Nuclear fuel pellet turning apparatus and method

A pellet turning apparatus for facilitating surface inspection of nuclear fuel pellets includes a pellet turner assembly and a pellet supply tray interface assembly. The pellet turner assembly includes a pellet turner deck and a swivel mechanism supporting the deck. The pellet turner deck is composed of a base frame mounted on the swivel mechanism, a plurality of elongated laterally-spaced pellet channel-defining members extending between and mounted at the opposite ends of the frame, a pellet rolling plate supported on the frame below the pellet channel-defining members, and an actuating mechanism coupled to the pellet rolling plate for moving the plate in oscillatory direction substantially perpendicular to the pellet channels for producing in situ turning of the pellets. The interface assembly is mounted to a pellet loading end of the pellet turner deck. The interface assembly is operable for disposing a pellet transfer end of a pellet supply tray at a desired elevation relative to the pellet loading end of the pellet turner deck. The interface assembly includes a tray elevating mechanism having engaging elements for coupling to the transfer end of the pellet supply tray, and an actuating cam mechanism coupled for moving the elevating mechanism to raise or lower the engaging elements and thereby raise or lower the transfer end of the supply tray respectively above or below the loading end of the pellet turner deck.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to nuclear fuel pellet inspection 
and, more particularly, is concerned with a nuclear fuel pellet turning 
apparatus and method for facilitating surface inspection of pellets. 
2. Description of the Prior Art 
In a typical nuclear reactor, the reactor core includes a large number of 
elongated fuel assemblies. Conventional designs of these fuel assemblies 
include top and bottom nozzles with a plurality of elongated transversely 
spaced guide thimbles extending longitudinally between and connected at 
opposite ends to the nozzles and a plurality of transverse support grids 
axially spaced along the guide thimbles. Also, each fuel assembly is 
composed of a multiplicity of elongated fuel elements or rods transversely 
spaced apart from one another and from the guide thimbles and supported by 
the transverse grids between the top and bottom nozzles. 
The fuel rods each contain fissile material in the form of a plurality of 
generally cylindrical nuclear fuel pellets maintained in a row or stack 
thereof in the rod. The fuel rods are grouped together in an array which 
is organized so as to provide a neutron flux in the core sufficient to 
support a high rate of nuclear fission and thus the release of a large 
amount of energy in the form of heat. A liquid, coolant is pumped upwardly 
through the core in order to extract some of the heat generated in the 
core for the production of useful work. 
During the manufacture of the fuel rods for the fuel assemblies, visual 
inspection of the nuclear fuel pellets is a key operation for the 
production of quality fuel assemblies. The entire cylindrical surface of 
the pellet is checked for dimensional quality, cracks and other defects, 
including chipped edges. The practice heretofore for inspecting pellet 
surfaces has been to provide side-by-side rows of aligned pellets on a 
first pellet support tray. After an operator visually inspects the exposed 
portions of the external cylindrical surfaces of the pellets, a second 
empty pellet support tray is placed upside down over the pellets loaded on 
the first support tray. With the two trays held together, they are 
manually inverted so as to transfer the pellets en masse from the first 
support tray to the second support tray. The operator again visually 
inspects the newly-exposed portions of the external cylindrical surfaces 
of the pellets to complete the inspection of the pellets. 
This conventional practice has several drawbacks. First, the weight of the 
pellets and the two trays is oftentimes excessive and unacceptable from 
the standpoint of the capabilities of the typical operators. Second, the 
trays are often warped slightly, which could permit pellets to fall out 
during the turn-over or inverting action. Third, and more importantly, the 
portion of the cylindrical surface of the pellet than occurs at the 
horizontal midplane of the pellet cannot be effectively inspected due to 
the geometry of the pellet array and the overhead position of the light 
source. This questionable region amounts to approximately ten percent of 
the cylindrical surface of the pellet. 
Consequently, a need exists for improvement of the manner in which nuclear 
fuel pellet surface, inspection is carried out so as to eliminate the 
problems associated with the prior art method and still further improve 
the quality of fuel fuel pellet inspection. 
