高速炉蒸気発生器伝熱管損傷リーク孔の自己拡大試験; 微小リーク・ナトリウム-水反応試験研究(第2報)

Study of micro-defect self-wastage phenomena on LMFBR prototype steam generators' tube; Studies of micro-leak sodium-water reactions (2)

黒羽 光男; 佐々木 和一*; 川辺 浩康*; 山田 隆雄*; 佐藤 稔*

Kuroha, Mitsuo; not registered; not registered; not registered; not registered

高速増殖原型炉「もんじゅ」蒸気発生器伝熱管の候補材料である21/4Cr―1Mo鋼およびSUS321を対象に,微小リーク時のリーク孔自己拡大(セルフウェステージ)現象を調査するための試験が,動燃大洗工学センターのSWAT―2および4装置を使用して実施された。計6体のヘアー・クラック状の貫通欠陥をもつノズル(製造時の孔径は円孔換算で1997mの範囲)が試験に使用された。試験はナトリウム温度が21/4Cr―1Mo鋼ノズルの場合で470,SuS321ノズルで505,注水圧力はどの試験ケースも約130kg/cm2g一定の条件であった。主な試験結果は以下のとおりである。21/4Cr―1Mo鋼の微小リーク(拡大前の平均リーク率は210-5g/sec)でも閉塞せずにリークが継続し,逐にはリーク孔が拡大完了してリーク率が急激に拡大することが3ケース中1ケースに確認された。他の2ケースはノズル孔が閉塞し,拡大しなかった。セルフウェステージ率は一般的に材料,リーク率およびナトリウム温度に影響されるが,本試験によるとリーク孔拡大後のリーク率はこれらに強く依存せずに,最終的な拡大リーク率は110g/secの範囲に達する傾向にあった。SUS321ノズルにおいてナトリウム-水反応部近傍の金属組織は結晶の粗大化が認められたが,組成上の変化は全くなかった。損耗部表面では,ナトリウム側と蒸気側で激しく凹凸していたが,その中間部では比校的平滑であった。

A series of micro steam leak tests has been carried out to accumlate the micro defect self-wastage data on LMFBR prototype MONJU steam generators' tubes, whose materials are planned to be 2.25Cr-1Mo and 321 stainless steels. The SWAT-2 test loop was used for the first stage of tests, and the SWAT-4 test rigs manufactured exclusively for the tests have been used since the following tests at the O-arai engineering center in PNC. The six test pieces, each of which had a micro crack nozzle through the thickness, were tested under the various conditions; the sodium temperatures were 470C and 505C, the steam pressure was about 130 kg/cmg throughout the sixt tests, and the average steam leak rates were in the range of 210 to 410 g/sec before the self-enlargements. The Main results obtained from the six tests are as followed; (1)It was obserbed in the case of 2.25Cr-1Mo steel nozzle that though the average leak rate of about 2 10 g/sec was very small, the leakage continued without any self-plugs until the self-wastage was completed through the thickness and finally increased the leak rate, which can cause wastage damage on adjacent tubes. (2)Self-wastage rates were apparently dependent on materials, steam leak rates and sodium temperatures. However, the increased leak rates were not strongly affected by those test parameters, and whose maxium values were apt to be in the range from to 10 g/sec in spite of the different test parameters. (3)The metallurgical structure of the stainless steel nozzles enlarged in size at the self-wasted sections due to the sodium-steam reactions, however, the composition did not changed at all. The surfaces of the self-wasted sections were rugged near the sodium and steam sides, but comparatively even midway between the two sides.