By-pass accident sequences are major contributors to the risk assessment of Light Water Reactors (LWRs) due to the large fraction of radioactivity that may escape from the plant. In the particular case of a Steam Generator Tube Rupture (SGTR), a sound understanding of potential mechanisms governing radioactivity retention is still missing. As a consequence, the source term is assumed to be released from the reactor coolant system to the environment with no or minimum credit to any potential retention within the secondary side of the steam generator.
The EURSAFE project considered SGTR scenarios as an issue that needed investigation. The SARNET project is addressing the issue within the Source Term area (WP15).
The available data, most of which were gathered during the SGTR project of the 5th Framework Programme of Euratom, are far from being conclusive. Nonetheless, they provided a good insight into the complexity of the scenario. Particular attention was paid to the in-tube retention (PSAERO and HORIZON experiments) as well as the secondary side retention (ARTIST and PECA-SGTR experiments).
This paper summarises the main observations from the set of available data and updates the advances achieved in their interpretation. In addition, some key aspects of aerosol behaviour closely related to their retention are discussed: particle clusters de-agglomeration under foreseen SGTR conditions, bubble hydrodynamics in wet scenarios, resuspension of particulate deposits, etc. Finally, the theoretical approaches presently under development are succinctly described and the main difficulties found highlighted.
(1) : PSI, Switzerland
(2) : CIEMAT, Spain
(3) : IRSN, France
(4) : FORTUM, Finland