Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes Ultimate pressure capacity of nuclear reactor containment buildings under unaged and aged conditions Sara Alhanaee a , Yongsun Yi b, ⁎ , Andreas Schiffer c a Federal Authority for Nuclear Regulation, Abu Dhabi, United Arab Emirates b Nuclear Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates c Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates ARTICLE INFO Keywords: Reactor containment building Ultimate pressure capacity Degradation Rebar corrosion ABSTRACT Using ABAQUS, a non-linear finite element analysis (FEA) was performed to evaluate and compare the effects of degradation mechanisms by aging on the ultimate pressure capacity (UPC) of APR1400 reactor containment building (RCB). As the primary degradation mechanisms, prestress loss, concrete aging, rebar corrosion, and liner corrosion were simulated in the modelling and calculations. The results for unaged reactor containment buildings showed that the failure sequence by the internal pressure build-up consisted of 4 stages and re- inforcement yielding strain of reinforced concrete would be the most important factor governing the UPC of RCBs. Among the four degradation mechanisms, corrosion occurring on the outer and inner rebar layers was identified as the main degradation mechanism affecting most significantly the ultimate pressure capacity of the APR1400 reactor containment building. 1. Introduction In the design of reactor containment buildings (RCBs) in nuclear power plants (NPPs), external events such as earthquake and internal events such as large break loss of coolant accidents (LBLOCA) are considered (IAEA, 1998). In such accidental cases, RCBs in NPPs play a role as the last barrier to the release of radioactive materials to the environment (Lee, 2011; Mishra et al., 2016; Sharma et al., 2017). The consequences of some major nuclear accidents we experienced have shown the importance of the structural integrity of RCBs. Recently, severe accidents occurred in the Fukushima Daiichi power plants by the 2011 Tohoku earthquake and resulting tsunami (Gauntt et al., 2012). During the accidents, the RCBs of Units 1 and 3 suffered from com- bustible gas explosion and destruction of portions of the buildings, re- sulting in the release of large amounts of radioactive materials. How- ever, in the Three Mile Island Unit 2 (TMI-2) reactor, its containment building remained intact and held almost all of the radioactive material released during the accident (U.S. Nuclear Regulatory Commission, 2013). The structural integrity of an RCB under internal pressurization from the design-basis accident and beyond design-basis accidents can be quantified by the ultimate pressure capacity (UPC) (Basha et al., 2003; Braverman et al., 2010; Chakraborty et al., 2017; Tavakkoli et al., 2017). On the other hand, the UPC of RCBs are significantly affected by aging (U.S. Nuclear Regulatory Commission, 2000; Sandia National Laboratories, 2000). Reviewing the documented performance of the 70 concrete containments in the USA, Shah and Hookham (1998) identi- fied primary degradation mechanisms, which can be categorized as: i) aggressive chemical attack, ii) alkali–aggregate reactions, iii) leaching, iv) corrosion of reinforcing and pre-stressing steels, and v) stress re- laxation of pre-stressing steel. Many studies have been performed on the effect of some individual degradation mechanisms on the structural integrity of RCBs. The effect of a loss of pre-stress on the structural behavior and integrity of RCBs has been extensively studied (Lang and Wienand, 2013; Hu and Lin, 2016; Huang et al., 2017; Balomenos and Pandey, 2017). Also, the effect of liner corro- sion on the failure of RCBs has been investigated (Sandia National Laboratories, 2000; Petti et al., 2008). However, the relative effects of dif- ferent degradation mechanisms on the UPC of RCBs have not been fully addressed in literature. In this study, the effects of the primary degradation mechanisms on the UPC of the APR1400 RCBs were evaluated through calculating their UPC values under unaged and aged conditions. The UPC values were calculated by a nonlinear analysis using a three dimensional (3D) finite element model of one-quarter segment of the RCB (Barbat et al., 1998; U.S. Nuclear Regulatory Commission, 2010). By simulating the aged conditions for each degradation mechanism in the calculation, its effect on the UPC was evaluated and compared. Finally, the failure sequence of RCBs by internal pressure build-up as well as the most significant degradation mechanism affecting the UPC are discussed. https://doi.org/10.1016/j.nucengdes.2018.05.017 Received 27 March 2018; Received in revised form 13 May 2018; Accepted 15 May 2018 ⁎ Corresponding author at: PO Box 112021, Abu Dhabi, United Arab Emirates. E-mail address: yongsun.yi@ku.ac.ae (Y. Yi). Nuclear Engineering and Design 335 (2018) 128–139 Available online 25 May 2018 0029-5493/ © 2018 Elsevier B.V. All rights reserved. T