Innovative nuclear fuel containing lumped Gd₂O₃ burnable absorber

Profs. Yonghee Kim and Ho Jin Ryu from the Department of Nuclear and Quantum Engineering (NQe) have developed an innovative burnable absorber fuel that is composed of lumped Gd₂O₃ inserted inside the UO₂ oxide fuel pellet. The unique neutronic performance of the newly developed burnable absorber fuel design presents a longer fuel cycle length and a less soluble boron loading in the power reactor coolant.

Article  |  Fall 2019

The commercial neutron absorber fuel which is used in current nuclear power reactors is a mixed oxide system where Gd₂O₃ with a high neutron absorption cross-section is homogenously mixed with UO₂. However, the use of Gd₂O₃ in the form of a solid solution mixture results in the fast burn-out rate of Gd₂O₃ and therefore limits its effectiveness in controlling the reactor reactivity during operation. Therefore, an innovative burnable absorber fuel design that is composed of oxide fuel pellet containing lumped Gd₂O₃ spherical in order to overcome the limitation of the mixed oxide fuel has been developed.

In order to control the reactivity of neutron in the nuclear power reactors efficiently, the use of neutron absorber fuel incorporating burnable neutron absorber material is necessary. However, the solid solution of Gd₂O₃ in the UO₂ matrix results in degradation of the densification, thermal, and mechanical properties of UO₂ fuel. In this study, it has been demonstrated that the fabrication of oxide pellet containing lumped Gd₂O₃ particles is achievable (Figure 1).

 

The effects of the shape (spherical particle, cylindrical pellet) and the initial density of lumped Gd₂O₃ on the formation of interfacial cracks during the fabrication process were investigated. It is found that by controlling the shape and the initial density of the lumped Gd₂O₃, the interfacial cracks which form during the fabrication process could be eliminated (Figure 2). Prof. Ho Jin Ryu’s research group found that the interfacial cracks are mainly formed due to the sintering stresses developed due to the shrinkage rate mismatch between the lumped Gd₂O₃ and the annular 8YSZ pellet. The result of this work entitled “Fabrication of oxide pellets containing lumped Gd₂O₃ using Y₂O₃‐stabilized ZrO₂ for burnable absorber fuel applications” (doi.org/10.1002/er.3995) was published in the February 2018 issue of International Journal of Energy Research.

 

Prof. Yonghee Kim’s research group has investigated the neutronic performance of the new burnable absorber fuel design and optimized the size and the distribution of the lumped Gd₂O₃ sphere in the nuclear fuel assembly to achieve a flat power distribution and long fuel cycle (Figure 3). This research entitled “An advanced core design for a soluble-boron-free small modular reactor ATOM with centrally-shielded burnable absorber” (doi.org/10.1016/j.net.2018.10.016) was published in the April 2019 issue of Nuclear and Engineering Technology.

 

A domestic patent for this invention has been registered (10-1925189) in November 2018 and a US Patent Application (20180151261) has been filed in 2017 and published in 2018.