NSUF 24-5142: In-situ TEM study of microstructural evolution and deformation in FFTF irradiated HT-9 cladding

HT-9, a tempered martensitic (TM) alloy with a nominal composition of Fe-12Cr-1Mo-0.5W-0.5Ni-0.25V-0.2C (in wt%), has shown promise for use as metallic fuel cladding material in Sodium-cooled Fast Reactors (SFRs) due to its attractive properties such as excellent swelling resistance and high-temperature mechanical performance. However, the harsh in-core environment of SFRs poses significant challenges to the microstructural stability and strength properties of the HT-9 cladding. This is due to the combined exposure to irradiation, mechanical stresses, and elevated temperatures. To ensure the prolonged and safe deployment of HT-9 in future SFRs, it is essential to thoroughly understand its response to these combined effects. While most studies conducted so far have focused on individual effects (such as irradiation alone), there remains a knowledge gap regarding the changes in mechanical properties due to the microstructural evolution of HT-9 when all three phenomena are present simultaneously. This project aims to bridge that gap. By studying samples from an HT-9 fuel pin that has experienced these conditions, we will obtain comprehensive and accurate data. To do so, we will perform in-situ transmission electron microscopy (TEM) nanomechanical testing on real metallic fuel/HT-9 cladding that has experienced thermal aging, mechanical stress, and radiation damage inside the Fast Flux Test Facility (FFTF). A freshly fabricated HT-9 sample will serve as a baseline to analyze the changes in mechanical properties and correlate them to the microstructural evolution of the FFTF-irradiated HT-9 cladding samples. The results of this project will benefit the R&D of advanced steels for next-generation nuclear reactors, ultimately supporting their optimization for greater microstructural stability and steady mechanical strength while in service. Foils will be extracted from fresh HT-9 and two irradiated samples (from different locations of the fuel pin) and mounted on push-to-pull (PTP) devices for TEM and nanotensile testing. The proposed methods will allow live monitoring and data collection while conducting the experiments. Therefore, the Irradiated Materials and Characterization Laboratory (IMCL) at Idaho National Labotatory (INL) is uniquely equipped for this work due to its capability of handling radioactive samples and its specialized equipment. Instrument time requested to complete the scope of the project is 2 weeks (8 days). The materials requested for this project are one fresh HT-9 sample and two FFTF-irradiated samples: MNT83T and MNT54C. The samples will be prepared using the focused ion beam – scanning electron microscope (FIB-SEM) instrument. Once the foils are mounted on the PTP devices and loaded into the TEM, a comprehensive characterization of the microstructure will be conducted. Identification of dislocation loops, precipitates, subgrain boundaries, and any other features encountered will be captured by imaging in TEM and scanning TEM (STEM) mode. Energy dispersive x-ray spectroscopy (EDS) maps will be collected to get chemical maps. Selected area electron diffraction (SAED) patterns will be obtained for dislocation analysis and phase identification. In-situ TEM nanomechanical experiments using the PI-95 picoindenter will allow us to collect force vs. depth datasets to extract mechanical properties. All experiments will be conducted at room temperature.

추가 정보

필드	값
Award Announced Date	2024-09-23T12:16:54.127
Awarded Institution	North Carolina State University
Facility Tech Lead	Alina Montrose
Irradiation Facility
PI	Lucia Rebeca Gomez Hurtado
PI Email	[email protected]
Project Type	RTE
RTE Number	None