Contents lists available at ScienceDirect Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene The seismic analysis of the core structure in a pool-type material test reactor using 3-D finite difference method Afshin Hedayat * , Mohammad Javad Alborzi Reactor and Nuclear Safety School, Nuclear Science and Technology Research Institute (NSTRI), End of North Karegar Street, P.O. Box 14395-836, Tehran, Iran ARTICLE INFO Keywords: Seismic MTR TRR Research reactor Safety ABAQUS ABSTRACT The integrity of nuclear reactors under seismic conditions is one of the most important items of safety analyses. In order to keep the first barrier of radioactive materials and a safe emergency shutdown system under earth- quake, the reactor components (particularly fuel elements) and the reactor control system must withstand against seismic loads without hazardous physical damage or failure. Among several qualification approaches of seismic analyses, the Finite Element Method (FEM) is the most common approach used in practical mechanical engineering problems. In this paper, a FEM is employed for detailed analyses; in which a 3-D homogenization model is chosen and used to study the overall static and dynamic behavior of Tehran Research reactor (TRR) core under seismic (level 2) excitations via 3-D visual effects of seismic stresses and damaged objects or displacement effects. Such visualization creates a unique sense of a realistic hazard. In this way, the ABAQUS software which is one of the leading applied FEM programs in the world are used for analyses. This software can easily and robustly solve dynamic, nonlinear, finite element models of structures. Two different kinds of seismic loading spectrum are used to cover and study a wide range of motivations and responses, conservatively. New safety assessment based on a 3-D accurate modeling and loading shows that the TRR core structures should be en- hanced against severe seismic loads (particularly hard fast shocks recommended by the US NRC and IAEA) via dampers or any type of additional supports. 1. Introduction A severe earthquake has a potential to cause damage to the reactor structures and engineering safety systems particularly in radiation ha- zard risks to the public. In nuclear reactors, it is mandatory to qualify the critical structures and equipment to the design seismic loads. The qualification procedure against seismic analyses is well-known for safety by design, analyses and reviews (AEOI, 1989, 2009; ANSTO, 2004; IAEA, 1992a, b, 2005, 2006, 2008, 2012). It is generally carried out either by analysis (usually 1-D reduced form of the FEM) or by the tests on shake-table or by comparison with the past experience or si- milar structures (AEOI, 1989, 2009; IAEA, 1992a). While nowadays, much more accurate and conservative seismic analyses have been performed for new multipurpose research reactors especially those ones recommended by the US NRC guides and IAEA safety series (ANSTO, 2004; IAEA, 1992b; NSTRI and IAEA, 2014; NSTRI and IAEA, 2015). Todays, lesson learnt from the Fukushima Daiichi accident shows that a severe accident can occur and the reactor design should be withstand against such natural disasters to omit or reduce the radiation hazard risks as much as possible (NSTRI and IAEA, 2014; NSTRI and IAEA, 2015). An international effort (NSTRI and IAEA, 2015) indicates that seismic analyses and resistance via additional core supports has the most important part of the new review safety assessment for well- known multi-purpose research reactors like the SAFARI (South Africa) or BR2 (Belgium). Anyway, the importance, type, and effects of external hazards and accidents can be different in different countries and re- gions. In this study, the Tehran Research Reactor (TRR) is chosen for following analyses. Studies indicates that Tehran has two major geo- physical faults with very high potential of risk so the seismic analyses and resistant are very important to ensure safety of the TRR. Previously, it was analyzed via a simple method of 1-D FEM according to the very old seismic data of Tehran by the SAP code without additional data and supports in details (AEOI, 1989, 2009). In this research, a complete 3-D FEM are analyzed and investigated via 3-D figures of the seismic loads and physical damage; also, two different standard seismic spectrums are introduced, used, and compared. FEM have been developed and much more completed until now especially based on the new powerful hardware and software. In bib- liography, much effort has spent on the development of mathematical models to predict the overall dynamic behavior. Among them, the two https://doi.org/10.1016/j.pnucene.2018.02.016 Received 4 January 2017; Received in revised form 10 February 2018; Accepted 12 February 2018 * Corresponding author. E-mail addresses: ahedayat@aeoi.org.ir, Af.Hedayat@yahoo.com (A. Hedayat), m.alborzi@sazeh.co.ir (M.J. Alborzi). Progress in Nuclear Energy 106 (2018) 162–180 0149-1970/ © 2018 Elsevier Ltd. All rights reserved. T