An influence of superfluidity on chemical reaction has been studied in the recombination reactions of hydrogen (H) and tritium (T) atoms, H + T --> HT and T + T --> T-2, in He-3-He-4 mixture solutions at 1.6 K. The reactive species, H and T atoms, were produced in the mixture through the nuclear reaction, He-3 + n --> p(H) + T. Experimental yield ratio of HT to T-2 was 110 +/- 17 in normal-fluid solution. However, in superfluid solution, the value decreased to 60 with a decrease in atomic fraction of He-3. A two-fluid model was applied to estimate the contribution of superfluidity. The calculated yield of HT to T-2 in the superfluid component became almost a constant value of 56 +/- 14 over the whole range of superfluid solution studied. On the basis of preferential formation of HT over T-2 and a computer simulation of relative rate constants, formation of hydrogen isotope bubbles and their tunneling recombination were proposed.