SUMMARY OF THE INVENTION 
The present invention provides a pellet turning apparatus and method 
designed to satisfy the aforementioned needs. The pellet turning apparatus 
and method of the present invention improves the quality of inspection by 
reducing the amount of effort required by the operator and by enabling the 
ability of the operator to see the entire surface of the pellet. The 
requirement to place an empty tray over the loaded tray and to invert the 
two trays and pellets is eliminated, relieving the operator of a difficult 
and heavy task. A substantially less cumbersome and time-consuming way is 
introduced for transferring the pellets to and from the inspection tray. 
Also, rolling or turning the pellets in situ, or while remaining in their 
original place, is introduced, permitting total circumferential sighting 
and inspection of the external surfaces of the pellets. 
Accordingly, the present invention is directed to a pellet turning 
apparatus for facilitating surface inspection of nuclear fuel pellets. The 
pellet turning apparatus includes: (a) a pellet turner assembly; and (b) a 
pellet supply tray interface assembly. The pellet turner assembly includes 
a pellet turner deck and a swivel mechanism for supporting the deck on a 
stand. The pellet turning apparatus also includes a pellet rake for use by 
an operator in loading and unloading pellets onto and from the pellet 
turner deck. 
More particularly, the pellet turner deck is composed of a frame mounted on 
the swivel mechanism, a plurality of elongated laterally-spaced pellet 
channel-defining members extending between opposite ends of the frame, and 
means for supporting the pellet channel-defining members at their opposite 
ends in spaced relation above the base frame. The pellet turner deck also 
includes a pellet rolling plate supported on the frame below the pellet 
channel-defining members for supporting pellets in rows between the 
channel-defining members and an actuating mechanism coupled to the pellet 
rolling plate. The actuating mechanism is operable to cause oscillatory 
movement of the plate relative to the channel-defining members for 
producing in situ simultaneous turning of the pellets within the channels 
to permit visual inspection of the entire circumferential surfaces of the 
pellets. Also, the swivel mechanism supporting the pellet turner deck, in 
turn, is operable for swiveling and tilting the pellet turner deck to 
thereby permit an operator to easily visually inspect the opposite edges 
of the pellets for the presence of cracks and chips. 
Further, the pellet supply tray interface assembly is mounted at a pellet 
loading end of the pellet turner deck. The interface assembly is operable 
for disposing a pellet transfer end of the pellet supply tray at a desired 
elevation relative to the pellet loading end of the pellet turner deck. 
The interface assembly includes a tray elevating mechanism mounted to the 
pellet loading end of the pellet turner deck. The tray elevating mechanism 
has at least one and preferably a plurality of engaging elements for 
coupling with the pellet transfer end of the pellet supply tray. An 
actuating cam mechanism is coupled to the tray elevating mechanism for 
moving the elevating mechanism to raise or lower the engaging elements of 
the elevating mechanism and thereby raise or lower the pellet transfer end 
of the supply tray respectively above or below the pellet loading end of 
the pellet turner deck. 
The present invention is also directed to a pellet turning method for 
facilitating surface inspection of nuclear fuel pellets. The pellet 
turning method includes the steps of: (a) supporting a plurality of 
nuclear fuel pellets in rows in laterally-spaced channels extending 
between opposite ends of a pellet turner deck; and (b) producing 
simultaneous turning of the pellets in situ within the channels to permit 
visual inspection of the entire circumferential surfaces of the pellets. 
The method also includes the steps of producing simultaneous tilting of 
the pellet deck to permit visual inspection of the opposite edges of the 
pellets for the presence of cracks and chips, and raking pellets along the 
channels for loading and unloading the pellets to and from the pellet 
turning deck. 
More particularly, the turning of the pellets is produced by moving in 
oscillatory fashion and in a direction extending in transverse relation to 
the channels a flat plate located below the channels and supporting the 
pellets in rows within the channels. For facilitating transfer of pellets 
between the supply tray and the pellet turner deck, a pellet transfer end 
of a pellet supply tray is either raised or lowered to a desired elevation 
above or below a pellet loading end of the pellet turner deck. 
