ISO 19226:2017

Overview

ISO 19226:2017 - "Nuclear energy - Determination of neutron fluence and displacement per atom (dpa) in reactor vessel and internals" - defines a systematic procedure to evaluate neutron irradiation exposure and damage between the reactor core and the inside of the containment vessel. The standard covers calculation and measurement-based determination of neutron fluence, displacements per atom (dpa), and related gas (Helium) production for reactor pressure vessels and internals. It applies to PWRs, BWRs, and PHWRs and combines neutron transport computations with in‑vessel and cavity dosimetry data to produce best-estimate fluence and damage metrics for reactor life management.

Key Topics

• Scope and objectives: Procedures for evaluating irradiation data (fluence, dpa, He production) and neutron-damage properties relevant to vessel embrittlement and component integrity.
• Transport calculations: Use of deterministic discrete-ordinates (SN) and Monte Carlo methods with fixed neutron sources, including requirements for input data (material composition, geometric model, cross‑section data, core neutron source).
• Output requirements: Multigroup 3D flux/fluence distributions, reaction rates, dpa rates, and response functions for dosimetry.
• Dosimetry and measurements: Guidance on in-vessel and cavity dosimeter selection (stable-product dosimeters), measurement validation, and uncertainty estimation.
• Comparison and adjustment methods: Direct calculation-to-measurement comparisons, least-squares adjustment procedures to derive the best-estimate fluence, and assessment of calculational uncertainties.
• Dpa and gas production: Procedures for converting fluence and spectra into displacements per atom and gas production estimates, recognizing strong dependence on neutron energy spectrum.

Applications

Who uses ISO 19226 and why:

• Reactor operators and engineers: For reactor life management, prediction of vessel embrittlement, and planning of inspections or material surveillance programs.
• Regulatory bodies: To support licensing, regulatory guidance, and evaluation of pressure-vessel integrity reports.
• Neutron metrologists and dosimetry labs: For design and interpretation of in‑vessel/cavity dosimetry campaigns and measurement validation.
• Transport-code developers and analysts: For benchmarking and validation of SN and Monte Carlo methodologies against dosimetry and measured data.

Practical outcomes include consistent estimation of fast-neutron fluence (e.g., E > 1.0 MeV and E > 0.1 MeV bands), best-estimate dpa, and quantified uncertainties used in life-extension decisions.

Related standards and references

• Normative references: ANSI/ANS 19.10, ASTM E170-16a.
• Cross-section libraries and data evaluations referenced include ENDF/B, JEFF, JENDL.
• Prepared by ISO/TC 85 (Nuclear energy, nuclear technologies and radiological protection).

Keywords: ISO 19226, neutron fluence, dpa, reactor pressure vessel, dosimetry, neutron transport calculations, PWR, BWR, PHWR, reactor internals.