Impact of N-isotope composition control of ferritic steel on classification of radioactive materials from fusion reactor

Hayashi, Takao; Kasada, Ryuta*; Tobita, Kenji; Nishio, Satoshi; Sawai, Tomotsugu; Tanigawa, Hiroyasu; Jitsukawa, Shiro

The impact of increasing the enrichment of N in low activation ferritic steel, F82H, of a fusion reactor has been investigated in order to increase the fraction of low level material (LLM), which can be disposed by shallow land burial. Carbon-14, mainly produced from nitrogen, is one of the most critical nuclei for qualifying as a LLM. The concentration of nitrogen in F82H is 200 ppm in the calculations. The enrichment of N was varied from natural abundance of 0.37% to 95%. The concentration of C at the outboard first wall decreased from 7.8 10 to 3.2 10 Bq/g by enriching N, which is lower than the C regulation (3.7 10 Bq/g) for LLM in Japan. In the permanent blanket, the highest C concentration with 95% N enriched nitrogen was 1.0 10 Bq/g. The C concentration on the inboard side was lower than the outboard side. Therefore, with regard to the C concentration, the F82H used in the inboard and outboard blankets can qualify as a LLM by enriching N.