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Evaluation of the Crack Tip Stress Distribution Considering Constraint Effects in the Reactor Pressure Vessel

구속효과를 고려한 원자로 압력용기 균열선단에서의 응력분포 예측

Kim, Jin-Su;Choe, Jae-Bung;Kim, Yeong-Jin
김진수;최재붕;김영진

  • Published : 2001.04.01

Abstract

In the process of integrity evaluation for nuclear power plant components, a series of fracture mechanics evaluation on surface cracks in reactor pressure vessel(RPV) must be conducted. These fracture mechanics evaluation are based on stress intensity factor, K. However, under pressurized thermal shock(PTS) conditions, the combination of thermal and mechanical stress by steep temperature gradient and internal pressure causes considerably high tensile stress at the inside of RPV wall. Besides, the internal pressure during the normal operation produces high tensile stress at the RPV wall. As a result, cracks on inner surface of RPVs may experience elastic-plastic behavior which can be explained with J-integral. In such a case, however, J-integral may possibly lose its validity due to constraint effect. In this paper, in order to verify the suitability of J-integral, tow dimensional finite element analyses were applied for various surface cracks. A total of 18 crack geometries were analyzed, and $\Omega$ stresses were obtained by comparing resulting HRR stress distribution with corresponding actual stress distributions. In conclusion, HRR stress fields were found to overestimate the actual crack-tip stress field due to constraint effect.

Keywords

Reactor Pressure;Pressurized Thermal Shock;Constraint Effect;$\Omega$ Stress;HRR Stress

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