On-line monitoring for further corrosion reduction and better understanding of the activity build-up in LWR primary coolant systems

Uniform corrosion rates of materials in contact with the coolant in boiling water reactors (BWRs) and pressurized water reactors (PWRs) are low and this kind of material degradation is very unlikely to compromise the integrity of the primary pressure boundary. In a properly controlled environment the initial corrosion rates decrease reaching the low corrosion rate, typical for the steady state between the outer oxide surface and the environment. The water chemistry practice modifications can be used to decrease fuel corrosion, improve material integrity and slow down activity build-up in the primary circuit. Therefore, on-line water chemistry monitoring at high temperatures should be conducted to obtain local, reliable and thus useful information over long measurement periods at a specific loop site. In this paper, the effect of water chemistry on the corrosion product formation, activation, transport and redeposition on out-of-core surfaces is discussed.