This paper explores the intricate interplay of three-dimensional effects on the operational dynamics of nuclear reactors employing natural circulation. Specifically, attention is directed towards reactors featuring a long chimney, also called riser, in which upward movement of hot fluid happens, together with a downflow with lower temperature in the surrounding downcomer. The study delves into the potential occurrence of recirculation phenomena within the chimney and the consequential risk of cold fluid ingress into the core region. Such occurrences may precipitate in instabilities including the neutronic-thermal hydraulic feedback. Recirculation in the chimney is affected by core power, which also determines natural circulation flow inside the vessel. In this work, we consider single phase flow including the presence of subcooled void and two-phase flow in the core region which are typical respectively of PWRs (Pressurized Water Reactors) and BWRs (Boiling Water Reactors). The performed study is preliminary considering that no experimental data is available, and the system code RELAP5-3D is used instead of a more powerful CFD code, perhaps more suited in case of single-phase conditions.
Investigation of Three-Dimensional Effects on Natural Circulation Nuclear Reactors: Chimney Recirculation
Zingales V.Writing – Original Draft Preparation
;Bestion DominiqueValidation
;D'Auria Francesco
Supervision
2024-01-01
Abstract
This paper explores the intricate interplay of three-dimensional effects on the operational dynamics of nuclear reactors employing natural circulation. Specifically, attention is directed towards reactors featuring a long chimney, also called riser, in which upward movement of hot fluid happens, together with a downflow with lower temperature in the surrounding downcomer. The study delves into the potential occurrence of recirculation phenomena within the chimney and the consequential risk of cold fluid ingress into the core region. Such occurrences may precipitate in instabilities including the neutronic-thermal hydraulic feedback. Recirculation in the chimney is affected by core power, which also determines natural circulation flow inside the vessel. In this work, we consider single phase flow including the presence of subcooled void and two-phase flow in the core region which are typical respectively of PWRs (Pressurized Water Reactors) and BWRs (Boiling Water Reactors). The performed study is preliminary considering that no experimental data is available, and the system code RELAP5-3D is used instead of a more powerful CFD code, perhaps more suited in case of single-phase conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
