Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates to systems for manu~act-
uring nuclear fuel green pellets and particularly to such
systems wherein the process is automated.
In many designs of nuclear reactors, the reactor
vessel has an inlet and outlet for circulation of a coolant
in-heat transfer relationship with a core contained therein
that produces heat. The core comprises~an array or-arrays
of fuel assemblies which contain fuel elements. The fuel
element is generally a cylindrical metallic sheath sealed a'
-- both ends containing nuclear fuel. The nuclear fuel which
may be, for example, ceramic fuel pellets of a uranium com-
pound, is stacked within the metallic sheath. During reacto~
operation, the nuclear fuel pellets decompose releasing
fission products such as fission gas while generating heat
in a manner well known in the art.
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1081~36
There are many known methods for manufacturing the
nuclear fuel pellets used in nuclear reactors. Most of
these methods generally consist of cold pressing a powder
which may be an oxide of fissionable material such as
uranium dioxide to form dense compacts. These dense com-
pacts are ~enerally referred to as green pellets. The green
pellets are then sintered in a non-oxidi~ing atmosphere to
produce a sintered pellet which may have slight irregulari-
ties on its surface. The sintered pellet may then be ground
to remove those irregularities thereby forming a right
cylindrical pellet. This finished pellet is then stacked
within the metallic sheath to form the fuel element that may
be used in a nuclear reactor.
A commonly known method for producing the nuclear
fuel pellets is described in U.S. Patent No. 2,991,601 to J.
Glatter et all issued July 11, 1961. In this process,
~; hydrogen reduction of uranium trioxide is employed to
produce uranium dioxide powder. As received from commercial
manufacturers, this uranium dioxide is not free flowing and
~,-
is, therefore, not adaptable for use in automatic machinery
for the production of the green pellets. In order to produce
a free flowing powder, the uranium dioxide powder is mlxed
- with a suitable binder such as aluminum stearate and water
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~ to form a wet granulate. The wet granulate is then forced
.
-~ through a screen and dried, after which it is dry-screened
'~6~' thereby separating the larger particles from the smaller
particles. The water may be substantially removed in the
later sintering process while the aluminum stearate wiIl re-
main and act as a lubricant in the compacting process. Once
the uranium dioxide powder has thus been converted into a
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:~081436
free flowing granulate, the granulate is then compacted in~o
green pellets in a cold pressing operation. The compactin~
process comprises flowing the granulate into a die and cold
pressing the granulate in the die into substantially cylin-
drical green pellets. The green pellets may then be heat
treated, sinteræd and ground to form the finished pellet for
use in nuclear fuel elemellts.
While the patent to ~-latter and other known methods
lllustrate conlmonly understood metllods of manufacturing
10 green pellets, these methods all involve relatively small -
volume production. Because the prior art methods involved
small volume production, these processes were performed in a
. .
glove box environment. Each process was performed in a
separate glove box type enclosure and then moved under
secure conditions to the next glove box where the succeeding
step was performed. This glove box arrangement not only
required long time intervals during bag-out transfer between
glove boxes, but it also required a large amount of floor
space to accommodate the glove boxes. Furthermore, the
glove box enclosure did not provide adequate accessibility
to the~apparatus therein due to the limlted oapability of
the typical glove box arrangements. With the demand for
nuclear fuel increasing it became a commercial necessity to
be able to mass produce the green pellets. Such mass pro-
duction would entaIl larger apparatus and faster throughput
both of which were not compatible with conventional glove
box arrangements. In addition, the recent use of plutonium
dloxide in a mixed oxide pellet increased the safeguards
which must be employed to assure accountability of the plu-
tonium. The necessity of moving the plutonium from one
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glove box to the next in a large volume process would crea~
serious accountability problems that result in substantial
time delays during such transfer between glove boxes. All
of these problems together render impractical a large volul~-
production of a mixed oxide green pellet in a typical glo~e
box arrangement.
;SUMMARY OF THE INV~NTION
~ An automated system for manufacturing nuclear fue
.
green pellets for use in nuclear fuel elements of nuclear
power reactors. The system comprises process components for
manufacturing nuclear fuel green pellets arranged in verti-
cal succession with each component displaced laterally with
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- respect to the other components. The vertical arrangement
provides for gravity f~ow of the products from one component
to the next while the lateral placement allows for unob-
structed overhead access to each component so that each
- component may be vertically removed without interference ~ -
from the other components. The components are eontained
; wlthin a single enclosure that provides access to three
20~ sides of each component for maintenance and operation.
