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.