These and other features and advantages of the present invention will 
become apparent to those skilled in the art upon a reading of the 
following detailed description when taken in conjunction with the drawings 
wherein there is shown and described an illustrative embodiment of the 
invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description, like reference characters designate like or 
corresponding parts throughout the several views of the drawings. Also in 
the following description, it is to be understood that such terms as 
"forward", "rearward", "left", "right", "upwardly", "downwardly", and the 
like, are words of convenience and are not to be construed as limiting 
terms. 
Referring now to the drawings, and particularly to FIGS. 1 and 2, there is 
illustrated a nuclear fuel pellet turning apparatus of the present 
invention, being generally designated 10. The pellet turning apparatus 10 
is used by an operator for handling a plurality of nuclear fuel pellets P 
at a time and facilitating surface inspection of the pellets P (FIGS. 18 
and 23). The pellet turning apparatus 10 is disposed upon a work table 12 
and under an exhaust hood 14 contained in an enclosed isolation chamber. A 
pair of spaced upright brackets 16, 18 are mounted on the work table 12 
adjacent the pellet turning apparatus 10 for receiving and supporting a 
pellet supply tray 20 next to the pellet turning apparatus 10. 
In its basic components, the pellet turning apparatus 10 includes a pellet 
turner assembly 22 cable of supporting the pellets P and an interface 
assembly 24 coupled to the pellet turner assembly 22. The pellet turner 
assembly 22 can be operated to accomplish two functions. First, the pellet 
turner assembly 22 is operable for producing simultaneous turning of the 
pellets P in situ (i.e., rolling in place) to permit visual inspection of 
the entire circumferential surfaces of the pellets. Second, the pellet 
turner assembly 22 is also operable for producing simultaneous tilting of 
the pellets P to permit visual inspection of the opposite edges of the 
pellets. The interface assembly 24 is coupled to a pellet loading end 22A 
of the pellet turner assembly 22 and is operable for disposing a pellet 
transfer end 20A of the pellet supply tray 20 at a desired elevation above 
or below the loading end 22A of the pellet turner assembly 22 to 
facilitate transfer of uninspected pellets from the pellet supply tray 20 
to the pellet turner assembly 22 and of inspected pellets from the pellet 
turner assembly 22 to the pellet supply tray 20. 
Referring to FIGS. 3-17, there is illustrated the pellet turner assembly 22 
which includes a pellet turner deck 26 and a swivel mechanism 28. The 
pellet turner deck 26 supports pellets P in side-by-side spaced rows. The 
swivel mechanism 28 supports the pellet turner deck 26 and, in turn, is 
operable for swiveling and tilting the pellet turner deck 26 to allow 
simultaneous tilting of the pellets P and thereby permit an operator to 
easily visually inspect the opposite edges of the pellets for the presence 
of cracks and chips. 
More particularly, referring to FIGS. 3-13, the pellet turner deck 26 
includes a base frame 30 mounted on the swivel mechanism 28, a plurality 
of elongated laterally-spaced rod-like members 32 extending between 
opposite ends of the base frame 30 and defining channels 34 between the 
members for receiving and arranging the pellets P in rows. The width of 
the channels 34 is greater than the diameter of the pellets P, as can be 
seen in FIG. 18, such that the pellets P are not supported upon the 
rod-like members 32. Also, means are provided on the base frame 30 for 
supporting the elongated rod-like members 32 at their opposite ends in 
spaced relation above the base frame 30. Such means takes the 
configuration of a support bar 36 attached on the right end and a base bar 
38 attached on the left end of a network 40 of interconnecting frame 
members and a flat plate 42 which also make up the base frame 30. The flat 
plate 42 rigidly mounts the network 40 and, in turn, is attached on the 
upper end of the swivel mechanism 28. The swivel mechanism 28 is setup to 
normally support the deck 26 slightly off horizontal, for example, 
preferably at a five degrees incline perpendicular to the rod-like members 
32. 
As best seen in FIGS. 8-13, the right ends 32A of the rod-like members 32 
are bent ninety degrees and extend within vertical grooves 44 defined in 
laterally-spaced relation on the exterior of the support bar 36. The left 
ends 32B of the rod-like members 32 are received through holes 46 in the 
base bar 38 and biased by fasteners 48 and spring washers 50 to retain the 
right ends 32A in the grooves 44. 
