Zachry Nuclear Engineering
System Analysis
Zachry Nuclear has completed many Generic Letter 2008-01 analyses including operability determinations, and analysis third party reviews.
  • Non-condensing gases can accumulate in in Piping Systems due to:
    • Draining, Filling and Venting Operations
    • Maintenance and Plant Modifications
    • Gas Evolution from Saturated Sources
    • Operator Error
    • System Leakage
  • Potential Consequences include
    • Pump Cavitation from Gas Voids
    • Reduced NPSH
    • Water Hammer
In this example, our staff was able to use GOTHIC to demonstrate the gas volume fractions at the pump suction were low enough that at least one Charging Safety Injection Pump would have remained operable for all scenarios. GOTHIC was qualified for this application based on benchmarks to applicable experimental date. From NRC Inspection Report 50-400/0206 - "The finding was of very low safety significance because mitigation systems were concluded to be operable based on the engineering analysis performed."

System Analysis

Zachry Nuclear has completed system analysis work for a wide range of clients worldwide. We have provided timely expertise and support for existing plants, small modular reactors (SMR) as well as next generation, non-water cooled plant designs. Zachry Nuclear is able to handle a wide range of analytical needs, including investigating system and equipment performance, design optimization, and verifying the capability of plant systems under normal and accident conditions. Support for our clients includes steady-state thermal hydraulics, heat exchanger performance, gas entrainment, water hammer & piping transient, particle and aerosol tracking and ventilation and filtration assessments.
Steady-State Thermal Hydraulics
Zachry Nuclear is able to analyze a wide range of steady-state thermal hydraulics, including investigating system and equipment performance, evaluating improvement options, and verifying the capability of plant systems under normal and accident conditions with a large part of this experience applying our PROTO-FLO, PROTO-HX, PROTO-HVAC AND PROTO-Sprinkler software packages. Zachry Nuclear is able to construct complex system and component models with these programs. The ability to construct and use these models demonstrates capabilities and provides clients with confidence in our ability to provide thermal-hydraulic, heat transfer, fire protection and HVAC analyses.
Heat Exchanger Performance
Zachry Nuclear is able to analyze the performance of a wide variety of heat exchangers and we have experience building heat exchanger models for specific situations. For example, we developed a model of a Spent Fuel Cooling System using PROTO-FLO to evaluate options in addressing the high temperature, high humidity, and the potential for personnel hazard associated with the Spent Fuel Pool (SFP) and the associated Spent Fuel Pool Cooling System (SFPCS). The model was used to gain an understanding of the various methods of reducing the SFP temperature following a full core off-load that were being considered.
Water Hammer and Piping Transients
Water hammer occurs when there is a pressure surge or wave in a piping system caused by a fluid (gas or liquid) in motion that is forced to stop or change direction suddenly. The large hydraulic loads from water hammer events can cause damage to pipes and structures. Zachry Nuclear has performed various water hammer analyses for nuclear power plants. We also maintain a strong experience base in nuclear plant operations and safety analysis requirements. We are exceptionally and uniquely qualified to complete water hammer analyses.
Gas Management in Piping Systems
Due to longstanding issues related to accumulation of non-condensable gases in Emergency Core Cooling Systems (ECCS), the NRC issued Generic Letter 2008-01 requiring all licensees to evaluate the licensing basis, design, testing, and corrective actions for their ECCS, Decay Heat Removal (DHR) system, and containment spray system (CSS) to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems. Even before the issuance of GL 2008-01, Zachry Nuclear was supporting plants with evaluations of gas transport in ECCS systems. We have extensive experience with gas entrainment and transport, having completed numerous analyses for suction and discharge piping in ECCS and CCW systems, and heat exchangers, including evaluation of as-found voids and determination of maximum void size. We have also identified system configurations susceptible to gas entrainment, evaluated the effectiveness of venting design/procedures, provided operability determinations, performed third party reviews of analyses, and conducted gas management training based on available industry guidance.
Bubble Migration
Ventilation and Filtration Assessments
Zachry Nuclear has performed many different types of ventilation and filtration assessments. Our assessment experience includes: evaluation of buoyancy-driven ventilation Flows, evaluation of alternative cooling strategies for cooling both trains of electrical equipment, assessing time to reach limiting temperatures inside equipment, demonstrating operability of a component in a diesel room cabinet for various failure scenarios using 3D modeling of ventilation flow and heat transfer and fire, smoke and exhaust propagation.