CA1093108A - Apparatus for feeding nuclear fuel pellets to a loading tray - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Apparatus for feeding nuclear fuel pellets at a uniform, predetermined rate between pellet centering and grinding apparatus and a tray used for loading pellets into a nuclear fuel rod. Pellets discharged from the grinder are conveyed by a woven wire belt to a drive wheel which develops a force available to to be applied to pellets preceding it on the belt. The pellets pass under the drive wheel which adds additional weight acting vertically on each pellet.
This total weight of pellet and drive wheel coupled with wire belt linear movement acts to push a line of about 36 pellets onto a pellet dumping mechanism. As the dumping mechanism is actuated to dump the pellets on to a loading tray, the pellets moving toward the mechanism are clamped in a stationary position and the drive wheel simultaneously is lifted from its pellet contacting position until the pellet dumping process is completed. The clamping device is then lifted from its pellet and the drive wheel simultaneously is lowered into a pellet contacting position.

Description

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BACKGROUND OF THE INVENTION
The invention described hereln relates to a system ', for handllng fuel pelléts ~or a nuclear reactor and more .;
particularly to apparatu~ u~cd ~or reedin~, ~uel pellets ~rom a grindlng machlne to tra~E3 uE3ed ror loading pellet~ into nuclear fuel rodE3.
The proce~ practlce~ ln manuracturin~, a nuclear ~ fueI pellet include~ ~he ~tep~ o~ slnterin~ the pellet in a : furnace and thereafter ~ub~ectlng it to a ~rinding operation ,. '~

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to help assure that its external alame~er will be sufflciently small to permit loading :Into a fuel tu~e. Upon completion of the grinding operation, the pellets are transferred to a tray which then serves a~ a source o~ ~uel pellet supply ~or fuel tube loadirlg purposes.
The sy~em Or tranf3fer include~ a ~rnall vibrakory feeder which transfers pellets from the dischar~e slde of the grinder to a surge con~eyor which includes a power driven woven metal belt. Since the surge conveyor belt spee~ is faster than the transfer rate of the vibratory feeder, the pellets discharged from the feeder are automati-cally spaced ~rom each other on the belt and alon~ the belt length. It is obvious that in thls known design, a pellet -~ on the belt has the sarne horizontal speed as the belt surface.
If the horizontal motion of the pellet is stopped by a resisting ~orce against the end of the pellet, such as a large number of abutting pellets, the pellet will slide on the belt, i.e., pellet horizontal movement stops but the belt continues to move under it. The force against the pellet that would cause it to stop must be equal to or greater than the force developed by the pellet weight times the coefficient of friction between the woven belt and pellet sur~aces. Therefore, a pellet being transported on the belt will develop a horizontal ~orce approxirnately equal to its weight tlme~ the coe~flci~nt o~ rr.lctlon between the two ~urface~. A re~ulkank rorce developed by a ~erlec o~
~llding pellets is capable o~ pu~hin~ an equlval~nt numb~r o~ pellets axially over a ~ta~lonary pla~e, and thl~ principle has been relied on in the pa~t to move pell~ts to a posltlon on the plate whlch ~equentially dumps ro~r~ of pellet~ into

