Overview - ISO 6863:2024 (Nuclear fuel technology - Preparation of spikes for IDMS)
ISO 6863:2024 specifies methods for preparing and validating standard materials (commonly called spikes or large-sized dried (LSD) spikes) used in isotope dilution mass spectrometry (IDMS) for measuring uranium and plutonium content. The standard targets uncertainty levels suitable for international nuclear safeguards and applies to samples from irradiated Magnox and light water reactor fuels (BWR/PWR), spent-fuel reprocessing plants, MOX feed/products, and uranium fuel fabrication.
Key technical topics and requirements
- Spike types and design
- Solution spikes (nitric acid solutions with quantified U/Pu isotopic composition) and dried spikes (aliquoted and dried into glass vessels).
- Large-sized dried (LSD) spikes contain milligram quantities of both U and Pu to simplify preparation and reduce dilution-related uncertainty.
- Preparation procedures
- Preparation of uranium, plutonium and mixed stock solutions (typically in 3–7 mol/L HNO3).
- Aliquoting, drying, and stabilization steps for LSD and other dried spikes.
- Procedures for liquid spikes and dried spikes for U, Pu, and U–Pu mixtures.
- Optimization and uncertainty
- Guidance on optimizing spike isotopic composition and sample:spike ratios to minimize measurement error (equations and design considerations included).
- Uncertainty budgeting combines contributions from certified reference materials (CRMs), balances, and analytical instrumentation; expanded uncertainty reported with k = 2 per ISO/IEC Guide 98‑3.
- Reference materials, reagents and apparatus
- Use of high-purity CRMs (e.g., uranium CRMs with elemental content certified to ±0.05 % (k = 2) where applicable) and analytical-grade reagents.
- Lists normative references including ISO 3696 (water for analytical use) and ISO 8299 (TIMS determination of U/Pu concentrations).
- Validation, storage and reconditioning
- Procedures for characterizing and validating spikes and for storing solution and dried spikes, including reconditioning of dried spikes.
Practical applications and intended users
- Laboratories performing IDMS/TIMS measurements of uranium and plutonium for:
- Nuclear safeguards and compliance verification.
- Spent fuel reprocessing and material accountancy.
- MOX production and uranium fuel fabrication quality control.
- Quality managers, analytical chemists, metrologists and nuclear safeguards inspectors who need standardized spike preparation methods to achieve traceable, low‑uncertainty isotopic measurements.
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 8299 - Determination of U and Pu concentrations by TIMS
- ISO/IEC Guide 98‑3 - Evaluation of measurement uncertainty (GUM)
ISO 6863:2024 provides practical, traceable procedures to produce robust spikes that reduce IDMS measurement uncertainty and streamline high‑precision U/Pu isotopic assays in nuclear fuel technology and safeguards contexts.