Author: D. W. Shoesmith

Publisher:

Published: 1997

Total Pages: 0

ISBN-13:

Recent inspections have indicated that carbon steel outlet feeder pipes in some candu reactors are experiencing wall loss near the exit from the reactor core. this phenomenon is not observed in inlet feeder pipes. examination of a sample of pipe removed from a candu 6 reactor has indicated that the mechanism causing the wall loss is flow-accelerated corrosion (fac), at rates higher than expected, but two orders of magnitude lower than those typically observed in secondary circuits of nuclear and conventional power plants. although the candu reactor outlet feeder operating temperatures and the use of lioh at a high ph should have ensured low corrosion rates, use of sa 106 grade b carbon steel with a low chromium content resulted in some susceptibility to fac. the main parameter influencing the rate of wall loss is the coolant velocity, with the bend angle playing a secondary role. a solubility-based mathematical model describing the effects of water chemistry and coolant hydrodynamics on the rate of fac has been developed and has been recently improved by the empirical incorporation of the effect of electrochemical potential on the solubility of magnetite. experiment and theory have indicated that the corrosion rates are lower at lower ph values within the permissible operating range. experiments are being conducted to obtain more information on the effects of water chemistry and material composition on fac. current results support the predicted effects of ph and carbon steel chromium content on the fac rate. remedial measures implemented include operation of existing reactors at the lower end of the specified ph range and the specification of a minimum of 0.20 wt% cr in the carbon steel of feeder pipes of future candu reactors.