Mechanical Engineering ETDs

Publication Date

Spring 4-15-2019

Abstract

The health of a nuclear reactor’s fuel is essential to the operational longevity of the reactor. The health of the fuel in the Annular Core Research Reactor (ACRR) is a topic of increased interest due to both a proposed new facility that would include the ACRR and the recent resurfacing of contradictory reports regarding thermal stresses in its fuel pellets. Unlike other reactor fuels, which are widely used and well-characterized, the fuel in the ACRR is unique. The ACRR’s fuel elements consist of UO­2-BeO fuel pellets, fluted niobium refractory liners, and stainless-steel cladding. The purpose of this thesis is to examine the thermal stresses in the ACRR’s peak fuel pellets under maximum pulse conditions. Because the properties are not well-characterized, the material properties of the fresh fuel pellets were first determined using approximations including the rule of mixtures and the Voigt-Reuss-Hill approximation. Then the material properties were adjusted to account for the effects of burnup and radiation. Next a transient thermal analysis was performed using the commercial finite element code ANSYS Mechanical 19.2. The temperature gradients calculated in the transient thermal analysis were used to calculate the thermal stresses in the fuel pellets. The thermal stresses were also calculated using ANSYS Mechanical 19.2. Using the same process, a material sensitivity study was performed to examine the sensitivity of the thermal stresses to the material properties. Finally, the effects of the thermal stresses were examined from a fracture mechanics perspective. The analyses showed that the fuel pellets experience large thermal stresses that are caused by the fuel element’s unique geometry. Despite the large thermal stresses, it was concluded that the thermal stresses are unlikely to cause fracture.

Keywords

FEA, ACRR, fuel element

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Dr. Yu-Lin Shen

Second Committee Member

Dr. Nima Fathi

Third Committee Member

Dr. Edward Parma

Document Type

Thesis

Language

English

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