Composite Materials for Nuclear Applications: TRISO Fuel
Sponsored by: TMS Structural Materials Division, TMS: Composite Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Anne Campbell, Oak Ridge National Laboratory; Dong Liu, University of Oxford; Rick Ubic, Boise State University; Lauren Garrison, Commonwealth Fusion Systems; Peng Xu, Idaho National Laboratory; Johann (Hans) Riesch, Max Planck Institute for Plasma Physics
Monday 8:30 AM
March 15, 2021
Room: RM 52
Location: TMS2021 Virtual
Session Chair: Dong Liu, University of Bristol
8:30 AM Invited
Tristructural Isotropic (TRISO) Fuel for High-Temperature, Passively-Safe Nuclear Reactors: John Stempien1; Paul Demkowicz1; John Hunn2; 1Idaho National Laboratory; 2Oak Ridge National Laboratory
The Advanced Gas Reactor (AGR) program, under the US Department of Energy, is in the process of qualifying tristructural isotropic (TRISO)-coated particle fuel with the US Nuclear Regulatory Commission to support design, construction, and operation of high-temperature reactors. TRISO fuel particles are < 1 mm in diameter and consist of a central fuel kernel made of a heterogeneous mixture of uranium oxide and uranium carbide that is coated in layers of pyrocarbon and SiC. This program encompasses all phases of TRISO fuel production, irradiation and post-irradiation examinations, and predictive fuel performance modeling and fission product transport. Each component of the TRISO fuel system serves a purpose. Using data acquired from post-irradiation microscopy, gamma-ray spectroscopy, and heating tests, it will be discussed how each material component of the TRISO fuel system functions to impart chemical stability, retain fission products, and maintain coating integrity under accident scenarios.
9:00 AM
Experimental Characterisation of the Variation of Local Residual Stresses in TRISO Coatings: Alexander Leide1; Steven Knol2; Arjan Vreeling2; Dave Goddard3; Dong Liu1; 1University of Bristol; 2NRG; 3National Nuclear Laboratory
Multi-layer components inherently experience internal stresses due to differences in the properties of their constituent materials, such as thermal expansion coefficient or elastic constants. TRISO coatings (SiC and pyrolytic carbon) processed by chemical vapour deposition will experience thermal stresses during cooling, causing residual stresses and potentially micro-cracking or layer debonding. During operation in a reactor, stresses in TRISO coatings evolve due to dimensional changes caused by neutron irradiation (shrinkage, swelling, creep) and gas pressure build-up. These operational stresses and dimensional changes are affected by the initial stress state and layer structure of the particles, resulting in different failure criteria than predicted. Local spatially varying residual stresses have been characterised using Raman spectroscopy, ring-core FIB-DIC, nanoindentation, and X-ray diffraction in particles with different coating layers. The stresses are correlated to processing conditions and local microstructure, and they are used to assist the understanding of the dimensional changes in neutron irradiated particles.
9:20 AM
Post-irradiation Examinations of TRISO Particles Corroded in Molten FLiBe Salt under Neutron Irradiation: Guiqiu Zheng1; David Carpenter1; 1Massachusetts Institute of Technology
Several advanced reactor designs incorporate tri-structural isotropic (TRISO) fuel particles with SiC and pyrolytic carbon coating layers to achieve fuel compatibility with high coolant temperatures and increased thermodynamic efficiency. TRISO particles embedded in graphite matrix fuel pebbles are being considered as a fuel for fluoride salt-cooled high-temperature reactors (FHRs). In support of FHR development, TRISO particles with ZrO2 surrogate kernels were tested in Li-7 enriched FLiBe (2LiF-BeF2) salt at 700°C for 1000 hours in the Massachusetts Institute of Technology Research Reactor (MITR) to evaluate their behavior in case of direct salt contact with the particles in the FHR. In this study nano-scale microstructural characterizations were performed to examine the condition of the TRISO particles post-irradiation. The synergistic effects of molten salt exposure and neutron irradiation at high temperature caused tangential cracks to form in the SiC layer and molten salt to infiltrate into the particle along these cracks.