‎E‎hsan ‎Boustani - Nuclear Science and Technology Research Institute (NSTRI)‎, ‎Reactor and nuclear safety school‎, ‎Tehran‎, ‎Iran
S‎amad ‎Khakshournia - Nuclear Science and Technology Research Institute (NSTRI)‎, ‎Accelerator and physics school‎, ‎Tehran ۱۴۳۹۹-۵۱۱۱۳‎, ‎Iran‎

‎A second shutdown system (SSS) is designed for the Tehran Research Reactor (TRR) completely independent and diverse from the existing First Shutdown System (FSS)‎. ‎Given limitations‎, ‎specifications‎, ‎and requirements of the reactor‎, ‎the design of SSS is based on the injection of liquid neutron absorber‎. ‎The plan has the ability to satisfy the major criterion of required negative reactivity worth‎, ‎to transfer the reactor to subcritical state in needed time‎, ‎with necessary shutdown margin and for the required duration‎. ‎Design calculations are performed using the stochastic code MCNPX2.6.0‎, ‎deterministic code PARET and Pipe Flow Expert software‎. ‎The ORIGEN2 code and HotSpot health physics code are also used for simulation of environmental pollution release‎. ‎The SSS chambers cause a decrease of about 5% and 15% in total and thermal neutron flux‎, ‎respectively‎. ‎To demonstrate the SSS role in enhancing reactor safety‎, ‎the probable accident of core meltdown is investigated‎. ‎As a consequence of this accident‎, ‎the radioactive pollution in and out of reactor containment is released‎. ‎Without existing the SSS and in case of failure of FSS‎, ‎the residents within 58000 m2 of the reactor perimeter would receive about 1 mSv which is more than the annual limit of absorbed dose for the community‎.

‎Tehran research reactor, ‎Safety, ‎Second shutdown system, ‎MCNPX code, ‎ORIGEN2 code, ‎PARET code, ‎HotSpot code‎