(An) innovative way of Co-60 production in CANDU6 reactors

Abstract

In addition to the electricity generation, CANDU6 reactors are often used to produce cobalt-60, which is an important radioactive nuclide used in many industrial and medical areas. In this study, an innovative way of producing Co-60 in CANDU6 reactors is introduced and evaluated in view of the neutronic performances. Unlike the conventional Co-60 production scheme using the adjuster rods in CANDU reactors, in this study the central fuel element is replaced by a Co-59 target in the standard fuel bundle and Co-60 is obtained after the fuel bundle is discharged. To improve the generic safety of the Co-loaded CANDU6 core, the CANFLEX fuel is also considered for comparison in the current study. To investigate such a new and innovative Co-60 production scheme in CANDU6 reactors, various lattice depletions are first performed by using the Monte Carlo code named Serpent to determine the possible amount of Co-59 loading and to derive an optimal cobalt target configuration in the center pin of a fuel bundle. Through the lattice depletion analysis, the achievable fuel burnup is evaluated and the possible Co-60 production capacity has also been evaluated with several neutronic assumptions. For the lattice analysis, the fuel discharge burnup is calculated based on the non-linear reactivity theory. Major safety parameters including fuel temperature coefficient, void reactivity, and coolant temperature coefficient are also evaluated and compared with those of the standard CANDU6 lattice loaded with natural uranium. The pin power distribution is also evaluated for the Co-loaded fuel bundles in this study. All the neutronics analysis are performed with the continuous-energy Monte Carlo code Serpent in this work. Additionally, 3-D whole-core analysis are also performed with a time-average core model for a Co-loaded CANDU6 reactor by using an advanced nodal code named COREDAX-2 in this work. To determine a time-average equilibrium core with the COREDAX-2 code, various lattice calculations are done using the Serpent code and the resulting two-group homogenized cross sections are used in the COREDAX-2 code. To compensate for the reactivity reduction due to the Co-59 loading in the core, some of the adjuster rods are removed from the core and the conventional 8-bundle shifting daily fuel management is adopted in this work. The coupled Serpent-COREDAX-2 calculation determines an equilibrium time-average model for the CANDU6 core. In the whole-core analysis, the bundle power distribution is analyzed and whole-core Co-60 production capability is evaluated and compared with that of the lattice analysis. Besides, the power coefficient of reactivity (PCR) is also evaluated for the 3-D time-average equilibrium core.