United States Patent IHM mi 3,965,757 Barrus [45] June 29, 1976 [54] SCRAM RELEASE FOR A CONTROL ROD 3,572,161 3/1971 Lichtenberger et al 176/36 R [ 75 ] Inventor: Donald Martin Barrus, Enfield, 3,778,345 12/1973 Maslenok et al 176/36 R Conn. Primary Examiner—Samuel Scott [73] Assignee: Combustion Engineering, Inc., Assistant Examiner—Wesley S. Ratliff, Jr. Windsor, Conn. Attorney, Agent, or Firm—Stephen L. Borst [22] Filed: Dec. 12, 1973 [57] ABSTRACT [21] Appl. No.: 424,125 A double-sided rack and pinion control element drive mechanism for a nuclear reactor is disclosed wherein [52] U.S. Cl 74/30; 74/422; scram release is accomplished by the dual action of 176/36 R withdrawing the pinion from its engagement with the [51] Int. Cl.2 F16H 19/04 rack while at the same time rotating the pinion in a di- [58] Field of Search 74/29, 30, 422, 425; rection consistent with the movement of the rack and 176/36 R the control rod in their downward travel. The pinion is withdrawn from engagement with the rack while re- [56] References Cited maining in engagement with its stationary driving UNITED STATES PATENTS means. The continuing engagement with the stationary driving means causes the pinion to rotate when the 195,638 9/1877 Nichols : 74/437 pinion is caused to move away from the rack during 3,356,874 12/1967 Chiapparelli et al 74/424.8 R disengagement. 3,405,032 10/1968 Barrus et al 74/422 3,494,827 2/1970 Zinn 74/422 10 Claims; 7 Drawing Figures U.S. Patent June 29, 1976 Sheet 1 of 3 3,965,757 44- 24-^n FIG. I U.S. Patent June 15, 1976 Sheet 2159 of 6 3,963,563 U.S. Patent June 29, 1976 Sheet 3 of 3 3,965,757 35' 68' FIG. 5 3,967,741 1 2 pinion is caused to rotate as it moves away from the SCRAM RELEASE FOR A CONTROL ROD control rod rack. T, . t •• . ... .. DESCRIPTION OF THE DRAWINGS This invention relates to the art of linear drive appa- ratus and more specifically it relates to the scram re- 5 The present invention may be better understood and lease of a control rod of a nuclear reactor. its numerous objects and advantages will become ap- Many attempts have been made heretofore to pro- parent to those skilled in the art by reference to the vide rack and pinion control rod linear drives for nu- accompanying drawings wherein like reference numer- clear reactors whereby the control rod drive mecha- als refer to like elements in the several figures and in nism is capable of withdrawing the control rod from 10 which: and inserting the control rod into the reactor core in a FIG. 1 depicts a portion of the control rod drive controlled manner, while also being capable of rapid mechanism utilizing a rack and pinion drive; disengagement which allows the control rod to fall or to FIG. 2 is a section of FIG. 1 taken along line 2—2; be thrust into the core in emergency situations. Rack FIG. 3 is a section of FIG. 1 taken along line 3—3; and pinion control rod drive mechanisms heretofore 15 FIG- 4 is a section of FIG. 1 taken along hne 4—4; proposed, generally, have suffered from the difficulty FIG- 5 is a section of FIG. 1 taken along line 5—5; that emergency disengagement of the driving means FIG- 6 depicts the detail of a second embodiment of resulted in excessive strains and wear and tear on one a contro1 rod dnve mechanism wherein the pinion is or more elements of the driving linkage. This necessi- „„ driven by a worm. tated frequent, costly and bothersome repairs. Use of a 20 FIG- 7 dePicts the detail of a thlrd embodiment of a clutch for engagement and disengagement of a control control rod drive mechanism wherein the pinion is rod drive mechanism of the rack and pinion type is well dnven by a chain dnve • known. The practice involves the utilization of the DESCRIPTION OF THE PREFERRED clutch intermediate the driving motor and the pinion 25 EMBODIMENT which engages the control rod rack, but incorporates „„ ., , _ , , ... , .,_ , . the disadvantages of clutch wear and tear resulting in While the preferred embodiment will be described in eventual control rod slippage which is unacceptable in terms °f a ™c>ear r®ac or rod dn ve , , ,, i . ,« , nism, it should be understood that the instan + tt invention the control of the nuclear reactor. A further disadvan- ,,,.,.,. • taee is that when an emergencv control rod release is has e1ual aPPllcability to any linear drive apparatus tage is mat wnen an emergency control rod release is 30 and ial l J to those linear drive mechanisms which required, the control rod scram is delayed