Session: CS-15-02 Mechanical Properties of Nuclear Graphite and Their Implementation in Codes and Standards (Joint with MF-29) – 2

Paper Number: 106343

106343 - Fission Product Transport Characterization in Nuclear Graphite Grades 

Graphite is used for neutron moderation and structural support in Generation IV very high temperature reactors (VHTRs) and molten salt reactors (MSRs). As a result of its contiguity to the fuel source, graphite components interact with the diffusing solid and gaseous fission products; these can further migrate and escape through the graphitic pore network. In this work, we investigate the diffusion pathways and mechanisms in four grades of nuclear graphite that are implanted with either ruthenium or silver at temperatures ranging from 500 to 1000 ⁰C and allowed to anneal over a 24 hour period.  The diffusivity profiles of both fission products are measured at the University of Central Florida (UCF) using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Curiously, a drop in diffusivity is noticed in samples annealed at 700 ⁰C for all graphite grades. Raman spectroscopy analysis indicate a trapping effect within the pore network that is most active at this temperature. Further investigation using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) reveals a clustering behavior that takes effect around the same temperature for all the grades and both fission products. Near 700 ⁰C, the deposited particles start transitioning away from uniform surface coverage to separate irregular islands before morphing into nearly spherical clusters at 1000 ⁰C, where little to no ruthenium or silver can be found in-between.

Presenting Author: Dina ElGewaily North Carolina State University

Presenting Author Biography: Dina ElGewaily is a PhD student in her 4th year, in NC State University, working with Dr. Jacob Eapen on two main nuclear materials characterization projects funded by the DOE. The first is concerned with the damage inflicted on SiC cladding in accident conditions due to steam attack, while the other projects investigate the diffusion and transport mechanisms of different fission products in nuclear-grade graphites as well as modeling their porosity.

Authors:

Dina ElGewaily North Carolina State University
Jacob Eapen North Carolina State University