ISO 24459:2021 PDF

Overview

ISO 24459:2021 specifies a quantitative method to determine uranium content in solutions and solids from the nuclear fuel cycle using L‑absorption edge spectrometry (X‑ray transmission at the uranium L‑edge, E ≈ 17.17 keV). The standard covers measurement principle, instrument and cell requirements, spectrum acquisition and processing, calibration, quality control and uncertainty evaluation for both process control and high‑accuracy (safeguards) applications.

Key topics and technical requirements

• Scope and sample types: Applicable to nitric acid and TBP‑diluent (e.g., TBP‑kerosene) solutions and to solid materials that can be fully dissolved in nitric acid.
• Concentration ranges:
  • Process control: 10 g/L to 300 g/L U.
  • High‑accuracy (safeguards): 100 g/L to 220 g/L U (nitric acid solutions).
• Interference limits for high accuracy: neptunium, plutonium and neutron poisons (e.g., gadolinium, erbium) should be <1% of uranium content to avoid significant interferences.
• Measurement principle: A collimated X‑ray beam passes through a well‑defined path length; the sharp transmission jump at the uranium L‑edge is used to derive concentration via calibration and spectrum‑fitting algorithms.
• Instrument and cell:
  • X‑ray tube voltage > 25 kV, stable current (adjustable, typically