Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: PRODUCTION OF MOLYBDENUM-99 USING ELECTRON BEAMS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. Application No. 13/901,213,
filed on
May 23, 2013.
TECHNICAL FIELD
The present disclosure pertains to processes, systems, and apparatus, for
production of
molybdenum-99. More particularly, the present disclosure pertains to
production of
molybdenum-99 from molybdenum-100 targets using high-power electron linear
accelerators.
BACKGROUND
Technetium-99m, referred to hereinafter as 99mTc, is one of the most widely
used
radioactive tracers in nuclear medicine diagnostic procedures. 991nTc is used
routinely for
detection of various forms of cancer, for cardiac stress tests, for assessing
the densities of bones,
for imaging selected organs, and other diagnostic testing. 99niTc emits
readily detectable 140 keV
gamma rays and has a half-life of only about six hours, thereby limiting
patients' exposure to
radioactivity. Because of its very short half-life, medical centres equipped
with nuclear medical
facilities derive 99mTe from the decay of its parent isotope molybdenum-99,
referred to
hereinafter as 99Mo, using 99mTc generators. 99Mo has a relatively long half
life of 66 hours
which enables its world-wide transport to medical centres from nuclear reactor
facilities wherein
large-scale production of 99Mo is derived from the fission of highly enriched
5Uranium. The
problem with nuclear production of 99M0 is that its world-wide supply
originates from five
nuclear reactors that were built in the 1960s, and which are close to the end
of their lifetimes.
Almost two-thirds of the world's supply of "Mo currently comes from two
reactors: (i) the
National Research Universal Reactor at the Chalk River Laboratories in
Ontario, Canada, and (ii)
the Petten nuclear reactor in the Netherlands. In the past few years, there
have been major
shortages of 99Mo as a consequence nf planned or unplanned shutdowns at both
of the major
Date recue/ date received 2022-02-17
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production reactors. Consequently, serious shortages occurred at the medical
facilities within
several weeks of the reactor shutdowns, causing significant reductions in the
provision of
medical diagnostic testing and also, placing great production demands on the
remaining nuclear
reactors. Although both facilities arc now active again, there is much global
uncertainty
regarding a reliable long-term supply of99Mo.
SUMMARY
The exemplary embodiments of the present disclosure pertain to apparatus,
systems, and
processes for the production of molybdenum-99 (99Mo) from molybdenum-100 (19
Mo) by high-
energy electron irradiation with linear accelerators. Some exemplary
embodiments relate to
systems for working the processes of present disclosure. Some exemplary
embodiments relate to
apparatus comprising the systems of the present disclosure.
DESCRIPTION OF THE DRAWINGS
The present disclosure will be described in conjunction with reference to the
following
drawings in which:
Fig. 1 is a perspective illustration of an exemplary system of the present
disclosure,
shown with protective shielding in place;
Fig. 2 is a perspective view of the exemplary system from Fig. 1, shown with
the
protective shielding removed;
Fig. 3 is a side view of the exemplary system from Fig. 2, shown with
protective
shielding removed from the linear accelerator components of the system;
Fig. 4 is a top view of the exemplary system shown in Fig. 3;
Fig. 5 is an end view of the from Fig. 3, shown from the end with the linear
accelerator
components;
3
Fig. 6(A) is a perspective view showing the target assembly component of the
exemplary
system from Fig. 2 partially unclad with the protective shielding component,
while 6(B) is a
perspective view showing the target assembly component unclad;
Fig. 7 is a side view of the target drive assembly (perpendicular to the
electron beam
generated by the linear accelerator);
Fig. 8 is a front view of the target drive assembly showing the inlet for the
bremsstrahlung
photon beam generated from the linac electron beam;
Fig. 9 is a cross-sectional side view of the target drive assembly shown in
Fig. 8;
Fig. 10 is a cross-sectional top view of the target drive assembly shown in
Fig. 8 at the
junction of the cooling tower component and the housing for the beamline;
Fig. 11 is a cross-sectional top view of the target drive assembly shown in
Fig. 8 showing
the energy converter and the target holder mounted in the beamline;
Fig. 12 is schematic illustration of the conversion of a high-power electron
beam into a
bremsstrahlung photon shower for irradiation of a plurality of i'Mo targets;
Fig. 13 is a close-up cross-sectional side view from Fig. 9 showing the energy
converter
and the mounted target holder;
Fig. 14 is a close-up cross-sectional top view from Fig. 11 showing the energy
converter
and the mounted target holder;
Fig. 15(A) is a perspective view of an exemplary target holder, while 15(B) is
a cross-
sectional side view of the target holder;
Fig. 16(A) is a perspective view from the top of an exemplary cooling tube
component,
while 16(B) is a perspective view from the bottom of the cooling tube
component, and 16(C) is a
cross-sectional side view of the cooling tube component;
Date recue/ date received 2022-02-17
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Figs. 17(A) and 17(B) show another embodiment of a cooling tube component
being
installed into a target assembly component from Fig. 9;
Figs. 18(A) and 18(B) show the cooling tube component from Fig. 17 being
clamped into
place within the target assembly component
Fig. 19 is a perspective view of an exemplary remote-controlled molybdenum
handling
apparatus mounted onto the protective shield cladding of the target assembly
station component
of the exemplary system shown in Fig. 1;
Fig. 20 is a perspective view of an exemplary frame support base for the
exemplary
remote-controlled molybdenum handling apparatus shown in Fig. 19;
Fig. 21 is a perspective view of an exemplary shuttle tray that cooperates
with the
exemplary frame support base shown in Fig. 20;
Fig. 22 is a perspective view if an exemplary shield cask that is mountable
onto the
exemplary shuttle tray shown in Fig. 21;
Fig. 23 is another perspective view of the exemplary remote-controlled
molybdenum
handling apparatus shown in Fig. 19;
Fig. 24(A) is a perspective view of an exemplary grapple component from the
exemplary
remote-controlled molybdenum handling apparatus shown in Figs. 19 and 23,
shown engaged
with a crane hook, while Fig. 24(b) is a cross-sectional side view of the
exemplary grapple
component shown engaged with an exemplary molybdenum target holder;
Fig. 25 is a perspective view of an exemplary tipping tower for demountable
engagement
with the exemplary remote-controlled molybdenum handling apparatus shown in
Figs. 19 and
23, wherein the exemplary tipping tower is configured for receiving and
holding a cooling tube
assembly; and
Fig. 26 is a horizontal cross-sectional view of the exemplary tipping tower
shown in Fig.
25.
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DETAILED DESCRIPTION
The exemplary embodiments of the present disclosure pertain to systems,
apparatus, and
processes for producing 991Vlo from imMo targets using high-energy radiation
from electron
beams generated by linear particle accelerators.
A linear particle accelerator (often referred to as a "linac") is a particle
accelerator that
greatly increases the velocity of charged subatomic particles by subjecting
the charged particles
to a series of oscillating electric potentials along a linear beamline.