It is an ob~ect of this invention to prov~de an
automated sy~tem for manufacturing nuclear fuel green pel-
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- ; lets in which the components are arranged vertlcally so that
the products Or the process may flow from one component to
the next by the force of gravity.
It is another obJect of this inventlon to provide
an automated system for manufacturing nuclear fuel green
. .
pellets ln which the components are arranged to allow un-
obætructed vertical access to each component.
` 30 It is another ob~ect of this inventlon to provide -
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46,581
108~436
an autonlated system for manufacturing nuclear green pellets
in which the components are arranged within a single enc-
losure that allows for access to each component from at
least three sides.
It is a particular ob~ject of this invention to
provide an autolll3ted syste!n for manufacturing nuclear fuel
~r~en pellet~ in which the components are arran~ed within a
single enclosure to provide unobstructed vertical access to
each component, gravity flow between components, and access
to each component from at least three sides.
- - BRIEF DESCRIPTION_~F THE DRAWINGS
While the specification concludes wlth claims
specifically pointing out and distinctly claiming the
subject matter of the invention, it is believed the in-
vention will be better understood from the following des-
crlption taken in con~unction with the accompanying drawings,
wherein:
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Figure 1 is a partial cross-sectional view in ele-
vation of the enclosure;
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20~ Figure 2 is a plan view of Figure l;
Figure 3 1s a partial cross-sectional.view in ele-
vation of the enclosure lncluding apparatus; and
Flgure 4 is a view alon~ llne IV-IV of Figure 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the commonly known processes used to manufac-
~ .
~ .' ture nuclear fuel pellets, the individual subprocesses are
... ~ . .
performed in separate glove box enclosures. Upon completion
of-each subprocess, the material is carefully moved to the
neXt glove box enclosure. The invention described hereln
provides method and apparatus for manufacturing nuclear fuel
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~- ~081436 46,581
~ green pellets in an automated fashion capable of large
: volume production.
Referring to Figure 1, a horizontal first floor 10 .
is supported by a vertical first wall 12. First wall 12 is
supported from second floor 14 with first floor 10, first
wall 12, and a portion of second floor 14 definin~ a first
chamber 16. A second wall 18 extends from second floor 14
down to third floor 20. A first partitioll 22, second parti-
tion 24, third pqrtitiorl '6, fourth yartition 28, and fifth
10 partition 30 together with second wall l8 and second floor :`
: 14 define second chamber 32 and third chamber 34. A third .
wall 36 extends downwardly from third floor 20 and encloses
fourth chamber 38. A fourth wall 40 that is parallel to
second wall 18 and third wall 36 extends from second floor
14 to fourth floor 42. The entire structure defined above
is contained within a single bullding the inner walls of
: which along with first wall 12 and second floor 14 define a .
: . first area 44. A second area 46 is defined below fir-st area
44 by second wall l8, third floor 20, and fourth wall 40.
In:addition, a third area 48 is defined below second area 46
by~fourth wall 40 and third wall 36. A tunnel 50 which is
: used for maintenance access ls supported through second area
46 and third area 48 while a sixth partition ~2 defines a
fifth chamber 54 thereunder.
Referring now to Figùre 4? first area 44 is fur-
ther defined by a fifth wall 56 which is perpendicular to
:flrst wall 12. .Similarly, second area 46 ls bounded on two
.~ sides by sixth wall 58 and seventh wall 60 which are per-
pendicular to second wall 18. Likewise, eighth wall 62 and
ninth wall 64 further define third area 48. Flrst area 44, -.
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lQ~L436
second area 46, and thiId area 48 together with their sur-
rounding structure establish areas such that fuel processing
equipment may be vertically arranged therein. The vertical
arrangement allows for gravity flow of the material from one
subprocess to another. This arrangement also allows for
vertical access to the equipment along with side access from
behind radiatioll protective walls.
Referring now to Figures 3 and 4, a compactor feed
hopper G6 is disposed in first area 44 near flrst wall 12.
A selected mixture of plutonium dioxide (Pu02) and uranium
dioxide (U02) known as mixed oxide fuel powder is introduced
into compactor feed hopper 66 through pneumatic line 68.