As shown more specifically in FIGS. 3, 4 and 13-15, the pellet turner deck 
26 also includes a pellet rolling plate 52 and an actuating mechanism 54 
coupled to the plate 52. The pellet rolling plate 52 has a flat 
configuration and is movably supported on opposite ledges 56, 58 defined 
on the interior sides of the support and base bars 36, 38 of the base 
frame 30 below the pellet channel-defining rod-like members 32. In such 
position underlying the rod-like members 32, the rolling plate 52 supports 
the pellets P (FIG. 18) between the pellet channel-defining members 32. 
The slightly inclined mounting of the deck 26 ensures that all the pellets 
P are disposed against the rod-like members 32 on the same side of the 
channels 34. Such relationship enhances the visual inspection carried out 
by the operator. 
The actuating mechanism 54 is mounted on the base frame 30 and coupled to 
the pellet rolling plate 52 The actuating mechanism 54 is operable to 
produce oscillatory movement of the plate 52 in a direction generally 
perpendicular to the channel-defining members 32 for producing rolling or 
turning of the pellets P in situ on the plate and the channel-defining 
rod-like members 32. More, particularly, as best seen in FIGS. 16 and 17. 
The actuating mechanism 54 includes a handle 60 attached on a circular 
disc 62 rotatably mounted in an opening 64A of a bracket plate 64 which is 
fixed on and extends outwardly from the base frame 30. The actuating 
mechanism 54 also includes a cam element 66 secured in the circular disc 
62 and extending upwardly through a slot 68 formed in a tab 70 which is 
fixed on and extends outwardly from the pellet rolling plate 52 above the 
bracket plate 64. 
As seen in FIG. 16, when the handle 60 is rotated clockwise from its solid 
line position to dashed line position, the pellet rolling plate 52 is 
moved linearly from the inwardly-displaced solid line position to 
outwardly-displaced dashed line position. Rotation of the handle 60 
counterclockwise produced movement of the plate 52 in the opposite 
direction. The total movement of the pellets P is preferably at least 
approximately on full revolution of the pellet circumference. 
Referring to FIGS. 1 and 18, there is illustrated the swivel mechanism 28 
having a universal ball joint 72 and a handle 74 movable between locking 
and unlocking positions. As mentioned above, the swivel mechanism 28 
supports the pellet turner deck 26 and, in turn, once the handle 74 has 
been moved to the unlocking position of FIG. 18 is operable for swiveling 
and tilting the pellet turner deck 26 to simultaneously place the pellets 
in a tilted or inclined position. When the deck 26 and pellets P have been 
placed in the desired tilted position, the handle 74 is moved back to the 
locked position shown in FIG. 1. The above-described actuating mechanism 
54 can be operated to oscillate the plate 52 to cause rolling or turning 
of the tilted pellets in situ. This permits an operator to easily visually 
inspect the entire perimeters of the end edges of the pellets for the 
presence of cracks and chips. After one end of the pellets are inspected, 
the swivel mechanism 28 is operated to rotate the pellet turner deck 26 
through 180.degree. and reverse the tilting of the deck 26 to inspect the 
opposite end edges of the pellets. 
Referring now to FIGS. 19-25, there is illustrated the interface assembly 
24 mounted on the right loading end 22A of the pellet turner deck 26 of 
the pellet turner assembly 22. The interface assembly 24 basically 
includes a tray elevating mechanism 76 and an actuating cam mechanism 78 
operable to cause raising and lowering of the elevating mechanism 76. The 
tray elevating mechanism includes a plurality of engaging elements 80 
mounted for reciprocal vertical movement on the exterior side of the 
support bar 36. Each engaging element 80 includes a plate 82 having a pair 
of vertical slots 84 which receive studs 86 extending from the support bar 
36 to mount the plate 82 for vertical reciprocal movement. Each engaging 
element 80 further has an upstanding pin 88 insertable into a hole 90 
(FIGS. 2 and 23) in the transfer end 20A of the pellet supply tray 20. 
