ISO 23018:2022

Overview

ISO 23018:2022 provides guidance for the preparation, verification and validation of group-averaged neutron and gamma‑ray cross sections used in radiation protection and shielding calculations for nuclear reactors. It defines the expected inputs (evaluated nuclear data files), energy ranges and materials of interest, recommended multigroup processing techniques, and verification/validation practices to ensure cross‑section libraries are fit for shielding and reactor radiation‑protection applications.

Key topics and technical requirements

• Evaluated nuclear data files: Source data (e.g., ENDF/B, JEFF, JENDL) must be documented, reviewed and suitable for shielding applications. Processing codes should perform resonance reconstruction, Doppler broadening and multigroup averaging.
• Energy ranges and materials: Recommended coverage includes roughly ~10 eV to ~20 MeV for neutrons and ~1 keV to ~30 MeV for gamma‑rays, and shield/structural materials relevant to reactor shielding.
• Group‑averaging techniques: Use verified numerical averaging and appropriate fine‑group structures that allow accurate collapse to practical coarse groups. Weighting functions must represent the intended spectrum; if resonance shapes are not explicit, apply self‑shielding corrections (e.g., Bondarenko factors).
• Self‑shielding and scattering matrix: Address strong self‑shielding in deep‑penetration problems and ensure scattering matrices are corrected where needed.
• Upscattering: Fine‑group libraries should include upscattering in the thermal range; collapsed libraries should retain upscattering if thermal neutrons affect results. The standard notes an ANISN truncation method option for computational efficiency with verification required.
• Angular dependence: Scattering cross sections must be available to sufficiently high Legendre order (higher order for light nuclides; a minimum expansion order is required for transport calculations) with order selection also informed by geometry.
• Verification & validation: Require documented numerical and experimental benchmarking. Collapsed‑group results must be compared with fine‑group solutions and refined until acceptable accuracy is achieved.

Applications

ISO 23018:2022 is directly applicable to:

• Reactor shielding design and radiation protection assessments
• Generation and quality assurance of multigroup cross‑section libraries for transport codes
• Coupled neutron–gamma calculations for dose, heating, activation and shielding
• Development of cross‑section processing and library management software

Who should use this standard

• Nuclear engineers and shielding analysts
• Cross‑section processing and transport code developers
• Nuclear data evaluators and library maintainers
• Regulatory bodies and organizations performing conformity, verification and benchmarking of shielding analyses

Related standards

• ISO 12749‑5 (vocabulary for nuclear reactors) - normative reference
• ISO 23018:2022 is based on ANSI/ANS‑6.1.2‑2013 and references established evaluated data formats and utility codes (e.g., ENDF utilities) for processing and checking.

Keywords: ISO 23018:2022, group-averaged cross sections, neutron cross sections, gamma-ray cross sections, shielding calculations, radiation protection, multigroup, self-shielding, upscattering, benchmark verification.