The design and safety assessment of nuclear reactors rely on a combination of calculations performed by several simulation packages, each dedicated to modeling a specific ensemble of phenomena. To treat the complexity of the physical problem, appropriate software architectures and methodologies to trace and implement user needs are of paramount importance to fulfill the needs of all the possible stakeholders. This work proposes a systematic approach to break the complexity of constructing a lattice neutronics platform that is one of the simulation packages needed in nuclear reactor analysis. After reviewing the state of the art of current methods applied in reactor physics engineering, the work concentrates on identifying the applicable software architecture strategies and on discussing advantages and drawbacks. While the specific target is the neutronics code APOLLO3®, the subsequent categorization and analysis of user needs written in the form of formal requirements allow for defining a unified approach to design an effective, industrial-grade, and future-proof calculation platform. Subsequent presentation of typical use cases involved in developing deterministic lattice calculation schemes allows linking the formal definition of use cases and software architecture with the actual application to a specific calculation setting. This work aims, therefore, at proposing an innovative viewpoint to tackle large software developments applicable in the nuclear industry. The research presented in this paper has been developed at Framatome in the context of the lattice neutronics work package of the H2020 CAMIVVER project.
