CA1057704A - Photoelectric sorting of chipped nuclear fuel pellets - Google Patents

Abstract

AUTOMATIC INSPECTION AND SORTING SYSTEM
FOR CHIPPED NUCLEAR FUEL PELLETS

ABSTRACT OF THE DISCLOSURE
Nuclear fuel pellets to be inspected for surface flaws, such as chips, are fed onto spaced rotating shafts or rollers which rotate each pellet at a predetermined speed.
A motor driven chain mounted for linear movement beneath the rollers carries outwardly extending arms which contact the ends of pellets on the rollers to advance them axially along the roller length and beneath a distance indicating optical probe. As each advancing rotating pellet moves under and is optically scanned by the probe, light reflected from inden-tations or flaws, such as chips, in the pellet surface, is converted to signals which correspond to the flawed area and feeds them to a flow-time integrating circuit. This circuit integrates the sum of surface flaw-time and compares the integrated signal to a standard reference. Should this exceed the standard, the circuit energizes a solenoid which effects removal of the defective pellet from the system.
The integrating circuit is controlled by a photocell which makes the circuit operative only during the time a pellet is advancing linearly under the probe.

Description

BACKGROUND O~ THE INVENTION
. . . _ The inventlcn described hereln r~lates to metrologJ
equipment and more partlcularly to an appar~tus and method for automatically measurlng flaws in the s~rface area of nuclear fuel pellets, and subsequently re~e^ting those fuel pellets which do not reach acceptable stanc~rds.
Thermal power generated in a nuclGar reactor is derived from uranium enriched fuel pellets having dimensions ~. .

of about .600" lg. x .365" dia., of uniform size placed in long cylindrical fuel tubes located in the reactor pressure vessel. During manufacture, these pellets undergo presslng and sintering operations to provide a pellet body of fragile ceramic material. Each pellet is then ground to a precise diameter ~ust slightly less than the fuel tube inner diame- -ter to facilitate pellet loading into fuel tubes and to effect maximum heat transfer between the pellets and fuel tube walls. During the course of carrying out the manu-facturing process, the pellets acquire surface flaws in the form of pits and fissures. Further, since high quantity production is necessary for ecomonical operations, the pellets are moved rapidly through the system, including the grinding operation, and as a result, inter-pellet contacting and pellet abrading forces cause additional flaws in the form of chips in the pellet cylindrical surface. If the total amount of ceramic material removed from each pellet as a result of flaws and chips exceeds a predetermined value, for a large number of pellets, reactor performance will be adversely affected because distortions will appear in the generated power, or the reactor power output may not reach its maximum level.
To help assure selection of pellets meeting design criteria, known practices involve manual inspectlon of the pellets after completion of the grinding operation and immediately prior to charging the pellets into fuel tubes.
The inspection process includes visually inspecting pellets in parallel rows and comparing them with a standard pellet to determlne whether the lost surface area exceeds a pre-determined amount. Since optimum reactor performance is 1~57709~

dependent on utilization of pellets having the proper weightand configuration, inspectors are overly conservative and often re~ect pellets which otherwise are completely accept-able for reactor use. Thls practice obviously leads to high production costs since the re~ected pellets must be reduced to powder form before being recycled through the pellet manufacturing operatlon.
Although manual lnspection of pellets customarily takes place ln the lndustry, prlor attempts have been made to achieve a fully automatic pellet measurlng and sorting system. Mechanlcal, alr, laser and other electronic systems have been suggested for detecting the existence of surface flaws in fuel pellets which exceed certain predetermined tolerances. The air gauging system locates a number of air nozzles relative to a pellet and utllizes alr back pressure techniques to detect the exlstence of flaws in the fuel pellet surface while elther ln a stationary or moving posi-tion. The disadvantage of this type system is that response is extremely slow compared to the number of pellets required to be examined wlthln certaln tlme perlods. Also, the multi-nozzle approach requlres that flow of pellets be divided among several senslng stations thus requiring pre-cise control over air pressures and the mechanically oper-ating parts in the system.
Mechanical gauglng or surface profiling equipment such as dial indicators, profllometers, and electronic gauges using linear varlable differential transformers or similar components all requlre mechanical contact with the fuel pellets whlch leads to tedious measurements and low quantity production because each fuel pellet must be physl-iO57704 cally contacted by the measuring apparatus. Further, multi-statlon requirements exist for this kind of equipment to accomplish reasonable production which leads to design complexity and questionable reliability.
