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The NEXUS framework is a whole-core fuel performance tool developed by NNL to improve fuel licensing and safety margin estimation, addressing limitations of current industry practice.

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What they did

System
MEC

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Abstract

Current industry practice in fuel licensing often relies on thermo-mechanical modeling of a fuel rod with an artificially constructed bounding power history. The benefit of this approach is that it is computationally efficient; however, the drawbacks are that 1) such an approach is not always conservative, for instance when modelling phenomena related to late onset pellet-clad gap closure; and 2) it can poorly estimate available safety margins for fuel operating at high local power densities and/or to high burnup. For these reasons NNL developed an in-house whole-core fuel performance framework – NEXUS – to enable modelling of all fuel rods in the core using the ENIGMA fuel performance code and computed power histories from core simulation packages (currently limited to PARCS or SIMULATE). One of the main objectives was to create a tool that was both computationally efficient and user friendly. The former was achieved by making use of parallelisable architecture, while the latter was achieved by minimising necessary user input and providing tools for easy interrogation of the fuel performance output. NEXUS has been applied to several LWR operational scenarios, which we summarise in this paper, including steady-state operation of an ABWR, and a rod ejection accident in a small modular soluble boron free PWR and a GWe-class PWR. We also summarise current development activities related to integrating NNL’s in-house fuel performance Monte Carlo uncertainty analysis software CASINO into the NEXUS framework.

Key findings

  • Current industry practice relies on thermo-mechanical modeling with artificially constructed power histories, which can be non-conservative and poorly estimate safety margins.
  • NEXUS framework uses ENIGMA fuel performance code and computed power histories from core simulation packages to model all fuel rods in the core.
  • NEXUS has been applied to several LWR operational scenarios with improved results compared to current industry practice.

Keywords

BurnupModular designNexus (standard)Core (optical fiber)Monte Carlo methodNuclear engineering

Identifiers

DOI
10.1051/epjconf/202124712001
Journal
EPJ Web of Conferences
Year
2020