The actuating cam mechanism 78 includes a handle 92 and a plurality of 
links 94 extending from the handle 92 and between and coupled with the 
engaging elements 80 of the tray elevating mechanism 76 via cam pins 96 on 
the links 94 extending through inclined slots 98 in the plates 82. The 
handle 92 is attached to a plate 100 which, in turn, is pivotally mounted 
to the base frame 30 by a stud 102. The pivotal movement of the plate 100 
produced by pivotal movement of the handle 92 is transmitted and converted 
to linear movement of the interconnected links 94 via a cam pin 104 which 
is attached to the leftmost one of the links 94 and extends through an 
arcuate slot 106 formed through the plate 100. The offset of the radius of 
the arcuate slot 106 from the pivot point of the plate 100 produces linear 
movement of the links 94 upon rotation of the plate 100 and handle 92. 
In such manner, the actuating cam mechanism 78 is coupled to the tray 
elevating mechanism 76 and operable for moving the elevating mechanism to 
position the pellet transfer end of the supply tray either above or below 
the loading end 22A of the pellet turner assembly 22 depending upon the 
direction of rotation of the handle 92. Positioning of the pellet transfer 
end 20 A of the pellet supply tray 20 above or below the loading end 22A 
of the pellet turner assembly 22 correspondingly facilitates transferring 
of pellets to or from the pellet turner assembly 22. 
Referring to FIGS. 26-28, there is illustrated a pellet rake 108 which can 
be employed by an operator with the pellet turning apparatus 10 to 
slidably move pellets onto and from the deck 26. The rack 108 has a handle 
110 at one end, a row of teeth 112 spaced apart by a distance adapting 
them to fit within the channels 34 of the deck 26, and interconnected by a 
flat connecting portion 114. The teeth 112 extend at a right angle to the 
flat portion 114. 
Referring to FIGS. 29 to 34, there are diagrammatic views of the operations 
involved in using the pellet turning apparatus 10 of the present invention 
for inspecting the entire cylindrical surfaces of the pellets (P) for 
dimensional quality, longitudinal cracks and chipped edges. FIG. 29 shows 
a pellet supply tray 20 disposed adjacent the pellet turner deck 26 of the 
turner assembly 22. The deck 26 is locked in stationary position and the 
transfer end 20A of the tray 20 is coupled to the interface assembly 24 
(FIG. 19). The interface assembly 24 is operated to elevate the transfer 
end 20A of the tray 20 slightly above the loading end 22A of the deck 26. 
The two rectangles with diagonal lines represent multiple adjacent rows of 
pellets supported on the supply tray 20. Using the rake 108 (FIG. 26), an 
operator sweeps a first group of pellets from the supply tray onto the 
deck 26 to the position shown in FIG. 30 and then sweeps a second group of 
pellets onto the deck 26 to the position shown in FIG. 31. In order to 
provide clearance for swiveling and tilting the deck 26, as seen in FIG. 
32 the emptied tray 20 is shifted to a position away from the deck 26. 
Next, as represented by FIG. 33, visual inspection commences with the 
operator moving the plate 52 (FIG. 15) to turn the pellets a full 
revolution for cylindrical surface inspection. The turning is accomplished 
by the operator manually swinging the handle 60 of the actuating mechanism 
54 (FIG. 16) coupled to the plate 52 through 180.degree.. Then, edge chip 
visual is performed by the operator utilizing the swivel mechanism 28 to 
tilt the deck 26 and by again manually swinging the handle 60 to oscillate 
the plate 52 and turn the pellets. Makeup pellets are inserted by the 
operator to replace rejected pellets removed by the operator. Finally, the 
deck 26 is repositioned to its original orientation and the supply tray 20 
is returned to the interfaced relationship with the deck as shown in FIG. 
34. However, this time the interface assembly 24 is operated to lower the 
transfer end 20A of the supply tray 20 slightly below the load end 22A of 
the deck to facilitate transfer of the inspected pellets from the deck 26 
to the supply tray 20. The rake 108 is again used by the operator to sweep 
the groups of inspected pellets from the deck 26 back onto the supply tray 
20. 
It is thought that the present invention and many of its attendant 
advantages will be understood from the foregoing description and it will 
be apparent that various changes may be made in the form, construction and 
arrangement thereof without departing from the spirit and scope of the 
invention or sacrificing all of its material advantages, the form 
hereinbefore described being merely a preferred or exemplary embodiment 
thereof.