Patent Description:
Technetium-<NUM> (Tc-<NUM>) is the most commonly used radioisotope in nuclear medicine (e.g., medical diagnostic imaging). Tc-<NUM> (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-<NUM> has a half-life of only six (<NUM>) hours. As such, readily available sources of Tc-<NUM> are of particular interest and/or need in at least the nuclear medicine field.

Given the short half-life of Tc-<NUM>, Tc-<NUM> is typically obtained at the location and/or time of need (e.g., at a pharmacy, hospital, etc.) via a Mo-<NUM>/Tc-<NUM> generator. Mo-<NUM>/Tc-<NUM> generators are devices used to extract the metastable isotope of technetium (i.e., Tc-<NUM>) from a source of decaying molybdenum-<NUM> (Mo-<NUM>) by passing saline through the Mo-<NUM> material. Mo-<NUM> is unstable and decays with a <NUM>-hour half-life to Tc-<NUM>. Mo-<NUM> is typically produced in a high-flux nuclear reactor from the irradiation of highly-enriched uranium targets (<NUM>% Uranium-<NUM>) and shipped to Mo-<NUM>/Tc-<NUM> generator manufacturing sites after subsequent processing steps to reduce the Mo-<NUM> to a usable form, such as titanium-molybdate-<NUM> (Ti-Mo99). Mo-<NUM>/Tc-<NUM> generators are then distributed from these centralized locations to hospitals and pharmacies throughout the countries. Since Mo-<NUM> 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-<NUM> 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-<NUM> material suitable for use in Tc-<NUM> generators in a timely manner.

<CIT> describes a means for installing material, through a fuel assembly instrument thimble insert, into the existing instrument thimbles in nuclear fuel assemblies for the purpose of allowing the material to be converted to commercially valuable quantities of desired radioisotopes during reactor power operations during a remainder of a fuel cycle and removing the radioisotopes from the core through the reactor flange opening once the fuel assemblies have been removed for refueling.

<CIT> describes a method of producing radioisotopes using a heavy water type nuclear power plant. The method includes inserting targets into a heavy water moderator of the heavy water reactor through a guide tube in a port in a reactivity mechanism deck of the heavy water reactor. The heavy water reactor operates to irradiate the target to convert the target into a radioisotope.

One embodiment of the present disclosure provides a target irradiation system for irradiating a radioisotope target in a vessel penetration of a fission reactor containing a moderator, including a target elevator assembly including a body portion defining a central bore and an open bottom end, a center tube that is disposed within the central bore of the body portion, a target basket that is slidably receivable within the center tube, and a winch that is connected to the target basket by a cable, the target elevator assembly being affixed to the vessel penetration of the reactor, and a target passage that is in fluid communication with the target elevator assembly, wherein the target basket is configured to receive the radioisotope target therein via the target passage and be lowered through the vessel penetration into the moderator of the reactor when irradiating the radioisotope target, and the target elevator system forms a portion of the pressure boundary of the reactor when in fluid communication with the reactor.

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.

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.

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.

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 <NUM> 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 <NUM> (<FIG>) that is designed to interface with the other system elements. There are several components which work together to form the system, <FIG> illustrating the system installed on a CANDU reactor.

As shown in <FIG> and <FIG>, the in-core target irradiation system <NUM> preferably includes a new target loader <NUM>, a path diverter assembly <NUM> (<FIG>) an airlock <NUM>, target elevator diverter assemblies <NUM>, a pneumatic target transfer system including target transfer piping <NUM>, one or more target elevator assemblies <NUM> (<FIG>), and a flask loader assembly <NUM> (<FIG>), each of which is described in greater detail below.

As best shown in <FIG> and <FIG>, the present target irradiation system <NUM> preferably includes four target elevator assemblies <NUM> including body portions <NUM> composed of stainless steel and target baskets <NUM> composed of Zirconium alloy (i.e., Zircalloy-<NUM>), the target elevator assemblies <NUM> being vertically inserted into existing penetrations on the reactor's reactivity mechanism deck <NUM>. Preferably, the intended penetrations for mounting of the target elevator assemblies <NUM> are out-of-service adjustor assembly ports <NUM>, however, in alternate embodiments, target elevator assemblies <NUM> may be installed in other reactor penetrations that meet the specifications for installation.

