 The chance that any given deuteron will hit one of the deuterium atoms in the metal foil is vanishingly small.The experiment only succeeded because it ran for extended periods, and the rare reactions that did occur were so powerful that they could not be missed.But as the basis of a system for power production it simply wouldn't work; the vast majority of the accelerated deuterons goes right through the foil without undergoing a collision, and all the energy put into accelerating it is lost.