Uranium Isotopic Analysis for the Nuclear Industry Using the Thermo Scientific NEPTUNE Plus MC-ICP-MS

Significance of the Topic

Uranium isotopic analysis by MC-ICP-MS is critical for nuclear fuel QA/QC, non-proliferation, and enrichment verification. It enables precise determination of 235U content in feed and product streams.

Objectives and Overview of the Study

This study evaluates the Thermo Scientific NEPTUNE Plus MC-ICP-MS performance for low-enriched uranium isotopic measurement following ASTM C1477-08, focusing on precision, stability, and throughput.

Methodology

The protocol includes:

• Dilution of uranium solutions to 100 ng/g U in 2% HNO3.
• Automated autosampler (Cetac ASX-112 FR) for 30 samples and quality controls over 8 hours.
• Data correction for blanks, hydride interferences, and mass bias using CRM IRMM-187.
• Triplicate sequences over three consecutive days with alternating certified reference materials NBS U-045, U-030 and U-010.

Instrumentation

The NEPTUNE Plus MC-ICP-MS setup:

• Central SEM and RPQ lens for improved abundance sensitivity (m/z 237.05/238U ~0.35 ppm).
• Compact discrete dynode SEM for 234U detection.
• Faraday cups for 235U and 238U.
• PFA spray chamber and standard wet plasma cones (sensitivity ~44 V/ppm; ~70 ng U consumption per analysis).

Main Results and Discussion

The method achieved:

• 235U relative standard deviation (RSD) <0.1% and minor isotopes (234U, 236U) RSD <1%.
• Stable mass bias and ion counter yield over 8-hour sequences (30 measurements each standard per day).
• Measured values closely match certified and literature reference data (Richter & Goldberg 2003).

Benefits and Practical Application

• High throughput: 30 samples plus controls in 8 hours with fully automated corrections.
• Fit-for-purpose uncertainty (<0.1% for 235U) suitable for nuclear industry QA/QC.
• Global support network for continuous operation in critical applications.

Future Trends and Opportunities

The NEPTUNE Plus can be further optimized with:

• Jet interface for ultra-low sample amounts and improved counting statistics.
• Custom collector configurations for minor isotopes on Faraday cups.
• Dual RPQ for enhanced sensitivity on 234U and 236U measurement.
• High-ohm amplifiers (10^10–10^12 Ω) to improve signal-to-noise for low-intensity beams.
• Adaptations for glove box or fume hood containment for enhanced safety.

Conclusion

The Thermo Scientific NEPTUNE Plus MC-ICP-MS effectively meets ASTM C1477-08 requirements, delivering precise, stable uranium isotope measurements for low-enriched samples. Its flexibility and robust performance make it a valuable tool for nuclear industry applications.

References

• Richter S., Goldberg S.A. Int. J. Mass Spectrom. 2003;229:181–197.
• Thermo Fisher Scientific. Application Note 30187. Breakthrough in Sensitivity using a Large Interface Pump and New Sample Cone.
• Thermo Fisher Scientific. Application Note 30136. Improvements in TIMS High Precision Isotope Ratio Measurements for Small Sample Sizes.
• Thermo Fisher Scientific. Application Note 30192. New Compact Discrete Dynode Multipliers Integrated into TRITON Array.
• ASTM International. ASTM C1477-08. Standard Test Method for Isotopic Abundance Analysis of Uranium by MC-ICP-MS.