As shown in <FIG>, target capsules <NUM> are the delivery vehicles for the radioisotope targets which allow for the separation of materials in an inert environment designed to eliminate corrosion related degradation from exposure to environmental mediums while in the core of the reactor. Target capsule <NUM> includes a body portion <NUM> and end caps <NUM> that are preferably constructed of a commercial grade Zirconium alloy, with other materials such as Titanium-Aluminum-Vanadium (Ti-6Al-4V) being an option. End caps <NUM> are welded to opposite ends of body portion <NUM> to provide a leak-tight interior compartment. Target capsule <NUM> is shaped to maximize flow performance through the pneumatic transfer piping <NUM>. <FIG> show the capsule design with a preferable target material of natural molybdenum <NUM> inside, although enriched molybdenum may be used as well. In order to ensure that target capsule <NUM> is secure prior to use in the reactor and to maintain its integrity, a comprehensive leak test and inspection process is utilized during manufacturing. The end cap <NUM> closure design preferably incorporates features, such as annular bulges <NUM>, to absorb end forces that may be experienced by target capsule <NUM> to help insure that the welded joints do not degrade or fail because of impact forces during transfer. Note, however, in alternate embodiments of target capsule <NUM> the annular bulges <NUM> may not be used. The weld joints, end caps <NUM>, and body portion <NUM> are preferably designed such that they are not stretched or jammed due to pressures experienced during operation of the system.

Referring now to <FIG>, a target irradiation sequence will be discussed. As shown in <FIG>, at the initiation of a target irradiation sequence, all the isolation valves within target irradiation system <NUM> are in the closed positions. To begin the sequence, an operator first loads a plurality of target capsules <NUM>, eight in the present example, into new target loader <NUM> and insures that path diverter assembly <NUM> is configured to receive the new target capsules <NUM> from new target loader <NUM>. Referring additionally to <FIG>, diverter assembly <NUM> includes a body portion <NUM> that defines an internal cavity <NUM> that is configured to rotatably receive cylindrical drum <NUM>. Cylindrical drum <NUM> defines a curved passage <NUM> therethrough that is configured to align either the first inlet pipe <NUM> or the second inlet pipe <NUM> with outlet pipe <NUM>, wherein first inlet pipe <NUM> connects new target loader <NUM> to diverter assembly <NUM> and second inlet pipe <NUM> connects flask loader <NUM> to diverter assembly <NUM>. A motor <NUM> is connected to cylindrical drum <NUM> by a shaft and is configured to rotate cylindrical drum <NUM> between two positions. As shown in <FIG>, a lock paddle <NUM> extends radially-outwardly from the shaft and indicates which of the first and second inlet pipes <NUM> and <NUM> is aligned with outlet pipe <NUM>.

A pair of first and second lock rams <NUM> and <NUM> is provided for securing lock paddle <NUM> and, therefore, passage <NUM> in either a first position aligned with first inlet pipe <NUM> or a second position aligned with second inlet pipe <NUM>, respectively. A pair of first and second lock switches <NUM> and <NUM> provides an indication as to whether first lock ram <NUM> is fully extended, thereby positively securing drum <NUM> and passage <NUM> in alignment with first inlet pipe <NUM>, or whether first lock ram <NUM> is fully retracted so that motor <NUM> may be used to rotate drum <NUM> and passage <NUM> to the second position in which they are aligned with second inlet pipe <NUM>. Referring specifically to <FIG> and <FIG>, the position of lock paddle <NUM> now indicates that drum <NUM> has been rotated to the second position so that passage <NUM> now aligns second inlet pipe <NUM> with outlet pipe <NUM>. Once closure switch <NUM> provides an indication that lock paddle <NUM> has been rotated to the second position, second lock ram <NUM> is fully extended, thereby engaging lock paddle <NUM> and positively securing passage <NUM> in proper alignment with second inlet pipe <NUM>. As with first lock ram <NUM>, a pair of first and second lock switches <NUM> and <NUM> is provided to indicate the position of second lock ram <NUM>.

