Author J.H. Lee 1), K.B. Yoon2), Y.J. Kim3)and U.B. Baek4) 1) Engineering Research Department, Korea Institute of Nuclear Safety, P.O. Box 114, Yoosung, Taejon 305600, Korea2) Department of Mechanical Engineering, Chung Ang University, 221 Huksuk, Dongjak, Seoul 156756, Korea3) Department of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun, Jangan, Suwon 440746, Korea4) Failure Prevention Research Center, Korea Research Institute of Standards and Science, P.O. Box 102, Yoosung, Taejon 305600, KoreaManuscript received 18 October 1998