Reactivity and flux characterization of the Jordan subcritical assembly

Nuclear subcritical assemblies are widely used for research, education, and training due to their inherently safe characteristics and operation at subcritical state. Following the construction of Jordan Subcritical Assembly (JSA) at the Jordan University of Science and Technology campus, a detailed computational neutronic analysis of the assembly was performed to investigate the criticality as well as the neutron spectrum within the facility. A three dimensional model of the JSA, as built, was developed using various computational tools including MCNP5, KENO-V.a (SCALE), and Serpent. The range of the keff of the JSA using different codes and libraries is 0.96151± 0.00009 - 0.96571± 0.00007 with a maximum difference of 420 pcm. The reference keff value was obtained at the optimal lattice pitch of 19.1 mm, moderator level of 132 cm, and reflector thickness of 40 cm. The effect of the change in the moderator temperature and fuel temperature on the reactivity of the JSA was investigated and found to be negative, which means that the facility is inherently safe. The value of the total effective delayed neutron fraction (βeff) for the facility is 6.645E-03. The radial and axial flux characterization in the JSA were performed in this study. In addition, the neutron flux was simulated in the seven experimental channels in JSA which can be used for validation purposes. The neutron spectrum inside JSA was calculated at different axial locations using 252 energy groups and the results showed that the fast flux dominates the spectrum at regions close to the external neutron source and diminishes further away from the source.