Overview - ISO 12183:2024 (Controlled-potential coulometric measurement of plutonium)
ISO 12183:2024 is an International Standard in the field of nuclear fuel technology that specifies a reproducible analytical method for the controlled-potential coulometric measurement of plutonium in nuclear-grade, pure plutonium nitrate solutions. The method delivers high-accuracy results with an expanded uncertainty not exceeding ±0.2 % (k = 2) for a single determination. It is applicable to aqueous solutions with plutonium concentrations > 0.5 g·L⁻¹ and to test samples containing 4 mg to 15 mg of plutonium; lower concentrations or smaller test samples can be measured only after user demonstration that data quality objectives are met.
Key topics and technical requirements
- Scope & uncertainty: Single-determination expanded uncertainty ≤ ±0.2 % (confidence level 0.95, k = 2).
- Sample preparation: Weighing, fuming to dryness with sulfuric acid to form anhydrous plutonium sulfate free of specific interferences (chloride, fluoride, nitrate, nitrite, hydroxylamine, volatile organics).
- Purification option: Anion-exchange separation (Annex A) when interferences must be removed.
- Electrochemical measurement: Controlled-potential reduction and oxidation to electrolyse > 99.8 % of plutonium fraction; measurement of equilibrium solution formal potential (E0') and control-potential adjustments.
- Blank and background correction: Measure supporting-electrolyte blank and correct integrator output for charging, faradaic and residual currents.
- Calibration & traceability: Coulometer calibrated against traceable electrical standards using Ohm’s law; conversion to moles via the Faraday constant and multiplication by a molar mass value obtained independently (e.g., mass spectrometry or process knowledge). Clause 12 covers traceability to SI units.
- Reagents & materials: ISO 3696 Grade 1 water; specified acid concentrations (examples: 0.9 mol·L⁻¹ HNO3, 1.5 mol·L⁻¹ amidosulfuric acid, 3 mol·L⁻¹ H2SO4).
- Apparatus & metrology: Analytical balance with installed standard uncertainty ±0.1 mg (k = 1); sample evaporation/fuming system and standard radiochemical laboratory equipment.
- Quality control & method performance: Includes repeatability, confidence intervals, analysis time, interferences, and procedural optimizations (Clause 9–11). Annex B explains formal potential determination.
Practical applications and typical users
- Accountability and materials control in nuclear fuel facilities where precise plutonium assay is required.
- Metrology and reference laboratories performing traceable plutonium mass determinations and validating measurement systems.
- Process control and safeguards applications where routine, high-accuracy plutonium assays (4–15 mg test samples) are required.
- Radiochemical laboratories implementing coulometric methods for plutonium in compliance with international best practice.
Related information and standards
- This document contains no normative references but cites ISO 3696 (Grade 1 water) and was prepared by ISO/TC 85 (Nuclear energy) in collaboration with CEN/TC 430.
- Informative annexes: Annex A (anion-exchange purification) and Annex B (determination of formal potential).
For implementation, laboratories should follow the method steps, ensure electrical and mass traceability, and use quality-control standards with traceable plutonium quantity values to demonstrate system performance.
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