報告書番号

Q04025

タイトル（和文）

試験炉により加速高照射された圧力容器鋼のナノ組織観察 -三次元アトムプローブ及び陽電子消滅測定-

タイトル（英文）

Nano-strucural changes in the RPV steels irradiated in MTR to high doses: 3D atom probe and positron annihilation study

概要 （図表や脚注は「報告書全文」に掲載しております）

軽水炉の運転期間の長期化に伴い精度の高い照射脆化予測を行うには高照射された圧力容器（RPV）鋼の脆化を詳細に把握することが重要である。本研究では、軽水炉温度で約60年運転時の中性子照射量相当まで試験炉照射された低Cu母材と高Cu溶接金属を対象に、クラスタ形成に及ぼす高照射の影響を三次元アトムプローブ（3DAP）等のナノ組織観察によって調べた。その結果、高Cu材では銅濃縮クラスタが高密度に観察され、Fe、Cu、Mn、Niの他Siが多く含まれている。また低Cu材でも2nm以下の固溶原子クラスタが観察されるが、Cuを殆ど含んでおらずSi濃度が高いことがわかった。これは高照射特有のクラスタと考えられる。硬さ試験及び陽電子消滅測定の等時焼鈍実験により、機械的性質に影響するのは140psec程度の陽電子寿命をもつ欠陥（転位ループなど）であることがわかった。

概要 （英文）

Reactor pressure vessel (RPV) steels of life-extended light water reactors are to be exposed to higher neutron fluence. The understanding of radiation embrittlement of RPV steels is very important in order to improve prediction of the embrittlement. The radiation embrittlement is mainly cased by copper-enriched cluster (CEC) and matrix damage (MD) due to irradiation. The state-of-the-art technique such as three dimensional atom probe (3DAP) and positron annihilation (PA) has enabled to observe these microstructural features. The effect of highly dose irradiation on the formation of clusters in a low copper base metal and a high copper weld metal is investigated by means of the 3DAP and PA observations in this paper. The materials were irradiated to a neutron fluence of 10^20n/cm^2 at 290 deg. C in a test reactor. The 3DAP observation shows that high dense CRCs in size of about 2nm are formed in the high Cu weld metal. The CRCs consist of Si in addition to Fe, Cu, Mn, and Ni. Solute atom clusters below 2nm are also observed in low Cu base metal, but the clusters include a large amount of Si and free from Cu. These clusters may be peculiar to highly irradiated materials because of no literature reporting such the clusters in the similar steels irradiated at the lower fluence. The data of the positron annihilation coincidence Doppler broadening measurement for both materials also shows the formation of clusters containing Cu, Ni, Mn, and Si. This means the clusters observed by 3DAP are uniformly distributed in the materials. Hardness tests and PA measurement combined with isochronal annealing show that defects, e.g. dislocation loop etc., having a positron lifetime of about 140psec influence on mechanical properties of the steels.

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