核燃料施設の事故影響評価手法に関する調査（ⅤⅠ）「溶融ガラスの漏えい」事故時の放射性物質移行率の調査・検討

摘要

A special committee of "Research on analysis methods for accident consequence in nuclear fuel facilities" was organized by the Atomic Energy Society of Japan under the entrustment of Japan Atomic Energy Agency (JAEA). The research results were summarized in a series of six reports, which consist of the general report and five technical ones. This is the fifth technical one dealing with airborne release fraction (ARF) in the case of accidental leakage of molten glass from a vitrification melter. In the effective dose assessment of the design basis accident of the molten glass leakage at the Rokkasho Reprocessing Plant, ARFs of 1 for Ru and Cs and of 0.1 for nonvolatile elements, such as Sr and minor actinides, were used. In the present report, more realistic values of 1 ×10~(-3) for Cs, 5 10~(-5) for Ru, and 10~(-8) for nonvolatile elements, such as Sr and minor actinides, were proposed for risk assessment; these values were obtained by calculation using the measured volatilities of these elements at high temperatures of 800-1,100℃ reported in the literature. Although these values depend on the scale and conditions of the leakage, they are given as maximums irrespective of the conditions.%日本原子力学会の「核燃料施設事故影響評価手法調査特別専門委員会」では，平成16年度より18年産まで鰯日本原子力研究開発機構からの委託を受けて，核燃料施設の確率論的安全評価（PSA：Probabilistic Safety Assessment）手法のうち，影響評価a）に用いる解析手法に重点をおいて調査検討を実施してきた1～3）。その成果を，「総説」1編および再処理工場で想定される代表的な事故ごとにまとめた5編の「技術資料」としている。本報は，5編の技術資料 のうち「ガラス溶融炉からの溶融ガラスb）の漏えい」（以下，「溶融ガラスの漏えい」という）に関わる放射性物質の気相への移行率（Airborne Release Fraction：ARF）に関する検討結果をまとめている。総説および他の技術資料はすでに本誌4～8）に掲載されている。