Analysis of nuclear reactions and material damage on neutron absorbers using the HANARO research reactor.

• Analyzed of neutron characteristics and material damage on neutron absorber by the irradiation test using HANARO research reactor. • Clarified the model specification of the HANARO reactor core and irradiation system. • Described the characteristics of boron carbide neutron absorber and its nuclear characteristics. • Explained the correlation between the nuclear absorption characteristics and material damage of neutron absorption materials. This study aims to verify the nuclear characteristics and material integrity of neutron absorbers through neutron irradiation using the HANARO research reactor. The nuclear reactions and material damage of boron carbide in the neutron irradiation environment of the external region of the reactor core were evaluated based on the Monte Carlo method. The irradiation conditions of the reactor core were assumed based on equilibrium core operation with a reactor power of 30 MW. In order to evaluate material damage over a one-year period, it was assumed that the concentrated boron carbide undergoes a 2 % boron depletion every 100 days. Reactivity test was assessed to verify the appropriateness of the assumptions established for the irradiation test. As a result, the reactivity level showed approximately 1.06 mk, which sufficiently proves its lower level compared to the criteria of 12.5 mk. In order to analyze the physical characteristics of neutron absorbers influencing material damage, the group fluxes and energy-dependent neutron spectra of the target material were evaluated. The neutron flux in Group I appears low, while the epithermal group flux is observed relatively high. The specimen material closer to the core generally showed higher flux, indicating a maximum difference of about 3 × 1013 #/cm2·sec compared to the minimum one. The 3rd specimen showed the highest in flux, while 7th specimen is the lowest. The shape of all the dpa values showed similar trends to the pattern of neutron absorption reaction rates. The neutron absorption was significant up to 100 days, and after this point, they showed gradual reductions in the damage increase rate. The total dpa values linearly increased along with the irradiation time, and showed about 12–13 dpa over one year of EFPD. The results of this study can be utilized as fundamental data for confirming changes in material damage due to high neutron irradiation on neutron absorbers in connection to nuclear characteristics. [ABSTRACT FROM AUTHOR]