Referring now to <FIG>, after verification that diverter assembly <NUM> is aligned with new target loader <NUM>, a string of eight target capsules <NUM> is propelled to airlock <NUM> by pneumatic force. Airlock <NUM> is defined by the section of transfer piping <NUM> disposed between first and second outboard isolation valves <NUM> and <NUM>, respectively, and a pair of first and second inboard isolation valves <NUM> and <NUM>, respectively. As shown in <FIG>, during transfer of target capsules <NUM> to airlock <NUM>, first and second outboard isolation valves <NUM> and <NUM> are opened whereas first and second inboard isolation valves <NUM> and <NUM> remain closed. A propellant air flow is applied to the string of target capsules <NUM> at new target loader <NUM> and an arresting air flow is provided through air inlet pipe <NUM> by opening air isolation valve <NUM>. The arresting air flow is provided to slow the string of target capsules <NUM> as they enter airlock <NUM>, thereby helping to prevent any potential damage due to impact. Upon the initiation of the propellant and arresting flows, exhaust isolation valve <NUM> is placed in the open position so that the combined flows may exit airlock <NUM> by way of exhaust pipe <NUM>.

Referring additionally to <FIG>, first, second, and third stop pistons <NUM>, <NUM>, and <NUM>, respectively, are selectively extendable into, and retractable from, airlock <NUM> in order to properly position the string of target capsules <NUM>. As shown in <FIG>, when inserting a new string of target capsules <NUM> into airlock <NUM>, only third stop piston <NUM> extends into airlock <NUM> so that the string of target capsules <NUM> is properly positioned within the airlock <NUM>. As shown in <FIG>, once the string of target capsules <NUM> is positioned within airlock <NUM>, first and second outboard isolation valves <NUM> and <NUM> are moved to the closed position so that airlock <NUM> is isolated from external environment of target irradiation system <NUM>. Prior to the step of delivering the string of target capsules <NUM> to a corresponding target elevator assembly <NUM>, airlock <NUM> and, therefore, the string of target capsules <NUM> is purged with helium through helium inlet <NUM> by placing helium isolation valve <NUM> in the open position. Similarly to the propulsion and arresting air flows, helium from the purge exits airlock <NUM> by way of exhaust pipe <NUM>. Once the helium purge is secured, exhaust isolation valve <NUM> is placed in the closed position.

Referring now to <FIG>, prior to transferring the string of target capsules <NUM> out of airlock <NUM>, the operator insures that target elevator diverters <NUM> are configured to be in fluid communication with the desired target elevator assembly <NUM>. In the preferred embodiment shown, three target elevator diverters <NUM> are utilized since the present embodiment includes four target elevator assemblies <NUM>. If an alternate embodiment were only two target elevator assemblies <NUM> are utilized, only one target elevator diverter <NUM> would be required. Target elevator diverters function identically to the previously discussed path diverter assembly <NUM>, so a repeat discussion is not provided.

Referring now to <FIG>, once target elevator diverters <NUM> are aligned with the proper target elevator assembly <NUM>, a propellant flow for the string of target capsules <NUM> is created by activating first pneumatic pump <NUM> and placing inboard isolation valve <NUM> of outlet pipe <NUM> in the open position. As with airlock <NUM>, an arresting flow for the string of target capsules <NUM> is provided by activating second pneumatic pump <NUM> and opening outlet isolation valve <NUM> of outlet pipe <NUM>. Simultaneous with the initiation of the propellant and arresting flows, an exhaust line for the two flows is provided by opening inlet isolation valve <NUM> of inlet pipe <NUM> of second pneumatic pump <NUM> so that the flows are recirculated back to the inlets of first and second pneumatic pumps <NUM> and <NUM> through inlet pipe <NUM>. With the propellant, arrest, and exhaust flows established, third stop piston <NUM> is retracted from within airlock <NUM> and the string of target capsules <NUM> is propelled through transfer piping <NUM> to the corresponding target elevator assembly <NUM>. As best in <FIG>, the arresting flow is configured to flow upwardly through target elevator assembly <NUM> so that the string of target capsules <NUM> is slowed as it begins to enter target elevator assembly <NUM>. The arresting flow may be selected to be forceful enough to suspend the string of target capsules <NUM> as they enter target elevators assembly <NUM>. By slightly reducing the level of the arresting flow, the string of target capsules <NUM> may be greatly lowered to the bottom of target basket <NUM>. Additional outlet and inlet piping, along with corresponding isolation valves, is provided so that outlet pipe <NUM> and inlet pipe <NUM> of second pneumatic pump <NUM> may be aligned with each of the target elevator assemblies <NUM>.