Generation of electron beams
with a linac generally requires the following elements: (i) a source for
generating electrons,
typically a cathode device, (ii) a high-voltage source for initial injection
of the electrons into (iii)
a hollow pipe vacuum chamber whose length will be dependent on the energy
desired for the
electron beam, (iv) a plurality of electrically isolated cylindrical
electrodes placed along the
length of the pipe, (v) a source of radio frequency energy for energizing each
of cylindrical
electrodes, i.e., one energy source per electrode, (vi) a plurality of
quadrupole magnets
surrounding the pipe vacuum chamber to focus the electron beam, (vii) an
appropriate target, and
(viii) a cooling system for cooling the target during radiation with the
electron beam. Linacs have
been used routinely for various uses such as the generation of X-rays, and for
generation of high
energy electron beams for providing radiation therapies to cancer patients.
Linacs are also commonly used as injectors for higher-energy accelerators such
as
synchrotrons, and may also be used directly to achieve the highest kinetic
energy possible for
light particles for use in particle physics through bremsstrahlung radiation.
Bremsstrahlung
radiation is the electromagnetic radiation produced by the deceleration of a
charged particle
when deflected by another charged particle, typically of an electron by an
atomic nucleus. The
moving electron loses kinetic energy, which is converted into a photon because
energy is
conserved. Bremsstrahlung radiation has a continuous spectrum which becomes
more intense
and whose peak intensity shifts toward higher frequencies as the change of the
energy of the
accelerated electrons increases.
However, to those skilled in these arts, it would seem that using electron
linacs to
produce high-energy photons through bremsstrahlung radiation to then produce
radioisotopes
through a photo-nuclear reaction would be an inefficient process for
production of radio isotopes
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because the electromagnetic interactions of electrons with nuclei are usually
significantly smaller
than the strong interactions with protons as the incident particles. We have
determined however,
that 100Mo has a broad "giant dipole resonance" (GDR) for photo-neutron
reactions around 15
MeV photon energy which results in a significant enhancement of the reaction
cross-section
between 1 Mo and 99Mo. Also, the radiation length of a high-energy photon in
the 10 to 30 MeV
range in 1 Mo is about 10 mm which is significantly longer than the range of
a proton of the
same energy. Consequently, the effective target thickness is also much larger
for photo-neutron
reactions compared to proton reactions. The reduced number of reaction
channels associated
with linac,-generated electron beams limits the production of undesirable
isotopes. In
comparison, using proton beams to directly produce 99Te from 1 0Mo often
results in the
generation of other Tc isotopes from other stable Mo isotopes that may be
present in the enriched
ioaMo targets. Medical applications place strict limits on the amounts of
other radio-isotopes that
may be present with 99Tc, and it would seem that production of "Tc from 1 Mo
with linac-
generated electron would be preferable because the risk of producing other Tc
isotopes is
significantly lower. Furthermore, it appears that photo-neutron reactions with
other Mo isotopes
present in 100Mo targets usually results in stable Mo.
Accordingly, one embodiment of the present disclosure, pertains to an
exemplary high-
power linac electron beam apparatus for producing 99Mo from a plurality of
100Mo targets
through a photo-nuclear reaction on the 111 Mo targets. The apparatus
generally comprises at least
(i) an electron linear accelerator capable of producing electrons beams having
at least 5 kW of
power, about 10 kW of power, about 15 kW of power, about 20 kW of power, about
25 kW of
power, about 30 kW of power, about 35 kW of power, about 45 kW of power, about
60 kW of
power, about 75 kW of power, about 100 kW of power, (ii) a water-cooled
converter to produce
a high flux of high-energy bremsstrahlung photons of at least 20 MeV from the
electron beam
generated by the linear accelerator, a flux of about 25 MeV of bremsstrahlung
photons, a flux of
about 30 MeV of bremsstrahlung photons, a flux of about 35 MeV of
bremsstrahlung photons, a
flux of about 40 MeV of bremsstrahlung photons, a flux of about 45 MeV of
bremsstrahlung
photons, (iii) of a water-cooled target assembly component for mounting
therein a target holder
housing a plurality of 1110Mo targets and for precisely positioning and
aligning the target holder
for interception of beam of high-energy bremsstrahlung photon radiation
produced by the water-
cooled converter, and (iv) a plurality of shielding components for cladding
the water-cooled
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target assembly component to contain gamma radiation and/or neutron radiation
within the target
assembly component and to prevent radiation leakage outside of the apparatus.
Depending on the
component being shielded and its location within the installation, the
shielding may comprise
one or more of lead, steel, copper, and polyethylene. The apparatus
additionally comprises (v) an
integrated target transfer assembly with a component for remote-controlled
loading and
conveying a plurality of target holders, each of the target holders loaded
with a plurality of 100Mo
targets, to a target drive component. An individual loaded target holder is
transferrable from the
loading/conveying component by remote control into a target drive component
contained within
the water-cooled target assembly component. The target holder is conveyed with
the target drive
component to a position which intercepts the bremsstrahlung photon radiation.
The base of the
target drive component is engaged with a target aligning centering component
which precisely
positions and aligns the loaded target holder for maximum interception of the
bremsstrahlung
photon radiation. The integrated target transfer assembly is additionally
configured for remote
controlled removal of an irradiated target holder from the target drive
component and transfer to
a lead-shielded hot cell for separation and recovery of 99mTe decaying from
99Mo associated with
the irradiated 100Mo targets. Alternatively, the irradiated 1"Mo targets may
be transferred into a
led-shielded shipping container for transfer to a hot cell off site.
It is apparent that the maximum achievable 99Mo yield is dependent on the
amount of
energy which can be safely deposited in the 1"Mo targets, and also on the
probability of giant
dipole resonance photons interacting with the target nuclei. The amount of
energy which can be
safely deposited in the 100Mo targets depends on the heat capacity of the
target assembly. If it is
possible to quickly transfer large amounts of heat from the 100Mo targets,
then it should be
possible to deposit more energy into the 1"Mo targets before they melt. Water
is a desired
coolant as it facilitates large heat dissipation and is also economical.
Unfortunately, as the
electron beam passes through cooling water within the bremsstrahlung converter
component, the
energy associated with the electron beam causes the water to undergo
radiolysis. The radiolysis
of water produces, among other things, gaseous hydrogen which creates an
explosion hazard and
also hydrogen peroxide which is corrosive to molybdenum and therefore, can
greatly decrease
the potentially achievable yields of "Mo from the 1"Mo targets. The energy
associated with the
bremsstrahlung photons passing through the cooling water in the water-cooled
target assembly
component housing the 100Mo targets also causes production of hydrogen
peroxide from the
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water but much lower amounts of gaseous hydrogen.
Accordingly, another embodiment of the present disclosure is that separate
cooling water
systems are required for the water-cooled energy converter and for the water-
cooled target
assembly component to enable separate heat load dissipation from the two
components, to
maximize 99Mo production from the 1 Mo targets.
It is within the scope of the present disclosure to incorporate into a first
cooling water
system for ,the bremsstrahlung converter component an apparatus or equipment
or a device for
combining the gaseous hydrogen with oxygen to form water within the
recirculating water. It is
optional to use gaseous coolants for cooling the bremsstrahlung converter
component or
alternatively, to supplement the water cooling of the bremsstrahlung converter
component.