-2-grooves in a tray. During the time re~ulred for the complete pellet dumping and tray removal and replacernent operat~on to take place, the pellets on the surge belt rnust ~e stopped to prevent run-over onto the ~umpln~ pla~e. Since the pellets pass between two parallel motor driven belts, when the last pellet, i.e. in this case the 36th pellet~ moves onto the dumping plate, a clamp becomes effective to clamp the 37th pellet and pellets behind it rnerely stack up behind it in a horizontal straight line. Simultaneously, the rnotor driving the belts is stopped thus preventing pellet movement toward the dumping section of the apparatus. The clamp releases and the motor starts arter the pellets are dropped into grooves in a tray.
The primary disadvantage of this design is that the line of pellets required to fill the discharge chute with pellets leaves no space for surge capacity during the time required ~or the tray loader to advance a new tray into loading position.
SUMMARY OF THE I~ENTION
Briefly stated, the above disadvantages of the prior art are overcome in accordance with the teachings of this invention by providing apparatus which provides ~or the t','.-~ ' application of a wei~ht, in additlon of that of a fuel .~ ~,¢, pellet, to advance fuel pellets to a po~.1,tion wh~re khey conveni~ntly can be dl~char~d lnto ~rooveL~ ln a tra~.
Durlng pellek dl~¢har~ onko khe ~ray, th~ movemerlt o~
pellets throu~h khe apparaku~ l~ t~mporarll~ halte~d by removing khe welght added ko each pellet and ln re~trainin~
pellet linear movement.

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BRIEF DESCRIPTION OF THE DRA~ r'S
The subJect matter of the lnvention 15 particu-larly pointed out and distinctly claimed ln the concludin~
portion of this specificatlon. The organization and rnethod of operation of ~he inventlon to~ether ~rith further obJects and advantage~ thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which:
Figure 1 is a front view arld elevation of a pellet , 10 surge conveyor used for transferring pellets between a grinding machine and a loading tray.
Figure 2 is a left r~ide view of the surge conveyor Or Figure l;
Figure 3 is a view taken on liner~ 3-3 of Figure l Figure 4 is an enlarged vlew of the drive wheel used for moving pellets through the apparatur~.
DESCRIPTION OF THE PREFERRED EMBO~IMENT
Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is generally shown in Flgure 1, a pellet surge conveyor lncluding a base having legs 10 sup-porting apparatus used for advancing fuel pellets linearly along it~ length. A fircst r)ellet grinder 12 which receives nuclear fuel pelle~ l rrom a l31nterlnp rurnace, not rshown, grinds the pelletr~ to a pre(lelermlned rnaxlrnum ~iaMeter ln accordance wlth well-known practlce~. The pel:Let~ are discharged ~rom th~ ~rlndln~ mach;lne orlto Mn-~n~nr~ v-l-brating ~eed trouph 16 _ ~uch that pellets are freely moved therealorlg by a vlbrator 1~ onto an endlesr~
woven wlre belt 20. A~ showrl ln Fl~ur~ n~ ~ t~le ~llre _1~_ ~1~0~3~ 8 belt is driven by a convention~l drive rnotor 22 h~in~ lower and upper sprockets 24, 26 and a chain 28 therebetween transmits torque to sha~t 30 which is supported in bearings 32. A roller 34 is keyed to ~haft 30 and ~ccordingly rot~tes therewith.
As more clearly shown in Fi~ure 1, the bel,t i~
supported by the roller 34, pulley 36, ad~ustable roller 38 and idler gear 40. Roller 38 is rnounted on bracket 42 pivotally mounted on frame le~s 10 and belt tension is ad~usted by nuts 44 on merrlber 46.
Since it i,s.important to keep pellet6 oriented in ; the sarne direction as the belt axis and lying horizontally - in a straight line on the belt, a pair of inverted angle ~ arms 48 are mounted on the bearing blocks and are spaced a : . distance sufficient to permit the lower surface of each pellet to contact the wire belt surfaces while belng guided by the angle lrons 48. Each pellet weighs about.7 to 10 grams so that its position on the belt does not move after it assumes its initial posltion.
, As indicated previously, a pellet on a moving wire belt wil]. develop a horizontal force agains~ any object it contacts, such as another pellet, and attempt to move it ~' within the limits of such force. When the ob~ect resistance to movement exceed~ the horizontal f'orce, the pe],let will slide on the be'lt becau~e the re~ultlrl~, l'orcc~ of' thc wel~ht of the pellet multiplled by the ¢oe~f'iclerlt o~' rrlctlon between the pellet and woven wire belt sur~'ace~ wlll be les8 than the force pre~ented by r~ tlnK body. Bec~u~e Or the mechanical inefflclency of tran~fer of forces~ one pellet there~ore cannot develop ~ufricient rorce to mo~e the next preceding pellet. In this ~ystem, if~ one pellet weighs approximately 10 grams~ the coefficient o~ friction at the pellet-wire belt interface is such that a 10 gram pellet will develop a horizontal force of approximately 8 grams.
Since this does not repre~ent a reasona~le method of pushin~
pellets toward a tray, a force which ~cts in addition to the pellet weight, is used to create an artlficially increased weight. In this invention such arti~icial weight takes the form of a spring loaded wheel arranged such that the pellets "roll1' under the wheel, thus developing the extra weight and a resulting force which wlll drive pellets on to a dump mechanism associated with a tray loader, As shown in Figure 3, the wheel type structure comprises a pair of threaded rods 52 attached a~ thelr lower ends to housing 54 by nuts 56. The upper ends of the rods are similarly fixed to a mounting head 58 having a central opening designed to contain bearing 60. A shaft-62 arranged ~or sliding movement in the bearing is ad~ustably attached at its lower end to block 64. The block has a pair o~
spaced depending arm 66 which support pellet ~eed wheel 50 by means of needle bearings and a dowel pin 68. In order to appropriately engage and move a pelle~ from belt 20 to a loading tray, the outer peripheral surface of the drive wheel ha~ a pair o~ ~space~ groo~e~-s whlch receiv~-3 0 rJnes 70.
These rings are relatively Esof't and pllable an~ I~eadlly conform to a pellet ~urrace a~ it pa~sSseEs beneath the wheel.
Slnce there mufst be rlexlblllty in the ~sy~tem, at least to - ~ ~ accommodate ve~tical di~placement ~f' th~ ~rheel as it engages -- each pellet, ~h~ 62 l~s connecte~ to a piEston 72 vertically movable in cylinder 7IJ ~urrnountln~ ~he wheel. The ~l~ton i~s 331 (~

