New burnable absorber for long-cycle low boron operation of PWRs

Fabrication of oxide pellets containing lumped Gd2O3using Y2O3-stabilized ZrO2for burnable absorber fuel applications

“…2 The use of control rods to compensate for this excess reactivity produces a nonuniform axial power distribution and incomplete burning of the fuel. [4][5][6] The main requirements for BA materials are (1) a high neutron absorption cross section, (2) a burn-out rate matching the fuel (U-235) depletion rate, and (3) the absence of fission product poisons. 3 Conversely, one possible way to overcome these problems is maximizing the use of BAs.…”

“…Because of He gas productions, high sintering temperatures, a relatively low neutron absorption cross section, and a lower burn-out rate compared to that of Gd 2 O 3 , boron compounds are usually applied either as thin coatings on fuel pellets (as used in the integral fuel burnable absorber, in which a thin ZrB 2 coating is applied onto the UO 2 fuel pellet) or in a separate fuel rod (as used in the wet annular burnable absorber, where thin-walled Al 2 O 3 -B 4 C annular pellets are enclosed within 2 concentric and sealed Zircaloy tubes in a separate fuel rod). 3,5,12 In addition, Gd has a higher residual reactivity than B due to the presence of high neutron absorbing radioisotopes in its decay chain. 10 The UO 2 -Gd 2 O 3 mixed oxide fuel is widely used as a BA for pressurized water-cooled reactors, because it offers a decreased water (moderator) displacement and also reduces the hazardous handling and personnel exposure in comparison with integral fuel burnable absorber.…”

“…8,9 On the other hand, lanthanide oxides have a high neutron absorption cross section and a relatively lower sintering temperature; therefore, they can be mixed with uranium oxide fuel. 5 Therefore, the concentration of Gd 2 O 3 in the fuel should be limited to 2 to 10 wt.%. 11 However, because Gd 2 O 3 is mixed with the UO 2 fuel, its addition results in a lower densification rate and reduced thermal conductivity of the UO 2 -Gd 2 O 3 fuel and a reduction in the amount of fissile fuel in the fuel assembly.…”

“…3 Conversely, one possible way to overcome these problems is maximizing the use of BAs. [4][5][6] The main requirements for BA materials are (1) a high neutron absorption cross section, (2) a burn-out rate matching the fuel (U-235) depletion rate, and (3) the absence of fission product poisons. 7 Burnable absorbers can be classified into 2 main categories, namely, boron compounds and lanthanide oxides.…”

“…11 However, because Gd 2 O 3 is mixed with the UO 2 fuel, its addition results in a lower densification rate and reduced thermal conductivity of the UO 2 -Gd 2 O 3 fuel and a reduction in the amount of fissile fuel in the fuel assembly. 3,5,12 In addition, Gd has a higher residual reactivity than B due to the presence of high neutron absorbing radioisotopes in its decay chain. 5 Therefore, the concentration of Gd 2 O 3 in the fuel should be limited to 2 to 10 wt.%.…”