Abstract: A latch assembly is disclosed for selectively preventing rotation of a shaft, such as a shaft used in a control rod drive for a nuclear reactor. The latch assembly includes a stationary housing for receiving the shaft, and a gear fixedly joined to the shaft. A latch arm is pivotally joined to the housing and includes at least one latch tooth facing gear teeth extending from the gear. The latch arm is selectively positionable in an engaged position to abut the latch tooth against a first one of the gear teeth for preventing rotation of the shaft in a first direction, and in a disengaged position to space the latch tooth away from the gear teeth for allowing the shaft to rotate without obstruction between the gear teeth and the latch tooth.
Abstract: An optical rotary switch is used in combination with an optically activated relay for causing make before break contacts between paired sets of relays including photoemitting and photoreceiving portions. The rotary switch comprises a switch base with an assembly rotatably mounted thereon for optically coupling the paired sets of relays including photoreceiving and photoemitting portions of the switch. A first optical exciter port and a first optical indicator port constitute a first relay and are disposed on the base for communication of optical signals. A second optical exciter port and a second optical indicator port constitute a second relay are also disposed on the base, angularly separated from the first optical exciter and first indicator port by a preselected angular interval.