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59,80 €ISBN 978-3-8191-0721-4Softcover210 pages82 figures278 g21 x 14,8 cmEnglishThesis
May 2026
Liviusz Lovasz
Further development of ATHLET-CD for simulations of accidents with asymmetrical characteristics
The focus of this dissertation is to enable the consideration of local effects during a severe accident in the code system ATHLET-CD/AC2. Local effects can have a strong influence on the accident sequence, not only in reactors but also in spent fuel pools. So far, however, the influence of local effects on the overall accident sequence has hardly been investigated because in ATHLET-CD/AC2, similar to the other relevant codes, the core is divided into concentric rings by default. This ring-shaped, hard-coded nodalisation method is based on the assumption that the occurring phenomena are cylindrically symmetrical and therefore does not allow the consideration of local effects and asymmetric conditions. To overcome this limitation, a new and flexible nodalization method was developed for the core region in both the reactor case and the spent fuel pool case.
Significant changes in the code basis were necessary to adequately model accidents with asymmetrical characteristics. The development of a required new thermal radiation model and the adaptation of various other models are explained in detail in the dissertation. The developed and adapted models, separately and together with the change in nodalization, were verified with increasing complexity, checked for plausibility and validated as far as possible.
The validation was based on the recalculation of the TMI-2 accident, because the accident exhibited asymmetric characteristics that could not previously be taken into account with the ring-like nodalization by definition.
The results of the verification and validation show that with the introduction of the new nodalization, together with the necessary model changes, ATHLET-CD/AC2 can successfully and realistically model local effects during a severe accident.
Significant changes in the code basis were necessary to adequately model accidents with asymmetrical characteristics. The development of a required new thermal radiation model and the adaptation of various other models are explained in detail in the dissertation. The developed and adapted models, separately and together with the change in nodalization, were verified with increasing complexity, checked for plausibility and validated as far as possible.
The validation was based on the recalculation of the TMI-2 accident, because the accident exhibited asymmetric characteristics that could not previously be taken into account with the ring-like nodalization by definition.
The results of the verification and validation show that with the introduction of the new nodalization, together with the necessary model changes, ATHLET-CD/AC2 can successfully and realistically model local effects during a severe accident.
Keywords: Severe Accident; AC2; Asymmetrical
Schriftenreihe der Arbeitsgruppe Plant Simulation and Safety
Edited by Prof. Dr.-Ing. Marco Karl Koch, Bochum
Volume 8
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Electronic publication (PDF): 978-3-8191-0663-7
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