ISO 13465:2024

Overview

ISO 13465:2024 - "Nuclear energy - Nuclear fuel technology - Determination of neptunium in nitric acid solutions by spectrophotometry" specifies a validated analytical method for measuring neptunium in nitric acid solutions produced during the dissolution of irradiated nuclear fuel. The procedure is adapted for high-activity samples handled in a hot cell or glove box, delivers a standard uncertainty of about 5 % (k = 1), and applies to solutions with neptunium concentrations between 10 mg·L⁻¹ and 400 mg·L⁻¹ and uranium up to 300 g·L⁻¹.

Key topics and technical requirements

• Analytical principle: quantitative conversion to neptunium(V) and spectrophotometric measurement of the absorbance peak at 981 nm using a calibrated spectrophotometer.
• Interferences addressed: uranium(VI) complexation (absorption peak ~992 nm), acidity effects, plutonium valence states, other redox species, and nitrite ions. The standard requires control of nitrate and acidity to limit bias.
• Redox buffering: use of a vanadium(V)/vanadium(IV) redox buffer to stabilize Np(V) and control redox conditions (recommended V(V)/V(IV) ratio ~0.5; final ratio between 0.25 and 1).
• Reagents: nitric acid solutions at defined molarities, vanadium and cerium solutions, uranyl nitrate matrix-matching solution, and a certified neptunium reference solution.
• Apparatus: double-beam grating spectrophotometer with low noise (absorbance fluctuation < 0.001), spectral range to ~1100 nm, appropriate measurement cell (typical path length 1 cm, longer paths optional), volume-calibrated glassware per ISO 1042, and precise pipettes.
• Procedure elements: calibration with reference standards, sample preparation/matrix matching, spectrophotometer setup, measurement on calibration and sample solutions, and expression of results (calculation, reproducibility and detection limit provisions).

Practical applications and users

This standard is intended for:

• Process control and monitoring in nuclear fuel reprocessing plants and other nuclear facilities handling dissolved fuel solutions.
• Routine radiochemical analysis teams performing neptunium quantification for safety, regulatory reporting, or material accountancy.
• Laboratory managers, radiochemists, nuclear analysts, and instrument suppliers who implement or validate spectrophotometric assays in controlled containment (hot cells/glove boxes). Practical benefits include reproducible, matrix-aware quantification suited to high-activity nitric acid solutions and compatibility with uranium-bearing matrices.

Related standards

• ISO 1042 - Laboratory glassware: one-mark volumetric flasks (referenced for volumetric equipment).
• ISO 3696 - Water for analytical laboratory use (grade 3) recommended for reagent preparation.
• Prepared under ISO/TC 85 (Nuclear energy) guidance.

Keywords: ISO 13465:2024, neptunium determination, spectrophotometry, nitric acid solutions, nuclear fuel reprocessing, Np(V), vanadium redox buffer, hot cell analysis.