Lifetime evaluation of graphite components for HTGRs

高温ガス炉黒鉛構造物の寿命評価

奥 達雄*; 石原 正博 

Oku, Tatsuo*; Ishihara, Masahiro

黒鉛材料の寿命と黒鉛構造物の寿命はそれぞれ異なる観点から論じられ、しばしば材料研究者や設計者に混同されることがある。黒鉛材料の寿命は、照射による寸法収縮が初期値に戻る照射量を材料の寿命と考えている。一方、黒鉛構造物の寿命は、構造物に生じる発生応力が許容応力に達した照射量を構造物の寿命と考えている。そこで、HTTR黒鉛ブロックを一例として、黒鉛ブロックの発生応力から評価される構造物の寿命と照射誘起寸法変化から評価される材料の寿命についての比較検討を行った。その結果、黒鉛構造物の寿命は、発生応力と許容応力の関係からの制限及び照射誘起寸法変化の両者の短い方によって定義すべきことを明らかとした。

The lifetime of graphite material and/or components has been discussed individually from different concepts, and sometimes gives confusion to material researchers as well as designers. The lifetime of graphite materials is determined based on the dimensional changes due to neutron irradiation, at which they return to their original dimensions after initially contracting. On the other hand, the lifetime of graphite components for HTGRs is defined based on a margin of the specified minimum ultimate strengths of the graphite to the stresses induced in the graphite components. As an example, the stresses induced in the graphite block for the HTTR were, then, compared with the limited stress value determined from the specified minimum ultimate strength, and the lifetime of the graphite component was evaluated and compared with that defined as dimensional changes. As a result, it was found that the lifetime of graphite components for HTGRs should be determined as the shorter one in the two lifetimes defined by the stress-strength relationship and by the dimensional changes.