Doctoral Dissertations

Date of Award

8-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Nicholas R. Brown

Committee Members

Brian D. Wirth, Livia Casali, Daniel P. Schappel

Abstract

The relatively recent growing development of advanced reactors such as High-Temperature Gas-Cooled Reactors (HTGRs) and Fluoride-Salt-Cooled High-Temperature Reactors (FHRs) has led to increasing need for safety analysis of TRISO fuel, which is utilized by such reactors. For these designs to be licensed, safety limits are to be determined for the adopted fuel and its constituents during reactor operation and design basis accidents to prevent fission products release.

The first goal of this dissertation is understanding how TRISO components material properties influence SiC response during transients. The relative impact of material properties and transient features, as well as burnup and power density, on SiC failure behavior is investigated. The illustrated steps are applied as a basis to build a SiC quality control approach that can be used to inform Fuel-Production Quality Assurance Plans (FPQAPs). An example application of the proposed method is presented for an HTGR. Subsequently, burnup effects are evaluated for a series of accident instances for an HTGR and an FHR design. An additional failure mechanism for SiC is also considered following Inner Pyrolytic Carbon (IPyC) failure. A preliminary analysis aimed at assessing burnup effects on pulsed tests irradiation tests is provided as well. All the contributions are achieved through the fuel performance code BISON which is used to simulate both TRISO pulsed tests and realistic accident scenarios.

The contributions of this dissertation include the in-depth study of SiC failure during reactor transients, as well as determining which factors affect SiC failure probability predictions the most. In addition, this work proposes a method to classify SiC quality based on its thermomechanical performance during the most challenging accident conditions for a given reactor design. The analyses performed in this work include thorough studies of Design Basis Accidents for an HTGR and an FHR which allow for the assessment of burnup and power density effects on SiC failure probability BISON predictions. This dissertation also includes a preliminary evaluation of burnup effects on more conservative pulsed transient tests.

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