Laser and other electronic systems utilize single laser beam equipment to detect pellet surface flaws by sensing light reflected from the pellet surface from two different directions to provide analog output signals and conversion circuitry to permit direct reading o~ flaw magni-tudes. The disadvantages are that response time and sensi-tivity is marginal because of relatively low frequencies used and because the light spot size may vary substantially from the size of chipped area or diameter of hole in the fuel pellet being measured. In some instances the equipment is not sufficiently sensitive to accurately discriminate between light reflected from pellet flaws and from pellet dark spots because of reflectivity characteristics of the pellet surface.
BRIEF SUMMARY OF THE INVENTION
Briefly stated, the above disadvantages of the prior art are overcome by providing a mechanical system which feeds fuel pellets to be inspected into apparatus which rotates each pellet while simultaneously advancing it through a zone where it ls scanned for defects by optical equipment. As light from the probe reflects from depres-sions or ~laws on the pellet surface as the pellet is advanced linearly, signals corresponding to the lncreased dlstance from the pellet surface, and therefore varying in magnitude, are measured electronlcally to determine whether flaws of ~ignificant depth are detected and the time periods 105';'704 of detection are stored in a flaw detecting and integrating circuit. As the pellet advances beyond the scanning probe, the integrated signals are compared to a standard reference and if in excess thereof, a pellet re~ection circuit is energized whlch acts to mechanically sort the defective pellet from the system. A time delay is incorporated in the re~ection circuit which corresponds to the distance a pellet travels from the end of the scanning operation until it reaches a pellet re~ection chute. To assure reception of signals representative only of pellet surface flaws, the flaw detecting and integrating circuit is controlled by a photocell which operates to isolate the signal storage section at all times except when a pellet is under the influence of the scanning equipment.
An ob~ect of the invention therefore is to provide fuel pellet inspection apparatus arranged to receive an interrupted flow of pellets and which measures flaws on a pellet outer surface and re~ects those pellets not reaching a predetermined standard.
Another ob~ect of the invention is to provide fuel pellet inspection apparatus which scans a pellet surface for flaws, stores information representative of lost cylindrical surface due to such flaws and compares the magnitude of the flawed area with a reference to determine whether a pellet should be retained or re~ected from the system.
Another obJect of the invention is to provide fuel pellet inspection apparatus which utllizes a distance in-dicating optical probe and a flaw integrating circuit for re~pectively detecting and storing information representa-tive of fuel pellet surface flaws, and including an arrange-llJ5~704 ment for activating and inactivatlng the circuit during thetime a fuel pellet is under the influence of the optical probe.
Another ob~ect of the invention is to provide a method wherein fuel pellets are optically inspected for surface flaws by utilizing metrology equipment which gener-ates and stores signals representative of such flaws, and compares the total of stored signals with a standard, and then acts to accept or re~ect the fuel pellet measured.
BRIEF DESCRIPTION OF THE DRAWINGS
The sub~ect matter of the inventlon is particularly pointed out and distinctly claimed in the concluding portion of this speci~ication. The inventlon however both as to organization and method of operation, together with further ob~ects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure 1 is a schematic showing of the fuel pellet automatic inspection and sorting system of this invention;
Figure 2 is a view in elevatlon, partly in section, illustrating the general assembly of the fuel pellet measur-ing and sorting system;
Figure 3 is an end view in elevation of the mechan-ism shown in Figure 2;
Figure 4 is a plan view of the mechanism illus-trated ln Figure 2;
Figure 5 is a detailed vlew in elevation, partly in section, illustrating the design used for advancing fuel pellets through the fuel pellet scannlng zone;
Figure 6 ls a side view of the mechanism shown in iOS~704 Figure 5;
Figure 7 is a section view taken on lines VII-VII
of Figure 5;
Flgure 8 illustrates the mounting arrangement for achieving micrometer ad~ustment of the distance indicating optical probe relative to a fuel pellet;
Figure 9 is a view in elevation, partly in sec-tion, illustrating the pellet re~ect mechanism;
Figure 10 is an end view of the mechanism shown in Figure 9; and Figure 11 is a flaw-time lntegrator and sorting circuit used for storing information representative of pellet surface flaws and including a time delay used for re~ecting nonacceptable pellets.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like refer-ence characters designate like or corresponding parts throughout the several views, there is shown in Figure 1 a schematic showing of the system used for automatically inspecting and sorting nuclear pellets received from a ~uel pellet grinding operation.
