  We calculate the energies for multi-nucleon ground states with the nuclear
mass number less than or equal to 4 in 2+1 flavor QCD at the lattice spacing of
a = 0.09 fm employing a relatively heavy quark mass corresponding to m_pi =
0.51 GeV. We investigate the volume dependence of the energy shift of the
ground state and the state of free nucleons to distinguish a bound state from
attractive scattering states. From the investigation we conclude that ^4He,
^3He, deuteron and dineutron are bound at m_pi = 0.51 GeV. We compare their
binding energies with those in our quenched studies and also with some recent
investigations.