Note, an alternate embodiment of the present system may include first and second hydraulic pumps rather than first and second pneumatic pumps <NUM> and <NUM> so that liquids may be used as the propellant and arresting flows for delivery of the string of target capsules <NUM> to target elevator assembly <NUM>. When liquids are used for the propellant and arresting flows, isolation valves are utilized on the portions of outlet pipe <NUM> and transfer piping <NUM> closest to target elevator assembly <NUM> in order to minimize the amount of fluid that is released into the calandaria as target basket <NUM> is lowered therein. Preferably, the liquid used in such an embodiment is reactor grade water, specifically heavy water when the reactor utilized is a CANDU reactor. Additionally, when liquids are used for target capsule <NUM> transfer, a drain is provided on airlock <NUM> for the movement from a liquid to an air environment.

Referring now to <FIG> and <FIG>, each target elevator assembly <NUM> of target irradiation system <NUM> is mounted to a corresponding adjustor assembly port <NUM>, or thimble, that is accessible from above the reactivity mechanism deck <NUM> and extends downwardly into calandaria <NUM> of the CANDU reactor. As best seen in <FIG>, target elevator assembly <NUM> includes an elongated body portion <NUM> that defines a central bore <NUM> and includes a mounting flange <NUM> that affixes target elevator assembly <NUM> to the top portion of adjustor assembly port <NUM>. A curved target passage <NUM> is formed in the upper end of body portion <NUM> and extends from transfer piping <NUM> to central bore <NUM>. Similarly, the upper end of body portion <NUM> defines a pneumatic passage <NUM> that is in fluid communication with both outlet pipe <NUM> of second pneumatic pump <NUM> and central bore <NUM>. As best seen in <FIG> and <FIG>, the bottom portion of central bore <NUM> includes a frustoconically-shaped entrance surface <NUM> that is configured to facilitate slidably receiving a corresponding target basket <NUM>.

A cylindrical center tube <NUM> is mounted within central bore <NUM> of target elevator assembly <NUM> by way of a flange <NUM> that extends radially-outwardly from an uppermost end of the tube's upper body portion <NUM>, as best seen in <FIG> and <FIG>. As shown in <FIG>, center tube <NUM> includes an annular ring <NUM> affixed to its uppermost portion, the annular ring <NUM> being secured to upper body portion <NUM> by bellows <NUM>, or in the alternative a spring set. As discussed in greater detail below, bellows <NUM> allow center tube <NUM> to be limitedly slidable with respect to body portion <NUM> of target elevator assembly <NUM>. As best seen in <FIG>, bottom end <NUM> of center tube <NUM> includes a bottom bushing <NUM>, an outer surface of which forms a seal with an inner surface of the elevator assembly's central bore <NUM> and a frustoconically-shaped inner surface <NUM> that is configured to form a seal with a corresponding frustoconically-shaped surface of a bottom flange <NUM> of target basket <NUM>. A plurality of flow apertures <NUM> is provided at bottom end <NUM> of center tube <NUM> adjacent bottom bushing <NUM>. Flow apertures <NUM> provide fluid communication between the interior of center tube <NUM> and a flow annulus <NUM> that is defined between the outer surface of center tube <NUM> and the inner surface of central bore <NUM> when target basket <NUM> is fully seated within target elevator assembly <NUM> (<FIG>).

