ISO 18213-3:2009

Overview

ISO 18213-3:2009 - Nuclear fuel technology: Tank calibration and volume determination - Part 3: Statistical methods - defines statistical procedures for analysing tank calibration and volume measurement data used in nuclear materials accountancy. It provides diagnostic tools, a statistical model for estimating a tank’s calibration or measurement equation from standardized height–volume data, and methods to estimate and propagate uncertainties for contained and transfer liquid volume determinations. The methods are intended to be used with the other parts of ISO 18213 but are broadly applicable to tank calibration and volume measurement problems.

Key topics and requirements

• Diagnostic plots and data checks - Procedures and example plots to evaluate, compare and validate tank calibration data and auxiliary measurements (Clause 5, Annex A).
• Uncertainty estimation for calibration measurements - Methods to estimate measurement-system response uncertainty (height) and uncertainties in tank content measurements (volume, mass) (Clause 6).
• Measurement model and parameter estimation - A statistical model to estimate the tank calibration equation or its inverse (measurement equation) from standardized calibration data, including parameter estimation and residual analysis (Clause 7).
• Variance propagation and confidence intervals - Procedures for computing uncertainty estimates, prediction intervals and confidence regions for volume determinations (Clauses 7.4–7.5, 8). Annex B gives degrees-of-freedom calculations (Welch–Satterthwaite); Annex C presents target uncertainty limits.
• Data standardization linkage - Methods are tailored to the data-standardization approach of ISO 18213-1/2 and to related algorithms in Parts 4–6, ensuring consistency between instrumentation, data standardization, and statistical analysis.
• Flexibility - Facilities may develop equivalent plant- or tank-specific statistical methods, but if ISO 18213 is adopted and no alternatives developed, ISO 18213-3 methods must be used.

Applications and users

Practical applications include:

• Calibrating accountancy tanks and deriving height–volume relationships
• Computing and reporting uncertainty estimates for contained and transferred nuclear material volumes
• Comparing and validating calibration runs and instrumentation performance
• Supporting nuclear safeguards, material accountancy, regulatory reporting and in-plant quality control

Primary users:

• Nuclear materials accountancy specialists and safeguards professionals
• Tank calibration engineers and metrologists
• Laboratory statisticians and QA personnel in fuel-cycle facilities
• Regulators and inspection bodies requiring reproducible uncertainty estimates

Related standards

• ISO 18213-1: Procedural overview
• ISO 18213-2: Data standardization for tank calibration
• ISO 18213-4 / -5: Accurate liquid-height determination (dip tubes, slow/fast bubbling)
• ISO 18213-6: In-tank liquid density determination

By integrating ISO 18213-3:2009 into tank calibration programs, facilities improve the statistical rigor of volume determinations, ensure consistent uncertainty reporting, and support robust nuclear materials accountancy.