outside of the CANDU reactor flux region affords the ability to arrest the target capsules  12  in a string and allow for the short half-life isotopes to decay away. This arresting feature enables the safe and economic removal of the targets while eliminating some of the radiation hazard associated with the target material and target capsules. The feature can be customized with a variety of durations for the arresting period, as this will be dependent on the material encapsulated and the duration of the irradiation performed. 
     It is anticipated that the control system for this feature will preferably include an operational set point based on the material that will calculate the required delay time for safe removal. The implementation of this feature assists the out of core portion of the system by reducing the shielding required, in turn reducing the weight load placed on the RMD  22 . This is desirable as the RMD  22  has design constraints related to maximum weight load and is seismically sensitive area. 
     As best seen in  FIGS.  6 A and  6 B , the construction of the dwell station  20  is a constriction of the inner well tube  24  in which the elevation piston  16  nests to form a seal, thereby reducing the flow on the target  12  such that they will return to an arrested position on the nested elevation piston  16 . Side channels  34  are disposed above the nesting point between the inner tube  24  and a central tube  23  disposed therein, to allow for the injection of fresh (un-irradiated) heavy water to reduce the radiation hazard presented by irradiated heavy water. Following the defined dwell period, the flow rate increases allowing for the transport of the string of target capsules  12  to the singulator  18  ( FIG.  3   ). During this phase of operations, the elevator piston  16  remains nested in the inner tube constriction  35 , as shown in  FIG.  6 B . 
     As shown in  FIG.  3   , another feature of the present system is the singulator  18 , which is an automated device attached to the top of the target well on the RMD  22 . The singulator  18  utilizes solenoids  37  that provide simple movement to alternate restraining a target capsule  12  and releasing a target capsule  12  into the out-of-core portion of the system. An electromagnet provides force without penetrating the heavy water pipe and a sealed thimble contains the activated rod  37   a  of the solenoid  35 . This feature also acts as a barrier in the event of a target capsule  12  being injected into the target well  14  in error. At this point, the target capsule  12  would be stopped prior to entering the reactor and becoming an operational or safety hazard to the CANDU station. Further, in the event of early activation of the system resulting in the target capsules  12  being extracted early this will act as a barrier to again protect CANDU station personnel and systems from injury, exposure or damage. 
     Still referring to  FIG.  3   , another feature of the present system are fast-acting, pneumatically-actuated isolation valves  38 . The isolation valves  38  are in place to allow the isolation of the in-core and out-core portions of the system from each other in the event of a breach of containment, or wherever isolation of either portion of system is required (i.e. for maintenance). 
     Referring to  FIG.  1   , the out-core portion of the system of several different elements, including hydraulic transfer system  40 , a pneumatic transfer system  42 , a flask loading station  44 , and a waystation airlock  46  ( FIGS.  7 A through  7 C ). Each of the components of the out-core portion are connected to one another and interface with one another to complete their defined actions. 
     The hydraulic transfer system  40  is a closed loop hydraulic system transports the target capsules  12  into and out of the reactor at variable flow rates. The hydraulic system interacts with the pneumatics system  42  by means of an airlock ( FIGS.  7 A through  7 C ). The airlock purges an inner volume  43  with the pneumatic medium or the hydraulic medium to move targets  12  between the two systems, while ensuring that the mediums to not contaminate one another. This is important to minimize the hazards that may occur when two propellant mediums become mixed. 
     The supply portion of the system consists of a propellant tank, circulation pump and filtration equipment (not shown). The supply portion provides the flow of propellant to the target well  14 . The propellant is pumped to the target well  14  using a series of control and shutoff valves  41  and  43 , respectively. These valves allow for the manipulation of flow directions, depending on the specific operation being performed. Two main propellant lines are used to flow into and out of the target well  14 . One line is used for the flow of target capsules between the target airlock (within this system) and the target well. 
