Ehsan Boustani - Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran.
Samad Khakshournia - Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran.

Many research reactors are used all over the world. There is more probability of accident in nuclear research reactors due to their broad applications in a wide spectrum of sciences and industries.Material Test Reactors (MTR) type are wide specie of nuclear research reactors in which moderator islight water and their fuels are plate type. Considering to safety criteria in the entire nuclear research reactor lifetime such as siting, design, commission, upgrade, quality assurance, regulation, management of safety and operation to satisfy the defense in depth criteria and then safety insurance is necessary.Engineered safety features (ESFs) are one of items considered for enhancing reactor safety in generaland especially Second Shutdown System (SSS) is one ESF which is able to make reactor subcritical when it is necessary. In this paper, the Tehran Research Reactor (TRR) is selected as a MTR case study andone SSS is studied and shown that it has a little defect on different capabilities and characteristics of thisreactor such as neutronics characteristics, safety criteria and performance applications instead ofequipping it with another shutdown system. This study is done using probabilistic approach using MCNPX 2.6.0 code

nuclear Safety, safety criteria, Engineered safety feature, Material Test Reactor, Second Shutdown System