NSUF 24-5129: Visualizing the impact of irradiation damage on alloy element redistribution accompanying Zr alloy corrosion via atom probe tomography

Dilute Zr alloys (e.g., Zircaloy-4, ZIRLO) are widely used as nuclear fuel cladding in pressurized water reactor where they experience waterside corrosion and irradiation damage, which can significantly impact components’ physical integrity, and thus lifetime. During reactor operations, a corrosion film is formed on the Zr alloy due to interaction with the primary water, and this film can be protective in nature, limiting further corrosion and breakdown of the cladding. While the corrosion of Zr alloys has been a well-studied phenomenon for decades, several knowledge gaps remain, particularly related to the development of nanoscale heterogeneities and the redistribution of alloying elements that occur during early stages irradiation and corrosion, which impact longer-term behavior.

Sn is a common alloying addition in Zr alloys used as fuel cladding, and can inhibit harmful effects of N and improve corrosion resistance. Unraveling the contribution of irradiation in Sn redistribution occurring during Zr alloy corrosion can help to understand the role of minor alloying elements in corrosion kinetics, and oxide space charge effects. It is well established that alloying elements’ concentration and distribution in the oxide can significantly impact oxidation kinetics, grain boundary transport behavior, oxide space charge, and defect concentrations; dopants in the oxide can impact transport mechanisms in the Zr oxide that contribute to corrosion mechanisms and kinetics. The behavior of Sn during concurrent irradiation and corrosion in reactor core operating conditions has implications in the design of low-Sn Zr alloys for fuel cladding applications, and in building predictive understanding of existing alloy systems and their performance in operating reactors. However, knowledge gaps remain about Sn redistribution during Zr alloy corrosion, including how irradiation impacts the following: composition of Sn-rich clusters in the oxide, if such clusters are metallic in a pre-transition oxide, and Sn grain boundary segregation and rejection by the advancing oxide front.

Here, we propose to investigate the effects of irradiation-induced redistribution Sn in the early stages of Zircaloy-4 corrosion with near atomic-scale resolution via atom probe tomography (APT). Sn distributions in irradiated and corroded and corroded- only Zircaloy-4 specimens at varying positions relative to the oxide/metal interface will be investigated. Proton irradiation will be used as a surrogate for neutron irradiation so that low dose rates can be easily controlled, and sample handling/characterization can be simplified/accelerated. The high mass and spatial resolutions provided by APT are required to directly observe solute redistributions across the oxide/metal interface in the presence and absence of irradiation. Low irradiation damage doses and corrosion times are specifically proposed to capture changes occurring in the pre-transition oxide.

Through this improved mechanistic understanding, predictive capabilities related to Zr irradiation and corrosion response can be developed, and mitigation strategies can be explored. The expected period of performance for the proposed work is nine months.

추가 정보

필드	값
Award Announced Date	2024-09-23T12:13:53.567
Awarded Institution	North Carolina State University
Facility Tech Lead	Adrien Couet, Stuart Maloy, Yaqiao Wu
Irradiation Facility	University of Wisconsin Ion Beam Laboratory
PI	Elizabeth Kautz
PI Email	[email protected]
Project Type	RTE
RTE Number	None