Recent Facility Progress at Oarai Center for Material Irradiation Testing and Actinide Materials Science

57 IMR KINKEN Research Highlights 2013 IMR KINKEN Research Highlights 2013 Neutron irradiation using material-testing reactors is common in research on the effects of irradiation on materials. For a more precise understanding of irradiation dose dependency, the maintenance of identical irradiation conditions, i.e., irradiation rate (neutron flux), neutron spectrum, and irradiation temperature, are necessary for different doses. We have started to develop new irradiation rig for providing such series irradiation to collaborators. Materials irradiation at the Oarai center has been performed using the BR2 reactor of SCK∙CEN, Belgium Nuclear Research Center, after the suspension of JMTR in 2006. A new irradiation rig system, LIfting Basket in the Experimental Rig for BR2 Thimble tube sYstem or “LIBERTY,” is being developed under the framework for collaboration between IMR and SCK∙CEN. LIBERTY’s irradiation specifications are approximately the same as those of JMTR’s rig system in terms of maintaining samples with references under identical conditions of neutron flux and temperature [1]. The new rig system has been improved for fulfilling the specifications and incorporating the following three features. 1) Individual needles can be lifted independently above the reactor core level when the specified fluence is reached, while the other needles remain in the neutron flux. 2) Individual needle can be instrumented separately. Therefore, electrical heating wires and thermo-couples can be installed into the needles for controlling specimen temperature during irradiation. 3) Relatively large specimens such as CT specimens (10 × 10 mm2) can be tested. The concept underlying LIBERTY is schematically shown in Fig. 1 (a); LIBERTY consists of one shroud tube containing up to five needles with samples inside. Initially all needles are inserted at the bottom position of the shroud, which is in the reactor’s core region. When the desired irradiation dose is achieved, the needle is lifted from the bottom to the top of the shroud. Each needle can be lifted individually, thus allowing for five different doses. In each needle, we can install holders with samples, thermocouples, and electric heating elements (heating wires). A cross-sectional view of LIBERTY’s core region is shown in Fig. 1 (b); it is worth noting that it is made of the stainless steel shroud tube, of the five larger needles and of the center tube containing the gamma thermometer. The cooling water first flows downward around the needles through the shroud tube, turns upward, and flows between the outer and inner walls of the shroud tube. The rig itself is reusable, and it does not need to be sent to the hot cell for needle loading and unloading; these operations can be performed in the water pool. LIBERTY is now being developed, as shown in Fig. 1 (c), and will be available in FY2013 for collaborative studies. It is now widely recognized that actinides Recent Facility Progress at Oarai Center for Material Irradiation Testing and Actinide Materials Science International Research Center for Nuclear Materials Science (Oarai Center)