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

摘要

The possibility of reducing the concentration of ~(14)C produced in irradiation of reduced activation ferritic steels (RAFS) intended as structural materials in first wall and blanket of fusion power plants was investigated. During RAFS irradiation ~(14)C is mainly produced from the more abundant of the two isotopes of nitrogen present in the steel, namely ~(14)N. The method proposed consists in increasing the enrichment of the other isotope (~(15)N). One-dimension transport calculations show that for a typical DEMO blanket configuration an ~(15)N enrichment from the natural value (0.37%) to 95% was sufficient to keep the end of life ~(14)C concentration in the RAFS below the limit (3.7 × 10~7 Bq/kg) fixed by the Japanese Nuclear Safety Commission for qualifying it as a low level material (LLM) which can be disposed by shallow land burial.