Measurement of effective Sr diffusion coefficients in IG-110 graphite

Highlights: • IG-110 graphite was loaded with Sr. • Time-release experiments examined Sr migration in graphite. • Experimental design simulates HTGR conditions: High temperature and flowing helium. • Diffusion coefficients were obtained for Sr diffusion in graphite IG-110. Radionuclide transport and release from operating HTGR cores during normal and off-normal operations carries the possibility of increased exposure risk to reactor personnel as well as radionuclide release to the surrounding environment in the event of a depressurization accident. Diffusion is one of the primary processes by which this radionuclide transport takes place. ⁹⁰Sr is one of several fission products which is commonly investigated within the context of high-temperature gas-cooled reactors due to its low volatility and ability to migrate through intact TRISO fuel particles. Effective diffusion coefficients for strontium in unirradiated IG-110 graphite have been experimentally determined over the temperature range 1773 K – 1973 K using a time-release method coupled to an inductively-coupled plasma mass spectrometer. The results of this work are: $D_{Sr,IG-110}=\left(1.7\times {10}^{-1}{m}^2/s\right)exp\left(\frac{-3.46\times {10}^{5}J/mol}{RT}\right)$