ISO 16797:2004

Overview

ISO 16797:2004 - "Nuclear energy - Soxhlet-mode chemical durability test - Application to vitrified matrixes for high-level radioactive waste" defines a standardized parameter test to measure the initial dissolution rate of nonporous vitrified materials (nuclear glass and similar vitrified matrices) in deionized boiling water. The method uses a Soxhlet-mode apparatus to accelerate alteration phenomena at the boiling point (~100 °C, corrected for laboratory altitude) and provides a reproducible metric for comparing materials whose early-stage dissolution is governed by surface-reaction mechanisms.

Key topics and technical requirements

• Purpose: determine the initial dissolution rate in pure boiling water as a short-term chemical durability parameter - not a substitute for long-term performance assessment.
• Applicability: glass, vitrified materials, and nonporous oxides that can be prepared as monolithic coupons with known surface area; excludes porous media where diffusion dominates.
• Soxhlet apparatus essentials:
  • Stainless-steel distillation flask (≥ 500 mL), regulated heater, overflow-type sample boat, stainless-steel condenser and water coil.
  • Flow control: solution renewal constant within ±10% and at least two renewals per hour of the sample-boat volume.
  • Temperature control: sample-boat solution temperature maintained within ±1 °C of the boiling point; record atmospheric pressure (boiling point varies with altitude).
• Specimen preparation and characterization:
  • Clean (ultrasonic 5 min in absolute ethyl alcohol recommended), handled with clips, dried to constant mass at 105 °C (mass stability within 0.1 mg).
  • Determine accurate geometric surface area and chemical composition; inspect porosity/cracking (optical or SEM) to ensure representativity.
• Measurements and quality criteria:
  • Test durations typically cover multiple intervals (e.g., 1, 3, 7, 10, 14 - up to 28 days) to determine the initial rate.
  • Measure specimen mass loss, solution pH (±0.1 unit), and solution chemistry (analytical accuracy: ~5% for majors, 10–15% for other elements).
  • Include blank tests and washing procedures to check device background (background ≤10% of test values).
• Practical limitations: results are comparable only among materials of the same type and dissolution mechanism; not sufficient alone for long-term behavior (see ENV 12920).

Applications

• Screening and ranking of nuclear glasses and vitrified waste forms for chemical durability and early-stage leaching performance.
• Laboratory parameter testing to support waste-form development, quality control, and comparative studies of vitrification processes.
• Input for source-term estimation and short-term leaching models used by researchers and regulators.

Who should use this standard

• Nuclear material scientists, glass and vitrification researchers, waste-form laboratories, regulatory agencies, and quality assurance teams involved in high-level radioactive waste (HLW) containment and performance testing.

Related standards

• ENV 12920 (referenced for long-term behaviour assessment and modeling).
• Prepared under ISO/TC 85 (Nuclear energy), SC 5 (Nuclear fuel technology).