During the manufacturing operation, green enrlched uranium fuel pellets undergo a pressing and sintering phase which occasionally produces pellets having a diameter out-side the range of established tolerances. To help assure productlon o~ pellets of uniform diameter, all pellets are then passed through a grinder which reduces oversize pellets to an acceptable size while those within tolerance pass through the grlnder untouched by the grinding wheels. The pellets are then successively moved onto a pair of rotating ~0577(~4 rollers 20 and 22, Figure 1, and as they llnearly move along the roller length, each pellet is optically scanned by a distance indicating optical probe 24 for pits, fissures, chips (flaws) and other defects which have the effect of diminishing the amount of material in the fuel pellet. A
power supply and readout 26 converts light from the optical probe to analog output signals which are supplied to flaw-time lntegrator and pellet sorter circuitry 28. Fiber optics head 30 and photocell scanner switch 32 sense the position of each pellet on rollers 20, 22 and acts to con-trol the integrator and sorter circuitry 28. As described more fully hereafter, should the integrator determine that an unacceptable amount of material has been removed from the pellet surface, it energizes a sorting solenold 34 which acts to remove the pellet from the system a~ter it leaves the rotating rollers 20 and 22. Those fuel pellets w'nich fall within established tolerances continue on their path to a fuel rod loading area 36 where they are subsequently loaded into fuel rods used in a nuclear reactor.
Referring more specifically to Figures 2, 3 and 4, the mechanism for i7nspecting and sorting the fuel pellets comprises a base ~which supports V-shaped pellet feed trough 38 mounted on vibrator 40. A vibrator support bracket 42 and rubber shock mounts 44 hold vibrator 40 and pellet feed trough 38 at an angle to the horizontal. The function of vibrator 40 is to move fuel pellets from the grinding area, down the feed trough, to the pellet scanning zone where they are inspected. Although different types f (~ tr~J~ ~a rk') vibrators may be used for this purpose, a ~ibra-drive~ unit, Model F-10, manufactured by the Syntron Corporation is ~05'7~04 designed to oscillate the feed trough 38 at a vibration frequency of about 60 cycles per second. This is accomplished by connecting the vlbrator 40 to the bottom side of the feed trough through driver 45, a plurality of flexible plates 46 and bracket 48 secured to the bottom of~the feed trough by bolts 50. To help assure the removal~chips and pieces of pellets from the feed trough before they reach rollers 20 and 22, a dropout hole having an opening less than a normal size pellet is formed in the bottom of feed trough 38. Such chips and pieces of pellet fall through the hole onto a chute 52 which discharges into an appropriate container.
The pellets are discharged from feed trough 38 into the inspection mechanism 54 where they are scanned for flaws and then subsequently sorted. As illustrated in Figures 2-7, the mechanism consists of a pair of spaced U-shaped supports 56~ 58 attached to base ~. Plates 60, 62having a triangular shaped opening 64 therein are respec-tively bolted to supports 56, 58. A pair of rollers 66~ 68 having their opposite ends mounted in bearings in the plates 20 are spaced a distance sufficient to support the fuel pellets as they move llnearly through the mechanism, i.e. from left to right as shown in Figures 2 and 5. The rollers are ro-tated by synchronous motor 70 coupled to a gear box 72 having a pair of output shafts 74 respectively connected to the rollers. Both rollers therefore rotate in the same direction at the same speed. Since it is convenient to locate the motor and gear box beneath feed trough 44, uni-versal ~oints 45 are used in the output shafts for facili-tating rotation of the rollers. By using a 25/65 gear teeth 30 ratio ln the gear box and rollers having a dlameter of 0. 625 _g_ l(~S77~

inches, a 0. 365 diameter pellet will spin at the rate of 1185 rpm. The synchronous motor shaft speed ls 1800 rpm.