     The control and shutoff valves  41  and  43  are located at the target airlock, off of the RMD  22  (as shown in  FIG.  1   ), in an accessible area of the CANDU control station. Flow to the airlock  46  and the well  14  is distributed by a header that is also at the off deck location. Shutoff valves  43  are also positioned on top of each well on the RMD  22 . The system utilizes full port ball valves in the target capsule travel lines, this is because these valves maintain a constant inner diameter to allow the passage of target capsule. 
     Referring to  FIGS.  8 A and  8 B , the system is rated as Nuclear Class 2, 3 or 6 dependent on the location within the system. In general, all containment boundary piping, tubing, or components are rated to Class 2. The piping, tubing and components that form the target capsule travel lines are rated to Class 3. And, the supply piping and components are rated to Class 6. Further, this system will have portions that are seismically qualified to Design Basis Event (DBE) - A. 
     The airlock waystation  46 , depicted in  FIGS.  7 A through  7 C , functions to extract/introduce the target capsules  12  from the hydraulic or pneumatic transfer systems, flood ( FIG.  7 A ) or dry ( FIG.  7 B ) them, prior to releasing them into the hydraulic or pneumatic transfer systems. The airlock waystation  46  consists of two main shutoff valves  43  and an interstitial volume  43   a  in between them where the target capsule  12  can be isolated from the rest of the system. 
     The function of the system is such that target capsules  12  will either arrive wet from the hydraulic system  40  or dry from the pneumatic system  42 . The system will perform one or two functions, either flow the internal cavity  43   a  to wet the target capsules  12  for entry into the hydraulic system  40  or purge and dry the target capsules  12  for entry into the pneumatic system  42 . The operation is dependent on the operation being performed by the system (injection or harvesting). 
     The drying of target capsules ( FIG.  7 B ) involves first isolating the target capsule  12  in the interstitial volume  43   a . Once inside the volume  43   a , the hydraulic propellant drains and purging of the volume occurs. The volume is then dried with heated air to remove any residual moisture, which may contain a hazardous such as tritium, before releasing the target capsule to the pneumatic system. This feature eliminates the potential for the two propellants to mix and eliminates hazards to workers and the station in the event that an airborne hazardous exist in the moist air which remains in the cavity prior to release into the pneumatics system. The use of a humidity sensor located in the drain lines of the airlock waystation  46  is used to signal when the interstitial volume  43   a  is sufficiently dry. 
     The flooding of new target capsules  12  utilizes a similar process. First, the target capsule  12  is isolated in the interstitial volume  43 . The hydraulic propellant is then introduced into the volume  43   a  and a vent valve  50  ( FIG.  7 B ) is opened to allow the air within the volume  43   a  to escape following the displacement by the hydraulic propellant. Finally, once the target is flooded with hydraulic propellant, it is released into the hydraulic system  40  and wet well  14 . 
     The pneumatic system  42  is a connecting system that connects the waystation airlock  46  and the flask loader  44 . The system is composed of the following elements: a compressor package, with inlet filtering, after-cooler and moisture separator; a “wet” receiver located downstream of the compressor package and upstream of the air dryer package; an air dryer package, with inlet coalescing filter and an outlet filter; a “dry” receiver located downstream of the dryer package; regulating valves downstream of the “dry” receiver to control and system pressure; a heating element downstream of the pressure relief valve; and control valves in multiple locations used to control direction and velocity of the flow. 
     During operation of the pneumatic system  42 , the compressor fills the receiver with ambient air until the high pressure point on the receiver pressure switch is achieved, at which point the compressor shuts off. As the system draws air from the receiver, the pressure in the receiver will reduce until the low-pressure switch set point is triggered, causing the compressor to start operations again. In the event that the high-pressure switch on the receiver fails, there is a pressure relief valve that will exhaust excess air to the CANDU stations vapor recovery system through the hydraulic propellant reservoir. 
     The pressurized air from the receiver is fed through the desiccant air dryer into a second dry receiver, where the dried air accumulates for use during the target capsule drying operations. Following the completion of target capsule drying operations, air from the system is introduced into the waystation allowing the transport of the target capsules to the flask loader station  44 . 
