Reactivity control optimization of boron-free small modular pressurized water reactor with helical-cruciform metallic fuel

Abstract

Small modular pressurized water reactors have the advantages of small size, modularity, inherent and passive safety, and flexible power generation for a wider range of users and applications. Helical-cruciform metallic fuel has the potential to be applied to small modular pressurized water reactors capable of its axial self-spacing plane, high power density, increasing heat transfer area, and extending the cycle length. A novel boron-free small modular pressurized water reactor NETH-HCF175M design using helical-cruciform metallic fuel is proposed in this paper. The reactivity of the core is completely controlled by burnable absorbers and control rods. Two different geometric structures of separate pins and integral pins are researched. Results indicate that Gd2O3 is a suitable neutron absorbing candidate, while Er shows the best reactivity control effect in the integral pin structure. The separate pin structure with Gd2O3 is selected as the burnable absorber design and the core depletion result shows that the core can achieve a cycle length of about 1360 effective full power days. Control rods are divided into 60 compensating rods and 60 shutdown rods for excess reactivity controlling and shutting the core. The genetic algorithm is applied to the optimization work of layout and concentration design for burnable absorbers and layout of compensating rods. Based on the optimized burnable absorbers and compensating rod designs, excess reactivity can be controlled and the core can achieve criticality at beginning of cycle. The core can be transitioned from hot full power to cold zero power with shutdown rods at BOC, which obtains a shutdown margin more than 3000 pcm. Finally, the physical characteristics of core are analyzed, including depletion simulation, pin power distribution, and reactivity equilibrium. This paper provides an overview and information practical for the reactivity control design of novel SMPWR with high-enrichment and geometric complex helical-cruciform metallic fuel.