History of Science and Engineering Annotation << Back The Problems of Zirconium Channels of RBMK Reactors. History Platonov P.A. Ivanov A.N. Frolov I.A. Ryazantseva A.V. The article describes history and results of investigations of pressure tubes made of alloy of zirconium and 2,5 % of niobium (alloy 125). This alloy was chosen for the production of RBMK channel tubes as it demonstrated the highest strength and resistance to creep in comparison to all other alloys developed up to that time, moreover it demonstrated the high resistance to corrosion. However there were no own data for radiation stability and particularly for radiation creep at that time. The investigations of radiation creep of channel pipes were delegated to Kurchatov IAE, and they were started at MR reactor in the 60-ies. Wide-ranging investigations led to replacement of all stainless steel loop channels for zirconium channels. As fuel rods /FRs/ in loop channels were tested in different modes (RBMK, VVER, ship installations), it facilitated relatively fast understanding of creep patterns (relation to stress, temperature and flux of fast neutrons) and obtaining of radiation growth of tubes made of alloy 125. It also facilitated to estimate of the depletion terms for the gap between a channel tube and graphite, which turned out to be twice as lower as in the project, which presumed 30 years. This circumstance led to the necessity of channels’ replacement as well as restoration of diameter of graphite cells, which then became a common procedure for all RBMK reactors. Also investigations were performed in respect of the creep of the tubes of various thermal treatments, which were designed for installation into reactors of Ignalinskaya NPP (RBMK-l500). The article also describes the problems relating to cracking of technological channels (delayed hydride cracking /DHC/), seal failure of transitional connections. The article points out that the reasons for seal failure of zirconium parts of channels in the way of DHC were pollution of blend as well as high residual stresses. Elimination of these reasons significantly reduced the possibility of seal failure in the future. Keywords: zirconium; pressure tube; RBMK; creep; delayed hydride cracking. Contacts: E-mail: platonov@irtm.kiae.ru Pp. 68-79.