Gary Was

Professor

gsw@umich.edu

1921 Cooley

T: (734) 763-4675

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Accelerator-Based Irradiation Creep of Pyrolicitc Carbon Used in TRISO Fuel Particles for the VHTR

Collaborators: L.Wang
Sponsor: DOE-NERI
Pyrolytic carbon (PyC) is used as one of the structural materials for the TRISO fuel particles in the next generation of gas cooled Very-High-Temperature Reactors (VHTR). Creep of pyrocarbon layers in the TRISO particles under irradiation can be significantly anisotropic via carbon atom displacements despite of the original isotropic nature of the PyC film. The creep strain occurring in the outer pyrocarbon layer may cause radial cracking that may lead to the catastrophic particle failure. Therefore, fundamental understanding of the creep behavior of PyC during irradiation is required for predicting the overall fuel performance. The primary objective of this project is to characterize the creep behavior of PyC through a systematic program of accelerator-based proton irradiation and in situ measurement of the creep behavior. PyC samples supplied by ORNL will be irradiated with energetic protons to doses as high as 3 dpa (displacements per atom) at the Michigan Ion Beam Laboratory. The samples will be held under tensile stress by a static load, at various temperatures between 400 ¡C and 1200 ¡C. Analyses of test data to determine creep coefficients will be jointly performed at the University of Michigan, INL and ORNL. These creep coefficients will then be correlated to existing coefficients measured under neutron irradiation. In addition, initial experiments on the transport of select fission products (e.g., Ag and Sr) in PyC under irradiation and stress will be conducted by ion implanting the elements into the surface of the sample prior to proton irradiation under load. The microstructure of PyC after irradiation and/or irradiation creep and the fission product distribution in PyC will be studied with advanced analytical transmission electron microscopy (TEM). The overall results of this research project will contribute to the validation and improvement for the modeling of irradiation creep and fission product transport in PyC that are critical to the prediction of TRISO fuel performance in the VHTR.