ISO 18213-5:2008

Overview

ISO 18213-5:2008 - Nuclear fuel technology specifies a validated procedure for accurately determining liquid height in nuclear-materials-accountancy tanks that use bubbler (dip tube) systems. This part of ISO 18213 applies specifically when a fast bubbling rate is employed: gas is forced through a submerged dip tube and the pressure required to induce bubbling is measured with a manometer. Results are used to build or verify tank calibration and volume measurement equations for nuclear materials accountancy.

Key topics and technical requirements

• Measurement principle: hydrostatic relation between pressure, liquid height and liquid density (P = g·H·ρ) underpins the method.
• System configuration: use of a major (immersed) probe and a reference probe above the liquid surface; manometer located at a fixed elevation.
• Fast bubbling-rate adjustments: Clause 4 describes corrections needed when bubbling is fast - accounting for gas column mass, flow resistance, bubble formation effects, surface tension and pressure drops in probe lines.
• Equipment and procedures: Clause 3 references required hardware, operating conditions and stepwise measurement procedures (see ISO 18213-1 for system descriptions and procedural overview).
• Standardization & environmental effects: temperature and density variation, atmospheric/off‑gas pressures and other factors affecting comparability of measurements are recognized; data standardization algorithms are addressed in ISO 18213-2.
• Uncertainty and statistical treatment: methods for estimating measurement uncertainty and statistical analysis of calibration data are provided in ISO 18213-3.

Practical applications and users

• Primary users: instrumentation engineers, metrology teams, nuclear fuel facility operators, safeguards/accountancy professionals and calibration laboratories engaged in nuclear materials accountancy.
• Typical uses:
  • Calibrating process tanks by correlating known added volumes to measured liquid height.
  • Determining in-service process liquid volumes for inventory and material balance calculations.
  • Validating transfer volumes where siphon levels or indirect methods are used.
• Why it matters: accurate height-to-volume relationships reduce systematic inventory errors, support regulatory compliance, and improve safeguards reporting.

Related standards

• ISO 18213-1: Procedural overview (tank calibration & volume determination)
• ISO 18213-2: Data standardization for tank calibration
• ISO 18213-3: Statistical methods & uncertainty estimation
• ISO 18213-4: Liquid height determination for slow bubbling rate (complementary method)
• ISO 18213-6: In-tank determination of liquid density

Keywords: ISO 18213-5:2008, nuclear fuel technology, tank calibration, volume determination, liquid height, dip tubes, bubbler probe, fast bubbling rate, manometer, hydrostatic pressure, nuclear materials accountancy.