NSUF 24-4952: Advanced characterization of irradiated FAST aLEU U-Mo rodlets using Transmission Electron Microscopy and Atom Probe Tomography

Low-enriched uranium (U) alloyed with molybdenum (Mo), U-Mo fuels, such as U-10wt%Mo are ideal candidates for research reactor programs as they can be manufactured into plates which helps in better heat removal. Moreover, the minimal swelling behavior at low temperatures due to the formation of fission gas super lattice within the body-centered cubic (BCC) microstructure also makes U-10Mo an attractive fuel option for research reactors. U-10Mo fuels exhibit longer core life compared to ceramic fuels such as UN and UO2. Additionally, U-10Mo fuel in plate geometries have also been found to have better performance compared to UO2, UC and UN in terms of power capability and peak heat flux. The limited data availability in previous studies resulted in assuming inferior fuel performance of U-Mo in terms of adverse fission gas and swelling behavior beyond 350°C. Many advanced reactor design and applications require potential fuel candidates to have geometries other than cylindrical configuration along with higher fissile density than oxide fuels. Therefore, U-10Mo testing became significantly important for determining the effectiveness of U-Mo as a potential candidate for light water reactors (LWRs). For this purpose, Fission Accelerated Steady-state Testing (FAST) method has been implemented at Idaho National Laboratory (INL) to investigate monolithic fuel behavior and validate many of these phenomena. All rodlets were irradiated in the Advanced Test Reactor (ATR) for a total of 63 effective full power days (EFPDs). U-10Mo rodlets were irradiated in a range of temperatures from 250˚C to 550˚C, encompassing the whole spectrum of temperatures from research reactors to SFRs along with U-7Mo at 350˚C and 450˚C. All rodlets were fabricated to a 75% smear density clad in HT9 stainless steel. The aLEU-FAST tests emphasized three major categories of novel fuel concepts including: (a) annular U-Mo fuel without Na bond, (b) annular fuel with cladding liner (Zr) for impeding FCCI, and (c) sandwiched fuel with embedded Nb for testing varying linear heat generation rates (LHGRs), creating burnup/temperature gradients and diffusion couples within the same fuel component. Profilometry determined from nominal rodlet diameter resulted in a maximum average strain of 0.13% in the rodlets. Constituent migration, with possible α-U and γ’-UMo phase driven redistribution was observed in rodlets with medium and high irradiation temperatures. Interestingly, grain boundary (GB) tearing, and cavity formation was seen only in one solid rodlet whereas any significant porosity and GB cavitation was absent in the annular rodlets irradiated at similar temperatures. One rodlet was irradiated at a higher temperature of ~540C to understand U-Mo behavior in prototypic SFR conditions. However, no porosity or GB tearing was observed. Such behavior could be hypothesized to grains starting to grow beyond certain threshold temperatures for U-Mo causing the GBs to break and consume the neighboring grain resulting in grain nucleation and growth. The rodlets irradiated at low temperatures, showed patchy sites of porosity with one of them showing potential Niobium (Nb) or Zirconium (Zr) inclusions in the fuel. This could be the diffusion of Nb/Zr into the U-Mo for this rodlet.

추가 정보

필드	값
Award Announced Date	2024-05-28T17:05:00.62
Awarded Institution	Idaho National Laboratory
Facility Tech Lead	Alina Montrose
Irradiation Facility
PI	Sobhan Patnaik
PI Email	[email protected]
Project Type	RTE
RTE Number	None