It is within the scope of the present disclosure to incorporate into a second
cooling water
system for the water-cooled target assembly component, one or more of buffers
for ameliorating
the corrosive effects of hydrogen peroxide on molybdenum, sacrificial metals,
and supplemental
gaseous coolant circulation. Suitable buffers are exemplified by lithium
hydroxide, ammonium
hydroxide and the like. Suitable sacrificial metals are exemplified by copper,
titanium, stainless
steel, and the like.
An exemplary high-power linac; electron beam apparatus 10 for producing 99Mo
from a
plurality of 1 Mo targets is shown in Figs. 1-5 and comprises a 35 MeV, 40kW
electron linac 20
manufactured by Mevex Corp. (Ottawa, ON, CA), a collimator station 25 to
narrow the beam of
electrons generated by the linac 20, and a target assembly station 30
comprising a target radiation
chamber 42 (Figs. 6-11), a cooling tower assembly 32, a cooling liquid supply
34, and vacuum
apparatus 36 connected to the target radiation chamber 42 by vacuum pipe 37.
The components
20, 25, 30 comprising the linac electron beam apparatus 10 are shielded with
protective shield
cladding 15 to contain and confine gamma radiation and/or neutron radiation.
The 35 MeV,
40kW electron linac 20 comprises three 1.2m S-band on-axis coupled standing-
wave sections,
three modulators plus high-duty factor klystrons having 5MW peaks, and a 60-kV
thermionic
gun. The linac 20 is mounted on a support framework 22 provided with rollers
23 to enable
disengagement of the linac 20 from the collimator station 25 for access to and
maintenance of the
converter station 25 components. The collimator station 25 comprises a water-
cooled tapered
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copper tube communicating with the first cooling water system, wherein the
tapered copper tube
is provided with a beryllium window for narrowing the electron beam generated
by the linae 20
to a diameter of about 0.075 cm to about 0.40 cm, about 0.10 cm to about 0.35
cm, about 0.15
cm to about 0.30 cm, about 0.20 to about 0.25 cm.
The target assembly station 30 comprises a support plate 39 for a support
member 38
onto which is mounted the target radiation chamber 42 with an inlet pipe 40
for sealingly
engaging the electron beam delivery pipe 28 (Figs. 6(A) and 6(B)). A cooling
tower component
32 is sealingly engaged with the target radiation chamber 42 directly above
the radiation
chamber wherein a target holder is mounted during the radiation process. A
vacuum pipe 37 and
a converter station cooling assembly 34 are sealingly mounted to the side of
the target radiation
chamber 40 (Figs. 6(A) and 6(B)). The cooling tower component 32 comprises a
coolant tube
housing 44 that is sealingly engaged at its distal end to a coolant tube cap
assembly 45 with a
plurality of nuts 45a. The coolant tube cap assembly is provided in this
example with rods 48 for
remote-controlled engagement by a crane (not shown) for lifting and separating
the cooling
tower component 32 from the target radiation chamber 42 (Figs. 7-9). A coolant
water supply
tube 100 (Figs. 16(A)-16(C) is housed within the coolant tube housing 44 and
communicates
with the second cooling water system via the water inlet ingress pipe 46 that
is sealingly engaged
with the coolant tube cap assembly 45.
The cooling water supply tube 100 (Figs. 16(A)-16(C)) comprises an upper hub
assembly
101 at its proximal end, a coolant supply tube 103, a plurality of guide fines
104 at its proximal
end, and a cooling tube body holder 105 for releasably engaging a target
holder 80. The upper
hub assembly 101 is provided with a hook 102 for remote-controlled
installation by an overhead
crane (not shown) of the cooling water supply tube 100 into and removal from a
coolant tube
housing 44. An outer shield 106 is provided about the coolant supply tube 103
to position the
coolant supply tube 103 within the coolant tube housing 44 and to provide
shielding against the
bremsstrahlung photon shower that may ingress into the coolant tube housing
44. The outer
surface of the outer shield 106 is provided with channels to allow the flow of
cooling water
therethrough. The coolant supply tube 103 is provided with an inner upper
shield 107 and an
inner lower shield 108 to provide shielding against the bremsstrahlung photon
shower that may
ingress into the coolant supply tube 103. Cooling water is delivered from the
second cooling
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AV85090CA1 10
water supply system through the water inlet ingress pipe 46 into the proximal
end of coolant
supply tube 103 through an ingress port (not shown) in the upper hub assembly
101 and is
delivered out of the distal end coolant s'apply tube 103 through cooling tube
body holder 105 and
then circulates back to the upper hub assembly 101 in the space between the
outside of coolant
supply tube 103 and the inside of coolant tube housing 44 and then egresses
the cooling water
supply tube 100 through ports 109, 110 provided in the upper hub assembly 10.
The coolant
supply tube 103 is provided with a plurality of fins 104 about its outer
diameter approximate the
cooling tube body holder 105 and function as a guide for remote-controlled
installation of the
cooling water supply tube 100 into and removal from a coolant tube housing 11,
by an overhead
crane (not shown). The coolant tube housing 44 is provided with a coolant tube
alignment
assembly 47 to enable precise alignment of the cooling water supply tube 100
within the coolant
tube housing 44. The coolant water supply delivered to and circulated through
the target
radiation chamber 42 by the cooling tower component 32 is subsequently
returned to the second
cooling water system.
The target radiation chamber 42 has an inner chamber 55 wherein is mounted a
bremsstrahlung converter station 70 adjacent to the electron beam inlet pipe
40 (Figs. 11, 13, 14).
The bremsstrahlung converter station 70 is accessible through the converter
station cooling
assembly 34 that is sealingly engaged with the side of the target radiation
chamber 42. The
converter station cooling assembly 34 comprises a cooling water pipe 50
receiving a flow of
cooling water from the first cooling water system, for circulation to, about,
and from the
bremsstrahlung converter station 70. The cooling water pipe 50 is housed
within a housing 35.
Also integrally engaged with the side of the target radiation chamber 42 and
communicating with
the inner chamber 55 is a vacuum pipe 37 interconnected with a vacuum
apparatus 36. After the
high-power linac electron beam apparatus 10 has been assembled, the integrity
of the beryllium
window and its seal in the collimator station 25 and the integrity of a
silicon window
(alternatively, a diamond window) interposed the inlet pipe 40 and the
bremsstrahlung converter
station 70 are assessed by application of a vacuum to chamber 55 by the vacuum
apparatus 36
via vacuum pipe 37.
The bremsstrahlung converter station 70 comprises a series of four thin
tantalum plates
26 (Fig. 12) placed at a 90 angle to the electron beam 21 (Fig. 12) generated
by the linac 20.
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However, it is to be noted that number and/or thickness of the tantalum plates
can be changed in
order to optimize and maximize photon production generated by the electron
beam. It is optional
to use plates comprising an alternative high-density metal exemplified by
tungsten and tungsten
alloys comprising copper or silver. Thi, tantalum plates 26, when bombarded by
the high-energy
electron beam, convert incident electrons into a bremsstrahlung photon shower
27 (Fig. 12)
which is delivered directly to a target holder 80 housing a plurality of1 Mo
target discs 85 (Figs.