Referring again to <FIG> and <FIG>, target elevator assembly <NUM> includes target basket <NUM> that is slidably received within center tube <NUM>. Target basket <NUM> includes a cylindrical sidewall <NUM> that defines a plurality of flow apertures <NUM>, as well as a target aperture <NUM> at its upper end. When target basket <NUM> is fully seated within target elevator assembly <NUM>, target aperture <NUM> is aligned with target passage <NUM> of body portion <NUM>. Target aperture <NUM> forms a continuous curved guide with both target aperture <NUM> of center tube <NUM> and target passage <NUM> of body portion <NUM> so that the string of target capsules <NUM> may slide freely into target basket <NUM>. As best seen in <FIG>, target basket <NUM> includes a nose <NUM> extending upwardly therefrom that is defined by two curved camming surfaces <NUM> that meet at an apex <NUM> at their upper ends. An alignment slot <NUM> is disposed between the lower ends of camming surfaces <NUM> and is configured to slidably receive an alignment pin <NUM> (<FIG> and <FIG>) that extends radially-inwardly into a recess <NUM> at the top of central bore <NUM> that is configured to receive nose <NUM> of target basket <NUM>. The upper portion of target basket <NUM> also defines an alignment flat <NUM> and lock recess <NUM> that are configured to receive a roller <NUM> disposed at the innermost end of piston <NUM> of lock pin assembly <NUM>, as discussed in greater detail below.

As best seen in <FIG> and <FIG>, a mechanical cable drive assembly <NUM> is mounted at the uppermost end of body portion <NUM> of target elevator assembly <NUM> and is configured to lower and raise target basket <NUM>. Cable drive assembly <NUM> includes a drum <NUM> that is rotatably received on drive screw <NUM> and a drive motor <NUM> disposed within housing <NUM>. Feed wire <NUM> is rotatably received about drum <NUM> and its bottom end is affixed to the upper end of target basket <NUM>. Drum <NUM> is configured to progress along its mounting shaft as feed wire <NUM> is both spooled and unspooled so that feed wire <NUM> remains on center with target basket <NUM>. Preferably, drum <NUM> is received on a cantilevered mounting shaft including a force sensor at the end so that it is capable of determining when a full target string has been received within target basket <NUM> based on the detected weight. As well, the cantilevered drum <NUM> is able to determine when the target basket <NUM> and corresponding string of target capsules <NUM> are positioned either within or above the moderator within calandaria <NUM> of the reactor based on the supported weight. Additionally, the force sensor detects jams and loss of tension on the feed wire <NUM> so that motor <NUM> may be strapped to avoid damage.

Referring now to <FIG>, <FIG>, and <FIG>, as previously discussed, as the target string <NUM> enters target elevator assembly <NUM> an arresting flow is provided by second pneumatic pump <NUM>. The arresting flow enters target elevator assembly <NUM> through pneumatic passage <NUM> and flows downwardly through flow annulus <NUM> until it reaches flow apertures <NUM> formed in bottom end <NUM> of center tube <NUM>. Further downward flow is prevented by bottom bushing <NUM> of center tube <NUM> which forms an airtight seal with both central bore <NUM> of body portion <NUM> and bottom flange <NUM> of target basket <NUM>, as shown in <FIG>. At this point, the arresting flow enters the interior of center tube <NUM> through flow apertures <NUM> and flows upwardly, at which point the flow encounters the target capsules <NUM>, until exiting transfer tubing <NUM> by way of exhaust line <NUM>.

