Online trace analysis of cations in the primary circuit of nuclear power plants

Importance of the Topic

The primary coolant circuit in pressurized water reactors (PWRs) operates under high pressure to transfer heat while isolating radioactive materials. Corrosion in this circuit leads to costly downtime and increased radiation risk. Monitoring trace cations such as lithium, nickel, and zinc is essential to maintain pH control, prevent material degradation, and limit the formation of radioactive corrosion products.

Objectives and Study Overview

This application note demonstrates an automated ion chromatography (IC) approach for online trace-level analysis of cations in PWR primary circuit water. The study aims to detect key ions at sub-µg/L concentrations, integrate continuous sampling, and provide real-time feedback to the plant control system.

Methodology and Instrumentation

The 2060 IC Process Analyzer from Metrohm forms the core of the setup. Its modular design supports up to 20 sample streams and remote cabinet placement. Key features include:

• Inline preconcentration to enhance sensitivity for low-level ions
• Inline matrix elimination and neutralization to remove high levels of boric acid and lithium hydroxide
• Automated eluent production for stable baselines
• Conductivity detection following ion separation
• ‘All-in-one’ software for scheduled runs, calibration, trend monitoring, and process communication (Modbus, Discrete I/O)

Main Results and Discussion

Tests on a simulated primary circuit sample containing 2 g/L H₃BO₃ and 3.3 mg/L LiOH spiked with nickel, zinc, calcium, and magnesium demonstrated:

• Detection limits in the sub-µg/L range for all target cations
• Effective removal of bulk borate and lithium backgrounds via inline matrix elimination
• High reproducibility and recovery rates through automated calibration
• Reliable alarm generation when preset concentration thresholds are exceeded

Benefits and Practical Applications

The integrated IC solution offers multiple advantages for nuclear plant water monitoring:

• Continuous, fully automated analysis reduces manual sampling errors and maintenance interruptions
• Early detection of corrosion-inducing ions protects pipes, turbines, and reactor components
• Automated feedback and alarms support proactive process control
• Single analyzer deployment across multiple sampling points lowers equipment costs

Future Trends and Opportunities

Advancements in process analytics for nuclear water circuits will likely focus on tighter integration with plant digital twins and control systems, application of machine learning for predictive maintenance, expansion to trace anion analysis, and further miniaturization of inline modules. Enhanced data communication and remote diagnostics will improve reliability and reduce operational overhead.

Conclusion

An automated 2060 IC Process Analyzer equipped with inline preconcentration and matrix elimination provides a robust solution for online trace cation monitoring in PWR primary circuits. The system delivers sensitive, reproducible, and real-time data critical for corrosion control and reactor safety.

Reference

• AN-PAN-1043 Online trace analysis of cations in the primary circuit of nuclear power plants, Metrohm AG