NSUF 24-4943: Low fluence effects of neutron irradiation on the phase evolution of U-10wt.%Zr specimens

Currently, advanced fast reactors are under consideration for deployment. Previous experience has demonstrated that uranium-zirconium (U-Zr) fuels can reach up to 20 at.% burn-up without fuel pin failure. Regardless of the performance of the U-10wt.Zr fuel, there is limited knowledge of the physical properties of U-10wt.%Zr fuel, specifically the irradiation and thermal effects observed in the irradiated fuel microstructure. The distribution of phases during operation and the mechanisms for retention of non-equilibrium phases in the fuel is not well-understood. The non-uniform distribution of temperature, and neutron fluence in the fuel pin during reactor operation does not allow for the deconvolution of irradiation-induced effects within the fuel microstructure. Moreover, most U-10wt.%Zr fuels characterization occurred at burnups higher than 1 at. %, and thus, the irradiation-induced phenomena (e.g. constituent redistribution or thermomigration of U and Zr, phase evolution, and swelling) were well formed. Consequently, there is a critical knowledge gap within the current understanding of the irradiation behavior of U-Zr fuels at low fluences. Irradiation at low fluences gives insight into the initial microstructural evolution of the complex and interconnected phenomena, specifically phase changes, constituent redistribution, and swelling. Hence, the current experiment aims to test the hypothesis: (1) does irradiation induce the retention/formation of non-equilibrium phases? and (2) at what dose and temperature do the non-equilibrium phase transformations initiate at? To test this hypothesis, we propose to characterize U-10wt.%Zr specimens irradiated to low neutron fluences and held at a constant irradiation temperature at low fluences to understand the microstructural evolution in the early stages of irradiation, eliminating the effect of thermal or compositional gradients. Various irradiation temperatures are considered: 500, 700, and 800 ºC to survey the different phase regions, as well as doses: 0.01, 0.1, and 1 dpa, to identify at what critical dose the non-equilibrium phase transformations are observed. The current study will characterize irradiated specimens available in the Nuclear Fuels and Materials Library. We propose to characterize the irradiated specimens, and an unirradiated control using high-resolution SEM (SE, BSE, and EDS) and TEM (BF, DF, EDS, SAED). We propose the use of a FIB-SEM due to the multi-modal nature, allowing us to obtain morphological and chemical data within the same equipment, as well as to identify and prepare in-situ the areas for TEM analysis using the FIB. Similarly, TEM examinations will permit for the definitive identification of the phases present via SAED and EDS. Specimens will be analyzed using the FEI Quanta 3D FIB and the Titan Themis 200 in the Irradiated Materials Characterization Laboratory at Idaho National Laboratory. SEM and TEM examinations will provide unique data on early microstructural evolution at low fluences, including compositional maps, phase identification, phase composition, and phase distribution in the irradiated fuel, as well as indications of phase decomposition. From the micrographs, phase fractions can be obtained using automatic image analysis or standard stereology practices. The phase distribution, composition, and phase fractions are variables that are required to further develop more accurate mechanistic models and fuel performance codes such as BISON and MARMOT.

추가 정보

필드	값
Award Announced Date	2024-05-28T16:57:26.397
Awarded Institution	Purdue University
Facility Tech Lead	Alina Montrose
Irradiation Facility
PI	Maria A Okuniewski
PI Email	[email protected]
Project Type	RTE
RTE Number	None