Compactor feed hopper 66 which is used to store the mixed
oxide powder has level sensors (not shown) that indicate the
level of the mixed oxide powder in the hopper. A star
feeder 70 is connected between compactor feed hopper 66 and
.
roll compactor 72 so as to control the flow rate of mixed
oxide powder from compactor feed hopper 66 to roll compactor
~ 72. Roll compactor 72 is located on second floor 14 at an
P~ ~ 20 elevation lower than star feeder 70 which allows the mixed
ox1de powder to flow into roll compactor 72 under the influ-
ence of gravity. Star feeder 70 has a first drive meohanism
74 and roll compactor 72 has a second drive mechanism 76
that are both located in first chamber 16 behind first wall
12. ~he driving arm of both drive mechanisms e~tend through
sealing mechanisms in first wall 12 to their respective
machinery. Because the mixed oxide powder in the apparatus
such as compactor feed hopper 66 and roll compactor 72 may
produce radiation levels that are unacceptable for a long-
term working environment, first wall 12 is constructed by
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~01 31436
common methods so as to limit such radiation in first chamber
16. First wall 12, therefore, allows working personnel to
operate and repair the apparatus in first chamber 16 such as
drive mechanisms 74 and 76 without exposing such personnel
to excessive radiation. In addition, the location of such
equipmellt behind a shielding wall decreases repair time
because such equipl1lent is not contaltlinated. In ~ddition,
glove holes are providæd at various locations alon~ the
walls so that a~cess may be had to the equipment in the
enclosures. For example, glove holes are provided at loca-
tions referred to generally by 78. It should be noted that
the equipment is placed near the walls such as 12 and 56 so
that access may be had to the equipment when necessary. As
shown in Figure 4, a person standing on second floor 14
could reach through glove holes 78 to reach star feeder 70
. ~
or roll compactor 72. Should this apparatus malfunction,
mlnor repalrs could be made in this manner or the non-
unct1aning equipment could be disconnected by hand and then
removed by mechanical apparatus such as a crane 80.
ZO~ Roll~compactor 72 comprises two opposing drums
that~rolls the powde~r into ribbon-like strips of various
leneths. These ribbon-like strlps fall by gravity into a
granulator 82 that granulates the strips into fine particles.
Granulator 82 is disposed in second area 46 and below roll
compactor 72 so that gravity may be employed to move the
ribbon-like strips. However, granulator 82 is not located
directIy under roll compactor 72, rather it is located
laterally from roll compactor 72 as shown in Figure 3.
Granulator 82 is not located directly below roll compactor
72 80 that should it need to be replaced it could be dis-
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46,581
1081436
connected by iland throu~h ~,love holes 78 and then be lifted
upwardly onto first floor 10 without having to remove roll
compactor 72. This arrangement provides for an automated
gravity flow without havlng the various components interfere
with each other during insertion or removal of a particular
component. As with roll compactor 72, granulator 82 has a
granulator drive mechanism 84 located in second chamber 32
behind second wall 18.
A cl~ssifier 86 is located below granulator 82 in
second area 46. Classifier 86 consists of three chambers
arranged vertically within a single housing with two vibrat-
ing screens separating the three chambers. Granules from
granulator 82 flow by gravity into the first chamber and
onto the first screen of classifier 86. Oversized granules
are caught on the first vibrating screen and carrled off by
the vibrating actlon into a scrap transfer can 88. The
remaining granules fall through the first screen onto the
second vibrating screen. The proper size granules are
~ ~ carried by the second vibrating screen to a bulk density
`~ 20 check station 89 that monitors the density of the granules. -
~- Granules having the proper density are permitted to flow to
rolling drum 90. The smaller granules fall through both the
first and second screens into the bottom of the classifer 86
-~ from where they are pneumatically transferred through re-
~ cycle line 92 back into compactor feed hopper 66.
-~ Rolling drum 90 is located on third floor 20 and
disposed laterally from classifier 86 so that the proper
size granules may flow from the second vibrating screen to
rolling drum 90 under the influence of gravity while being
able to be lifted vertically by crane 80 without interfering
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~081436 46,5~1
onents. As is well underst~od in the art, the granules that
are formed as previously described do not readily compact.
In order to promote compaction of the granules into pellets
a lubricant is added. A typical lubricant so used is
aluminum stearate. A stearate feed hopper 94 is disposed on
fifth wall 56 with a stearate line 96 attached to the under-
side thereof. Stearate line 96 is also attached to the top
portion of ste~late feeder 98 so that the stearate may flow
from stearate feed hoppeI 94 through stearate line 96 into
- 10 stearate feeder 98 under the force of gravity. Stearate
feeder 98 serves to accumulate stearate therein to insure a
constant flow to rolling drwn 90. Rolling drum 90 is a drum
which mechanically rotates about its longitudinal axis to
, ~ . .
thereby mix the granules with the stearate. As with the
other components in the system, the stearate feeder 98 is
lntended to be located near the enclosing walls such as
sevénth wall 60 so that maintenance and operational access
may be had through glove holes 78. Furthermore, stearate
feeder 98 is located so that gravity flow may be utilized
20~ while crane 80 may be employed to manipuIate the component.