As the vibrating feeder trough 38 advances pellets toward the inspection mechanism, the lead pellet is dls-charged under a hold-down sprlng 75 and onto a pair of wear pads 76 and into a posltlon to be moved llnearly along the length of rollers 66, 68. The hold-down sprlng serves to minlmlze ~umplng of the pellet as it moves from feed trough 38 on to the rotating rollers.
As lndicated in Flgures 2 through 7, the mechanlsm used for advanclng the pellets along the roller length con-slsts of a chain drlve assembly mounted on the U-shaped upstandlng plates 56 and 58. Each of these plates lncludes a shaft 78, Flgures 5-7, held in place by collars 80. A cog wheel or sprocket 82 mounted for free rotation on each of the shafts includes outwardly pro~ecting cogs 83 spaced a dlstance sufficient to accept an endless roller chain 84 which consists of the series of interconnected multiple links. To achieve movement o the roller chain on sprockets 82, a synchronous motor 86, Figure 3, mounted at the side of the mechanlsm has its output shaft connected to a slip coupling 88 which ln turn is connected to an extension 90 on the shaft 78 by clamp 91 thus causing the roller chain to move at a unlform speed around the sprockets 82.
To move the pellets at a uniform rate through the inspection zone, the roller chain 84 is equipped with a number of upstandlng pusher arms 92 attached to the chaln by a sllp-type connection 94. As the chain moves llnearly under the spaced rotatlng rollers 20, 22, the outwardly 30 extendlng pu~her arms describe an arc as the chaln moves around the sprocket 82 prior to advancing into a positlon between the spaced rollers. At ~ust about the top of the arc, a tungsten carbide ball 96 welded to an end of each pusher arm which extends upwardly between the spaced rollers, engages the back end of a pellet on its spin axis and thus moves the pellet along the roller length at the same advance speed as the chain. As the chain continues moving, the pusher 92 advances the pellet through the zone where it is lnspected for flaws in the fuel pellet surface. In the event ~amming of pellets in the mechanism occurs for any reason, the slip-type ~oint 94 used for connecting the pusher arm to the chain, will slip and move down to a hori-zontal position thus relieving the load otherwise imposed on the system by the ~ammed fuel pellets in the mechanism.
In order to automatically and rapidly measure the extent of surface flaws and diameter variations in each fuel pellet, careful coordination of the mechanical and optical-electronic components in the equipment is necessary to assure that the required functions remain within the capa-bilities Or each component. As disclosed above, the mecha-nical components serve to deliver fuel pellets to the rotat-ing rollers which spin the pellet at a predetermined speed.
To advance each pellet along the roller length and through a zone where it is optically scanned for surface flaws, small tungsten carbide balls mounted on the pusher arms attached to a constant speed roller chain, contact each pellet and impart the least disturbance to the spinning pellet and to move the pellet through the scanning zone.

Scanning of each pellet for flaws is performed by a commercially available distance indlcating optical probe lOS'77~)4 24 and its associated power supply and readout circuitry 26, Model 1100, manufactured by Systems Research Labs, Inc., Dayton, Ohio, and of the type disclosed in U.S. Patent 3,788,741 issued January 29, 1974 to L. W. Buechler. This optical probe contains a fiber optic head and lens system used both for projecting light on to the pellet surface and re-ceiving reflected light returned from the pellet surface.
Such light is transmitted by the probe 24 and return light from the pellet is converted to electric signals in the probe 24 and the power supply 26 which supplies an analog output to the logic circuit identified as flaw-time integrator and control 28. The logic circuit acts to discriminate be-tween acceptable and nonacceptable fuel pellets and serves to control a pellet reject solenoid which removes unacceptable pellets from the system.
The optical probe 24 is mounted on structure 108 above the rollers 20, 22 and in a position to project light onto a rotating pellet as it is moved by pusher arms 92 along the roller 20, 22 length. As illustrated both in Figures 3 and 8, the probe head initially is mounted within about 0.5" of a pellet surface. To accommodate differences in pellet diameter, the probe head is adjustably mounted on a micrometer machine slide 109, Figure 8, and such adjustment is made by means of a hand actuator 110.
It has been determined that flaws in a pellet surface having a dep-th less than .0025" are insignificant because the amount of pellet material represented by a chip depth of -this arnount would have no important effect on reactor perforrnance. To detect chip or flaw depths greater -~0 than .0025", the probe head is adjusted by the rnicrometer to a po"it;ion rea(ling -~0.0055" from an unSIawe(l pellet surface _ L~ _ iOS~7704 thus giving a reading which is normally 0.0025" above the flow detection level of 0.0030" which is determined elec-tronically in the flaw-time integrator and control 28.
