ISO 18075:2018

Overview - ISO 18075:2018 (Steady‑state neutronics methods for power‑reactor analysis)

ISO 18075:2018 is an International Organization for Standardization (ISO) guidance standard for performing and validating steady‑state neutronics calculations for commercial UO2‑fuel power reactors. It defines the recommended sequence of calculations and sets out criteria for selecting computational methods, verifying and validating calculation systems, evaluating accuracy and applicability of data and methods, and documenting results. The standard supports prediction of reaction‑rate spatial distributions, reactivity, and nuclide composition changes (depletion) in operating reactors.

Key topics and technical requirements

• Selection of computational methods: Guidance on choosing appropriate neutron transport and diffusion methods, multigroup and few‑group approaches, and cell/supercell modelling strategies.
• Cross‑section processing: Requirements for preparation and use of fine‑group and broad‑group cross‑section libraries, weighting functions, and system‑dependent spectrum calculations.
• Group collapse and few‑group constants: Procedures for collapsing multigroup data to application‑specific few‑group structures and accounting for temperature and spectrum dependence.
• Reactivity and flux calculations: Models and assumptions for predicting eigenvalues, neutron flux distributions, reaction rates, and associated uncertainties.
• Depletion (fuel burnup): Sequences and considerations for nuclide inventory prediction over operational time.
• Verification & validation (V&V): Criteria for unit and integral testing, bias and uncertainty assessment, and acceptance of calculation systems against experimental and benchmark data.
• Documentation requirements: Mandatory documentation of methods, data, validation evidence, and limitations (see standard’s documentation section and summary of requirements).

Practical applications and users

ISO 18075:2018 is intended for professionals and organizations involved in reactor core neutronics and safety analysis, including:

• Reactor core analysts and nuclear engineers (PWR, BWR, LMR, HWR, HTGR)
• Physics code developers and data processing teams
• Fuel management and depletion analysis groups
• Licensing and regulatory reviewers performing code validation
• R&D teams benchmarking new methods against established practice

Typical uses include core design and reload analysis, power distribution and thermal‑limits checks, control‑rod and reactivity worth calculations, fuel cycle and depletion studies, and preparation of V&V evidence for licensing.

Related standards

• ANSI/ANS‑19.3 (reference basis for this ISO document)
• ANSI/ANS‑19.1 (averaged nuclear data sets for reactor design - cited in the standard)
• Complementary ISO and IEC standards on nuclear terminology and quality systems (see ISO/TC 85 publications)

ISO 18075:2018 provides structured, practical guidance to ensure neutronics computations are robust, validated, and traceably documented - essential for safe reactor operation, licensing, and advanced core analysis.