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ISO 26062:2010 Nuclear Technology — Nuclear Fuels — Procedures for the Measurement of Elemental Impurities in Uranium- and Plutonium-Based Materials by Inductively Coupled Plasma Mass Spectrometry
Comprehensive Analysis of ICP-MS Procedures for Trace Elemental Impurity Determination in Nuclear Fuel Materials
1. Standard Overview and Application Background
ISO 26062:2010 is a critical standard in nuclear fuel technology, specifying detailed procedures for the determination of trace elemental impurities in uranium-based, plutonium-based, and mixed uranium-plutonium materials using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Developed by ISO/TC 85 (Nuclear energy) SC 5 (Nuclear fuel cycle), this standard provides a unified analytical methodology framework for global nuclear fuel quality control.
ICP-MS can quantitatively measure virtually all elements except H, He, C, N, O, F, Cl, Br, and noble gases, with detection limits reaching the ng/g level, making it the preferred technique for nuclear fuel purity analysis.
In the nuclear fuel cycle, the types and concentrations of impurity elements directly impact fuel performance, reactor safety, and waste management. Elements with high neutron absorption cross-sections (e.g., B, Cd, rare earth elements), even at trace levels, can significantly affect reactor neutron economy. ISO 26062 provides comprehensive operational guidance from sample preparation to data reporting for nuclear fuel manufacturers, power plants, and regulatory bodies.
ISO 26062 covers multiple sample forms: uranyl/plutonium nitrate solutions, uranium/plutonium oxide solids, and unirradiated mixed oxide (MOX) fuel, making it broadly applicable across the nuclear fuel cycle.
2. Sample Preparation and Matrix Separation
2.1 Dissolution Methods
The standard describes three dissolution options, allowing engineers to select based on sample characteristics and laboratory conditions:
| Method | Sample Type | Reagents | Conditions | Advantage |
|---|---|---|---|---|
| Open-beaker hot-plate | PuO2, MOX, UO3 | 12 M HNO3 / 0.05 M HF | 150 deg C, 3-4 hours | Simple equipment, glove-box compatible |
| Reflux dissolution | MOX (4g) | 16 M HNO3 + 0.1 M HF | 130 deg C reflux, 80 deg C 2h de-nitration | Large capacity, low volatile loss |
| Microwave dissolution | PuO2, MOX (0.5-0.8g) | 12 M HNO3 / 0.1 M HF | 10 min to 215 deg C, hold 20 min, 2758 kPa limit | Fast, fully automated |
2.2 Matrix Separation Techniques
To eliminate interference from the uranium/plutonium matrix during ICP-MS measurement, the standard provides two validated separation approaches:
Chromatographic separation: Eichrom UTEVA resin columns retain uranium while allowing impurity elements to pass through. Recovery rates for most elements reach 94-100%, with residual actinide below 1 ug/mL and separation efficiency exceeding 99.9%.
TBP solvent extraction: Using 30% tributyl phosphate in odourless kerosene, this method exploits the extractability of tetravalent and hexavalent uranium/plutonium ions into the organic phase, leaving impurities in the aqueous phase. A minimum of 4 extractions is required for uranium matrices, and 5 for plutonium matrices.
| Separation Method | Efficiency | Recovery Range | Application Notes |
|---|---|---|---|
| UTEVA chromatography | > 99.9% | 90% – 100% | Most elements suitable; Ag/Th require HCl elution |
| 30% TBP solvent extraction | > 99.9% | 55% – 100% | Suitable for batch processing; Th recovery lower (55-75%) |
When selecting a matrix separation method, careful attention must be paid to analyte recovery. For example, Th recovery in TBP extraction is only 55%-75%, requiring mandatory recovery correction. Recovery should be monitored for every analytical batch and included in uncertainty evaluation.
3. Mass Spectrometric Analysis and Interference Control
3.1 Interference Types and Solutions
ICP-MS analysis of nuclear fuel materials faces three primary interference types:
Isobaric interference: Arising from isobars of other elements, e.g., Cd-114 interfered by Sn-114. Solutions include pre-measurement removal, blank correction, and mathematical correction.
