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.

READ MORE

Structural Integrity Associates Achieves Milestone with Pegasus Code Development

Structural Integrity Associates Achieves Milestone with Pegasus Code Development

Structural Integrity Associates | Structural Integrity Associates Achieves Milestone with Pegasus Code Development

Structural Integrity Associates | Structural Integrity Associates Achieves Milestone with Pegasus Code DevelopmentOn October 28th, the Structural Integrity (SI) Nuclear Fuel Technology Team achieved a major milestone in completing the first Verification & Validation phase in the development of its nuclear fuel performance and behavior code Pegasus©.  “This is a significant step by the SI Team” commented Vick Nazareth, SI Fuel Director.  “We have been developing Pegasus© since 2017 to incorporate cutting edge computational technology and four decades of fuel behavior modeling and analysis expertise into a software program”.  The code addresses a need for deeper fuel integrity insights within the nuclear industry to achieve next level fuel performance and licensing.  Dr. Joe Rashid, Scientist and Senior Technology Developer of the code added “this code will analyze fuel behavior through the entire fuel cycle from initial startup to used-fuel storage”.

SI announced the development of Pegasus© in the SI newsletter in 2019, Introducing Pegasus: State-of-the-Art Nuclear Fuel Behavior with the objective of enhancing the fidelity of fuel behavior and performance in support of advanced fuel technologies.  The Pegasus© code will go through additional validation testing over the next several months to meet a production roll-out in early 2021 in support of fuel performance behavior analysis across a broad spectrum of light water reactor and advanced reactor fuel designs.

” I am proud of the SI Fuel Team”, said Mark Marano, SI CEO.” This milestone exemplifies our ability to provide innovative structural integrity solutions for clients across structures, systems, components, water chemistry and nuclear fuel.”

Structural Integrity is an employee-owned specia­­lty engineering and services company providing innovative engineering solutions and services to achieve asset management excellence across multiple industries including Nuclear, Fossil, Oil & Gas, Renewables, and Critical Infrastructure.

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.

READ MORE

News & View, Volume 46 | Evaluation of Reconfiguration and Damage of BWR Spent Fuel During Storage and Transportation Accidents

News & Views, Volume 46 | Evaluation of Reconfiguration and Damage of BWR Spent Fuel During Storage and Transportation Accidents

By:  Bill Lyon

News & View, Volume 46 | Evaluation of Reconfiguration and Damage of BWR Spent Fuel During Storage and Transportation AccidentsStructural Integrity Associates is participating in a Department of Energy (DOE) Integrated Research Projects (IRP) program focused on storage and transportation of used nuclear fuel (UNF). The project, entitled Cask Mis-Loads Evaluation Techniques, was awarded to a university-based research team in 2016 under the DOE Nuclear Fuels Storage and Transportation (NFST) project. The team is led by the University of Houston (U of H) and includes representatives from the University  of Illinois at Urbana-Champaign, the University of Southern California, the University of Minnesota, Pacific Northwest National Laboratory, and staff members from the Nuclear Fuel Technology and Critical Structures and Facilities divisions of SI. The primary objectives of NFST are to 1) implement interim storage, 2) improve integration of storage into an overall waste management system, and 3) prepare for large-scale transportation of UNF and high-level waste.  The goal of the cask mis-load project is to develop a probabilistically informed methodology, utilizing innovative non-destructive evaluation (NDE) techniques, determining the extent of potential damage or degradation of internal components of UNF canisters/casks during normal conditions of transport (NCT) and hypothetical accident conditions (HAC).

READ MORE

News & View, Volume 43 | LatitudeUsing Falcon to Develop RIA Pellet-Cladding Mechanical Interaction (PCMI) Failure Criteria

News & Views, Volume 43 | Using Falcon to Develop RIA Pellet-Cladding Mechanical Interaction (PCMI) Failure Criteria

By:  John Alvis

IntroductionNews & View, Volume 43 | LatitudeUsing Falcon to Develop RIA Pellet-Cladding Mechanical Interaction (PCMI) Failure Criteria
The goal to achieve higher fuel rod burnup levels has produced considerable interest in the transient response of high burnup nuclear fuel.  Several experimental programs have been initiated to generate data on the behavior of high burnup fuel under transient conditions representative of Reactivity Initiated Accidents (RIAs).  A RIA is an important postulated accident for the design of Light Water Reactors (LWRs). It is considered the bounding accident for uncontrolled reactivity insertions.

The initial results from RIA-simulation tests on fuel rod segments with burnup levels above 50 GWd/tU, namely CABRI REP Na-1 (conducted in 1993) and NSRR HBO-1 (conducted in 1994), raised concerns that the licensing criteria defined in the Standard Review Plan (NUREG-0800) may be inappropriate beyond a certain level of burnup.   Figure 1 is an example of a typical high burnup fuel cladding showing the oxidized and hydrided cladding of higher burnup fuel rods.  Figure 2 shows the typical radial crack path in oxidized and hydrided cladding, subjected to RIA simulation tests.  As a consequence of these findings, EPRI with the assistance of the Structural Integrity’s Nuclear Fuel Technology Division (formally ANATECH) and other nuclear industry members conducted an extensive review and assessment of the observed behavior of high burnup fuel under RIA conditions.  The objective was to conduct a detailed analysis of the data obtained from RIA-simulation experiments and to evaluate the applicability of the data to commercial LWR fuel behavior during a Rod Ejection Accident (REA) or Control Rod Drop Accident (CRDA).  The assessment included a review of the fuel segments used in the tests, the test procedures, in-pile instrumentation measurements, post-test examination results, and a detailed analytical evaluation of several key RIA-simulation tests.

READ MORE