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Rebollo M.J.,Technical University of Madrid | Queral C.,Technical University of Madrid | Jimenez G.,Technical University of Madrid | Gomez-Magan J.,NFQ Solutions | And 2 more authors.
Reliability Engineering and System Safety

The current main figure of merit for risk based decision making process based on Probabilistic Safety Assessment level 1 is usually related with the fuel failure (i.e., Peak Cladding Temperature (PCT)>1477.15 K). In this approach, the core damage is the first and necessary step in a potential radiological release, being the containment failure the second one. Nevertheless, SGTR sequences in PWR plants are able to release large quantities of radioactive products without previous core damage or containment failure. For that reason, it seems necessary to analyze which sequences exceed the allowed offsite dose criteria prior to the core damage criterion. The aim of this analysis has been to evaluate the risk contribution due to the offsite dose and the core damage in case of Steam Generator Tube Rupture (SGTR) sequences at full power in a 3-loop Pressurized Water Reactor (PWR) Westinghouse-design. The study has been performed with SCAIS/MAAP and RADTRAD codes. For that purpose, this analysis unfolds the SGTR Dynamic Event Tree for both the core damage and the offsite dose risk metrics. The results indicate that dose criteria complement the PCT criterion and allow quantifying both risk contributions in SGTR sequences. © 2015 Elsevier Ltd. Source

Ibanez L.,Technical University of Madrid | Hortal J.,Consejo Seguridad Nuclear | Queral C.,Technical University of Madrid | Gomez-Magan J.,NFQ Solutions | And 8 more authors.
Reliability Engineering and System Safety

The Integrated Safety Assessment (ISA) methodology, developed by the Consejo de Seguridad Nuclear, has been applied to an analysis of Zion NPP for sequences with Loss of the Component Cooling Water System (CCWS).The ISA methodology proposal starts from the unfolding of the Dynamic Event Tree (DET). Results from this first step allow assessing the sequence delineation of standard Probabilistic Safety Analysis results.For some sequences of interest of the outlined DET, ISA then identifies the Damage Domain (DD). This is the region of uncertain times and/or parameters where a safety limit is exceeded, which indicates the occurrence of certain damage situation. This paper illustrates application of this concept obtained simulating sequences with MAAP and with TRACE.From information of simulation results of sequence transients belonging to the DD and the time-density probability distributions of the manual actions and of occurrence of stochastic phenomena, ISA integrates the dynamic reliability equations proposed to obtain the sequence contribution to the global Damage Exceedance Frequency (DEF).Reported results show a slight increase in the DEF for sequences investigated following a power uprate from 100% to 110%. This demonstrates the potential use of the method to help in the assessment of design modifications. © 2015 Elsevier Ltd. Source

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