Validation of the AC2 Codes ATHLET and ATHLET-CD

Abstract

Abstract Verification and validation are basic quality assurance elements in code development and essential for code release. Therefore, the codes of AC2 (ATHLET – ATHLET-CD – COCOSYS) are tested on separate effect tests, integral tests as well as plant scenarios to verify and validate the models after new implementation or updates. The verification assures that the models are implemented and working correctly while the validation checks if the models predict the right phenomena and combined with other models and modules. The selected experiments are summarized in GRS's validation matrices, which in turn are based on the CSNI validation matrices derived from OECD/WGAMA task groups as well as current activities on experimental test campaigns. For ATHLET several test series are used to cover a wide range of phenomena which can occur in PWR, BWR and VVER. Additionally, plant transients are considered for German LWR. The ATHLET-CD validation matrix contains experiments covering most phenomena which can occur during a severe accident. But due to the interaction of several effects even in small scale experiments mainly integral experimental campaigns are used for the validation. Over the last decades the validation of the AC2 codeds ATHLET and ATHLET-CD has reached a high degree of fulfilment of GRS's validation matrices over all code versions. Innovative and advanced reactor concepts come with new or newly relevant phenomena, which AC2 needs to provide models for. Extending the validation base of AC2 for these models is one challenge for further code validation efforts besides the on-going update of the validation basis to recent code versions.