Structural Integrity Associates | News and Views, Volume 51 | Structural Integrity Associates | PEGASUS A Versatile Tool for Used Fuel Modeling

News & Views, Volume 51 | PEGASUS A Versatile Tool for Used Fuel Modeling

By:  Wenfeng Liu

PEGASUS, a finite element fuel code developed at SIA, represents a new modeling paradigm. This new paradigm treats all fuel behavior regimes in one continuous analysis.

Introduction
PEGASUS, a finite element fuel code developed at SIA, represents a new modeling paradigm.  This new paradigm treats all fuel behavior regimes in one continuous analysis.  This approach differs significantly from the current conservative practice of bounding analysis to ensure uncertainties are accounted for which results in sub-optimal used fuel management strategies.  Using PEGASUS in used fuel evaluation results in significant savings in engineering cost and work force utilization, reduces conservatism, and provides flexibility in the management of used fuel.

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News & Views, Volume 49 - PEGASUS- Advanced Tool for Assessing Pellet-Cladding Interaction

News & Views, Volume 49 | PEGASUS: Advanced Tool for Assessing Pellet-Cladding Interaction

By:  Bill Lyon, PE and Michael Kennard

News & Views, Volume 49 - PEGASUS- Advanced Tool for Assessing Pellet-Cladding Interaction

PEGASUS provides a fully capable computational environment to solve the unique, detailed 3D analyses required for the evaluation of PCI.

In the current economic environment in which nuclear units compete with less costly energy sources, a quicker return to full power correlates to more power generated and increased operating efficiency.  This may be achieved with shorter startup post-refueling or a quicker return-to-power following any number of plant evolutions including load follow, control blade repositioning, equipment outage or maintenance, testing, extended low power operation, scram, etc.  Such strategies to increase operating efficiency may enhance the risk of pellet-cladding interaction (PCI), a failure mechanism that occurs under conditions of high local cladding stress in conjunction with the presence of aggressive chemical fission product species present at the cladding inner surface.  These conditions can occur during rapid and extensive local power changes and can be further enhanced by the presence of fuel pellet defects (e.g., missing pellet surface, MPS).  Several commercial reactor fuel failure events in the last eight years, as recently as early 2019, suggest a PCI-type failure cause.  To safely manage changes in core operation, the margin to conditions leading to PCI-type failures must be determined prior to implementation of such operating changes.

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News & View, Volume 47 | PEGASUS State-of-the-Art Nuclear Fuel Behavior

News & Views, Volume 47 | Introducing Pegasus: Optimize Fuel Performance

By:  Vick Nazareth and Bill LyonNews & View, Volume 47 | PEGASUS State-of-the-Art Nuclear Fuel Behavior

The Pegasus code is a culmination of nuclear fuel behavior knowledge and experience that spans a period of over five decades. It is a total fuel-cycle simulation of fuel response from initial insertion in reactor to deposition in permanent storage. The goal of Pegasus is to treat, with equal fidelity, the modeling of fuel behavior during the active fuel cycle and the back-end cycle of spent-fuel storage and transportation in a single, self-consistent, and highly cost-effective analysis approach. In the active part of the fuel cycle, Pegasus’s superior three-dimensional thermo-mechanics, coupled with validated nuclear and material behavior models, and robust fuel-cladding interface treatment make it a high-fidelity predictor of fuel-rod response during flexible power operations and operational transients.

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