Method for sampling nuclear fuel pellets with a robot gripper mechanism

Abstract

A gripper mechanism for sampling nuclear fuel pellets at a predetermined depth in a stack of pellets includes a housing and gripping fingers movably mounted to the housing. The fingers are preferably three relatively thin, arcuate-shaped, blade-like fingers angularly displaced from one another for grasping the pellet at spaced locations about its circumference. The fingers have lower facing surfaces which are brought adjacent to one another for engaging and grasping a pellet when the fingers are moved toward their closed position and retracted remote from one another for disengaging and releasing the pellet when the fingers are moved toward their opened position. Guide members interconnecting the housing with a movable support structure, together with coil springs received about the guide members and extending between the housing and support structure, resiliently and yieldably mount the housing and fingers for movement toward the stack of pellets along a generally linear path ahead of the support structure as the support structure is moved toward the stack. Concurrently the yieldable mounting permits the housing to rock slightly about an axis extending transverse to the linear path for facilitating a burrowing-type movement of the gripping fingers into the stack of pellets to be sampled. Also, a proximity switch detects when the fingers are closed and a load transducer senses when an overload condition has been reached.