Critical Structures & Facilities

SI is an expert in evaluating critical structures and facilities for normal operating loads and extreme events. Some of the largest utilities and engineering companies in the world have looked to SI for seismic and advanced structural analysis solutions including root cause analysis, equipment qualifications, non-linear steel and concrete modeling, material aging and degradation, dynamic and non-linear seismic analysis, soil-structure interaction, and equipment/structure fragility analysis. Our capabilities include the use of explicit software programs that model load drops, tornado missile impacts, fluid-structure interaction, barrier design, shock propagation and isolation system design, and blast protective design. Our services are unique in that we provide seismic qualification of equipment through both analysis and shake table testing.

Thermal Hydraulics

Thermal-hydraulic analyses of nuclear plant components and structures are used to determine loadings from fluid flow at various temperatures to support structural integrity evaluations.

Structural Integrity conducts a full array of steady-state and transient thermal-hydraulic analyses, using first principle methods, ANSYS CFX Computational Fluid Dynamics (CFD) software or other specialized software, including proprietary codes. Examples of project experience involving complex thermal-hydraulic analyses include: (i) cold and hot fluid mixing at piping tee-junctions, (ii) interaction of reactor coolant system swirl penetration with cold in-leakage in attached branch piping, (iii) pressurizer surge line and vessel stratification during insurge and outsurge transients, and (iv) blow-down in a BWR annulus after a postulated recirculation line break.

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Soil Structure Interaction (SSI)

Soil-structure interaction (SSI) models the interdependency in behaviors of structures and their supporting/surrounding foundations. SSI occurs as a physical phenomenon for any structure-foundation system (under static or dynamic loading), but becomes particularly important when structures are massive, embedded within the ground, and/or founded on flexible subsurface materials (e.g., ranging from soft rock to soft soil).

Such conditions are encountered at a significant number of nuclear plant structures for various input load conditions (static case, seismic, aircraft impacts, explosions and fluid impacts, etc.). SSI analysis is most often employed in the dynamic case, where both kinematic and inertial interaction effects, as well soil nonlinearity (for shear moduli and damping) and motion incoherence are addressed for accurate/realistic assessment. Appropriate modelling of nonlinearity and incoherence effects often provides benefits of reduction of in-structure responses over significant ranges of vibration frequencies and input load intensities. Structural Integrity Associates performs SSI studies for the various static and/or dynamic load conditions, and employs industry accepted methods and software (e.g., SASSI, in the case of seismic loading). The scope of approaches employed by Structural Integrity for SSI includes deterministic and probabilistic methods, ranging from simplified to highly advanced.

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