As shown in <FIG>, the string of target capsules <NUM> is only inserted into target basket <NUM> when target basket <NUM> is fully seated within target elevator assembly <NUM> and locked in place by lock pin assembly <NUM>. Roller <NUM> of piston <NUM> is only able to engage lock recess <NUM> of target basket <NUM> when nose <NUM> of target basket <NUM> is fully received within recess <NUM> of target elevator assembly <NUM>. The engagement of lock pin assembly <NUM> with lock recess <NUM> insures that target aperture <NUM> of target basket <NUM> is properly aligned, both vertically and rotationally, with target passage <NUM> and also helps to reduce stress on the connection between feed wire <NUM> and target basket <NUM> as lock pin assembly <NUM> provides support as the string of target capsules <NUM> impacts the bottom of target basket <NUM>. As shown in <FIG>, once the string of target capsules <NUM> has been received within target basket <NUM>, propellant and arresting flows are stopped by deactivating first pneumatic pump <NUM> and second pneumatic pump <NUM>, respectively, and closing the corresponding inboard isolation valves <NUM> and <NUM>, respectively, as well as isolation valve <NUM> of the exhaust line, as shown in <FIG>. Referring now to <FIG> and <FIG>, after the string of target capsules <NUM> is received within target basket <NUM>, piston <NUM> is retracted so that roller <NUM> no longer engages lock recess <NUM>. Motor <NUM> is used to lower target basket <NUM> and, therefore, the string of target capsules <NUM> into the heavy water moderator that is disposed in the calandaria <NUM> of the reactor. The string of target capsules <NUM> is exposed to a neutron flux of the reactor while disposed within the moderator.

After the string of target capsules <NUM> has been irradiated for the desired amount of time, motor <NUM> of cable drive assembly <NUM> is once again activated to raise target basket <NUM> out of the moderator. Preferably, target basket <NUM> is suspended in the gas space above the moderator to allow both drainage of moderator from target basket <NUM> and allow short half-lived radioiosotopes to decay to acceptable levels before retrieving the string of target capsules <NUM> from target elevator assembly <NUM>. As shown in <FIG>, frustoconical entrance surface <NUM> at the bottom of target elevator assembly <NUM> is configured to guide nose <NUM> of target basket <NUM> into center tube <NUM>. Cable drive assembly <NUM> continues to raise target basket <NUM> until bottom flange <NUM> of target basket <NUM> comes into contact with frustoconically-shaped inner surface <NUM> of bottom bushing <NUM>, as shown in <FIG>. In this position, it is possible that target basket <NUM> is not properly aligned within center tube <NUM> for the removal of the string of target capsules <NUM>. For example, as shown in <FIG>, target basket <NUM> is approximately <NUM>° out of position. In most cases, by slightly raising target basket <NUM>, alignment pin <NUM> will come into contact with one of the two camming surfaces <NUM> of the basket's nose <NUM>, thereby causing target basket <NUM> to rotate until alignment pin <NUM> is slidably received in alignment slot <NUM>. When alignment pin <NUM> is received within alignment slot <NUM>, target basket <NUM> is properly positioned for the retrieval of the string of target capsules <NUM>. Alignment flat <NUM> is provided for the sole instance in which apex <NUM> of the target basket's nose <NUM> is directly aligned with alignment pin <NUM>, as shown in <FIG>. In this instance, piston <NUM> of lock pin assembly <NUM> is extended radially-inwardly until roller <NUM> engages alignment flat <NUM>, thereby causing a slight rotation of target basket <NUM> that results in the desired misalignment of apex <NUM> and alignment pin <NUM>. Note, during this further upward motion of target basket <NUM>, bellows <NUM> (<FIG>) of center tube <NUM> are compressed. Bellows <NUM> help to insure that the hard stop <NUM> (<FIG>) that engages the top of target basket <NUM>, and the sealing surfaces <NUM> and <NUM> (<FIG>), may simultaneously be in contact, thereby allowing for vertical alignment and sealing regardless of manufacturing tolerances between and possible age-related lengthening of the body of target basket <NUM>.