loaded in a pellet engaging direction by ~pring 76 and ltthere~ore always biases wheel 50 into contact ~lith a pellet.
To help preclude lateral d~splacement o~ wheel 50~ an an~rjle iron 78 or other guide member is attached to frarne 58 and positioned to be contac~ed ~y block 64 ~urin~ the tlrne of vertical reciporcation of wheel 50.
As indicated previously, the weight of the drive wheel plus that o~ each pellet is ~u~ficlent to provide a horizontally directed force capable of movin~ the pellets to a loader where they are dumped onto a tray which subse-quently is used as a ,source of fuel pellet supply during ~he time of loading a fuel tube with pelle~s. In the preferred embodiment of this invention, the total weight of the feed wheel and its support structure, including the weight of shafts 62 and piston 72 plus the downwardly actin~ f'orce of the spring plus the 10 grams for each pellet results in a total downwardly acting force of 918 grams. This weight provides a total horizontally acting force of 734.4 grams which is used for pushing the pellets along a V section appearing on the discharge side of the feed wheel. These weights are specifically chosen to permit the feed wheel to push 36 pellets into the V section ~ince that number of pellets can be accomodated by the specific tray used for fuel tube treating purpo~e~.
As pellets are di~charged from beneath th~ wheel, they leave the V-shaped inv0rted an~le arm~ ~18 and move into a second V-shapecl trou~h 80 o~ slmilar ~lesl~rl. S~nce the last pellet leaving the ~/hee:l pu~he~ a~ln~t the pellet~
immediately preceding lt, they as~ume a horlzontal end to end relation~hip ~Jith the pellet ends abuttinK one another.

