An investigation was performed on possible penetration of sodium into Type-304L stainless-steel grain boundaries when the steel was exposed to the liquid metal at 1200°F. The method used consisted of progressive penetration with a laser through sodium-filled thin wall stainless-steel tubes ∼0.0005 in. at a time. Simultaneous recording of the emission spectrum of each sample on photographic film resulted in the production of a comparative record which was analyzed for the intensity of the sodium 5890 and 5895.5 Å doublet. Entry into a sodium-rich region was attended with intensification of the sodium lines. Results with a series of tubes exposed to sodium at 1200°F up to 1425 h and compared with a control sample not treated at 1200°F did not show any evidence of sodium penetration through Type-304L stainless steel.