System Analysis

NAS 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. NAS 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.

NAS 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 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. NAS 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.

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, NAS 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.

NAS 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.