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This row of pellets is then pu~hed on to a pi~o~ally mounted loader 82. The loader is designed and o~ a size to accept 36 pellets, this total length representinK the length o~ a pellet groove in a tray 84 located immediately therebeneath.
When the lead pe]let 86 clo~e~ mlcro~witch 88 o~ relay 90 an appropriate control mechanism, not ~hown, dumps the pellets from loader 82 into a ~roove in tray 84. The speci~lc mechanical-electrical arr~ngement used for actuatlng the loader 82 and moving the tray 84 are well known in the art and do not constitute a part of thi~ invention. As each groove is filled, the tray is indexed to the next groove position to permit the dumping of fuel pellets thereinto until the tray is full. It then i5 removed by appropriate means and delivered to an area when the fuel pellets are loaded into fuel rods.
Since it is important to stop linear movement o~
pellets from trough 80 into the loader 82 durin~ the time dumping of 36 pellets is taking place, a pellet stop member in the form of clamping device 90 is used for this purpose.
The device includes a cylinder housing a piston 92 connected to a connecting rod 94 having a solid æection 96 mounted on the bottom end thereof. The member 96 ac'cs to clamp a pellet in po~ition in trough 80 when the pi~ston i~ moved downwardly against the upward ~lclf~lnK actlon of' sprln~ 98.
When this occurs, movem~nt Or pell~t~s rrom trough 80 on to the loader is po~sitively pr~cluded.
lt will be apparent that th~ whe~l 50 cnnnot continue to move pelletEs toward loader ~ when pelletEs are belng discharged on to the tray. To accommodate thics situa-tion, when lead pellet ~6 clo~e~s mlcro~switch 88, relay 90 _3_ acts to open ~olenoid operated valve 100. Thig valve ~imul-taneously connects air source 104 to the hottom o~ wheel cylinder 76 and top of clamp cylinder ~. Alr pre~sure then causes wheel piston ~ to move upwardly again~t the action ;` ;~ of spring 74, and clamp plston 92 to move downwardly agalnst the actlon of sprin~ 98. The~e actlons move the ~rheel out of the pellet contacting area thus removing the horizontal driving force. The pellets on trough 80 are already in a continuous line, end to end, and since clamp member g6 is ln 10 engagement with the first pellet in a line, it holds it against movement and pellets normall1J stack up behind it on the surge conveyor. After pellet dumping i5 completed, microswitch 88 opens thu~ deenergizing the solenold valve 100, which vents air from cyllnders 76, 90 and wheel 50 moves downwardly to engage pelletæ while clamp member moves upwardly out of lts pellet contacting position.
OPERATION
This invention is ba~ed on the premise that a pellet traveling on a level woven w~re belt will develop a t 20 horizontal force and that it will slide on the belt surface when opposed by a greater resisting force. This horizontal force is the product of the weight of the pellet and the coefficient of friction between the pellet and the belt surfaces. Slnce the force gen0rated by a multitude Or pellets i~ not rea~onably ef'ficient and errectlve in movlng pellets from a trough onto a loader, a wheel ha~ been added to the ~ystem to provlde an artlriclal rOrce errectlve in moving the pellet~ o~er th~ de~ired dl~tance and direction.
A~ pellet~ are dellver~d from a pellet grindlng 3o machine to the ~urface of the wlre belt 20, they are conveyed