Molecular ion interference: Arising from argon plasma species (Ar+, ArO+, etc.) and solvent-derived molecular ions. In uranium/plutonium matrices, doubly charged and oxide ions (U2+, UO+, UO2+, Pu2+, PuO+, PuO2+) are particularly important as they interfere with elements in the mass range 110-140.
| Actinide Parent | M2+ Mass | Affected Element | MO2+ Impact |
|---|---|---|---|
| U-238 | 119 | Sn | UO2+ affects Ba (mass 135) |
| Pu-239 | 119.5 | — | PuO+ complex interferences |
| Pu-240 | 120 | Te, Sn | PuO2+ mass range effects |
| Th-232 to Am-242 | 116-121 | Cd, Sn, Sb, Te | Ba, Cs, Ce affected |
Peak overlap interference: Tail spillover from adjacent major peaks. For example, a 100 ug/mL U-238 peak produces approximately 1 ng/mL overlap at mass 237 (abundance sensitivity ~1e-5).
For nuclear fuel analysis, UC+ interference on Al (from organic carbon), ArO+ interference on Fe, and ArCl+ interference on As are the most common pitfalls in routine analysis. Collision/reaction cell technology or high-resolution sector field ICP-MS is recommended to address these challenges.
4. Quality Assurance and Control Framework
ISO 26062 establishes a comprehensive QA/QC framework comprising:
- Instrument performance verification: Mass calibration, resolution check, detector calibration, and sensitivity trending
- Internal standardization: Three internal standards recommended covering low, medium, and high mass ranges (e.g., Be/Sc for low masses, In/Rh for mid-masses, Bi/Ir for high masses)
- Method blanks: Required at sample preparation, extraction (where applicable), and instrument measurement stages
- Quality control standards: From different sources than calibration standards to verify calibration integrity
- Recovery control: Certified reference materials (CRM) or spiked recovery assessment for method validation
Recommended instrument precision: conventional quadrupole ICP-MS coefficient of variation (1 sigma) 10-20%, sector field ICP-MS approximately 12%. Detection limits depend on the chosen approach: quadrupole instruments typically achieve 0.1-1 ug/g relative to original sample; sector field instruments can reach 0.2-200 ng/g.
5. Frequently Asked Questions (FAQ)
Q1: What are the advantages and disadvantages of direct analysis versus post-separation analysis?
Direct analysis offers speed, minimal sample handling, and low analyte loss/contamination risk, but suffers from matrix effects (signal suppression) and instrument contamination. Post-separation analysis significantly improves detection limits and protects the mass spectrometer from radioactive contamination, but carries risks of analyte loss and contamination during processing.
Direct analysis offers speed, minimal sample handling, and low analyte loss/contamination risk, but suffers from matrix effects (signal suppression) and instrument contamination. Post-separation analysis significantly improves detection limits and protects the mass spectrometer from radioactive contamination, but carries risks of analyte loss and contamination during processing.
Q2: Why is hydrofluoric acid (HF) needed for dissolution?
HF is essential for dissolving refractory plutonium oxide (PuO2) and mixed oxides (MOX), which have extremely low solubility in pure HNO3. HF promotes dissolution by forming stable complexes with Pu4+. Concentrations of 0.05 M to 0.1 M HF are typically sufficient.
HF is essential for dissolving refractory plutonium oxide (PuO2) and mixed oxides (MOX), which have extremely low solubility in pure HNO3. HF promotes dissolution by forming stable complexes with Pu4+. Concentrations of 0.05 M to 0.1 M HF are typically sufficient.
Q3: How should internal standard elements be selected?
Internal standards should: not be present in blanks/standards/samples; have isotopes free from interference; not interfere with analyte isotopes; ideally be mono-isotopic; and have similar physico-chemical behavior to analytes. A three-internal-standard mixture covering the full mass range is recommended.
Internal standards should: not be present in blanks/standards/samples; have isotopes free from interference; not interfere with analyte isotopes; ideally be mono-isotopic; and have similar physico-chemical behavior to analytes. A three-internal-standard mixture covering the full mass range is recommended.
Q4: What special considerations apply to fission product elements (e.g., Zr, Mo, Gd)?
Fission products exhibit non-natural isotopic abundances. Quantification must use specific isotope ratios or total element concentration calculations. Annex A.1 of the standard lists these elements and their considerations. Certified reference materials are strongly recommended for method validation.
Fission products exhibit non-natural isotopic abundances. Quantification must use specific isotope ratios or total element concentration calculations. Annex A.1 of the standard lists these elements and their considerations. Certified reference materials are strongly recommended for method validation.
