Integral Fuel Burnable Absorbers with ZrB₂ in Pressurized Water Reactors

The design advantages achievable from the use of zirconium diboride (ZrB₂) integral fuel burnable absorbers (IFBAs) in two- and three-loop pressurized water reactor (PWR) cores are examined. The ZrB₂ IFBAs were designed and have been extensively tested for use in PWRs. Two fuel loading patterns that utilize IFBAs are analyzed: (a) a three-loop core with an 18-month cycle, very low radial leakage loading pattern, and reduced vessel fluence concerns; and (b) a two-loop core with an annual cycle, very low radial leakage loading pattern, and natural uranium axial blankets (low axial leakage). Both designs demonstrate the versatility of IFBAs in difficult fuel loading patterns. Both designs demonstrate well-behaved radial and axial power peaking factors for annual (two-loop core) and 18-month (three-loop core) cycles. The ZrB₂ IFBAs also provide added flexibility in the placement of fresh fuel. This flexibility can improve shutdown margin by placing fresh fuel under control rod locations and can improve fuel cycle cost. Neither design would have been possible with discrete burnable absorbers. By analyzing the two very different designs, it can be seen that ZrB₂ IFBAs can be used in tightly constrained fuel loading patterns and will provide added flexibility and/or fuel cycle cost savings in future fuel management strategies.