Overview
ISO 12803:1997 specifies precautions and practical procedures to obtain representative samples of plutonium nitrate solutions for accurate determination of plutonium concentration. It applies to pure, final‑product plutonium nitrate solutions free of organic phases and suspended solids and provides guidance on tank mixing, sampling, storage and verification so that sample concentrations reliably reflect the tank contents (the standard notes sample vs. batch differences can be kept below 0.2%).
Key topics and requirements
- Tank mixing and homogenization
- Draw up and experimentally verify a mixing procedure for each tank installation (geometry, circulation, stirring, sparging or recirculation).
- Ensure thorough homogenization to avoid density/temperature stratification and stagnant zones.
- Sampling system design
- Use short, direct sampling lines with small cross‑section; rinse lines with the solution before sampling and discard the first sample to avoid cross‑contamination.
- Take samples during recirculation or transfer; collect several samples from different locations where practicable.
- Physical/chemical controls
- Ensure no organic phase or suspended solids (>0.01 g·L‑1) are present; filter or centrifuge if necessary.
- Keep plutonium concentration well within solubility limits for expected acidity and temperature (example: at ~2 mol·L‑1 HNO3 and 20 °C, concentrations around 300 g·L‑1 are acceptable).
- Sample handling and storage
- Use clean, dry, leak‑proof bottles; recommended fill is 5–10 mL in a 15 mL bottle (balance between evaporation and radiolytic pressurization).
- Store upright, keep neck dry, and close immediately. Beware of radiolytic gas pressure when opening.
- Complete analysis within 48 hours unless using validated alternative techniques (weight‑correction, pre‑weighed aliquots, or dilution).
- Options: weigh bottles before/after storage to correct concentration for mass loss; store pre‑weighed aliquots for later quantitative transfer; dilute to ~20 g·L‑1 Pu for improved stability.
- Apply Pu‑241 decay correction for samples stored longer than four months.
- Verification
- Validate mixing, sampling and storage procedures for each installation and revalidate after modifications.
- Use density measurements (per ISO 11597) as a routine homogeneity test where applicable.
Applications
- Nuclear material accountability and inventory control
- Quality assurance of plutonium nitrate product batches
- Process control in plutonium conversion and storage facilities
- Safeguards and regulatory sampling for custody transfer
- Design and validation of tank mixing/sampling systems to support accurate analytical measurements
Who should use this standard
- Nuclear fuel and plutonium processing plant engineers
- Analytical laboratories measuring plutonium concentration
- Safeguards, safeguards inspectors and regulatory bodies
- Criticality safety and process design teams
Related standards
- ISO 11597:1995 - Verification of samples of uranyl or plutonium nitrate solutions by density measurement (referenced for homogeneity testing).
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