13, 14). It should be noted that converter may be provided with more than four
tantalum plates,
or alternatively with less than tantalum four plates. For example, one
tantalum plate, two
tantalum plates, three tantalum plates, five tantalum plates or more.
Alternatively, the plates may
comprise tungsten or copper or cobalt or iron or nickel or palladium or
rhodium or silver or or
zinc and/or their alloys. The structure and configuration of the converter
station 70 is designed to
and to dissipate the large heat load carried by the high-energy electron beam
to minimize its
transfer to the photon shower to reduce the heat-load transferred to the 100Mo
targets during
radiation. Furthermore, the tantalum plates 26 and the target holder 80
housing a plurality of
icoMo target discs 85 are cooled during the irradiation process by constant
circulation of: (i)
coolant water through the tantalum plates 26 by the first cooling water
system, and (ii) coolant
water through the 1 Mo target discs 85 by the second cooling water system.
Another embodiment of the present disclosure pertains to target holders for
receiving and
housing therein a plurality of 1 04o target discs. An exemplary target holder
80 housing a series
of eighteen 1 Mo target discs 85 is shown in Figs. 15(A) and 15(B). The ends
of the target
holder 80 are provided with slots for engagement by the cooling tube body
holder 105 at the
distal end of the coolant water supply tube 103. It is to be noted that
suitable target holders for
irradiation of 100Mo targets with the exemplary high-power linac electron beam
apparatus 10 of
the present disclosure may house in series any number of 1 Mo target discs
from a range of
about 4 to about 30, about 8 to about 25, about 12 to about 20, about 16 to
about 18. Suitable
io Mo target discs can prepared by pressing commercial-grade 100Mo powders or
pellets into
discs and then sintering the formed discs. Alternatively, precipitated 100Mo
powders and/or
granules recovered from previously irradiated 100Mo targets may be pressed
into discs and then
sintered. It is optional, after 1 Mo powders or pellets are formed into
discs, to solidify the 1 Mo
materials by arc melting or electron beam melting or other such processes.
Sintering should be
done in an inert atmosphere at a temperature from a range of about 1200 C to
about 2000 C,
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about 1500 C to about 2000 C, about 1300 C to about 1900 C, about 1400 C
to about 1800
C, about 1400 C to about 1700 C, for a period of time from the range of 2-7
h, 2-6 Ii, 4-5 h, 2-
h in an oxygen-free atmosphere provided by an inert gas exemplified by argon.
Alternatively,
the sintering process may be done under vacuum. Suitable dimensions for the 1
Mo target discs
5 are about 8 mm to about 20 mm, about 10 mm to about 18 mm, about 12 nun
to about 15 mm,
with a density in a range of about 4.0 g/cm3 to about 12.5 g/cm3, 6.0 g/cm3 to
about 10.0 g/cm3,
about 8.2 g/cm3. The end components 81 of the target holder 80 are provided
with two or more
slots 82 for engagement by the cooling tube body holder 105 of the cooling
water supply tube
103, or alternatively, cooling water supply tube 154 (Figs. 18(A), 18(B)).
10 Fig. 9 shows a vertical cross-sectional view of an exemplary target
holder 80 housing a
series of 18 InVlo target discs securely engaged within the target radiation
chamber 42 for
irradiation with a bremsstrahlung photon flux generated by the bremsstrahlung
converter station
70. Figs. 13 and 14 are close-up views from the side and the top respectively,
of the target holder
80 secured in place by the body holder component 105 of the cooling water
supply tube 100
.. (Figs. 16(A)-16(C)) and positioned for irradiation with a bremsstrahlung
photon flux.
Figs. 17 and 18 show another exemplary embodiment of a cooling water supply
tube
assembly 153 being installed into a coolant tube housing 144. The cooling
water supply tube
assembly 153 generally comprises a cooling water tube 154 provided with a
plurality of cooling
tube guide fins 155 about its proximal end, a cooling tube body holder 156 at
its distal end (Fig.
17(A)), and a retaining ring 162 approximate its proximal end (Fig. 17(B)).
The cooling water
supply tube 154 has an outer shield 157, an inner upper shield 158 (Fig.
17(B)), and an inner
lower shield (not shown). The upper end of the coolant tube housing 144 is
provided with a
coolant tube cap assembly 141 comprising a coolant tube cap body 142
integrally engaged with
the upper end of the coolant tube housing 144 (Figs. 17 and 18). The coolant
tube cap body 142
has an integral shoulder portion 143 for seating thereon the coolant tube
retaining ring 162 (Figs.
18(A) and 18(B)). The coolant tube cap assembly 141 also comprises a flange
147 interposed the
coolant tube cap body 142 and a collar 145 integrally engaged with the top of
the coolant tube
cap body 142. The coolant tube cap collar 145 has a plurality of vertical
channels 146 provided
around its inner diameter, with each vertical channel 146 having a contiguous
horizontal side
channel 146a (Fig. 17(A)). Also provided is a coolant tube cap 151 for sealing
engaging the
13
coolant tube cap collar 145 after a cooling water supply tube assembly 153 is
installed into the
coolant tube housing 144 (Figs. 18(A), 18(B)). The coolant tube cap 151 has a
plurality of outward-
facing lugs 151a spaced around its side wall for slidingly engaging the
vertical channels 146 and
horizontal side channels 146a of the coolant tube cap collar 145. A coolant
tube cap
lifting loop 152 is secured to the top of the coolant tube cap 151 for
releasable engagement by a
crane hook 266 that is manipulated by remote-controlled operation of a
molybdenum handling
apparatus (Figs. 19(A), 19, 23).
Another exemplary embodiment of the present disclosure relates to a remote-
controlled
molybdenum handling apparatus for transferring target holders loaded with a
plurality of 1 Mo
target discs into a target assembly station for irradiation with a high flux
of high-energy
bremsstrahlung photons, recovering irradiated target holders from the target
assembly station,
transferring and sealing the irradiated target holders into a lead-shielded
cask, and then
transferring the lead-shielded cask into a conveyance apparatus for removal
from the linac
irradiation facility. The remote-controlled molybdenum handling apparatus 200
is also used for
inserting and recovering the cooling water supply tube assembly into and out
of the target
assembly station.
A suitable exemplary remote-controlled molybdenum handling apparatus 200 is
shown in
Figs. 19, 23 and generally comprises a framework 230 onto which is mounted a
"X"-carriage
assembly 240 for remote-controlled conveyance of a "Z"-carriage assembly 250
in a horizontal
plane. The Z-carriage assembly 250 moves a grapple assembly 256 (Figs. 24(A),
24(B)) in a vertical
plane. The remote-controlled molybdenum handling apparatus 200 is mounted onto
a frame
support base 202 (Fig. 20) which in turn, is secured onto the protective
shield cladding 15 (Fig. 19)
encasing the target assembly station component 30 of the exemplary system 10
shown in Fig. 1.
