R&D of Invar duct for fabrication of 2nd JSNS moderators

In Japan Spallation Neutron Source (JSNS) in Japan Proton Accelerator Research Complex (J-PARC), a fabrication of the second moderator from 2013 is planned. Invar ducts having a low-thermal expansion coefficient are used as the moderator piping. For the fabrication, examinations of the Invar duct were carried out; tensile tests of dissimilar joints by friction welding, a bending test by a bender and a welding test by TIG welding. As the results, it was found that bonding strengths of the Invar dissimilar joints at 77 K were larger than those at room temperature. It was also found that the dissimilar joints of Invar-A6061-T6 and Invar-SS316L have larger bonding strengths than base materials. The Invar ducts of 22 mm in diameter could be bent into an elbow with 44 mm in radius with slow speed after pre-cooling at 77 K. There wasn’t any failure in butt welding testes by TIG-welding. These results indicate that the Invar duct is available as the moderator piping of the second moderators.