Modeling & Simulation

Dynamic Response Analysis: For more than 15 years, DEI has supported design of the Hanford waste treatment plant as a key technical consultant, evaluating the risk and consequences of hydrogen accumulation and potential detonation when processing transuranic (TRU) waste streams. DEI contribution to this project have included:

• Over 70 calculations and technical position papers advancing the state of the art in understanding and analysis of response of piping systems and components to the effects of internal hydrogen deflagration, detonation and deflagration-to-detonation transition (DDT)
• Development of custom quantitative risk assessment software for analyzing hydrogen risks and failure modes to nuclear safety-related quality assurance standards (ASME NQA-1 2000, Subpart 2.7)
• Dynamic analysis of other system transients including from shock waves associated with waste processing activities and from gas build-up and acceleration of waste slugs with Bingham rheological properties
• Experimental evaluation of explosions and other transients to validate and qualify modeling and simulation results

DEI has presented technical findings and recommendations to the US DOE and the US DNFSB.

EPRI Research Program: DEI has more than 30 years of experience welding simulation and recently led a multi-year EPRI research program to validate residual stress models for dissimilar metal welds in nuclear components. As documented in EPRI reports MRP-316 and MRP-317 (3002005498 and 3002005499), DEI’s contributions to this effort included:

• Development of finite element analysis models for predicting residual stresses in dissimilar metal welds, including consideration of different component and weld geometries, material properties, weld parameters and thermal and structural models
• Comparison to independent models developed by others, including the NRC Office of Regulatory Research
• Model validation using residual stress measurements performed on various weld mockups using neutron diffraction, deep hole drilling, x-ray diffraction, hole drilling and ring core, and contour method
  This project improved the understanding and quality of residual stress models for dissimilar metal welds. In addition to the research effort highlighted above, DEI also authored ASME Code Case N-899, which provides standardized welding residual stress distributions for use in flaw growth calculations.

CFD Modeling & Experimental Validation: The integrated waste treatment unit (IWTU) in Idaho uses sonic gas pulses to backwash and regenerate gas filters operating at high temperature. Optimization of the gas pulse system and downstream Venturi block geometry is needed to ensure the desired performance is achieved, maximizing filter regeneration. DEI has provided the following technical consulting and support for this effort:

• Transient computational fluid dynamics (CFD) modeling of the sonic jet, including flow into and through the porous filter elements
• Design and construction of a test rig for molecular tagging velocimetry (MTV) acquisitions to validate CFD modeling results
• Lumped-parameter modeling of the backpulse gas volumes from an upstream reservoir to a choked flow nozzle using a custom transient Python solver

DEI modeling and experimental validation has supported improved understanding of the design and operation of both pilot-scale and full-scale plant conditions, and optimization of the process gas filters for reliable long-term operation.

Root Cause Investigation: The line which feeds liquid hydrogen to space shuttle main propulsion systems includes a flexible joint which accommodates relative motion between the space shuttle structure and main engine. Cracks were detected in Inconel 718 flow liners in this joint for several space shuttles, including Atlantis, Discovery and Endeavor. In support of investigation of the issue by NASA’s Langley Research Center, DEI completed a root cause investigation of this issue. Specific assistance and insights provided by DEI in this investigation included:

• Modeling and finite element analysis of the flowliner flexible joint, and stress intensity and fracture mechanics calculations
• Identification of the cracking root cause as flow-induced alternating stresses during operation, combined with high tensile residual stresses from production welding

These results contributed to NASA’s resolution of the issue, which included identification appropriate inspection intervals and the development of a high resolution surface replication technique for precise detection of crack initiation locations.

EPRI Research Program: Nuclear plants have experienced cases of material degradation and primary water leaks due to turbulence-driven thermal fatigue. DEI has supported a multi-year EPRI research program to develop high-resolution industrial models for thermal fatigue using computational fluid dynamics (CFD) and other numerical solvers. DEI efforts in this area have included:

• CFD modeling of residual heat removal system mixing tees coupled with thermal, structural, and fatigue analysis
• CFD modeling of turbulent swirl penetration in normally stagnant branch lines, including comparison to semi-empirical industrial models and experimental validation using high-resolution particle image velocimetry
• Inverse system analysis to determine piping in-leakage and cross-flow using custom Python codes and field measurements
• Assessment and modeling of craze crack growth and arrest

The efforts above benefit the industry by reducing the risk of unplanned outages due to thermal fatigue degradation, while reducing O&M costs through optimized inspection intervals.