Numerical Advisory Solutions
Operating Plant Support

Operating Plant Support

NAS provides robust engineering, design and project management services to support the safe and efficient operation of nuclear facilities worldwide. We apply the industry's most advanced computer software and engineering analysis techniques to provide a full range of analytical services for plant systems, equipment and structures. We have supported power uprates, steam generator replacements, fuel cycle changes as well as operability assessments, plant modification evaluations, Engineering Change (EC) packages, outage efficiency improvements and resolution of regulatory issues to provide operations flexibility and cost savings for our clients. Our operations, systems and licensing experience ensures accurate and licensable models/results are delivered on-time and within budget.
Operability Assessments
Our analyses frequently support safe continued operation of plants, operational evolutions to improve schedule/cost and mitigation of regulatory issues and findings. NAS's unique capabilities allow us to assure that the solutions we develop provide safe, correct, and cost-effective solutions. Advanced modeling and simulation can often be used to demonstrate margin in the existing design and allow continued operation.
Emergent Issues
NAS has a demonstrated history of providing timely support for our clients to resolve emergent issues. As an example, we modified an existing GOTHIC reactor vessel model to evaluate a loss of shutdown cooling equipment being inadvertently misaligned. The evaluation supported a final Finding significance determination of Green as opposed to higher than Green as originally proposed by the NRC.
Thermally Induced Currents (TIC)
The Analysis Division has completed multiple analyses evaluating the effects of thermally induced currents (TIC) on high range radiation monitors (HRRM) under accident and transient conditions to address IN 97-45 and IN 97-45 Supplement 1. Our analysis evaluates the vulnerability of the affected cables to TIC under accident conditions and assists the clients in choosing replacement cabling, conduits, and the conduit routing.
Probabilistic Risk Assessment (PRA)
NAS has supported numerous PRA and risk-informed projects, including:
  • Evaluating the significance of incorrect relay replacements on HVAC and pump/diesel compartment temperatures
  • 10CFR50.69 evaluations for Control Building equipment
  • 10CFR50.69 evaluations for Auxiliary Building to demonstrate chillers could be downgraded to non-safety-related based on building temperatures
  • Inclined fuel transfer tube PRA, thermal-hydraulic and structural analyses to support new fuel movement in Mode 1.
  • PRA support analyses crediting operator actions
Plant Modification Evaluations
NAS provides detailed designs for existing power plant modifications and new power plants. We make sure plant modifications are recommended only when necessary and that when plant modifications are completed, they resolve the plant issue in the most efficient manner possible. For example, we developed GOTHIC models to demonstrate that temperatures and pressures remain within acceptable limits even after proposed modifications. Those results were used to reduce outage times and provide cost savings for the plant.
Predictive Maintenance
NAS has operating nuclear plant preventive maintenance optimization and predictive maintenance application experience including Reliability Centered Maintenance (RCM). As an example, one RCM effort resulted in an approximate 30% reduction in annual maintenance burden with an improvement in the effectiveness of the program with respect to equipment functionality and availability.