Chemical Neutralization to Control Denting in Nuclear Steam Generators

Abstract

Laboratory testing at Combustion Engineering has indicated promise in controlling simulated steam generator tube denting through chemical neutralization. Testing was limited to on-line treatment, and two neutralizers have been evaluated: (i) calcium hydroxide, and (ii) boric acid. On-line treatment with calcium hydroxide successfully halted active denting whenever the bulk calcium concentration (in ppm) equaled or exceeded the bulk chloride concentration (in ppm). Calcium hydroxide also was effective as an alternative to ammonia as a pH controlling agent in two tests conducted without ingress of chloride. On-line treatment with boric acid consisted of a four-day soak at simulated low (approximately 30 percent) power with 50 ppm B followed by one month full-power operation with 10 ppm B. This treatment also halted denting. Nondestructive and destructive examination of test boilers gave no indication of adverse side effects associated with either neutralizer.