Online analysis of trace anions in borated water of a pressurized water reactor (PWR)

Significance

Borated water in the primary circuit of pressurized water reactors serves to absorb neutrons but poses analytical challenges because high borate concentrations mask low-level anions. Reliable inline removal of boron and sensitive detection of trace anions supports reactor safety monitoring and quality control in nuclear facilities.

Study Objectives and Overview

This study demonstrates an online ion chromatographic method integrating Inline Neutralization with variable preconcentration and Inline Matrix Elimination (MiPCT-ME). The approach aims to eliminate boron interference as boric acid prior to injection, enabling accurate quantification of trace anions such as fluoride, glycolate, acetate, formate, chloride, bromide, nitrate, phosphate and sulfate in borated PWR water.

Methodology

An artificial primary circuit water matrix containing 2 g/L boron and 3.3 mg/L lithium hydroxide was prepared and spiked with anions at 5 µg/L. Inline Neutralization converted borate ions into boric acid for removal before the concentrate step. Variable-volume preconcentration enriched target anions by a factor of 40. Following Inline Matrix Elimination, the cleaned extract entered the chromatographic system. Separation employed a sequential suppression conductivity detector, with a 2000 µL injection volume at 0.8 mL/min flow, 45 °C column temperature and a 32 min run time. Calibration spanned 0.5 to 20 µg/L via standard additions and inline eluent preparation using 3.6 mmol/L sodium carbonate. Regenerants included 100 mmol/L sulfuric acid for the suppressor and 10 mmol/L oxalic acid for the preconcentration module.

Used Instrumentation

• 850 Professional IC Anion with MCS-Prep 3 (Metrohm 2.850.2190)
• IC Conductivity Detector (Metrohm 2.850.9010)
• 872 Extension Module Liquid Handling (Metrohm 2.872.0060)
• 800 Dosino for inline dosing (Metrohm 2.800.0010)
• 849 Level Control for inline eluent preparation (Metrohm 2.849.1030)

Results and Discussion

All target anions were quantified at spiked levels of 5 µg/L except nitrite, which remained below quantifiable limits due to matrix background. The inline boron removal step effectively prevented peak interference, and the method achieved a consistent enrichment factor of 40. Chromatographic resolution between closely eluting anions was maintained across repeated runs, demonstrating robustness under 15 MPa pressure conditions.

Benefits and Practical Applications

The MiPCT-ME approach streamlines sample handling by automating boron removal and preconcentration inline. It enhances sensitivity for regulatory compliance and real-time monitoring in nuclear power plants. Reduced manual preparation lowers contamination risks and laboratory turnaround times, supporting continuous process control in PWR cooling circuits.

Future Trends and Possibilities

Advances may include coupling with mass spectrometric detectors for improved selectivity, miniaturization of flow paths for lower reagent consumption, and remote system integration for in situ monitoring. Expansion to other challenging matrices such as high-saline or geothermal waters could extend the technique’s applicability.

Conclusion

The described inline method offers reliable trace anion analysis in borated reactor water by effectively removing boron interference and achieving low detection limits. Its automation and robustness make it suited for routine quality assurance and safety monitoring in nuclear facilities.

Reference

Metrohm IC Application Note Q–6 Version 1