A PbLi thermal convection loop with the flow rate of a few centimeters per second was designed and constructed to perform an in-situ tritium release experiment in a neutron source of the YAYOI reactor of The University of Tokyo. Tritium was generated by the nuclear reaction of Li with neutrons released through a 1-mm-thick steel tube and followed the reactor power with some time lag, which was affected by the hydrogen concentration in the sweep gas. The overall permeation rate coefficients, around 10-5 m/s, were almost the same as those acquired in former works performed in static tests. Formation or reduction of a surface oxide layer on the permeation tube would affect the tritium release behavior.