Experimental investigation of alumina coating as tritium permeation barrier for molten salt nuclear reactors

This study experimentally investigates the reduction efficiency of tritium permeation through 316 stainless steel tubing coated with alumina as a tritium permeation barrier (TPB) in support of the development of molten salt nuclear reactors, particularly for fluoride salt-cooled high-temperature nuclear reactors (FHRs). The TPB coatings composed of an intermediate bond layer of NiCr, a transition layer of NiCr + alumina, and a pure alumina layer were successively added onto the outer surface of commercial 316 stainless steel tubing via plasma thermal spray. In order to generate a continuous gaseous tritium source, 35 g of purified natural-lithium FLiBe salt was irradiated by thermal neutron flux at 620 degrees C in the Massachusetts Institute of Technology Research Reactor (MITR). The preliminary results suggest that the TPB coatings on tube surfaces significantly reduced the tritium permeation rate at 700 degrees C. To get a better understanding of the TPB, the microstructure of the coated tubes was characterized with various techniques.