Preliminary neutronic analysis on core performance improvement using honeycomb-structured fuel assembly and U-Pu-Be metal fuel

Kuwagaki, Kazuki  ; Chikazawa, Yoshitaka  ; Yan, X. 

The technology of additive manufacturing by 3D printing, which is being developed in JAEA, permits application of more complex geometry and material that are unavailable to fabrication of nuclear fuels by traditional methods. As a first step, preliminary neutronic analyses are performed to examine the potential of core performance improvement to sodium-cooled fast reactor core through the use of a honeycomb-structured fuel and U-Pu-Be fuel, both of which may be fabricated by 3D printing. The honeycomb-structured fuel has the opposite configuration to the conventional fuel assembly, i.e., the fuel pin region becomes the coolant channel, and the coolant region in the conventional assembly becomes the fuel, as the name "honeycomb" suggests. By using such a structure, the fuel volume fraction can be increased compared to the conventional fuel pin type assembly, which will lead improvement of the breeding ratio. A comparative neutronic analysis of the honeycomb structure and the conventional pin type was performed. The results showed the possibility that the breeding ratio could be improved by the use of honeycomb-structured fuel. In U-Pu-Be fuel, the presence of Be in the fuel softens the neutron spectrum in the core, which is expected to improve the safety by increasing negative feedback effect of the Doppler reactivity and reducing the sodium void reactivity. A comparative study of U-Pu-Be and MOX fuel was performed. The results showed that the U-Pu-Be fuel can enhance the negative feedback effect of Doppler reactivity and reduce the sodium void reactivity compared to the other conventional fuel.