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Report No.
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Activation properties of Nb$$_{3}$$Sn, NbTi and GFRP irradiated with D-T neutrons

Ochiai, Kentaro; Nishimura, Arata*; Nishitani, Takeo; Nishijima, Shigehiro*

Nb$$_{3}$$Sn, NbTi wires and glass fiber reinforced plastics (GFRP) are prospective candidate materials of the superconducting coil assembly for fusion reactors. These materials are activated by D-T neutrons penetrating through the reactor core. From the radioactive waste point of view, it is important to investigate the activation properties for these candidate materials. However, no experiment has been done to investigate the activation properties for these materials. Therefore, we have carried out the experimental investigation of the activation properties of Nb$$_{3}$$Sn, NbTi wires and GFRP materials. The neutron irradiation experiment has been done by the FNS D-T neutron source of JAEA. We used complex multi-filaments wires of Nb$$_{3}$$Sn and NbTi produced by FURUKAWA-electric Ltd. and a commercial GFRP (G10CR) plate. These samples were irradiated up to the neutron fluence of 4$$times$$10$$^{19}$$n/m$$^{2}$$ corresponding to about one twentieth neutron fluence expected for ITER life time. After the cooling time, the dose rates and the emitted $$gamma$$-ray spectra were measured with a survey meter and a Ge detector, respectively. Induced major radioactive nuclides are Nb-92m, Sn-117m, Sn-113 and Co-60 for Nb$$_{3}$$Sn, and Nb-92m, Sc-46 and Co-60 for NbTi. Also Na-24, Na-22, Sc-47, Co-57, As-74, Rb-83, Mn-54 and some unknown radioactive nuclides were observed from the irradiated GFRP. It is considered that those radioactive elements are due to the activation of the additive compounds in GFRP. The initial dose rates of the irradiated Nb$$_{3}$$Sn, NbTi and GFRP samples were 160$$mu$$Sv/h, 120$$mu$$Sv/h and 20$$mu$$Sv/h, respectively. After 5 months from the irradiation, these dose rates were reduced to 2-4$$mu$$Sv/h. Also, from the measured $$gamma$$-ray spectra, it was found that the final dose rates of Nb$$_{3}$$Sn and NbTi wires were dominated by Co-60 (5.27y) and the that of GFRP was dominated by Na-22 (2.60y).

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