In traditional power engineering hydrogen may be one of the firstprimary sources of equipment damage. This problem has high actuality for both nuclear and thermonuclear power engineering. Study of radiation-hydrogen embrittlement of the steel raises the question concerning the unknown source of hydrogen determined in steel specimens irradiated in inert environment reactors. Later unexpectedly high hydrogen concentrations were detected in irradiated graphite. So alloying of steel and graphite by hydrogen in nuclear reactor takes place. It is necessary to look for this source of hydrogen especially because hydrogen flakes were detected in reactor vessels of Belgian Nuclear Power Plants. As a possible initial hypothesis about the enigmatical source of hydrogen one can propose protons generation during beta-decay of free neutrons inasmuch as protons detected by researches at nuclear reactors as witness of beta-decay of free neutrons.