Comparative Performance of Black vs. Gray Control Rods in the Engineering Test Reactor

Flux changes caused by withdrawing black and gray control rods in the ETR have been compared. The flux changes are shown to be the same for each type of rod at distances greater then three inches from the rod. Closer to the rod, the gray rod is successful in reducing the flux change. In terms of the flux change per unit reactivity effect, the differences between the black and the gray rod is not noticeable beyond 1.5 in.