The framework 230 of the remote-controlled molybdenum handling apparatus 200
is
fixed to the frame support base 202 (Fig. 20) and comprises two main support
elements in the
fonn of, for example, fabricated stainless inverted tee rails 203 having a
mounting hole pattern
matching the target chamber shielding bolt holes (not shown). The tee rails
203 run parallel to the
linac and rest on top of the protective shield cladding 15, and are bolted
down into steel blocks (not
shown) underlying the protective shield cladding 15 and encasing the target
assembly
station component 30. Several cross bars 204 span the two support tee rails
203 to provide
Date recue/ date received 2022-02-17
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AV85090CA1 14
structural support. The end closest to the linac has a fabricated structural
channel 206 which
supports one end of the framework 230 and the stationary end of the shuttle
tray pneumatic
cylinder 209. Mounting plates 208 for the other end of the framework 230 are
located farther
along the support tee rails 203. A shuttle guide rail 210 is bolted to a
backing plate (not shown)
which in turn, is bolted across the support tee rails 203. The shuttle guide
rail 210 vertically
supports and horizontally guides the linear motion of the shuttle tray 212
perpendicular to the
main support tee rails 203. A long drip tray 220 is also supported on several
of the cross bars
204. The drip tray 220 serves to collect and contain any contaminated cooling
water that may
drip from the cooling tube assembly or flow chamber lid as they are being
handled (as will be
described later). The drip tray 220 is fabricated in two pieces to allow
assembly around a port
222 that provides access to the cooling tower 32 station of the target
assembly 30 (shown in Figs
4, 5). The joint and opening around the port 222 are dammed and sealed to
minimize leaks. Each
end of the drip tray 220 is equipped with a bottom drain point connected to a
capped elbow (not
shown). Temporary drain hoses may be attached to these elbows to collect
effluent from
decontamination fluids. The drip tray 220 is provided with four pins that
serve as the
demountable mounting point 219 for the tipping tower assembly (reference 270
in Fig. 25) and
with a tipping tower rest 221. As used herein, the term "demountable" means
that a component,
for example a tipping tower assembly, may be temporarily secured to a mounting
point and then
later, unsecured and removed.
The shuttle tray 212 (Fig. 21) may be, for example, in the shape of a formed
and welded
stainless steel pan about 700 mm long X 250 mm wide X 30 mm deep. The shuttle
tray 212 is
equipped with (a) four-stud mounted track rollers (not shown) for vertical
support during motion,
and (b) two track rollers (not shown) to maintain horizontal alignment during
motion. The shuttle
tray 212 securely positions and laterally transports the shield cask base 292
on vertical dowels
214, shield cask lid 295 (Fig. 23) in receptacle 216, and the coolant tube cap
151 (Figs. 18(A),
18(B)) in receptacle 281, into position underneath the remote-controlled
molybdenum handling
apparatus 200 for further remote handling. The shield cask 290 is manually set
on (and retrieved
from) the shuttle tray 212 prior to the beginning and after the end of the
remote handling
operations. The two vertical dowels 214 are used to align and stabilize the
shield cask base 292
on the shuttle tray 212. The shield cask lid 295 and coolant tube cap 151 are
both remotely
removed and installed on the shield cask base 292 or coolant tube housing 145,
respectively, by
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AV85090CA1 15
remote-controlled molybdenum handling apparatus 200 with a crane hook 266
engaged by the
grapple assembly 256 (Figs. 23, 24). The shuttle tray 212 slightly overlaps
the end of the drip
pan 208 to ensure a continuous collection path for possible drips of
contaminated water that may
occur during recovery and handling of a cooling tube assembly 153 after
irradiation of a loaded
target holder 80. The shuttle tray 212 is also equipped with a bottom drain
port 213 and capped
elbow for future drainage of decontamination fluids. The shuttle tray 212 is
moved by two 10.0"
stroke x 1.5" bore heavy duty pneumatic cylinders 209 bolted together in a
back-to-back
arrangement. Bolting two cylinders back to back to achieve three possible
positions allows for
two unique cylinder configurations to achieve the center position. The coolant
tube cap
receptacle 218 position is achieved with both cylinders extended. The shield
cask lid receptacle
216 position is achieved with either cylinder extended and the shield cask
base 214 position is
achieved with both cylinders retracted.
The remote-controlled molybdenum handling apparatus 200 is the primary remote
handling mechanism for transferring target holders 80 loaded with 100114o
target discs into and out
of the cooling tower 32 station of the .arget assembly 30 by providing all of
the beam paths for
horizontal (X) and vertical (Z) motion to the remotely handled components. The
remote-
controlled molybdenum handling apparatus 200 is equipped with a grapple
assembly 256
provided with a pneumatic clamping tip 264, a downward looking camera 225 and
twin light
emitting diode (LED) spot lights (not shown) for overhead viewing and
illumination of the work
area within and about the remote-controlled molybdenum handling apparatus 200.
The exemplary framework 230 is a four legged structure bolted to the frame
support base
202. The framework 230 may be built from extruded aluminum structural framing
components.
The framework 230 has two main beams 232 running parallel to the linac, which
are braced
together at each end to maintain accurate spacing and to provide structural
rigidity. The beams
and braces provide support to the X-drive motor and gearboxes, a cable
carrier, electrical
conduits and a junction box. In the exemplary embodiment shown in Figs. 19 and
23, the two
main beams 232 directly supporting the two X drive linear actuators are
located about 440 mm
apart. The X-carriage 240 is mounted between X-drive linear actuators 242. The
X-carriage 240
supports the motor, gearboxes and linear actuators of the Z-carriage 250 as
well as the LED spot
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fights and camera. The vertical Z-drive actuators 252 are spaced about 270 ram
apart to fit
between the X-drive actuators 242 and to provide adequate clearance between
the Z-drive
actuators 252 for remote handling operations performed on the tipping tower
assembly 270 (see
Fig. 25). The Z-carriage 250 supports the grapple assembly 256.
Suitable linear actuators for both the X-drive and the Z-drive are a ballscrew-
driven
internal profile rail-guided style. Each unit consists of a square extruded
aluminum body
equipped with an internal recirculating ball carriage with an integral ballnut
riding an internal rail
driven by a 5-mm pitch rotating ballserew. The external load carriage is
attached to the internal
guided carriage through a stainless steel cover band to protect the internal
drive components
from splash water and dust. The actuators and the gearboxes are factory
lubricated with a
proprietary radiation resistant polyphenol polyether based grease. Both the X
and Z motions are
driven (powered) on both of their linear actuators to prevent jamming of the
fabricated X and Z
carriages. The X and Z drive motors are each a radiation hardened stepper
motor equipped with a
fail-safe (spring applied, power to disengage) brake and a brushless resolver.
Resolvers are
provided for this environment as the read discs of optical encoders are prone
to browning and
premature failure in high radiation fields. Each motor output drive shaft is
connected to a tamper-
proof torque limiting safety coupling to prevent mechanical overload of the
drive components.
