Possibility of existence of nn ground state was discussed in 2011 by H. Witala and W. Glöckle based on anomalous enhancement of nn QFS (Quasi-Free Scattering) cross section in nd breakup at En = 26 MeV reported in 2002. To search for the nn ground state, we have made a feasibility study of D(3H,3He)nn and D(n, p)nn experiments. 3H and n secondary beams are produced respectively by D(d,3H)p and D(d, n)3He reactions at forward angle, and are injected on a CD2 foil target. If an nn ground state exists, a single peak is observed in the 3He and p energy spectra. We conclude that these experiments are feasible.