Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
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Evaluation for Weld Residual Stress and Operating Stress around Weld Region of the CRDM Nozzle in Reactor Vessel Upper Head

원자로 압력용기 상부헤드 CRDM 노즐 용접부의 용접잔류응력 및 운전응력 평가

  • Lee, Kyoung-Soo (Central Research Institute, Korea Hydro and Nuclear Power Co. Ltd.) ;
  • Lee, Sung-Ho (Central Research Institute, Korea Hydro and Nuclear Power Co. Ltd.) ;
  • Bae, Hong-Yeol (Dept. of Mechanical Engineering, Korea Univ.)
  • Received : 2012.02.27
  • Accepted : 2012.07.19
  • Published : 2012.10.01
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Abstract

Primary water stress corrosion cracking (PWSCC) has been observed around the weld region of control rod drive mechanism (CRDM) nozzles in nuclear power plants overseas. The weld has a J-shaped groove and it connects the CRDM nozzle with the reactor vessel upper head (RVUH). It is a dissimilar metal weld (DMW), because the CRDM is made of alloy 600 and the RVUH is made of carbon steel. In this study, finite element analysis (FEA) was performed to estimate the stress condition around the weld region. Generally, it is known that a high tensile region is more susceptible to PWSCC. FEA was performed as for the condition of welding, hydrostatic test and normal operation successively to observe how the residual stress changes due to plant condition. The FEA results show that a high tensile stress region is formed around the weld starting point on the inner surface and around the weld stop point on the outer surface.

원자력발전소의 원자로압력용기 상부헤드에는 출력제어 및 정지용 제어봉이 통과하는 노즐이 있으며 이 노즐은 상부헤드 노즐과 J 형태의 홈으로서 용접 되어 있다. 최근 외국의 원자력발전소에서 이 용접영역 주변의 노즐 및 용접부에서 일차수응력부식 균열이 발생한 사례가 보고되고 있다. 본 논문에서는 이 용접부의 용접잔류응력과 운전 중에서의 응력상태를 유한요소해석을 이용하여 평가함으로써 고응력 위치를 확인하고 응력관점에서 균열발생 가능성이 높은 지역을 예측하고자 하였다. 해석결과 용접에 의해서 형성된 잔류응력이 수압시험과 운전조건에 의해 다소 변동되기는 하나 응력분포형태는 큰 변화가 없었다. 전반적으로 노즐내면에서는 용접이 시작되는 지점 주변에서 최대 인장응력이 형성되고 노즐외면에서는 용접이 끝나는 지점 주변에서 최대인장응력이 형성되는 것을 확인하였다.

Keywords

References

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