     The flask loader station  44 , as shown in  FIG.  9   , utilizes a cradle  54  to allow the placement of a transportation shield flask  58 . The cradle  54 , mounted to a linear drive system  56 , transports the flask  58  inside of a shield cabinet  60  ( FIG.  1   , interior of the flask loader) which is not shown in  FIG.  9    for ease of viewing the internal components. A shielded door  68  is closed to prevent the release of radioactive particles or any radiation emission. At a first position within the flask loader, the flask’s shield plug  61  is removed using an air actuated cylinder to lower an energized magnet  63  onto the shield plug  61  of the flask  58 . The flask  58  with shield plug removed then proceeds the next position and a target capsule magazine  59  ( FIG.  10   ) is elevated from the flask. 
     The target capsule magazine  59  is elevated using a vertical linear device with a locking hollow shaft. The shaft is first lowered to a predetermined height inside of a central hole then the shaft is rotated a calculated number of degrees and hooked onto the magazine  59  cross-pin. At this point, the shaft ascends to present the magazine to the pneumatic system  57  to load the magazine  59 . The magazine  59  is indexed in place to ensure alignment with the pneumatic system. 
     Once the magazine  59 , as best seen in  FIG.  10   , is in position, the target capsule is released into the position by free-fall. The bottom of the receiving position on the magazine  59  is fitted with a landing pad composed of high strength material which absorbs shock so that the target capsule is not damaged. The magazine  59  is then indexed to the next position and the operation is repeated. Once a magazine  59  is filled, it is returned to the flask  58  and the reverse of the unload process is performed. A crane  52  ( FIG.  1   ) is used to move the flask  58  to the desired transportation area. 
     As shown in  FIGS.  11  and  12   , an alternate embodiment of a target irradiation delivery system  70  in accordance with the present disclosure includes a mechanical cable drive assembly  72  ( FIG.  16   ) to raise and lower the target capsules  12  ( FIGS.  2 A and  2 B ) directly into the moderator, thus eliminating the need for the hydraulic system disclosed in the first embodiment ( FIGS.  1  through  10   ). After being raised and purged, the target capsules  12  are pneumatically transferred to the flask loader  44 . 
     Referring additionally to  FIGS.  13 A and  13 B , the target capsules  12  are held and lowered into the core within a basket  74 , which also acts as a starting point for the pneumatic transfer operation. The basket  74  is formed in such a way that it can be held on center by the cable  76  of the cable drive assembly  72  while providing a pneumatic exit path  78  for the target capsules as they are ejected to the pneumatic piping system  42  via a partial tube bend to the side. The basket  74  is drawn into the body  71  target delivery system  70  which is mounted on top of the existing adjuster port. The cable drive assembly  72  includes a winch  75  ( FIG.  16   ) mounted on top of the body  71  target delivery system  70 , thereby forming part of the containment boundary of the reactor similar to the existing reactivity mechanism drives. 
     While the target capsules  12  are being irradiated, the operational containment boundary is established by the first of two ball valves  80   a  and  80   b  ( FIGS.  14 A and  14 B ) located just off the RMD  22 , as best seen in  FIG.  15   , and two solenoid valves  82   a  and  82   b , which isolate the helium and air systems. Redundant valves provide a secondary containment boundary in the event of a failed primary containment valve, or a button up command. The basket  74  and cable  76  extend into the reactor through the maintenance valve and the lower containment valve  84 , both of which are open for target insertion. During harvesting and seeding operations, while the target basket is raised into the target delivery system  70 , operational containment is established by the lower containment valve  84  below the target delivery system  70 . 
     The lower containment valve  84  and first upper containment ball valve  80   a  function as an airlock and at no time are both valves open. The maintenance valve (not shown) located below the lower containment valve acts as a service valve to isolate the system from containment should the lower containment valve (or rest of the system) require maintenance. Preferably, the locations of the existing AA ports being used for target irradiation are advantageous since they not only provide access to the highest flux in the core, but are also only 18″ away from the peripheral portion of the RMD  22 , as best seen in  FIG.  15   , where no drives are located. 