It is apparent that the optlcal probe must commence scanning the pellet surface only when the leading edge of a pellet comes under the influence of light pro~ected from the optical probe head. Since the probe and associated cir-cuitry cannot discriminate between a pellet or other reflec-tive surface, it is necessary that the probe circuit be pre-pared to accept signals representative only of pellet flawsas soon as the pellet moves under the optical probe head.
Although it will occur to those skilled in the art that many different structures or methods may be used for making the probe circuit operable at the proper time 3 the arrangement disclosed herein includes a fiber optics unit 30 and photocell scanner switch 32 manufactured by Dolan-Jenner Industries, Monroeville, Pennsylvania. This control unit generally comprises the fiber optics head and lens 3Q, a photocell and an amplifier in photo-scanner switch 32 which converts light reflected from reflector 104 to an amplified signal to be supplied to the logic circuit of Figure ll.
Referring more specifically to Figures 2-4 and ll, khe retroreflective fiber optics head 30 is mounted on brackek 100 attached to plate 62 and is oriented in a direc-tion to pro~ect a light beam through transmitting fibers directly toward the pellet surface, and to receive light returned from the surface through receiving fibers in the optics head. The fiber optics head and its associated photocell is deslgned to make the distance indicating optical probe 24 operative (stark time) on a reductlon in the quantity 1057'704 of light returned through the fiber optlcs head to the photocell and therefore a reduction in voltage output from the photocell. Accordingly, the reflector 104 is positioned directly across from the fiber optics head so that light returned from the reflector into the head causes a rela-tively high output voltage from the photocell. As a pellet advances into position and cuts off light reflected to the fiber optics head, the sharp reduction in photocell voltage causes actuation of a relay which allows the flaw-time integrator circuit to become operative as explained in more detail in the description of the Figure 11 circuit.
The optical probe likewise is equipped with a fiber optics head which preferably includes two sets each of light transmitting and light receiving fibers so that the probe operates on the quantity of light reflected to the probe from out of focus images pro~ected on the fuel pellet surface being inspected. The total sensing pattern pro-~ected on a fuel pellet surface spans a width of about 0.030 inch. As disclosed in aforementioned U.S. Patent 3,788,741, a lens system is used to pro~ect light images onto the fuel pellet and the image size, shape, and intensity are pre-established to optimize linearity, range, and sensitivity.
When the light images are in focus on the fuel pellet sur-face, zero or a very low output voltage is supplied to the unit 26. As the fuel pellet moves relative to the probe, and transmitted light enters a chip or other flaw in the pellet surface, the light reflected to the receiving fibers wlll be of different intensities and each are converted to dlfferent level voltages in the power supply and readout unit 26. The output voltage is an analog signal repre-senting dlstance from the optical probe head 24 to the fuel pellet surface.
Wlth the synchronous motor 70 operating to rotate rollers 20 and 22 at a constant speed, and with the roller chain 84 likewise being moved at a constant speed, a pusher arm 92 moves the pellet into the area of the fiber optics head 30. At this time the pellet is rotating rapidly and light is being reflected from the reflector 104 which pro-vides a photocell 32 output voltage, which in Figure 11, is fed to comparator 116. This voltage is compared with a voltage provided by voltage divider 117. If the photocell voltage is greater, the output of comparator 116, and thus the control input of electronic switch 118 is high, thus activating switch 118 and shorting the capacitor 120 to ground. This high voltage level keeps the switch closed and capacitor 120 is maintained at a zero charge. As pusher arm 92 advances the pellet beneath the light spot from the fiber optics head 30, the reflected light from reflector 104 is cut off, the voltage goes low and switch 118 opens, discon-necting capacitor 120 from ground. This action prepares theFigure 11 circuit to process the analog output from unit 26.
