[en] The so-called 'cold nuclear fusion' is a phenomenon that is considered to be nuclear fusion around room temperature. This was observed in electro-lysis of heavy water containing some impurities, and was first reported by 2 groups of researchers almost simultaneously in March 1989. Fusion rates reported before are too high to be explained by conventional nuclear reaction theory. It is generally accepted that some additional factors, which are not yet clear, must be considered. Author considers that material aspects, especially lattice defects aspects of cathode materials, as above mentioned additional factors, are important, and he proposes to consider interstitial deuterium dynamic crowdions and multi-deuterium atoms trapped at vacancies. (author). 12 refs., 5 figs