GNDS: A standard format for nuclear data

In 2013, the NEA launched a project with all the nuclear data evaluation projects from around the world to review the requirements for an international replacement for the ENDF-6 format. Over a three-year process, representatives from all member countries developed an extensive set of requirements that cover not only the necessary nuclear physics, but also rules for data interpolation, the storage of cross-correlations between data, mechanisms to build-in documentation as part of Quality Assurance procedures, and much more. Experts convened by the NEA proposed a new format specification for a Generalised Nuclear Data Structure (GNDS) in 2016 that has been further developed over another three-year process and subjected to rigorous international review. The Generalised Nuclear Database Structure 1.9, published in May 2020, is the outcome of this work. The international community of nuclear data centres has responded to the GNDS project by adopting GNDS into their work-flows and releases. A large body of computer codes have been developed that rely on ENDF-6 formatted data and the re-factoring of these to accommodate a wholly new structure from scratch would be a challenging task. This issue can be significantly simplified with the implementation of an application programming interface (API), which serves as an intermediary between the data files and the software that requires the data within those files. GNDS is technically a structure, in that it can be realised in multiple file formats that are commonly used. GNDS has been engineered as a replacement and extension of the ENDF-6 format. As such, it maintains a strict one-to-one translation capability with the legacy file format and files that are compliant with the ENDF format rules