Overview
ISO 10645:2022 - "Nuclear energy - Light water reactors - Decay heat power in non-recycled nuclear fuels" establishes a standardized method for calculating decay heat from non-recycled fuel in light water reactors (LWRs). The standard covers the decay heat contribution from fission products, actinides, and isotopes formed by neutron capture in fission products for fuels composed of 235U and 238U. It is intended as an alternative, conservative calculation framework to dedicated validated codes and supports decay‑heat estimates from immediate shutdown through long‑term cooling (up to roughly 10^9 s).
Key technical topics and requirements
- Scope and applicability
- Applies to pressurized water reactors (PWRs) and boiling water reactors (BWRs) loaded with non‑recycled U fuel (235U/238U).
- Not permissible for recycled fuels (e.g., MOX or reprocessed uranium).
- Fission product contribution may be transferred to other thermal reactor designs only if actinide and neutron‑capture terms are assessed for that reactor.
- Component breakdown
- Explicit separation of decay heat into: fission product contribution, actinide contribution (including U and Np), and neutron‑capture in fission products (including special handling for Cs isotopes).
- Calculation methodology
- Use of a power histogram to represent operating history by intervals of constant power and composition.
- Decay heat from fission products represented by multi‑exponential fits (based on experimental spectroscopic and calorimetric data).
- Requires input of fission fractions (not supplied by the standard - to be obtained from literature or reactor physics codes).
- Conservatism and uncertainty
- Values for non‑fission‑product components are developed conservatively; uncertainty estimation and systematic error from histogram approximation must be considered.
- Updated data
- Decay heat curves revised using data adopted from ANS‑5.1‑2014; extended enrichment (up to ~5% 235U) and burnup ranges (up to 62 GWd/t) relative to prior edition.
Practical applications and users
- Who uses it
- Reactor engineers, safety analysts, thermal‑hydraulics modelers, regulatory bodies, and licensing teams working on LWR shutdown, cooling systems, spent‑fuel handling, and emergency planning.
- Typical applications
- Estimating post‑shutdown heat loads for decay heat removal system design.
- Preliminary safety analyses where full validated codes are not available or where a conservative standardized approach is preferred.
- Supporting licensing documents, operational limits, and spent‑fuel pool cooling requirements.
Related standards and references
- ANS‑5.1‑2014 (source for revised decay heat curves)
- ISO/TC 85 (technical committee on nuclear energy and reactor technology)
Keywords: ISO 10645:2022, decay heat, light water reactors, non‑recycled nuclear fuel, fission products, actinides, neutron capture, PWR, BWR, power histogram, burnup, 235U/238U.