Determination of Organic Acids and Inorganic Anions in Lithium-Containing Boric Acid-Treated Nuclear Power Plant Waters

Significance of the Topic

Pressurized water reactors use boric acid and lithium hydroxide to control neutron flux and pH, but trace anionic impurities such as fluoride, formate, chloride, and sulfate at µg/L levels can catalyze corrosion and degrade materials. Sensitive, reliable monitoring of these species in lithium‐containing borated coolant is critical for reactor safety and longevity.

Objectives and Study Overview

This work extends large‐volume direct injection ion chromatography with reagent‐free tetraborate eluent generation to samples containing milligram‐per‐liter lithium. A continuously regenerated cation trap (CR-CTC II) removes lithium interference, enabling sub-µg/L determination of target anions on a single-pump system without a concentrator column.

Methodology and Instrumentation

• Instrument: Dionex ICS-2100 IC with isocratic pump, vacuum degasser, EGC II KOH cartridge, high-pressure injector, column heater, conductivity detector, ASRS 300 suppressor (external water mode), CR-CTC II trap.
• Columns: IonPac ATC-HC borate trap, AG22 guard (2×50 mm), AS22 analytical (2×250 mm).
• Eluent: 200 mM boric acid titrated with electrolytically generated KOH; gradient from 14 mM to 90 mM KOH over 25 min at 0.38 mL/min, 35 °C.
• Sample: 1 mL direct injection (full loop) of filtered (0.2 µm) sample; autosampler rinse and filter best practices.
• Surrogate matrices: 1000–2500 mg/L boron with 2–5 mg/L lithium to assess removal and method performance.

Main Results and Discussion

• Chromatographic separation achieved baseline resolution of fluoride, formate, chloride, sulfate, and interfering acetate in both pure water and lithium‐bearing matrices.
• System blank showed minimal background (<15 nS drift); deionized water blank contained sub-µg/L anionic impurities; surrogate matrix blank contributed 0.4–2.0 µg/L of target species.
• Calibration curves were linear (r² ≥ 0.999) over 1–67 µg/L; estimated MDLs: fluoride 0.015 µg/L, formate 0.056 µg/L, chloride 0.022 µg/L, sulfate 0.28 µg/L.
• Precision over 17 sequential injections (12 h): retention time RSD <0.1 %, peak area RSD <3 % for all analytes.
• Accuracy evaluated in three surrogate matrices yielded recoveries between 78 % and 107 % after blank correction.

Benefits and Practical Applications

• Rapid, automated monitoring of corrosive anions in reactor coolant with minimal sample preparation.
• Efficient removal of lithium interference via CR-CTC II trap without manual cleanup.
• Reagent‐free eluent generation reduces contamination risk and operational costs.
• Suitable for QA/QC laboratories and high-throughput industrial environments.

Future Trends and Opportunities

• Online implementation for continuous reactor coolant monitoring and early corrosion detection.
• Extension to additional trace anions or small organic acids through gradient optimization.
• Miniaturized IC systems and trap devices for field diagnostics and remote deployments.
• Integration with mass spectrometry for enhanced selectivity, speciation, and low‐level detection.

Conclusion

The described large‐volume, reagent‐free ion chromatography method with a CR-CTC II lithium trap and high‐capacity AS22 column provides reliable, sub-µg/L analysis of key anions in lithium‐containing borated waters, delivering excellent linearity, precision, and accuracy for nuclear power plant coolant monitoring.

References

1. Nordmann F. Aspects of Chemistry in French Nuclear Power Plants; Proc. Properties of Water and Steam, Kyoto, Japan, 2004, 521–530.
2. Dionex Application Note 166: Trace Anion Analysis of Borated Waters; LPN 1654, 2004.
3. Dionex Application Note 185: Trace Organic Acids and Inorganic Anions in Boric Acid-Treated Power Plant Waters; LPN 1996, 2008.