NSUF 24-4848: Advanced characterization of irradiated FAST rodlets using Transmission Electron Microscopy and Atom Probe Tomography

The Advanced Fuels Campaign (AFC) has recently completed the first phase of the Fission Accelerated Steady-state Testing (FAST) project, an accelerated irradiation test campaign, within the ATR on several metallic fuel samples. One objective of the FAST-1 experiments (first phase of FAST tests within the AFC) is to evaluate the effects of accelerated irradiation via control rodlets and comparing the behavior to that of historical fuel test in EBR-II. Fuel phenomena of interest to the program include fission gas behavior in smaller geometries, fuel swelling in smaller geometries, fuel constituent redistribution mechanisms, and fuel cladding chemical interaction (FCCI). Current post-irradiation examination (PIE) plans include the use of optical microscopy, scanning electron microscopy (SEM), and thermal-mechanical property testing. The proposed study will help in understanding validating the application of the FAST method for fuel testing and being able to provide data for mechanistic understanding of metallic fuel phenomena. All rodlets tested under FAST were 75% smear density (SD) U-10Zr (Uranium-10 weight % Zr) fuel pins with HT9 cladding. SD is defined as the ratio of the cross-sectional area of the fuel slug to the inner cladding and is used to convey the allowance for pore formation and fuel swelling. One of the innovative designs tested was a helium bonded annular fuel pin where a center annulus accommodates fuel swelling. In addition to this innovative fuel design, a sister rodlet was irradiated in the same capsule as a control. The control pin is a Na bonded, solid pin also in HT9 cladding. Lastly, two solid fuel pins were also irradiated at temperatures much lower than normal operating temperatures in order to understand low temperature swelling behavior. Initial PIE has been reported on these tests which includes details from neutron radiography (nRAD), precision gamma scanning (PGS), profilometry, fission gas analysis, and optical metallography. Two curious observations were made in the initial PIE that would benefit from atomic level characterization. First, the FAST-007 and FAST-008 specimens showed indications of alloy redistribution in spite of the fact that the peak fuel temperatures were below both the β and γ transition temperatures. Conventional fuel models predict that this phenomenon is triggered by these transitions and so this redistribution suggests alternative mechanisms are responsible. Additionally, fuel swelling is expected to maximize at burnup levels of approximately 2%FIMA where the fuel is fully smeared. This is driven by pore formation and fission gas driven swelling. However, neither FAST-035 nor FAST-036 showed this behavior in spite of it having reached burnups in excess of 2%FIMA. These two controversies are the focus of this proposed work as the mechanisms driving this behavior require atomic level investigation. The results obtained from this study will be submitted as manuscript to peer-reviewed scientific journals such as the Journal of Nuclear Materials, Progress in Nuclear Energy, Nuclear Engineering and Technology, etc.

추가 정보

필드	값
Award Announced Date	2024-02-02T12:16:29.687
Awarded Institution	Idaho National Laboratory
Facility Tech Lead	Alina Montrose
Irradiation Facility	Fuels and Applied Science Building
PI	Sobhan Patnaik
PI Email	[email protected]
Project Type	RTE
RTE Number	None