On-line monitoring of low level metals with application to zinc injection and corrosion products

In most plant, iron and other metal measurements are confined to off-line methods. If metal analysis is brought into on-line category, several benefits will be obtained. This paper describes automated instrumentation by which metal monitoring is made on line in several plants at present. The new on-line instrument, in which X-ray fluorescence spectroscopy is used as the measurement technique was briefly described here along with recent plant applications and results of on-line metal monitoring with particular focus on injected zinc monitoring in BWR plant. The practice of zinc injection is gaining acceptance in PWR plants for radiation field control in their primary loop. Zinc dose requirements and chemical costs for various levels of feedwater corrosion product were presented and these data suggest that meticulous monitoring of particulate iron as well as dissolved zinc can assist the plant operator to obtain maximum benefit at minimum cost during a zinc injection program. As utilities strive for more efficient operation, under pressure from deregulation, competition, and down-sized workforces, on-line methodology takes on added value. (M.N.)