The X-drive torque limiter is rated at 1.131\1-in (10in-lbs) of torque and the
Z-drive torque limiter
is rated at 2.26N.m (20in-lbs) of torque. If tripped (disengaged), the torque
limiters will
automatically attempt to reengage upon every motor shaft revolution. Once the
overload is
removed and the speed is reduced they will reengage. As the torque limiters
are bidirectional and
are rated beyond the heaviest payload of the manipulator, they will not allow
a hoisted payload
to descend in an uncontrolled fashion if they disengage during hoisting. They
are not a friction
style limiter so no adjustment is ever required. Motor speed is infinitely
adjustable via the
joystick control from zero up to a maximum set speed of about 300 revolutions
per minute (rpm).
With a ballscrew pitch of about 5 min and all gear ratios at about 1:1, this
provides a maximum
linear actuator speed of about 25 mm/see. On both the X and Z drives, the
safety overload
coupling is attached to the input shaft of a dual output shaft gearbox. A
right angle gearbox is
coupled to each end of the dual output gearbox. The output shaft of each right
angle gearbox is
coupled to the input shaft of the linear actuator through a coupling. As the
dual output gearbox is
a solid shaft, one output shaft rotates clockwise with respect to the mounting
face and the other
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AV85090CA1 17
rotates counterclockwise, As a result, the linear actuator pairs consist of a
right hand threaded
ballscrew and a left hand threaded ballserew. Each pair of linear actuator
ballscrews is matched
in pitch over their travel length to about 0.04 nun which is less than the
free play in the shaft end
bearing. This match prevents the two driven screws from binding against each
other when joined
through the rigid X or Z fabricated carriage.
The total travel range for the linear actuators is about 1850 mm in the X
direction and
about 1250 mm in the Z direction. However, proximity detectors are placed near
the ends of
travel to prevent running the internal actuator carriages into their ends.
Hence, the actual travel
range is approximately 1800 mm and 1200 mm for the X and Z motions
respectively. The near X
and high Z proximity detector positions arc set as the home position of the
remote-controlled
molybdenum handling apparatus 200 for re-zeroing the resolver readouts. All
remote handling
motions are monitored by closed circuit television camera from a minimum of
two camera views
e.g., overhead and orthogonal, to ensure correct positioning, alignment and
engagement of the
remote-control operated equipment.
Spotlights may be provided, for example twin LED spotlights, to enhance
operators'
ability to perceive depth through use of shadows. To enable this, each light
is individually
controlled. The cameras are networl, enabled color cameras featuring pan, tilt
and zoom
capabilities.
The grapple assembly 256 (Fig. 24) is a miniature custom engineered lifting
device that
engages and lifts with its pneumatic clamping tip 264 either the target holder
80, or the crane
hook 266 and its payload. Engagement with either of these two components
occurs first in the
horizontal direction of motion to center the component in the grapple's
pneumatic clamping tip
264, then in the vertical direction to contact and lift the component. To
enable centering in the
horizontal direction, the grapple framework 258 is fork-shaped with two
tapered prongs leading
to a semi-circular open ring. The prongs and ring have a lip on their lower
edge. This lip engages
the underside of a flat surface provided on both lifted components. Generally,
the grapple is also
designed a category A lifter in accordance with ASME B30.20, Below-the-Hook
Lifting Devices
and ASME BTH-1, Design of Below-the-Hook Lifting Devices. The grapple assembly
should
have a safe working load rating of 100 kg (220 lbs) and have been subjected to
a proof load test
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AV85090CA1 18
of 125% of rated load per the load test tequirements of ASME B30.20.
As this exemplary embodiment does not have any vertical features on the lip of
the
grapple framework 258 to resist horizontal sliding of a lifted component, the
grapple is equipped
with a spring retract pneumatic clamping cylinder 264 that inserts a plunger
tip into a matching
recess in the top of either of the lifted components. The plunger tip enters
this recess and exerts a
force of approximately 175 N (40 lbf) to ensure the lifted component does not
slip out of the
grapple during operations. When the lock plunger is engaged, the component is
effectively
locked to the grapple. However, to avoid a trapped component on the grapple,
the spring retract
plunger will automatically retract upon removal of the air supply to it.
Inadvertent loss of air
would also retract the plunger but this does not equate to a dropped
component. It simply means
the component could slide forward out of the grapple if sufficient horizontal
forces were
developed though impact or rapid deceleration. The clamping cylinder also
provides a degree of
mechanical compliance in the horizontal direction when operating the hook
adapter. The conical
shape surrounding the flat engagement portion on the hook adapter allows it to
rock in the
forward and back direction on the grapple. Slight rocking is necessary when
traversing the arc
trajectory required for the tipping tower operation. The plunger allows this
rocking motion
without disengagement.
To assist with horizontal moth n, the grapple assembly 256 may be equipped
with three
miniature ball transfer units 257 on the bottom of the grapple body. These
ball transfer units 257
allow the grapple assembly 256 to be rolled along a surface when moved in the
horizontal
direction. Ideally, the grapple assembly 256 is lowered until the ball
transfer units 257 lightly
physically contact the appropriate mating surface for the component to be
acquired. They then
act as a positive downward stop. However, as the manipulator is not equipped
with any force
feedback, and all operations are under remote control, a degree of vertical
mechanical
compliance is built into the grapple. The upper body of the grapple assembly
256, which is
attached to the bottom of the Z-carriage 250, is bolted to the lower body of
the grapple
framework 258 through a spring-loaded sliding sleeve 254 (springs 259). This
sliding-sleeve
arrangement allows about 10 mm of over travel in the vertical downward
direction without
overloading the Z-drive and causing the safety torque limiter to inadvertently
disengage. This
also limits the force on the ball transfer units 257 to allow smooth
horizontal rolling motion. The
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AV85090CA1 19
springs 259 only allow over travel in the downward direction, they do not form
part of the lifted
load path.
Another exemplary embodiment of the present disclosure pertains to a tipping
tower is
both a piece of remote handling equipment and a piece of equipment that is
remotely handled. A
suitable exemplary tipping tower assembly 270 is shown in Figs. 25, 26, and
generally comprises
the tower weldment, a pivot guide base with a lever arm assembly, and a tower
rest assembly.
The tipping tower assembly 270 is used for supporting a cooling tube assembly
153 carrying a
target holder 80 while the cooling tube assembly 153 is pivotably lowered from
a vertical
position to a horizontal position and orientated as necessary by rotation with
the grapple
assembly 256 within the remote-controlled molybdenum handling apparatus 200.
Rotation of the
target holder 80 is necessary to orientate it (i) vertically for insertion
into and removal from the
shield cask 290, and (ii) horizontally for insertion into and removal from the
cooling tube
assembly 153 engaged with the tipping tower assembly 270 after the tipping
tower assembly 270
has been pivotably lowered into a horizontal position.