The precise location of fiber optics head 30 with respect to optical probe 24 is chosen such that as a pellet moves under the fiber optics head to cause the voltage reduction which opens switch 118, the trailing edge of the optical probe light spot is fully on the fuel pellet surface, but ~ust .015 inch inside the leading edge of the fuel pellet. This arrangement eliminates the possibillty of the flaw-time integrator integrating excess signals. Since the fuel pellet i~ being advanced by the puPher arm while simultaneously 1057'704 rotating, the optical probe head will scan a helical trace of about .030" width on the fuel pellet and so long as there are no indentations, such as chips or other flaws on the ~uel pellet surface, light reflected to the optical probe will not appreclably change. However, as a chip or other ~law ls detected, the light image plane pro~ected by optical probe 24 on the pellet surface changes with a corresponding decrease in the analog output voltage supplied to the flaw-time integrator and control circuit 28. This voltage is fed to amplifier 122, acting as an impedance transformer, and supplied to comparator 124 which compares the signal to a reference level furnished by voltage divider 126. The voltage divider re~erence level is set slightly below that voltage which results from the scanning of an unflawed pellet surface by the optlcal probe 24. When there is an indentation of sufficient depth, the probe voltage will be lower than the bias placed on the comparator 124, and thus lts output will go high. Switch 128 will then connect the positive power line through resistor 129 to capacitor 120 thus charging it to a level which corresponds to the area of the chip indentation detected in the fuel pellet. As the distance indlcatlng optical probe 24 continues to scan the pellet as it spins and advances along the roller length, any flaws detected in the pellet surface are converted to signals which are integrated in capacitor 120.
A voltage divider 130 establishes a reference level for comparator 132. If the capacitor 120 charge voltage does not exceed the reference level established on voltage dlvider 130, the comparator 132 will not change its output ~tate, and thus the pellet wlll be acceptable and ~U577V4 will move uninterrupted through the system.
In the event that the capacitor 120 charge voltage does exceed the reference level on voltage divider 130, the pellet should be re~ected. When the capacitor 120 charge voltage exceeds the reference level on voltage dlvider 130, the output of comparator 132 will go high. At the moment this occurs nothing else will happen. The pellet will move steadily through the scanning motion, and the system time synchronization is maintained. By the time the pellet leaves the inspection area, fiber optics probe 30 will detect the end of the pellet, thereby increasing the output of the photocell 32, which in turn will result in the output of comparator 116 going high, and thus closing of the switch 118. At this moment capacitor 120 will discharge, and thus the voltage will drop below the reference level on voltage divider 130. This in turn will cause the output level of comparator 132 to go low again, and this will start the re~ect cycle.
The mechanical layout is such that the pellet travels for a time of two seconds after leaving the inspection area before it arrives at the re~ect chute. This means that the re~ect signal has to be delayed for 2 seconds before the re~ect chute can be activated. Furthermore, the pellets enter the inspection area at the rate of one for each 0.7 seconds. Thus while the re~ect signal ls being delayed~
another one can be created. Therefore the electronic delay circuit is divided in three parts, each with a delay time of 0.66 seconds. The delay circuit is comprised of three identical quick recovery monostables, which trigger on a negative going signal. Thus when the output of comparator ~l)57704 132 goes low, the first monostable 134 triggers, and lts output goes high. After 0. 66 seconds its output goes low again, thereby triggering monostable 136, which in the same way after 0. 66 seconds will trigger monostable 138 and finally again after 0. 66 seconds monostable 140 will be triggered. This last monostable has a much shorter time constant than the other ones, and determines only how long the chute will stay open to allow the re~ected pellet to fall through. This time is about 50 milliseconds.
The succession of three quick recovery monostables allows the system to react on a succession of re~ected pellets, since each monostable can be retriggered almost immediately after its discharge, and therefore of succession of pulses 0. 7 seconds apart can be transmitted through this

2 second delay circuit.
As the delayed signal reaches transistor 166, it conducts and energizes relay 168 which closes switch 170 - thus connecting the 110 voltage source across the diode bridge 172 and counter 174. The diode bridge 172 supplies a ; 20 DC pulse to a rotary solenoid 176, Figures 3, 9 and 10, which acts to re~ect the pellet while the counter 174 advances to show that the pellet has been re~ec'ced. The re~ect solenoid 140 is mounted on plate 178 extending out-wardly from support 180 attached to the base. An arm 182 ad~ustably mounted on the solenoid armature shaft 184 carries a plate 186 which is aligned with the V-shaped pellet trough 188 used for transporting pellets from the , inspection zone to the first rod loading area. The plate 186 attached to 'che end of arm 182 comprises part of the feeder trough and is of the slze slightly longer than a fuel lOS7~04 pellet so that when the pulse is delivered to solenoid 176, lt rotates clockwise thus creating an opening through which the pellet falls into chute 188. Since acceptable pellets do not send a re~ect signal through the logic circuit, the solenoid will not be energized and those pellets will move uninterruptedly through the system.
