Evaluation of alternatives for upgrading double shell tank corrosion monitoring at Hanford

Recent discovery of low hydroxide conditions in Double Shell Tanks have demonstrated that the current corrosion control system of waste sampling and analysis is inadequate to monitor and maintain specified chemistries for dilute and low volume waste tanks. Moreover, waste sampling alone cannot provide adequate information to resolve the questions raised regarding tank corrosion. This report evaluates available technologies which could be used to improve on the existing corrosion control system. The evaluation concludes that a multi-technique corrosion monitoring system is necessary, utilizing ultrasonic and visual examinations for direct evaluation of tank liner condition, probes for rapid detection (alarm) of corrosive conditions, and waste sampling and analysis for determination of corrective action. The probes would incorporate electrochemical noise and linear polarization resistance techniques. When removed from the waste tank, the probe electrodes would be physically examined as corrosion coupons. The probes would be used in addition to a modified regimen of waste sampling and the existing schedule for ultrasonic examination of the tank liners. Supporting information would be obtained by examination of in-tank equipment as it is removed