Once the irradiation of the string of target capsules <NUM> is complete and target basket <NUM> is fully seated and locked in position within target elevator assembly <NUM>, as shown in <FIG>, the removal of the string of target capsules <NUM> from target elevator assembly <NUM> is initiated. Referring now to <FIG>, removal of the string of target capsules <NUM> from target assembly <NUM> is accomplished with a propellant flow from second pneumatic pump <NUM> and an arresting flow provided by first pneumatic pump <NUM>. Prior to initiation of the propellant and arresting flows, the operator positions first and second airlock inboard isolation valves <NUM> and <NUM> to their open positions so that the string of target capsules <NUM> may enter airlock <NUM>. Upon activation of second pneumatic pump <NUM>, outlet isolation valve <NUM> is placed in the open position and a propellant flow is provided through outlet pipe <NUM>. Referring additionally to <FIG>, propellant flow enters pneumatic passage <NUM> of target elevator assembly <NUM> and flows downwardly through flow annulus <NUM> until it enters the interior of center tube <NUM> by way of flow apertures <NUM> (<FIG>). At this point, the propellant flow engages the string of target capsules <NUM>, thereby urging the string upwardly and outwardly of target basket <NUM> and into transfer piping <NUM>, as shown in <FIG>. Simultaneous to the initiation of the propellant flow, the arresting flow is initiated by activating first pneumatic pump <NUM> and placing inboard isolation valve <NUM> of outlet pipe <NUM> in the open position. An exhaust flow is not required at this stage in the operation as the propellant and arresting flows are recirculated to the inlets of the first and second pneumatic pumps <NUM> and <NUM>, respectively, by way of inlet pipe <NUM> of first pneumatic pump <NUM>. As shown in <FIG>, during removal of the string of target capsules <NUM> from target elevator assembly <NUM>, first stop piston <NUM> is extended inwardly into the interior of airlock <NUM> to provide an overshoot stop for the string of target capsules <NUM> within airlock <NUM>.

Referring additionally to Figure 6I, once the string of target capsules <NUM> is properly positioned within airlock <NUM>, airlock <NUM> is isolated from the remainder of target irradiation system <NUM> by moving first and second inboard isolation valves <NUM> and <NUM> to the closed position. Additionally, the propellant flow, the arresting flow, and the recirculating flow are secured by deactivating the first and second pneumatic pumps <NUM> and <NUM>, respectively, and positioning isolation valves <NUM>, <NUM>, and <NUM> in the closed position. Similarly to inserting the string of target capsules <NUM> into target elevator assembly <NUM>, during the removal of the string of target capsules <NUM> from target elevator assembly <NUM> an purge is applied to airlock <NUM> once the string of target capsules <NUM> is isolated therein. Because the outbound target capsules <NUM> are being released to an air environment, an air purge may be utilized rather than a helium purge. The air purge is provided through air inlet <NUM> by placing air isolation valve <NUM> in the open position and providing an exhaust flow through exhaust pipe <NUM> by placing exhaust isolation valve <NUM> in the open position. Upon completion of the purge, air isolation valve <NUM> and exhaust isolation valve <NUM> are placed in the closed position.

Referring now to Figure 6J, prior to releasing individual target capsules <NUM> to flask loader assembly <NUM>, an operator insures that path diverter assembly <NUM> is aligned with second inlet pipe <NUM> that leads to flask loader assembly <NUM>. Next, a propellant flow is established by placing air isolation valve <NUM> of air inlet pipe <NUM> in the open position as well as placing first and second outboard isolation valves <NUM> and <NUM> of airlock <NUM> in the open position. An exhaust flow is provided by flask loader assembly <NUM>, as discussed in greater detail below. Once the propellant flow is established, second stop piston <NUM> is extended into airlock <NUM> so that it engages the second target capsule <NUM> in the string, thereby securing it in position. Next, first stop piston <NUM> is retracted from the airlock <NUM> so that the first target capsule <NUM> of the string is now free to be propelled to flask loader assembly <NUM>. After the release of the first target capsule <NUM>, first stop piston <NUM> is extended into airlock <NUM> once again and second stop piston <NUM> is retracted so that the remaining seven target capsules <NUM> of the string are free to progress until abutting the first stop piston <NUM>. At this point, second stop piston <NUM> is extended into airlock <NUM> until it engages what is now the second target capsule <NUM> of the remainder of the string. At this point, first stop piston <NUM> is once again withdrawn from airlock <NUM>, thereby releasing another target capsule for transfer to flask loader assembly <NUM>. This process is repeated until all eight target capsules <NUM> have been individually released to flask loader assembly <NUM>. Upon completion of the transfer of all eight target capsules <NUM> to flask loader assembly <NUM>, propellant flow is secured by placing air isolation valve <NUM> in the closed position and placing first and second outboard isolation valves <NUM> and <NUM> of airlock <NUM> in the closed position, as shown in <FIG>.

