Towards a New Generation of UHPC Spent Nuclear Fuel Storage Systems
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Authors
Igrashkina, Nataliia
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
CFD , horizontal storage modules , nuclear structures , seismic performance , thermal stress analysis , UHPC
Alternative Title
Abstract
Spent nuclear fuel (SNF) is currently stored in a growing number of dry cask storage systems (DCSSs) across the U.S. As policymakers have not yet reached consensus on defined strategies for permanent fuel disposal, the DCSSs will likely be used significantly longer than initially anticipated. The desired extended service life raises concerns about the long-term performance and potential degradation of the commonly utilized concrete shielding structures, which mandates the rethinking of current and future designs with a focus on enhanced durability and longevity. This potential can be realized through the incorporation of advanced materials like ultra-high performance concrete (UHPC), which possesses superior mechanical and durability properties, and is currently making major strides across the globe to use for critical structural applications. However, despite its potential, limited research exists on utilizing UHPC specifically for SNF storage. This doctoral study aims to bridge this gap by comprehensively exploring the viability of a new generation of DCSSs using UHPC with focus on canister-based horizontal storage modules (HSM) that heavily incorporate concrete and susceptible to aging and durability issues. The research methodology integrates a critical review with a suite of advanced numerical simulations. Initially, the dedicated review study identifies concrete degradation mechanisms in DCSSs, and assesses UHPC’s projected performance against these compared to normal strength concrete (NSC). A summary of emerging data on UHPC’s radiation attenuation properties, suggested mix modification, and key knowledge gaps in this domain are provided. Following this foundational review, advanced numerical modeling of an archetype HSM is performed. First, coupled steady-state computational fluid dynamics (CFD) and linear finite element (FE) analyses are used to compare thermal and structural performance of NSC and UHPC under normal operating conditions, evaluating temperature distributions and demand-to-capacity ratios under combined thermal and mechanical loads. Subsequently, transient CFD and nonlinear FE analyses, incorporating a coupled damage-plasticity microplane model and steel reinforcement for NSC and UHPC, are performed to study severe accident thermal conditions (i.e., 40-hour vent blockage), assessing thermal response, structural damage evolution, and the influence of temperature-dependent material properties. Finally, triaxial time-history FE seismic analysis investigates the seismic behavior, examining the effect of global HSM stiffness, using both baseline and thermally degraded properties of NSC and UHPC, on the global and local dynamic responses, including canister and fuel assemblies.
This doctoral research provides compelling evidence that demonstrates the enhanced performance capabilities of UHPC for HSM in DCSSs compared to NSC. The numerical analyses consistently reveal UHPC’s significant advantages in thermal performance under both normal and accident conditions. Furthermore, UHPC exhibits substantially improved structural performance with no damage against severe thermal loads, indicating greater structural robustness for long-term storage. The study also confirms the comparable seismic performance UHPC-based systems while advancing the understanding of the overall seismic behavior of HSMs; an aspect of the behavior that is also needed to assess the what-become long-term storage risks.