by the inertia . r. , ,. , . , e . • e „ . j jjv , . .. .. ., . J f . ,. are loaded or biased with a force to move in a preferred ana additional rtnct.on ot tne spinning parts including . direction This biasi or loading force may be pro- £ the pinion which remains in engagement with the rack vided b a ; or *soure e of p ressurized gas, or, as F B and the clutch face which is connected to the pinion. jn the c^se Q f a n uclear reactor control rod mechanism, An even more serious disadvantage is that the pinion, 35 fe ; In some nuciear applications the biasing the clutch or any of the linkage which connects the ^ or /he load force is by a combination of pinion to the clutch may become inadvertently bound, a lurali of the above.mentioned loading forces, thereby preventing the successful emergency insertion FIG. 1 represents a portion of the invention which is of the control rod into the reactor core since the bound a scram release mechanism for a nuclear reactor con- part remains connected to the control rod. 40 trol rod drive mechanism generally indicated by 10. In the present invention these disadvantages are alle- The drive mechanism 10 has a housing 12 with a flange viated by providing disengagement of the pinion from 24 which is connected to the reactor pressure vessel the control rod rack in a manner which minimizes wear head 20 by means of a nozzle 22. On the interior of the and structural fatigue, while at the same time allows the housing 12 is a longitudinally extended linearly mov- control rod to move into the core entirely free from 45 able element, the control rod 14, the uppermost por- external interference. tjon Qf which is formed with spaced teeth 16 on oppos- SUMMARY OF THE INVENTION ing sides thereof to form a double sided rack 18, here- after referred to as the control rod rack. The control These and other objects are accomplished by provid- rod 14 extends down through the nozzle 22 and ing a movable pinion which can be withdrawn from the 50 through the reactor pressure vessel head 20 through a rack for its disengagement from the rack. The essential head penetration into the interior of the reactor pres- feature ofthe present invention contemplates the with- sure vessel and into the reactor core (not shown). The drawal of the pinion from the rack in such a manner control rod rack 18 is sealed from the internal atmo- that the pinion is caused to rotate during its withdrawal sphere of the reactor by bellows 26 which is attached to from the rack in a direction consistent with control rod 55 the lower portion of the control rod rack and to the insertion into the core. The pinion is mounted on a housing 12. A possible alternative arrangement would movable support member which, during driving opera- be to attach the bellows to the reactor head nozzle 22. tions, holds the pinion in engagement with both the The control rod drive mechanism 10 of the present control rod rack and a toothed driving means. The invention consists of a double-sided drive designed to toothed driving means, e.g. a spur gear, is caused to 60 maximize drive with a minimum of friction. It will be rotate to impart driving motion to the pinion but: is recognized by those skilled in the art that unnecessary otherwise held in a fixed position so that it is not al- friction represents an unnecessary danger as it not only lowed to move relative to the control rod rack. When slows down the reaction time Of the drive mechanism control rod scram is required, the movable support but also increases the possibility of binding or jamming, member moves the pinion away from the rack in such 65 As seen in FIG. 2 the preferred embodiment of the a manner that the pinion engagement with the toothed scramming control rod drive consists of a pair of op- driving means is maintained: As a result of this continu- posed gears adapted to engage opposite sides of the ing engagement with the toothed driving means the double-sided rack hereafter called the pinions 28. As 3,967,741 the two sides are identical in their structure, only one drives the two intermediate worm gears 44 and 44' to side will be described in detail. When it is appropriate split the drive into two separate drive linkages which to refer to the identical reflected side, the correspond- deliver the drive to both sides of the control rod rack ing elements will be designated by primed numbers 18. Worm 46 is driven by shaft 47 which is in turn 5 corresponding to their unprimed counterparts.