The tipping tower assembly 270 comprises a tipping tower weldment pivotably
engaged
with a pivot guide base. A suitable exemplary tipping tower weldment (best
seen in Fig. 25)
comprises a pair of elongate angle bars 274 spaced apart by an upper support
plate 272 and a
lower support plate 273. The support plates 272, 273 are structurally
strengthened in place with
support braces 275. The upper support, plate 272 and lower support plate 274
are provided with
matching tapered slots having arcuate ends for receiving and positioning
therein the cooling tube
assembly 153. The cooling tube assembly 153 is supported on the upper support
plate 272 by
placing and resting thereon the coolant tube retaining ring 162 of the cooling
tube assembly 153.
The lower support plate 273 provides the necessary second point of support to
the cooling tube
assembly 153 when it is in the horizontal orientation. The tipping tower
weldment has three
round bars passing between the two main support angles. The upper round bar
276 (also referred
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AV85090CA1 20
to as the upper round shaft) is engageable with the crane hook 266 in
cooperation with the
grapple assembly 256, for raising and lowering the tipping tower assembly 270.
The upper round
bar 276 is provided with two tapered discs positioned about the centre of the
bar 276 for guiding
the crane hook 266 into position. The bottom round bar 284 (referred to as the
bottom round
shaft) serves the pivot point for lowering the tipping tower assembly 270 into
a horizontal
position. The intermediate round bar 279 (also referred to as the intermediate
shaft) acts as a stop
when the tipping tower assembly 270 is raised to the vertical position and as
an activating
mechanism for the lever arm 286 (Fig. 26) when tipping tower assembly 270 is
lowered to the
horizontal position. The ends of the bottom round bar 284 and the intermediate
round bar 279
extend through the sides of the elongate angle bars 274.
The tipping tower assembly 270 is provided with pivot guide base that
cooperates with
the tipping tower weldment to pivotably lower the tipping tower assembly 270
into a horizontal
position and to pivotably raise the tipping tower to a vertical position. The
pivot guide base has a
bottom plate 284 to which is securely fixed a pair of matching spaced-apart
side plates 282. The
side plates 282 are provided with: (i) a sloped top edge receding downward
from a first side end
to the opposite side end, (ii) matching vertical guide slots that are parallel
to and adjacent to the
"long" side ends of the side plates 282, (iii) matching vertical guide slots
that are parallel to and
adjacent to the "short" side ends of the side plates 282, (iv) matching lower
crossbars 287 fixed
across the matching vertical guide slots adjacent to the "long" side ends of
the side plates 282 at
a selected first position above the bottom plate 284, and (v) matching upper
crossbars 288 fixed
across the matching vertical guide slots adjacent to the "long" side ends of
the side plates 282 at
a selected position above the lower crossbars 287. The ends of the bottom
round bar 284
extending outward from the elongate angle bars 274 also extend outward through
the matching
vertical guide slots adjacent to the "long" side ends of the side plates 282
between the lower
crossbars 287 and upper crossbars 288. The ends of the intermediate round bar
279 extending
through the sides of the elongate angle bars 274 also extend outward through
the matching
vertical guide slots adjacent to the "long" side ends of the side plates 282
above the upper
crossbars 288. A lever arm assembly 286 is pivotably mounted to the bottom
plate 284.
The slots on the side plates 282 trap, guide and position the ends of the
bottom round bar
284 and intermediate round bar 279 that extend outward through the sides of
the elongate angle
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AV 85090CA1 21
bars 274. In the vertical orientation, the ends of the bottom round bar 284
are trapped in the
"long" vertical guide slots between the lower crossbars 287 and the upper
crossbars 288, while
the end of the intermediate round bar 279 are trapped within the "long"
vertical guide slots above
the upper crossbars 288 thus keeping the tipping tower assembly 270 upright.
During operation
wherein a cooling tube assembly 153 is mounted into and onto the tipping tower
assembly, the
bottom plate 284 of the pivot guide base is mounted onto the four pins on the
drip tray that serve
as the mounting point 219 (see Fig. 20) for the tipping tower assembly 270.
When it is desired to
move the tipping tower assembly 270 from a vertical to horizontal position, or
vice versa, the
upper round bar 276 is engaged by a crane hook 266 attached to the grapple
assembly 256 of the
remote-controlled molybdenum handling apparatus 200. The tipping tower
assembly 270 may be
lifted until the outward-extending ends of the bottom round bar 284 abut
against the upper cross
bars 288. In this position, the outward-extending ends of the intermediate
round bar 279 will
' have moved out of the "long" vertical slots in side plates 282. As a
consequence of remote
control of the molybdenum handling apparatus 200, the tipping tower assembly
270 will be
pivotably lowered from the vertical position to a horizontal position by
remote controlled
movement of the grapple assembly 156 in a horizontal plane long the frame
support base 202
while concurrently lowering the top of the tipping tower assembly 270 so that
the outward-
extending ends of the intermediate round bar 279 slides along the sloped top
edge receding
downward from the first side end to the opposite side end of the side plates
282 thereby
pivotably lowering the top of the tipping tower assembly 270. When the outward-
extending ends
of the intermediate round bar 279 reach the end of the sloped top edge of the
side plates 282,
they arc stopped by engagement with the "short" vertical slots in side plates
282. In a fully
lowered position, the tipping tower assembly 270 is supported by engagement of
its upper
support plate 272 with the tipping tower rest 221 provided on the drip tray
(Figs. 20, 26). As the
top of the tipping tower assembly 270 is pivotably lowered, the portion of the
intermediate round
bar interposed the elongate angle bars 274 presses down on one end of the
lever arm 286 causing
the other end of the lever arm 286 to elevate. The raising end of the lever
arm 286 is provided
with a rounded extension tip (not shown) that contacts a target holder 80
engaged by the coolant
tube assembly 153, and raises it a few millimeters to enable the pneumatic
clamping tip 264 of
the grapple assembly 256 to properly engage the target holder 80 for its
removal from the coolant
tube assembly 153.
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AV85090CA1 22
Operation of the high-power linac electron beam apparatus 10 of the present
disclosure
generally comprises the following steps.
