報告書番号

L10009

タイトル（和文）

主蒸気配管分岐部における音響共鳴現象の評価（その１）－蒸気の湿り度が音響共鳴現象に及ぼす影響－

タイトル（英文）

Evaluation of Acoustic Resonance at Branch Section in Main Steam Line (Part 1) - Effects of Steam Wetness on Acoustic Resonance -

概要 （図表や脚注は「報告書全文」に掲載しております）

軽水炉の出力向上は，原子力発電所の新設に比べ安価に発電量の増加が可能であるため，欧米では多くのプラントで実施されており，国内でも実施予定である．しかし，出力向上は流量の増加を伴うため，FIVや配管減肉など流動に起因する事象が顕在化する可能性がある．
米国のBWRでは17.8％出力向上運転時に蒸気乾燥器の損傷が見られており，主蒸気系配管の逃がし安全弁（SRV）管台での音響共鳴現象の発生が原因であると考えられている．音響共鳴発生可能性を評価する上では，蒸気流中における事象の特徴や湿り度の影響の把握が重要であるが，蒸気体系での研究例はこれまでに殆ど見られず基本的な特性も明らかとなっていない．
そこで本研究では，蒸気流動実験の実施により，乾き・湿り蒸気流での音響的な基本特性を明らかにすることを目的とした．その結果，共鳴時の変動圧力振幅が湿り蒸気では乾き蒸気に比べて1/10程度に低減することがわかった．

概要 （英文）

The power uprating of the nuclear power plant (NPP) is conducted in United States, EU countries and so on, and also is planned in Japan. However, the degradation phenomena such as flow-induced vibration and wall thinning may increase or expose in the power uprate condition.
In U.S. NPP, the dryer had been damaged by high cycle fatigue due to acoustic-induced vibration under a 17% extended power uprating (EPU) condition. This is caused by acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSL). Increased velocity by uprating excites the pressure fluctuations and makes large amplitude resonance.
To evaluate the acoustic resonance at the stub pipes of SRVs in actual BWR, it is necessary to clarify the acoustic characteristics in steam flow. Although there are several previous studies about acoustic resonance, most of them are not steam flow but air flow.
Therefore in this study, to investigate the acoustic characteristics in steam flow, we conducted steam flow experiments in each dry and wet steam conditions, and also nearly saturated condition. We measured pressure fluctuation at the top of the single stub pipe and in main steam piping. As a result, acoustic resonance in dry steam flow could be evaluated as same as that in air flow. It is clarified that resonance amplitude of fluctuating pressure at the top of the stub pipe in wet steam was reduced to one-tenth compared with that in dry.

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