; From rolling drum gO, the mixture of stearate and
granules flows by gravity into pellet press feed hopper 100.
,: ~
Pellet press feed hopper 100 is disposed below rolling drum
90 to facilitate gravity flow but not directly thereunder so
as to facilitate removal by crane 80. From pellet press
feed hopper 100, the mixture flows through dual powder lines
102 into pellet press 104. Pellet press 104 consists of an
,
upper punch 106, lower punch 108, and die 110 as is commonly
known in the art. Pellet press 104 is disposed in third
area 48 so that gravity may be utilized to flow the mixture
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1081436 463581
from pellet press feed hopper 100 to pellet press 104.
Upper punch 106 is mounted in tunnel 50 and ex-
tends downwardly through a sealing mechanism into third area
48. Similarly, lower punch 108 is mounted in sixth chamber
54 and extends upwardly into opposition with upper punch
106. The arr~n~,elnent of u~per pullch 106 in tunnel 50 and
lower punch 10~ in sixth chamber 54 provides for an auto-
mated operation while allowing access to the machinery from
an enclosure to avoid exposure to radlation. For example,
repairs may be made to upper punch 106 from within tunnel 50
without exposing the personnel to radiation. Furthermore,
since tunnel 50 extends through second area 46 and third
area 48, personnel in tunnel 50 nlay access other equipment
through glove holes 78,
When one of the dual powder lines 102 is altern-
ately placed over die 110, a predetermined amount of the
mixture in pellet press feed hopper 100 is allowed to flow
into dle 110. Upper punch 106 and lower punch 108 are then
advanced into opposite ends of die 110 which compresses the
mlxture into nuclear fuel pellets conforming to the shape of
dle 110. Such pellets are referred to as green pellets.
The punches are then withdrawn and pellet loader 112 or dual
powder lines 102 pushes the green pellet onto conveyor 114
which moves the green pellet to the next operation which may
~ ~ be a sintering operatlon.
-`~ As can be seen from the foregoing descriptlon,
first area 44, second area 46 and third area 48 define a
restricted access area that is exposed to radiation and
other contaminants. Because of the nature of the radiation
and contamination due primarily to plutonium in the re-
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1081436 4~,581
stricted access area, it is recommended that personnel
not be present therein for extended lengths of time. It is,
therefore, recommended that the working personnel remain
behind radiation protection such as first wall 12, second
wall 18, ~ilird wall 36, and fourth wall 40. The areas
- behind such protective walls including but not limited to
first chamber 1~, second chamber 32 and third chamber 34
define a limited access area wherein working personnel may
be present for controlled periods of time. As described
above, parts of the equipment extend through the protective
walls into the limited access area so that personnel may
have access to them without being unnecessarily exposed to
radiation. The gloves holes 70 provide access from the
limited access area to the restricted access area while a
higher pressure is maintained in the limited access area so
that the flow of air and particles will be into the re-
strlcted access area thereby preventing outward flow. The
equipment in the restricted access area is, therefore,
arranged close to at least one of three protective walls so
as to increase this access. In addition, to this three-
sided accessibility the equipment is arranged vertically but
not directly under each other so that removal and replace-
ment of the equipment may be facilitated by means such as
crane 80 without interfering with the remaining equipment.
Moreover, the vertical arrangement provides for gravity flow
.~
of the products while minimizing the required floor space.
The gravity flow feature is particularly important because
it provides for rapid product throughput with minimal hold-
up periods and allows for efficient material clean-out, more
commonly known as run-out. Efficient material run-out
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108~436 46,581
assures that no material remains in the components
after each batch is completed. The importance of this liesin the fact that strict accountability of the plutonium is
necessitated by governmental and industry standards and that
a previous batch will not contaminate a subsequent batch
wlth a diffeIetlt materi~l composition. The invention,
therefore, provides an autolllated system for manufacturing
nuclear fuel gleen pellets withill ~ sin~le enclosure to
provide unobstructed vertical access to each cQmponent,
~r~vity flow between components, and access to each compo-
nent from at least three sides. `
While there is described what is now considered to
be the preferred embodiment of the invention, it is, of
course, understood that various other modifications and
varlations will occur to those skilled in the art. The
clalms, therefore are intended to include all such modi-
~; fications and variations which fall within the true spirit
and scope of the present invention.
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