Alternative Absorber Materials for Control Rods in ALFRED

The next-generation reactors require improved safety performance and longer cycle length, which initiate the research on alternative absorber materials. In this context, potential absorber materials including borides (B₄C, HfB₂, and ZrB₂), rare earth oxides (Eu₂O₃, Gd₂O₃, Sm₂O₃, and Dy₂TiO₅), metals/alloys (Hf and AIC), and metal hydride (HfH_x) were compared in a large sodium fast reactor. The design of control rods for Generation-IV fast reactors strongly depends on the core characteristics. In this paper, some alternative absorbers are assessed in a lead fast reactor ALFRED using depletion capability in the Monte-Carlo particle transport code OpenMC. Results show that the ALFRED reference control rod design with B₄C largely satisfies the shutdown and operation requirements. 60% ¹⁰B enriched HfB₂ and HfH_1.18 can replace the operation part of the reference design. In the future, the safe operating life of B₄C and HfB₂ should be assessed taking into account the irradiation-induced swelling, temperature margin, and gas release. HfH_1.18 has a limited and local influence on the core power distribution. Eu₂O₃ has little loss on the absorption ability after 5 cycle irradiation. This oxide absorber satisfies the shutdown function even with only half control rod insertion, while its critical insertion depth at beginning of the cycle should be increased to realize reactivity compensation function.