Lithium in borated water of a pressurized water reactors (PWR)

Importance of the topic

In pressurized water reactors (PWRs), precise monitoring of boron and lithium concentrations in the primary coolant is essential for reactor safety and corrosion control. Boric acid serves as a neutron absorber to regulate reactivity, while lithium hydroxide maintains pH above 7 to minimize material degradation. An analytical method capable of quantifying lithium in the presence of high boron levels enhances reactor coolant quality assurance.

Objectives and study overview

This application note describes the development and validation of an ion chromatography (IC) method for simultaneous determination of lithium in artificial PWR primary cycle water containing 3 g/L boron. The main goals were to achieve reliable quantification, low relative standard deviation, and a broad calibration range despite the challenging matrix.

Methodology and Instrumentation

The method integrates inline preconcentration with matrix elimination (MiPCT-ME) to separate lithium from the high boric acid background, followed by conductivity detection. Key operational parameters and hardware include:

• Sample matrix: Artificial PWR coolant (3 g/L boron, 5 mg/L lithium)
• Inline preconcentration: MiPCT-ME column for selective retention and matrix removal
• Analytical column: Metrosep C4-250/2.0 guard and separation columns
• Eluent preparation: 2.5 mmol/L nitric acid and 0.5 mmol/L oxalic acid generated inline
• Flow rate: 0.4 mL/min; Injection volume: 20 µL; Column temperature: 32 °C; Backpressure up to 25 MPa; Total run time: 10 min
• Calibration: Six levels covering 0.2 to 10 mg/L lithium achieved by a 50× dilution factor using standard additions

Instrumentation setup:

• Metrohm 850 Professional IC – Cation analysis
• IC Conductivity Detector
• 858 Professional Sample Processor for automated sample handling
• 2 × 800 Dosino for precise eluent and standard dosing
• 849 Level Control module for continuous inline eluent generation

Key results and discussion

The validated method demonstrated:

• Accurate lithium quantification at 5 mg/L with an RSD of 0.78% (n=6)
• Effective suppression of boric acid interference through inline matrix elimination
• Linear response across the calibration range (0.2–10 mg/L) enabling trace-level detection

These results confirm the robustness of the MiPCT-ME approach for complex reactor coolant matrices.

Benefits and practical applications

Implementation of this IC protocol delivers:

• High precision monitoring of lithium in the presence of elevated boron concentrations
• Rapid analysis time (10 min) supporting routine quality control in nuclear power plants
• Automated eluent preparation and sample processing reducing manual intervention

Future trends and potential applications

Emerging directions include adapting the inline preconcentration strategy for other light cations in nuclear and industrial aqueous media, further lowering detection limits with advanced detectors, and integrating real-time online monitoring to enhance reactor coolant management and safety.

Conclusion

The described ion chromatography method with inline matrix elimination offers a reliable, precise, and efficient solution for lithium determination in PWR coolant. Its automation and interference suppression capabilities make it well suited for demanding nuclear industry quality assurance.

Reference

IC Application Note C–140, Version 1