Patent Number: 051026139
Section: claims

1. A brake assembly for a control rod drive for selectively preventing travel of a control rod in a nuclear reactor vessel comprising: a shaft having a longitudinal centerline axis;  means for translating said control rod upon rotation of said shaft;  means for selectively rotating said shaft in a first direction and in a second direction, opposite to said first direction;  a stationary housing having a central aperture receiving said shaft;  a frame fixedly joined to said housing and having a guide hole;  a rotor disc fixedly connected to said shaft for rotation therewith and having at least one rotor tooth extending radially outwardly from a perimeter thereof, said rotor tooth having a locking surface and an inclined surface extending therefrom in a circumferential direction;  a brake member disposed adjacent to said rotor disc perimeter and including a base, at least one braking tooth having a locking surface extending radially inwardly from said base and an inclined surface extending therefrom in a circumferential direction, and a plunger extending radially outwardly from said base and slidably joined to said frame through said guide hole;  said rotor tooth and said braking tooth being complementary to each other; and  means for selectively positioning said brake member in a deployed position abutting said rotor disc perimeter for allowing said braking tooth locking surface to contact said rotor tooth locking surface for preventing rotation of said shaft in said first direction, and in a retracted position spaced radially away from said rotor disc for allowing said rotor disc and said shaft to rotate without restraint from said brake member, said positioning means including a tubular solenoid fixedly joined to said frame and having a central bore disposed around said brake member plunger and effective for sliding said brake member plunger relative to said frame for positioning said brake member in said deployed and retracted positions.  a spring disposed in said brake member plunger and being initially compressed for engaging said braking tooth against said rotor tooth in said brake member deployed position when said solenoid is deenergized; and  said solenoid being energizable for electromagnetically drawing said plunger further into said solenoid bore and further compressing said spring for positioning said brake member in said retracted position. 2. A brake assembly according to claim 1 wherein said positioning means in effective for resiliently supporting said braking tooth for allowing said rotor tooth inclined surface to displace said braking tooth inclined surface to intermittently free said rotor tooth locking surface from said braking tooth locking surface for allowing said shaft to rotate in said second direction when said brake member is in said deployed position. 3. A brake assembly according to claim 2 wherein said rotor disc includes a plurality of said rotor teeth spaced circumferentially around said rotor disc perimeter. 4. A brake assembly according to claim 3 wherein said brake member base is arcuate and includes a plurality of said braking teeth spaced circumferentially thereon. 5. A brake assembly according to claim 4 further comprising two of said brake members including first and second, circumferentially spaced brake members, and said positioning means is effective for positioning both said first and second brake members in said deployed and retracted positions. 6. A brake assembly according to claim 5 wherein said first brake member is spaced about 180.degree. from said second brake member. 7. A brake assembly according to claim 4 wherein said rotor tooth locking and inclined surfaces form an obtuse angle therebetween. 8. A brake assembly according to claim 4 wherein said plunger is hollow and said positioning means further includes: 9. A brake assembly according to claim 8 wherein said plunger is disposed perpendicularly to said shaft longitudinal centerline axis. 10. A brake assembly according to claim 9 wherein said rotor tooth locking and inclined surfaces form an obtuse angle therebetween. 11. A brake assembly according to claim 9 wherein said rotor tooth locking surface is disposed at an angle of 90.degree. relative to said rotor tooth inclined surface. 12. A brake assembly according to claim 8 wherein said plunger and said guide hole have complementary, square cross-sections.