Neutronic safety assessment of an in-core irradiation rig for NTD applications in the Tehran research reactor

In-core irradiation devices should be introduced in research reactors through a neutronic safety margins assessment. The present study is directed at the evaluation of the effects that a proposed Neutron Transmutation Doping irradiation rig would impose on the Tehran Research Reactor. Changes in core reactivity and thermal neutron flux distribution and axial flux uniformity due to the addition of graphite reflector elements and thermal-absorbing flattening filters were quantified using MCNPX 2.6 simulations. The graphite structure increased excess reactivity by +579 pcm, while the stainless steel, Inconel, and nickel filters effectively countered such an increase and achieved lower than ±1.7% axial flux uniformities. There was no significant distortion introduced in the core spatial flux shape, and all neutronic performance measures remained within IAEA-proposed limit recommendations. These results suggest that the proposed irradiation system could be implemented in TRR without significantly compromising reactor safety, thereby forming a validated basis for future experimental implementation of silicon NTD at TRR. • A full neutronic safety assessment of an in-core NTD rig for TRR is performed. • Graphite insertion increases reactivity by +579 pcm and reshapes local spectra. • Stainless-steel filters provide optimal axial flux uniformity below ±1.7%. • Calculated φ th /φ fast ratios exceed 10, and flux symmetry satisfy all IAEA NTD criteria. • The optimized design enables safe in-core NTD implementation at TRR.