Nuclear Component Wear Measurements

Abstract

Cobalt-60 has been identified as the principal isotope responsible for the buildup of radiation in light water reactors. The 60Co is produced from stable cobalt being released to the coolant and becoming activated to ⁶⁰Co during residence in the core. The release occurs because of the corrosion and wear of cobalt-containing alloys exposed to the coolant. This study was directed toward measuring the cobalt released by wear of cobalt-based alloys. Plastic replicas were made of worn components during maintenance outages. Subsequent profilometer measurements were made on the replicas using nearby unworn areas as reference surfaces to enable a calculation of the cobalt released by wear. The calculated release rates on a variety of seven components were estimated from 0.04 g/yr for a main coolant pump on a pressurized water reactor to 30 g/yr for a feedwater regulator valve on a boiling water reactor.