JT-60Uにお相るW型ダイバータタイル中の軽水素および重水素蓄積挙動と損耗·再堆積分布

摘要

核融合炉内のトリチウムを含む水素同位体挙動を把捉することは核融合炉安全の観点から重要な研究課題である[1,4]．我々は，三Ⅰ本原子力研究所（現：日本原子力研究開発機構）と大学との協力研究の一環として，日本原子力研究開発機構那珂核融合研究所に設置されているJT－60Uにおいて重水素放電に曝されたプラズマ対向グラファイトタイル中の水素同位体音積挙動評価を行ってきた．これまでの研究において，DD反応によって生成されたトリチウムは数ミクロンの探さに打ち込まれているのに対して，軽水素および重水素は表面近傍に蓄積されていることがわかっている[5－7]またダイバータ領域における樫水素と重水素の分布は明らかに異なり，軽水素は表層近傍に局在していた[8－10]．このことは，ITERダイバータにおけるトリチウム挙動を予測するためには，JT－60Uにおける暇水素および重水素の挙動，将に再堆積屑中での水素同位体の挙動を明らかにする必要があることを意味している．Distributions and retentions of hydrogen and deuterium retained in graphite tiles placed in the W-type divertor of JT-60U were studied by secondary jon mass spectroscopy and thermal desorption spectroscopy, respectively. Poloidal profiles of hydrogen and deuterium retention were compared to those of the erosion;deposition thicknesses observed by a scanning electron microscpe and/or micro meter.It was found that the large amount of hydrogen isotopes was retained in the redeposited layers appeared at the inner divertor and the outer sing area,Most of hydrogen isotopes were retained uniformly in the re-deposition layers with the hydrogenisotope cocentration of 0.02-0.03 in (H+D)/C atomic ratio,thich is much lower than that with saruration concentration of 0.4-1 in other tokamaks operated below 500K.Because the operation temperature of JT-60U was kept to be above 573 Kand the surface temperature of the divertor tiles were likely heated up above 800 J during a discharge. Only small amount of hydrogen was retained in the eroded area appeared at the outer divertor and the inner wing area. Only small amount of hydrogen was retained in the eroded area appeared at the outer divertor and the inner wing area. In all cases, the top most surface layers were dominated by hydrogen indicating easy replacement of deuterium and satuation of hydrogen isotope concentration during the discharge.