본 논문에서는 노심용융사고 시 관통노즐이 제거된 원자로용기 하부헤드의 구조 건전성 평가를 수행하였다. 열응력, 노심용융물의 질량 그리고 내압조건의 해석결과를 고려할 때, 하부헤드의 열응력에 의한 영향이 가장 크게 나타났다. 손상 가능성은 파손기준에 따라 평가하였으며, 등가소성변형률이 임계변형률 파손기준보다 낮은 수준으로 평가되었다. 열-구조물 연성해석 결과 하부헤드의 두께 중간층에서 항복강도보다 낮은 응력이 발생한 탄성영역 구간을 확인하였다. 내압이 커지면서 탄성영역 범위가 점차 좁아지면서 탄성영역이 내벽으로 이동하는 결과를 확인하였고, 노심용융사고 시 구조적 건전성을 만족하는 것으로 평가되었다.

In this paper, structural integrity evaluation of reactor pressure vessel bottom head without penetration nozzles in core melting accident has been performed. Considering the analysis results of thermal load, weight of molten core debris and internal pressure, thermal load is the most significant factor in reactor vessel bottom head. The failure probability was evaluated according to the established failure criteria and the evaluation showed that the equivalent plastic strain results are lower than critical strain failure criteria. Thermal-structural coupled analyses show that the existence of elastic zone with a lower stress than yield strength is in the middle of bottom head thickness. As a result of analysis, the elastic zone became narrow and moved to the internal wall as the internal pressure increases, and it is evaluated that the structural integrity of reactor vessel is maintained under core melting accident.

• 이연주(한국전력기술주식회사 원자로설계개발단, KEPCO Engineering and Construction Company, Nuclear Steam Supply System Division) | Yun Joo Lee
• 김종민(한국전력기술주식회사 원자로설계개발단, KEPCO Engineering and Construction Company, Nuclear Steam Supply System Division) | Jong Min Kim Corresponding author
• 김현민(한국전력기술주식회사 원자로설계개발단, KEPCO Engineering and Construction Company, Nuclear Steam Supply System Division) | Hyun Min Kim
• 이대희(한국전력기술주식회사 원자로설계개발단, KEPCO Engineering and Construction Company, Nuclear Steam Supply System Division) | Dae Hee Lee
• 정장규(한국전력기술주식회사 원자로설계개발단, KEPCO Engineering and Construction Company, Nuclear Steam Supply System Division) | Chang Kyu Chung