A hypothesis is proposed where low energy nuclear reactions involve three-body recombination of deuterons injected between the nuclei of D 2 molecules trapped in a dense lattice of a chemical compound of transition metal and impurity. Two D's fuse to 4 He, and the energy is converted by expulsion of the third deuteron. Measurable fusion occurs when two D's are confined within 0.1 angstrom of each other. Three boson (efimov) interactions can have longer range than two boson interactions. The best known example is triple alpha fusion to carbon-12 in stars. Triple deuterium interaction could perhaps be possible in the 0.5-1.0 angstrom range; the distance between D's in a D 2 molecule are 0.74 angstrom. The hypothesis accounts for the low reproducibility and short duration of the effect because of rapid destruction of the active structure by sputtering, radiation damage, bubble formation and chemical reduction of the impurities to compounds like D 2 O, ND 3 , CD 4 , or BD 3 . The hypothesis also accounts for the observed prevalence of 4 He >> tritium >> neutrons.