ISO 7097-1:2025

Overview

ISO 7097-1:2025 - "Nuclear fuel technology - Determination of uranium in solutions, uranium hexafluoride and solids - Part 1: Iron(II) reduction/potassium dichromate oxidation titrimetric method" specifies a validated analytical titrimetric procedure for accurate determination of uranium in product materials from the nuclear fuel cycle. The method is designed for use on solids and solutions such as U metal, UO2, UO3, U3O8, uranyl nitrate hexahydrate and uranium hexafluoride (UF6). It is precise enough for nuclear materials accountability and routine quality control.

Key topics and technical requirements

• Analytical principle: Uranium(VI) is reduced to U(IV) with iron(II) in phosphoric acid; excess Fe(II) is removed and uranium is then quantified by titration with standardized potassium dichromate to a potentiometric end point.
• Mass titration recommended: An aliquot containing about 15 mg to 50 mg of uranium is weighed and titrated (mass titration) to improve precision and accuracy.
• Reagent and calibration: Potassium dichromate titrant must be standardized against an internationally recognized reference material (e.g., NIST SRM equivalents); water conforming to ISO 3696 is required and analytical-grade reagents must be used.
• Kinetics and auxiliaries: Vanadium(IV) is used to speed reaction kinetics and shift redox potential; sulfamic acid removes nitrite; molybdenum catalyses oxidation steps.
• Interference control: The method tolerates fission products equivalent to up to 10% burn‑up without significant interference. The standard details allowable impurity levels and species that can bias results (e.g., certain halides, platinum-group elements, As/Sb species) and specifies limits/conditions to avoid bias.
• Environmental and operational constraints: Titration timing (complete within minutes after dilution), controlled temperature range (noted effects outside typical 20–24 °C), and precautions for potentially radiolytic or high-activity samples are addressed.
• Sample-specific preparation: Clauses and normative annexes address preparation and subsampling procedures for solids and UF6 test solutions.

Practical applications and users

• Laboratories performing nuclear materials accountability, safeguards and regulatory verification.
• Quality control and production labs at uranium conversion, enrichment and fuel fabrication facilities.
• Analytical and research labs analyzing reactor fuels (irradiated or un‑irradiated), uranium oxides and nitrate solutions.
• Forensic and environmental labs involved in uranium assay where trace interferences and measurement traceability are important.
• Routine high‑throughput testing benefiting from partial automation of critical steps (the standard permits and recognizes advantages of automated devices).

Related standards

• ISO 7097 series (other parts, e.g., cerium(IV) titrimetric alternative in Part 2)
• ISO 3696 (water for analytical laboratory use)
• ISO 5725-1 (accuracy of measurement methods)
• ISO 9894 (subsampling of UF6)
• ISO 10980 (titrant verification and calibration guidance)

Keywords: ISO 7097-1:2025, uranium determination, iron(II) reduction, potassium dichromate titration, nuclear fuel technology, uranium hexafluoride, UO2, uranium nitrate, potentiometric titration, nuclear materials accountability.