In order to provide an accurate count of all pellets run through the system, a counter 190, Figure 11, is connected at 152 between amplifier 116 and electronic switch 118. The counter would operate on a reduction in voltage which occurs when a pellet moves between the reflector and photocell fiber optics head 24.
In those situations where the vibratory feeder is ad~usted too fast or the su~ply of pellets is excessive, a l,not S~n~
pellet ratcheting mechanism~may be used at the end of the feed channel near the rolls to separate the pellets ~ust prior to entering on the rolls. The ratchet is tripped by each pusher arm as it rises so that one pellet is released to enter the space between ad~acent pushers as the spaces become available. This arrangement prevents a pileup of pellets and erratic feeding which otherwise may occur.
Although the disclosure is directed toward the inspection and detection of flaws in nuclear fuel pellets, it will be apparent that the teachings herein are applicable equally to other ob~ects whose surfaces are to be examined optically for defects. It further will occur to those skilled in the art that many modifications and variations in the design disclosed are possible in light of the above teachings. It therefore is to be understood that within the scOpe of the appended claimY, the invention may be practiced other than as ~pecifically descrlbed.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for automatically inspecting and sorting nuclear fuel pellets comprising:
a base supporting a feeder trough used for trans-ferring pellets from a source to a pellet inspection mechanism which examines pellets for flaws in their outer surface;
said mechanism comprising a device which receives and rotates each of said pellets and includes means for advancing each pellet linearly therethrough, said advancing means comprising a linearly movable member mounted adjacent said device, means associated with said member for moving it along the device length, said member having multiple fingers thereon arranged to respectively contact each pellet to move it linearly through the mechanism;
an optical probe including a light source associated therewith mounted on said base in a position to direct a light beam onto the surface of each pellet as it moves through said mechanism;
reflected light receiving means in said optical probe for receiving light returned from said pellet;
conversion means connected with said probe for converting the reflected light to electric signals;
electric circuit means coupled to said conversion means for comparing the light reflected signals with a voltage reference wherein the voltage reference represents the amount of light reflected from an unflawed pellet, and for storing the difference voltage representative of flaws in pellet surface in a storage device;

means in said circuit for comparing the voltage across said storage device with a voltage reference which represents an acceptable pellet, and for providing an output voltage indicative of an unacceptable pellet when the storage device voltage exceeds the last named reference voltage; and pellet reject means mounted adjacent said mechanism, said reject means being actuated by said output voltage to effect the rejection of unacceptable pellets from the system.

2. The method of automatically inspecting and sorting nuclear fuel pellets comprising the steps of:
supplying pellets to a pellet inspection mechanism, contacting each of said pellets with a movable arm and simultaneously rotating said pellets while moving said pellets linearly through said inspection mechanism;
sensing the presence of a pellet by a light responsive device when the pellet moves under an optical probe mounted adjacent said inspection mechanism;
converting light reflected to the responsive device from the pellet surface to first electric signals which are supplied to an electric circuit including a switch which is responsive to a decrease in the magnitude of said first electric signals; utilizing said first electric signals to prepare said electric circuit to receive second electric signals from the optical probe when it examines the pellet;
optically examining each of said pellets for flaws in its exterior surface by projecting light from said optical probe on to the pellet surface and receiving light reflected from flaws on the surface;
converting the reflected light to said second electric signals;
comparing the second electric signals with a voltage reference in said electric circuit which is representative of an unflawed pellet surface to determine the existence of indentations or flaws on the surface of said pellet being examined;
storing and integrating the sum of said second signals representing flaws in a storage device;
comparing the voltage across said storage device when each pellet passes from beneath said optical probe with a second voltage reference representative of the maximum allowable flawed area of the pellet surface;
providing an output voltage when the storage device voltage exceeds the second voltage reference;
applying the output voltage to an operating circuit which causes operation of a pellet reject mechanism and rejects unacceptable pellets; and transferring acceptable pellets to a remote area.