Charles Cheron
Advised by Dr. Maria Avramova

10:00am – 12:00pm
1121 Duke Energy Conference Room

Abstract

As nuclear fuel technology develops, updated methodologies and computational tools are needed for safety analysis prior to commercial operation. For high burnup nuclear fuel simulations in system and subchannel thermal-hydraulic codes, a need is present for updated modeling of phenomena such as the steady state and transient fission gas release, changes in fuel and cladding material structure, fuel fragmentation, relocation and dispersal, fuel pellet-cladding mechanical interaction, among others. A literature review is performed on the relevant phenomena and their state-of-the-art modeling. An analysis of the current capabilities and shortcomings in the high burnup nuclear fuel models of the advanced subchannel thermal-hydraulic code CTF is presented. CTF is updated to include both steady state and transient fission gas release models and supporting sub models for the modeling of high burnup and high enrichment fuels. Following implementation, a verification process is conducted using a wide range of burnup and enrichments values, and the code is validated for use in high burnup reactivity insertion calculations.

Test cases are taken from the HERA Modeling and Simulation benchmark to ascertain CTF’s fuel performance capabilities. The steady state fission gas release model is verified and validated using data from the FRAPCON integral assessment. The transient fission gas release model is validated using data from the FRAPTRAN integral assessment. The joint depletion and transient performance of CTF is validated using the same data from the FRAPTRAN integral assessment.

A sensitivity study using HERA benchmark data shows good agreement in CTF’s enthalpy prediction capabilities compared to experimental RIA data at low burnup.  The steady state fission gas release model verification obtains mixed results. CTF overpredicts fission gas release, maintaining conservatism. However, the overprediction is significant in situations where axially uniform power profiles are input, especially at lower burnups. Taking all cases, CTF overpredicts by 11% FGR. The accuracy of the CTF prediction excluding the axially uniform cases is 3.25% FGR. The transient release model validation also shows good agreement with the FRAPTRAN fission gas release predictions. The complete validation of the joint steady state and transient model shows reasonable accuracy compared to the FRAPCON/FRAPTRAN cases.

In short, multiple fuel performance models were implemented or enhanced in CTF to improve its predictive capabilities with respect to fuel performance in reactivity insertion accidents. The range of applicability of this updated version of CTF is presented, as well as validation metrics. Future work is proposed for continuous improvement of CTF’s fuel performance capabilities.