Pressure tube assembly for pressure tube type reactor

Object: To provide a pressure tube assembly for a pressure tube type reactor, in which the material characteristics of portions of extension tubes joined to the pressure tube are improved. Structure: Upper and lower extension tubes each coupled by a rolled joint to each end of a zirconium alloy pressure tube are made of austenite stainless steel, and portions of both extension tubes in contact with the pressure tube and also their portions in contact with inserted seal plugs are made of martensite stainless steel composed of 11.50 to 13.5% Cr, 0.12 or less % C and 3.20 to 3.80% Ni, the rest being substantially Fe (referred to as improved material of SUS 403), thus providing an improved corrosion resisting property. Further, the requisite hardness of the extension tubes with respect to the pressure tube is increased to maintain gas-tightness at the rolled joint portions to thereby prevent leakage of light water flowing through the pressure tube assembly. (Kamimura, M.)