Impact of Resin Leakage on Corrosion: Previous studies have demonstrated that resin leakage occurs from both deep bed and resin precoat condensate polishing systems, particularly during transients. Such leakage is of concern in all types of power generating units since thermal degradation of cation resin leads to the formation of a variety of corrosion related sulfur-bearing compounds, including sulfuric acid. Anion resin, on the other hand, does not form aggressive degradation products unless it is exhausted to chloride or sulfate to a significant extent. In PWR nuclear systems, cation resin ingress is of particular concern since several sulfur compounds have been shown to accelerate stress corrosion cracking of Alloy 600 steam generator tubing. In BWRs, cracking of sensitized stainless steel has been shown to increase with sulfate concentration, particularly under hydrogen water chemistry conditions. As such, intermittent monitoring of resin leakage from each polisher vessel is encouraged to allow corrective actions to be taken if resin leakage is present.
Resin Leakage Quantification: To quantify resin leakage at the ppb level during normal operation and distinguish between anion and cation resin, a radioanalytical procedure was developed by NWT in 1985 (1). In the NWT resin leakage quantification approach, membrane filters are used to collect resin fines from polisher outlet sample points. Samples are collected by site personnel and shipped to NWT for analysis. At NWT, the membranes are exposed to cationic and anionic radiotracers and then analyzed by high-resolution gamma spectroscopy. The amount of cation and anion resin on each filter is calculated from known anion and cation resin capactities, tracer solution concentration and activity on the filter. Resin concentrations in the condensate are calcuated from the pertinent sample volume. Sensitivities are in the low ppb range when approximately four liters of sample is passed through each membrane. Lower detection levels (ppt) can be achieved with increased sample volumes. Sampling instructions are supplied by NWT.
Additional information on resin leakage monitoring can by provided by Mr. M. R.
Miller, Laboratory Supervisor, at (408) 281-1100 or email@example.com.
(1) Miller, M. R., Suhonen, C. H., and Sawochka, S. G., "Resin and Organic Transport in PWR Secondary Cycles", Electric Power Research Institute, November 1985 (NP-4311).
Evaluating condensate polisher ion exchange resin and equipment performance at operating plants is a difficult task. Even more difficult is relating the performance to resin characteristics such as capacity, moisture content, etc., which are measured under static conditions in the absence of exposure to contaminants. ASTM and the EPRI condensate polisher guidelines (2) describe a battery of such tests for utility consideration. While assisting clients in assessing resin performance, NWT personnel have found that evaluations of resin kinetic characteristics, i.e., assessments of ionic removal efficiencies during a dynamic test at applicable resin column flowrates and bed depths and condensate chemistries, provide more pertinent and valuable information on which to base decisions. Such testing is described in Appendix C of the Guidelines.
On this basis, NWT normally recommends that kinetics testing be performed as a part of routine and problem related resin performance assessments. During such tests, a mass transfer coefficient, that can be related to the extent of fouling or ability to remove impurity ions from condensate under dynamic conditions, is determined. Values can be measured for any ion, but generally the focus is on sulfate exchange on anion resin since fouling of this resin is the most common problem encountered in high flowrate polishing. When appropriately employed, the mass transfer coefficient can be used to predict sulfate removal efficiency during condenser leakage and to compare the performance of used to new resin, thus providing a quantitative basis for resin replacement/cleaning decisions.
Tests are tailored to plant design and operation, so amine chemistry or unusual conditions can be simulated. Radioactive resin is acceptable.
Pricing information can be provided on request. Please contact Mr. M. R. Miller at (408) 281-1100 or firstname.lastname@example.org for further information.
(2) "Condensate Polishing Guidelines for PWR and BWR Plants: 1997 Revision", prepared by the Condensate Polishing Guidelines Committee, September 1997 (EPRI TR-101942-R1).
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