Studying the In-situ Irradiation Creep Effects of Zirconium and Its Alloys Using Proton Irradiation

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Moore, Jordan B.
Irradiation Creep , Nuclear Materials , In-situ , Proton Irradiation , Zirconium
Materials commonly used in nuclear power reactors, such as steel and zirconium alloys, demonstrate significant changes to their material properties over the course of their in-service lifetime. Exposure to the high radiation fields, coupled with the high temperature and stresses inside the core, can lead to several competing and simultaneous phenomena that can drastically affect the in-service performance of materials and components. One of the most notable phenomena is irradiation-induced creep, commonly referred to as “irradiation creep”, in which a material experiences gradual shape change in response to the applied irradiation-induced damage and stress. This shape change can compromise the performance of critical reactor components and have disastrous consequences if not accounted for in reactor maintenance and operation. As such, being able to study and develop a mechanistic understanding of irradiation creep behavior is essential to reactor safety, lifetime extension, and future reactor design. However, studying this behavior in a conventional reactor setting is often met with many challenges such as time constraints, restrictions on experimental control, and large costs. For these reasons, it is becoming common place to use ion irradiations to mimic reactor conditions in a controlled laboratory setting and conduct irradiation damage effect studies. This thesis details the design and implementation of an in-situ testing apparatus capable of simulating the complex environment inside of a reactor using proton irradiations. The primary purpose of this apparatus is to measure the in-situ irradiation creep behavior of material samples while systematically manipulating experimental variables such as temperature, stress, and irradiation damage rate. A detailed summary of the system design and capabilities as well as the results from the apparatus commissioning experiment are provided in manuscript one. A linear fit between the sample creep rate and applied proton flux over the range of 0 – 2.1E17 m-2s-1 was observed and a flux exponent of 1.24 ± 0.21 was determined for pure zirconium. Manuscript two presents an investigation into the viability and limitations of using proton irradiations to mimic the dynamic effects of neutron irradiation seen in a reactor core. It was determined that samples irradiated using proton irradiation must accumulate a minimum ‘saturation damage’ of ~0.1 dpa to reach steady state a-loop density and morphology before their behavior can be considered indicative of the long-term behavior of in-reactor materials. Finally, manuscript three presents an investigation of the in-situ creep behavior of Zircaloy-4 at varying stresses and temperatures and compares the proton irradiation results to values from the literature of other proton irradiation studies as well as neutron irradiation studies. A stress exponent of 4.3 ± 0.8 and an activation temperature of 5000 ± 1700 K was determined for recrystallized Zircaloy-4 at the conditions tested.
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