Analysis of the source term and prediction of the radioactivity releases for a hypothetical accident at ETRR-2

Evaluating radioactive release and its impact is very important for the safety of research reactors, especially those located near populated areas. In this work, a deterministic and conservative analysis is carried out to study the source term and the possible radiological consequences of a hypothetical beyond design basis accident at the ETRR-2 Research Reactor. The accident scenario assumes a large break loss of coolant due to rupture of the tangential irradiation tube, together with failure of cooling systems, which may lead to severe core damage. The radionuclide inventory is calculated using the ORIGEN-S code in the SCALE package, assuming a maximum irradiation time of 220 full power days. The total uranium mass and irradiation history are based on equilibrium core conditions obtained from WIMS/CITATION fuel management calculations. Since no dedicated cross-section libraries are available for material testing reactors, different ORIGEN libraries are evaluated and compared with MCNP depletion results for the same irradiation conditions. The comparison shows that libraries representing softer neutron spectra provide better agreement, supporting the selection of an appropriate library and improving the reliability of the inventory estimation. A conservative assumption of 80% core damage is applied. The source term is developed based on the updated U.S. Nuclear Regulatory Commission Regulatory Guide 1.183, Revision 1 (2023), which introduces revised radionuclide grouping and release fractions compared to the older 2000 version used in most previous studies. Atmospheric dispersion is analyzed using the HOTSPOT code with site-specific meteorological data covering more than ten years. The results show that noble gases and iodine isotopes are the main contributors to the release. The maximum dose reaches about 1.9 Sv at around 400 m, and it is strongly affected by atmospheric stability conditions, highlighting the sensitivity of the results to atmospheric parameters.