Overview
EN ISO 18256-2:2021 (ISO 18256-2:2019) is a CEN-adopted international standard in nuclear fuel technology that specifies validated procedures for the dissolution of MOX pellets and powders (mixed oxide fuels containing plutonium dioxide). The method produces representative aliquots suitable for subsequent elemental concentration and isotopic composition analysis of plutonium and uranium in MOX samples.
Key topics and technical requirements
- Scope and purpose: Dissolution techniques tailored to different MOX fabrication routes and degrees of sintering to ensure complete and reproducible sample dissolution.
- Sample mass guidance: Typical sample masses recommended range from 0.1 g to 10 g, balancing radiological safety and analytical needs.
- Apparatus: Laboratory equipment for plutonium handling (analytical balance 0.001 g accuracy, dissolution vessels with PTFE-lined caps, reflux caps/condensers, shielded hotplates, fume hood, PTFE-coated tweezers).
- Reagents and solutions:
- Nitric acid in the range of about 8–14 mol·L−1 (concentrated HNO3 ~14.4 mol·L−1).
- Catalytic fluoride from HF (≈0.05–0.1 mol·L−1) or ammonium bifluoride (~2 g·L−1) to assist dissolution.
- Guidance on preparing mixed nitric–hydrofluoric solutions and cautions (never add concentrated HF to a plutonium nitrate solution to avoid insoluble plutonium fluoride).
- Container materials: Trade-offs between glass and polymer (HDPE, PTFE, Nalgene) vessels are discussed - glass can be attacked by fluoride (allowing SiF4 removal) while polymers resist HF but can promote plutonium fluoride precipitation under some conditions.
- Analytical approaches: Gravimetric dissolution is recommended for highest assay accuracy; volumetric approaches may be acceptable for less critical assays.
- Quality & safety: Emphasis on radiological controls - work in glove boxes or hot cells, strict procedures for handling corrosive reagents (HF and HNO3), and measures to minimize waste and contamination.
Applications and users
This standard is intended for:
- Nuclear fuel fabrication and quality-control laboratories.
- Radiochemistry and safeguards laboratories performing plutonium isotopic analysis.
- Nuclear forensics and regulatory labs requiring reproducible sample preparation for elemental and isotopic assays.
- Organizations needing standardised MOX dissolution protocols for inter-laboratory comparability and traceable results.
Keywords: EN ISO 18256-2:2021, dissolution of MOX, MOX pellets and powders, plutonium dioxide dissolution, nuclear fuel technology, plutonium isotopic analysis, sample dissolution method.
Related standards
- The document is part of the ISO 18256 series; users should consult other parts of the series and national/adopted CEN versions for complementary guidance and regulatory context.