     The target basket  74  ( FIGS.  13  and  13 B ) is raised out of the core at the required speed and parked for a dwell period of up to one hour at a location in the shield tank area to allow for activity to decay prior to transport. It is expected that the target capsules  12  and basket  74  will be relatively dry from dripping/residual heat left in the target capsules  12  after the dwell period. 
     After the dwell period is complete, the target basket  74  is raised and accepted into the body  71  of the target delivery system  70 . A helical groove  77  ( FIGS.  12  and  20   ) aligns the target exit  78  in the basket  74  with the pneumatic piping system  42  as it enters the mechanism. Helium is then injected into the system to flush MCG back into AA port, expelling airborne impurities (such as Ar41) back into containment. 
     After purging the target delivery system  70  with helium, the lower containment valve  84  at the bottom of the target delivery system  70  is closed, and the system undergoes a pressure test using helium to ensure the integrity of the seal. Upon successful completion of the pressure test, the lower air purge solenoid valve opens, as does the upper exhaust solenoid valve, and air is blown in from the pneumatic system to purge the helium out to contaminated exhaust. This purging both expels the helium and also dries the target capsules  12 , if necessary. The exhausted air is monitored for moisture to ensure the target is dry before exiting the target delivery mechanism. 
     Upon successful drying sequence, the upper containment valve  80   a  is opened and the lower exhaust solenoid valve is closed. The target capsules  12  are then blown either as a string or one at a time by use of a singulating mechanism, through the flight tubes and directly to the flask loading station  44  ( FIG.  1   ). 
     Referring now to  FIGS.  1  and  17   , new target capsules  12  are placed into the pneumatic piping system  42  by an operator. A seeding drawer  86 , or breach, is recommended on each target capsule line to simplify target loading with minimal complexity. Once the string of new target capsules  12  is loaded, pneumatic pressure is applied to the piping system and the string of target capsules is blown directly into the basket  74 . A means of slowing or arresting the string of target capsules  12  is preferably incorporated in the bottom of the basket  74  to limit shock fatigue on basket  74  and cable  76  during seeding. 
     After all target capsules  12  are in the basket  74 , the upper containment valve  80   a  is closed, the lower exhaust valve and upper helium valves are opened, and the chamber is purged of air and replaced with helium. After the air is purged, the lower exhaust valve is closed and the cavity is pressurized for a leak down test using helium. The upper helium valve is closed and pressure decay is monitored. This test ensures that the integrity of all containment valves is established. The lower containment valve  84  is then opened and the basket  74  and target capsules  12  are lowered into the Calandria  19  ( FIG.  1   ) to begin the next irradiation cycle. 
     Referring now to  FIGS.  19  through  22   , yet another alternate embodiment of a target irradiation delivery system  90  in accordance with the present disclosure is shown. This third embodiment is practically identical to the previously discussed second embodiment  70 , as shown in  FIGS.  11  through  18   , with the exception that the overall height of the present embodiment  90  above the RMD  22  is less than that of the second embodiment  70 . This difference in height is best seen in  FIGS.  19  and  22    (the present embodiment  90 ) as compared to  FIGS.  11  and  14    (the second embodiment  70 ), and achieved by extending the body  91  of the present embodiment downwardly into the AA port rather than allowing it to extend upwardly from the AA port. The reduced height of target delivery system  90  is preferable in that it reduces the likelihood of excessive vibration during potential seismic events. As well, the reduced height lessens the chance that the target delivery system  90  will be inadvertently contacted by personnel or equipment that is moving about the RMD  22 , such as during maintenance. As the other elements of the second and third embodiments  70  and  90 , respectively, are almost identical, these discussions are not repeated here. 
     These and other modifications and variations to the invention may be practiced by those of ordinary skill in the art without departing from the spirit and scope of the invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and it is not intended to limit the invention as further described in such appended claims. Therefore, the spirit and scope of the appended claims should not be limited to the exemplary description of the versions contained herein.