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to the feed wheel 50 and roll under the wheel which develops the extra weight, thus providing a re~ultlng force to rlrive the pellets into the dump rnechan-lsm on the tray loader. The dump mechanism is de~igned to accept 36 pellets and as the lead pellet en~ages ~icroc;witch 8g at the end of the mechan-ism, the solenoid valve 100 in an alr llne are actuated to an open position, and air 1~ fed slmultaneou~ly to the bottom of the feed wheel cylinder a~d the top of the clamp cylinder. The air acting under the piston in the feed wheel causes the piston and attached wheel to move ve~tlcally out of contact wlth the pellet thus rellevin~ the force which normally is used ~or pushing the pellets toward the dump mechanism. Likewi~e, as air is applled to the top of the clamp cylinder, pi~3ton 92 therein and it~s connected clamp member is moved downwardly to engage a pellet whlch in this case is the 37th pellet ln the line. Thi~s clamp mechanism merely preclude~3 movement o~ the pellets onto the dump mechanism and they accordingl~ ~stack up in end to end abut-ting relationship. After the dump mechani~sm discharges the pellets into a groove in the tray, and returns to its initial position for accepting pellets, the microswitch again opens the circuit to the solenoid and the air val~e~ move ~o the second po~itlon to ~en~ air from the feed whèel cylinder and the clamp cyllncler. Thl~ a~tiorl p~rrnits the ~sprlrly, in t~le feed wheel cylinder to move tle reed rc~ L dowrlwlrdly into engagemen~ wl~h the pellet~3 on thc,~ w;lre b~:Lt. I,lk~wl~e, the r~pring in cllrnp cyllrld~r ralrsels th~ p;~rstc)rl~arld lt~s connect~d clamp member upwardly~ ~.I.nc~ the wlre belt lrs in MotLon the pellet~3 accordin~ly will he mo~ed by ~he wlre belt and the feed wheel on to ~he dump meGhanl.~m ror repctltion Or the 3~

cycle.
It will be apparent that many modifications and variations are possible in light of the above teaching~. It therefore is to be understood that within the scope Or the appended claims, the invention rnay be practiced other than as speci~ically described.

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Claims (4)

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

1. Apparatus for transferring nuclear fuel pellets from a grinding machine to a tray loader comprising:
a frame supporting a member which bridges spaced legs in the frame;
an endless belt on said frame which rides on said member;
a generally V-shaped trough mounted immediately above said belt and extending axially thereof for accepting pellets from said grinding machine and thereafter guiding said pellets as the belt moves them linearly along said frame;
an adjustable force producing means mounted above said belt, and means connected with said force producing means for moving it into a pellet engaging position to thus produce an artificial weight which when multiplied by the coefficient of friction between the pellet and belt surfaces, will produce a force capable of moving the immediately ahead pellets linearly from the belt on to a stationary plate and from there, on to pellet receiving means;
clamping means mounted above said plate and at a point adjacent said receiving means, said clamping means including a member having a solid surface arranged to contact a pellet to preclude further pellet movement onto said receiv-ing means; and control means on said receiving means engageable by said pellets which act to lift the force producing means from said pellets and separately move said clamping Means into contact with a pellet, when the receiving means is loaded with pellets.

2. Apparatus according to claim 1 wherein said receiving means includes a dump mechanism of V-shaped con-figuration which forms a trough in alignment with the V-shaped trough on said frame, and said control means includes a switch arranged to be contacted and closed by pellets on said V-shaped trough when a predetermined number of pellets reside therein, said switch being in a circuit with a selectively operable valve which controls the supply of energy from a source to the clamping means and to the force producing means to operate the same when a predetermined number of pellets appear on said dump mechanism.

3. Apparatus according to claim 2 wherein said clamping mechanism includes a cylinder having a piston therein, a shaft interconnecting said piston with a clamping member having said solid surface thereon which engages a pellet;
a spring in said cylinder arranged to urge said piston in an upward direction to thereby move said clamping member out of contact with a pellet during the time pellets are being moved on to the Y-shaped trough of said dump mechanism; and means connecting said cylinder which said valve so that as the switch acts to open said valve, energy from the source moves said clamping member into contact with a pellet.

4. Apparatus according to claim 2 wherein said switch on said dump mechanism is closed when a predetermined number of pellets are in said V-shaped trough;
means connecting said switch with a solenoid having a valve in an air line extending to said force producing means and said clamping cylinder, the arrangement being such that as the switch is closed thus indicating that the dump mechanism is full of pellets, the solenoid opens the valve in the air lines thus providing the air pressure to said pistons to lift the drive wheel out of contact with the pellet and to cause the clamping member to engage a pellet and thus preclude pellet movement onto said dump mechanism.