材料の熱膨張差を利用した受動式クリープ疲労試験技術の確立のための研究

A Study for establishment of passive creep-fatigue test techniques using the difference of thermal expansion coefficients of materials

若井 隆純 ; 安藤 勝訓 ; 岡島 智史 ; 豊田 晃大 ; 石上 勝夫*; 小沼 輝充*; 高橋 亮耶*; 浅山 泰 

Wakai, Takashi; Ando, Masanori; Okajima, Satoshi; Toyota, Kodai; Ishigami, Katsuo*; Onuma, Terumitsu*; Takahashi, Ryoya*; Asayama, Tai

ナトリウム冷却高速実証炉への適用を目的として、新たな材料監視技術の開発に取り組んだ。この技術は、試験体を原子炉内に挿入し、試験片を観察・評価して劣化の程度や残存寿命等の情報を得ることにより、材料劣化プロセス、すなわち疲労およびクリープ疲労損傷の把握を可能とする。この技術を確立するため、受動式クリープ疲労試験体を設計・製作し、電気炉を用いて繰返し温度変化を与える実証試験を実施した。実証試験後の観察の結果、座屈は生じておらず、また、破面観察の結果、疲労またはクリープ疲労によって破損が引き起こされたと推測され、この技術のナトリウム冷却高速実証炉への適用見通しを得ることができた。

This paper describes current efforts within the Japan Atomic Energy Agency to develop a new materials surveillance technology for sodium-cooled fast reactors that aims at raising the confidence levels in operating reactors' structural integrity to the ones which could otherwise be achieved only by a vast amount of long-term material test data that needs decades to accumulate. The technology would allow for monitoring on-going materials degradation processes in an actual reactor, namely fatigue and creep-fatigue, by inserting a newly developed specimen for this purpose into the reactor and establishing procedures to observe and evaluate the specimen to get desired information such as the extent of degradation and residual life. To establish the test procedure, a passive creep-fatigue test model was developed in the framework of the "Civil Nuclear Energy Research and Development Working Group (CNWG)", a collaboration agreement between the US and Japan, and a demonstration test was performed under cyclic thermal loads using an electric furnace. Temperature conditions had been determined based on finite element analyses. As a result, the test specimen failed by several hundred thermal cycles. Macroscopic inspection of the specimen after the test showed the test had been performed successfully without buckling. Fracture surface observations suggested that the failure caused probably by fatigue or creep-fatigue.