As shown in <FIG>, flask loader assembly <NUM> includes a slidable drawer <NUM> having an annular cradle <NUM> and an outer door <NUM>. Cradle <NUM> is configured to receive a flask casket <NUM> therein, as shown in <FIG>. Casket <NUM> defines an internal cavity <NUM> (<FIG>) that is configured to slidably receive a target flask <NUM>, and includes a closure plug <NUM> that is secured to the body of casket <NUM> by plurality of threaded fasteners <NUM>. Closure plug <NUM> also includes a pair of lift eyes <NUM> so that casket <NUM> may be raised and lowered by jib crane <NUM> (<FIG>) of the reactor facility. Casket <NUM> is further received in a road transfer overpack <NUM> that defines an internal cavity <NUM> that is enclosable with lid <NUM>. After casket <NUM> is placed in cradle <NUM> of drawer <NUM>, threaded fasteners <NUM> are removed and closure plug <NUM> remaining in position as drawer <NUM> is slid inwardly into a first compartment <NUM> of flask loader assembly <NUM>, as shown in <FIG>. Once drawer <NUM> is slid inwardly so that casket <NUM> is disposed in first compartment <NUM>, a magnetized plug puller <NUM> is lowered into contact with closure plug <NUM> and subsequently raised so that closure plug <NUM> is removed from casket <NUM>. Note, when casket <NUM> is received within first compartment <NUM>, door <NUM> to drawer <NUM> seals, or partially seals, the interior volume of flask loader assembly <NUM> from the external environment. Note, some inflow into flask loader assembly <NUM> may be desired when providing the exhaust flow. As well, exhaust piping <NUM> is provided so that the interior of flask loader assembly <NUM> can be subjected to an exhaust flow during the loading of the target capsules <NUM>.

With the removal of closure plug <NUM>, target flask <NUM> is now accessible and moved to a second compartment <NUM> of flask loader assembly <NUM>, as shown in <FIG> and <FIG>. Target flask <NUM> preferably includes a plurality of target cavities <NUM>, each target cavity being capable of slidably receiving a pair of previously irradiated target capsules <NUM>, and a central recess <NUM>. Central recess <NUM> is configured to slidably receive a bayonet fitting <NUM> that includes a pair of opposed projections <NUM> and is disposed at a lowermost end of a vertical lift spear <NUM>. After central recess <NUM> of target flask <NUM> is aligned beneath vertical lift spear <NUM>, vertical lift spear <NUM> is lowered into central recess <NUM> and rotated approximately <NUM>° so that projections <NUM> of bayonet fitting <NUM> engage corresponding recesses (not shown) defined in the interior of central recess <NUM>. Once properly engaged with target flask <NUM>, vertical lift spear <NUM> is raised so that one of the flask's target cavity <NUM> is aligned with an exit opening of a pneumatic delivery tube <NUM> of flask loader assembly <NUM>, as shown in <FIG> and <FIG>.

Claim 1:
A target irradiation system (<NUM>) for irradiating a radioisotope target in a vessel penetration of a fission reactor containing a moderator, comprising:
a target elevator assembly (<NUM>) including a body portion (<NUM>) defining a central bore (<NUM>) and an open bottom end, a center tube (<NUM>) that is disposed within the central bore of the body portion, a target basket (<NUM>) that is slidably receivable within the center tube, and a winch (<NUM>) that is connected to the target basket by a cable (<NUM>),
the target elevator assembly being affixed to the vessel penetration of the reactor; and
a target passage (<NUM>) that is in fluid communication with the target elevator assembly,
characterised in that the target basket is configured to receive the radioisotope target therein via the target passage and be lowered through the vessel penetration into the moderator of the reactor when irradiating the radioisotope target, and the target elevator system forms a portion of the pressure boundary of the reactor when in fluid communication with the reactor.