The first step is to prepare molybdenum-100 target discs for loading into the
target holder
80. The molybdenum discs may be prepared from naturally occurring molybdenum
powder
(9.6% Mo-100 isotopic abundance) or from highly enriched Mo-100 powder. The Mo-
100
powder may be finely ground or otherwise conditioned prior to dispensing and
placement into a
disc-forming die. The die is placed into a hydraulic press and the discs are
pressed. The pressed
discs are nominally about 15 mm in diameter and about 1 mm thick. Subsequent
sintering at
high temperatures in a reducing or inert atmosphere furnace causes the discs
to shrink by
approximately 4% in diameter and 3% in thickness. After pressing and
sintering, the individual
target discs are manually loaded into the target holder 80 and the loaded
target holder 80 is
manually loaded into a lead-lined shield cask 290. Handling of the Mo-100
during preparation
and pressing into discs prior to sintering, and then loading of sintered discs
into the target holder
80 is preferably done within a glove box to confine the molybdenum powder from
spreading out
and about the work environment. After removal from the glove box, the loaded
shield cask can
be lifted by a crane book engaging the handle 296 on the shield cask lid 295
(Fig. 22), and then
moved by an overhead crane (not shown) to be placed on the shuttle tray 212 by
lowering the
shield cask base 292 onto pins 214 provided therefor on the shuttle tray 212
(Figs. 19, 21). After
the shield cask lid 295 is unsealed from the shield cask base 292 by unlocking
the handles 294,
the shield cask lid 295 is moved by the crane to the shuttle tray 212 and
placed onto the
receptacle 216 provided therefore in the shuttle tray 212. Then, the coolant
cap lid 151 is
removed from the coolant tube cap assembly 141 (Figs 18 (A),18(13) that
extends upward from
the coolant tube housing 44 that communicates with the target irradiation
chamber 42 (Fig. 9), by
the grapple assembly 156 of the remote-controlled molybdenum handling
apparatus 200 and
placed onto a receptacle 218 provided therefore in the shuttle tray 212. The
top of the cooling
tube assembly 153 is engaged by the grapple assembly 156 and lifted out of the
coolant tube
housing 44 and placed into the tipping tower assembly 270 by positioning the
coolant tube
retaining ring 162 onto the upper support plate 272 of the tipping tower
assembly 270. The
tipping tower weldrnent is then moved from the vertical position into a
horizontal position as
previously described, by remote control of the grapple assembly 256. The
grapple assembly 256
is then remotely manipulated to engage slots 82 in the end of the target
holder 80 with the
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AV85090CA1 23
grapple pneumatic clamping tip 264, after which by remote control, the target
holder is removed
from the shield cask base 292 and inserted into and secured in the cooling
tube body holder 105
at the bottom end of cooling supply tube 154. The tipping tower weldment is
then moved from
the horizontal position into the vertical position by remote control with the
grapple assembly
256. The grapple assembly is 256 then used to remove the loaded cooling tube
assembly 153
from the tipping tower assembly 270 and then lower the loaded cooling tube
assembly 153 into
the cooling tube housing 44 until the target holder 80 enters the target
irradiation chamber 42.
The target holder 80 is then precisely positioned and aligned by remote-
controlled manipulation
of the coolant supply tube 103 (or the coolant tube assembly 153) for maximum
irradiation with
a photon flux produced by the bremsstrahlung converter station 70. The upper
hub assembly of
the cooling water supply tube 141 is then sealed into the coolant tube housing
44 by mounting of
the coolant tube cap 151. A first pressurized supply of coolant water is then
sealingly attached to
the coolant water supply pipe 50 for separately circulating coolant water
through the
bremsstrahlung converter station 70. A second pressurized supply of coolant
water is then
sealing attached to the water inlet pipe 46 for circulation through the target
holder 80, the 1-"Mo
target discs 85, and the radiation chamber 55 of the target radiation chamber
42. The linac 20 is
then powered up to produce an electron beam for bombarding the tantalum plates
26 homed
within the bremsstrahlung converter station 70 to produce a shower of
bremsstrahlung photons
for irradiating the target holder 80 loaded with the plurality of 1 Mo target
discs. It is suitable
when using the high-power linae electron beam apparatus 10 disclosed herein
comprising a 35
MeV, 40kW electron lime 20 for irradiating a target holder housing a plurality
of 1 IVlo target
discs, to irradiate the target holder and discs for a period of time from a
range of about 24 hrs to
about 96 hrs, about 36 hrs to 72 his, about 24 hrs, about 36 hrs, about 48
hrs, about 60 his, about
72 his, about 80 his, about 96 hrs. After providing irradiation to the 100Mo
target discs for a
selected period of time, the linae 20 is powered down, the two supplies of
coolant water are shut
off, and the target irradiation chamber 42 is drained of coolant water. The
cooling water supply is
disconnected from the water inlet pipe 46 after which the coolant tube cap 151
is disengaged
from the coolant tube cap assembly 141 by remote control of the grapple
assembly 256 of the
molybdenum handling apparatus 200 and placed onto receptacle 218 provided
therefor on the
= shuttle tray 212. The cooling tube assembly 153 is then manipulated by
remote control of the
grapple assembly 256 to securely engage the irradiated target holder 80, after
which, the cooling
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AV85090CA1 24
tube assembly 153 is removed from the coolant tube housing 44 and placed into
the tipping
tower assembly 270 by positioning the coolant tube retaining ring 162 onto the
upper support
plate 272 of the tipping tower assembly 270. The tipping tower weldment is
then moved from the
vertical position into a horizontal position as previously described, by
remote control of the
grapple assembly 256. The grapple assembly 256 is then remotely manipulated to
engage slots
82 in the end of the irradiated target holder 80 with the grapple pneumatic
clamping tip 264, after
which the irradiated target holder 80 is removed from the shield cask base 292
and inserted into
the shield cask base 292 by remote control of the grapple assembly 256. The
shield cask lid 295
is then placed onto shield cask base 292 by the grapple assembly and locked in
place by
engaging the shield cask handles 294 with the shield cask lid. The shield cask
290 can then be
moved with the overhead crane into a glove box for removal of the irradiated
target holder 80.
At this point, it is optional to transfer the target holder 80 with the
irradiated imMo target
discs into a lead-lined container for shipping to a facility for recovery of
99mTe therefrom.
Alternatively, the target holder 80 with the irradiated 100Mo target discs can
be transferred by
remote control into a hot cell wherein 99mTc may be separated and recovered
from irradiated
looMo target discs using equipment and methods known to those skilled in these
arts. Suitable
equipment for separating and recovering 99mTc is exemplified by a TECHNEGEN
isotope
separator (fECHNEGEN is a registered trademark of NorthStar Medical
Radioisotopes LLC,
Madison, WI, USA). After recovery of the 99mTe has been completed, the ImMo is
recovered,
dried, and reformed into discs for sintering using methods known to those
skilled in these arts.
The exemplary high-power linac electron beam apparatus disclosed herein for
generating
40 kW, 35 MeV electron beam that is converted into a bremsstrahlung photon
shower for
irradiating a plurality of 1 9Mo targets to produce 99Mo through a photo-
nuclear reaction on the
ImMo targets, has the capacity to produce on a 24-hr daily basis about 50
curies (Ci) to about
220 Ci, about 60 Ci to about 160 Ci, about 70 Ci to about 125 Ci, about 80Ci
to about 100 Ci of
99Mo from a plurality of irradiated 1 Mo target discs weighing in aggregate
about 12 g to about
20 g, about 14 g to about 18 g, about 15 g to about 17 g. Allowing 48 hrs for
dissolution of 99Mo
from the plurality of irradiated ImMo target discs will result in a daily
production of about 35 Ci
to about 65 Ci, about 40 Ci to about 60 Ci, about 45 Ci to about 55 Ci of 99Mo
for shipping to
nuclear pharmacies.
CA 02892495 2015-05-25
AV 85090 CA1 25
It should be noted that while the exemplary high-power linac electron beam
apparatus
disclosed herein pertains to a 35 MeV, 40kW electron linac for producing "Mo
from a plurality
of lix'Mo targets, the apparatus can be scaled-up to about 100 kW of electron-
beam power, or
alternatively, scaled-down to about 5 kW of electron-beam power.
