ISO 18213-2:2007

Overview

ISO 18213-2:2007 - part of the ISO 18213 series on nuclear fuel technology - specifies procedures for data standardization for tank calibration used in nuclear materials accountancy. The standard describes algorithms and thermodynamic methods to adjust raw calibration measurements (liquid height and volume) to a fixed set of reference conditions, reducing the effects of changing ambient conditions during calibration runs. It is intended to produce standardized height–volume data that can be used to derive reliable tank calibration and volume measurement equations.

Key topics and requirements

• Scope and purpose: Standardize calibration data so calibration equations reflect reference conditions despite variability in ambient temperature, pressure, humidity and measurement conditions.
• Input data: Pairs of measurement-system responses (normally liquid height) and independent volume measures from one or more calibration runs.
• Ambient conditions: Temperature (liquid and ambient), barometric pressure, relative humidity, and gas flow rates in bubbler probe lines should be recorded; algorithms work best when these are measured for each observation.
• Measurement systems: Applies generally to liquid-height and volume measurements; when using pressure-based bubbler probe systems, heights must first be derived using ISO 18213-4 or ISO 18213-5 as appropriate.
• Thermodynamic corrections: Algorithms adjust for thermal expansion of tank/prover materials, density changes of the calibration liquid (annex includes density of water), buoyancy and related effects.
• Prover standardization: Specific steps for gravimetric and volumetric provers to produce standardized delivered volumes.
• Multiple runs: Methods to align and combine multiple calibration runs, including heel-volume determination and statistical alignment procedures (informative annexes provide methods).

Practical applications and users

• Who uses it: Metrology engineers, calibration technicians, nuclear materials accountancy specialists, plant operators, regulatory and safeguards organizations, and calibration laboratories in the nuclear fuel cycle.
• Why it matters:
  • Ensures accurate, traceable determination of tank volumes for inventory and safeguards reporting.
  • Minimizes calibration bias introduced by ambient fluctuations during filling runs.
  • Enables consistent calibration-model estimation from multiple runs and measurement systems (especially bubbler probe systems).
• Typical use cases: Tank calibration campaigns, periodic verification of tank measurement systems, converting pressure-based measurements to standardized height/volume for accountancy tanks.

Related standards

• ISO 18213-1: Procedural overview
• ISO 18213-3: Statistical methods
• ISO 18213-4 & ISO 18213-5: Converting pressure (bubbler) measurements to liquid height (slow/fast bubbling rates)
• ISO 18213-6: In-tank determination of liquid density

Keywords: ISO 18213-2:2007, tank calibration, data standardization, nuclear materials accountancy, bubbler probe systems, liquid height, volume determination.