C Reactor horizontal control rods were originally designed to have 32 feet of poison, made of 64 six inch ``cans`` each consisting of two concentric cylinders sealed at each end and the annular space between them filled with boron carbide powder. It was discovered before startup that under irradiation the neutron, alpha reaction in the boron could cause a pressure buildup and rupture of the sealed section. As an expediency cylinders wrapped with 72 miles thick cadmium metal were substituted for the boron ``cans`` and the pressure buildup problem was eliminated. However, since for a unit volume, natural cadmium contains fewer high cross-section nuclei than natural boron, the lifetime of one of these cadmium rods in Hanford flux levels is limited. Five of the original 15 cadmium rods were replaced in 1957 with boron rods of improved design. The primary purpose of this document is to present the results of a study to evaluate the extent of burnout in the remaining ten cadmium rods and their present rate of burnout so that replacement can be scheduled before these rods start losing significant reactivity poisoning effectiveness.