ISO 8298:2000

Overview

ISO 8298:2000 specifies a precise, selective analytical method for the determination of milligram amounts of plutonium (1–5 mg Pu per ml) in nitric acid solutions. Developed for nuclear fuel technology, the method uses potentiometric titration with potassium dichromate after chemical manipulation of plutonium oxidation states: oxidation by Ce(IV) to Pu(VI) and controlled reduction with Fe(II). The standard replaces ISO 8298:1987 and is intended for routine assays of product and mixed-material solutions (U/Pu ratios up to 20:1).

Key topics and technical requirements

• Principle: Oxidize plutonium to Pu(VI) with Ce(IV); remove excess Ce(IV) by reduction with sodium arsenite (OsO4-catalysed) and secondary redox clean-up (permanganate → oxalic acid). Reduce Pu(VI) quantitatively with a standardized Fe(II) sulfate solution; back-titrate excess Fe(II) with standardized potassium dichromate potentiometrically.
• Range and selectivity: Designed for 1–5 mg Pu/ml; selective for plutonium in the presence of many matrix elements. Documented for mixed uranium/plutonium solutions up to 20:1 (ratios 20:1–33:1 not fully documented).
• Standardization: Both dichromate and Fe(II) titrants are standardized against a plutonium reference solution prepared from certified Pu metal. Plutonium reference strength is verified against NIST SRM 136 dichromate and validated per ISO 10980.
• Interferences and controls: Details limits for matrix elements (e.g., rubidium, lanthanides tolerated at specified levels). Notable interferences include vanadium (IV/V) and neptunium (co-titrates with Pu; correction factor described). Control of nitrite, amidosulfonic acid, fluoride (complexed by Al(III)) and other reagents is required to avoid bias.
• Reagents & apparatus: Lists analytical-grade reagents (Ce(IV), osmium tetroxide warning, arsenite, permanganate, oxalic acid, 3 M H2SO4, Fe(II) sulfate, K2Cr2O7) and instrumentation such as a high-impedance millivoltmeter and gravimetrically calibrated burettes. Emphasis on reproducible reaction conditions and benefits of automation.
• Quality metrics: Procedure includes standardization, repeatability, accuracy sections and prescribes gravimetric calibration of burettes and weighed aliquots for best precision.

Applications and users

• Analytical laboratories in nuclear fuel fabrication, reprocessing, and radio-chemical quality control.
• Nuclear safeguards and material accounting teams requiring accurate Pu assay in nitric acid solutions.
• Research groups and metrology laboratories validating reference solutions and titrant strengths.

Related standards

• ISO 10980 - Validation of the strength of reference solutions used for measuring concentrations.
• NIST SRM 136 - potassium dichromate reference material used for cross-verification.

Keywords: ISO 8298:2000, plutonium determination, potentiometric titration, potassium dichromate, Ce(IV), Fe(II), nitric acid, nuclear fuel technology, reference solution, ISO 10980.