Fuel performance evaluation of two high burnup PWR core designs during normal operation, control rod withdrawal, and control rod ejection scenarios

• Published in: Nuclear engineering and design 2023-12, Vol.415 (C), p.112730, Article 112730
• Main Authors: Lindsay, Isabelle O., Fox, Mason, Sweet, Ryan T., Capps, Nathan, Brown, Nicholas R.
• Format: Article
• Language: English
• Subjects: BISON; Burnable absorbers; High burnup fuel; Increased enrichment; RIA
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2023.112730

•We compared increased enrichment IFBA fuel and an increased enrichment fuel concept with blended gadolinium for PWRs.•Due to cladding hoop strain, the IFBA fuel design does not meet available NRC guidance when incorporated into this core design.•The gadolinium fuel design operates with greater safety margins in normal operation when compared to NRC performance guidelines.•The pins that experienced the most strenuous conditions during the accident scenarios were not high burnup pins.•Fuel pins at high burnup and were shuffled to the periphery of the core, minimizing the impact of control rod withdrawal/ejection. There is interest among utilities to extend the current, 18-month operating cycle to 24 months. Economically, this extension would require greater than 5 % enrichment and peak rod average discharge burnup levels above 62 GWd/MTU. A notable challenge of increasing enrichment is the resulting additional excess reactivity encountered during the early stages of fuel life. To accommodate, burnable absorbers beyond soluble boron are introduced into the fuel system. In high burnup fuels, the possibilities of cladding lift-off and fuel melting increase due, in part, to increased rod internal pressures and limited fuel thermal conductivity, respectively. This work collaboratively employs PARCS, RELAP5-3D, and BISON to compare the fuel performance of two high burnup fuel candidates with higher than 5 % enrichment. The fuel performance parameters were compared to current NRC guidance. The results demonstrate an annular fuel design with homogenously blended gadolinium as a burnable absorber operates with greater safety margins during normal operation, allowing for additional operational flexibility. During normal operation, the core design utilizing Integral Fuel Burnable Absorber pins contained fuel pins which reached plenum pressures above 15.5 MPa by the end of the first fuel cycle and fuel pins experienced cladding hoop strains above 1 %. In the Gd core design, only two observed pins experienced plenum pressures above 15.5 MPa and no pins exceeded 1 % cladding hoop strain. During the control rod withdrawal scenario, plenum pressures for pins in both designs marginally exceeded system pressure, however neither experienced excessive hoop strain. The Gd core design experienced a maximum fuel temperature of 2418 K, which is significantly higher than the Integral Fuel Burnable Absorber design at 2157 K, but still within regulatory guidance. We predicted that th