A Rational identification of creep design area using negligible creep curve

Negligible creep curveを用いたクリープ設計域の合理的設定法

祐川 正之*; 磯部 展宏*; 柴本 宏; 田中 良彦*; 笠原 直人

Sukekawa, Masayuki*; Isobe, Nobuhiro*; Shibamoto, Hiroshi; Tanaka, Yoshihiko*; Kasahara, Naoto

非クリープ設計域の拡張による許容応力の拡大及び設計手順の簡素化のため、NC(Negligible Creep)カーブを用いたクリープ設計域の合理的な設定法について検討した。この結果、国産の材料データに基づき、6種類の高速炉用の鋼種について、応力レベル1.5Sm時のNCカーブを設定した。従来の高温構造設計基準では、一定の温度上限値を用いて、非クリープ域を保守的に制限していた。実用高速炉で使用予定の316FR鋼,12Cr-Mo鋼は特に優れた材料特性を有しており、NCカーブを用い非クリープ設計域の拡大を図る効果が大きい。本クリープ設計域の合理的な設定法はFDS暫定案に採用された。NCカーブを用いることにより通常時、比較的低温で用いられる機器の低温設計が可能となる。

For expansion of non-creep design area and simplification of design procedures, a rational identification method of creep design area by negligible creep (NC) curves was studied. NC curves of six kinds of stainless and ferrite steels for fast reactors were determined at 1.5Sm (Sm: design stress intensity). These NC curves are based on domestic material data. NC curves provide the relation between temperature and time that does not induce meaningful creep strain under the constant primary stress. As for 316FR steel, which is used for reactor vessel in Japanese fast reactor, non-creep design area is identified with comparing the highest temperature and 425C (constant upper limit for austenite stainless steal) by existing Japanese Guides. However, this temperature limit can be enhanced by NC curve concept when operating (thermal transient) time is long. NC curves under higher primary stress, and the curves under secondary stress were also studied. However, at the present stage, NC curves for stress level 1.5Sm were adopted to identify creep design area. The concept of NC curve was introduced into the interim FDS (fast reactor design standard for commercialized fast reactors in Japan) to simplify the creep design of fast reactor systems. Utilizing these curves, design becomes easier for components which are employed at comparatively lower temperature under normal condition and short holding time at high temperature.