Licensing and Regulatory Support

We work with clients on licensing submittals for methodology changes and regulatory compliance of any modification to existing design/licensing bases. For example, NAS's staff addressed cooling issues in a pump room by creating several transient thermal analyses. Results were used for operability assessments and modifications of the design/licensing bases. In addition, a GOTHIC model of a three unit auxiliary building and control complexes was created as part of a Protected Service Water (PSW) project to predict the extent of modifications needed to meet NRC requirements. The results generated a successful NRC PSW Inspection. An additional GOTHIC model of the Standby Shutdown Facility (SSF) was created for the same plant. Results showed that if minor modifications were implemented to adjust the airflow then the SSF Control Room AC System, a problematic system with a high failure rate, may not be required. Furthermore, additional GOTHIC models of the Blockhouse and Relay house for the same plant provided modifications needed to prevent overheating of the electrical equipment in the event of a HVAC system failure in these buildings.

Additionally, we have prepared a 10CFR50.59 Safety evaluation to allow a new GOTHIC analysis to become the site design/licensing basis. NAS personnel evaluated the removal of a containment liner insulation due to potential containment pressure and temperature issues after correcting non-conservative errors in previous mass and energy release analyses. It was demonstrated that the containment temperatures and pressures remained within acceptable mass and energy release values. The results prevented the removal of the containment liner insulation which could have been a significant project for the plant and the analysis became a part of the site design/licensing basis.

NAS personnel have developed several full scope and selective Alternative Source Term (AST) radiological analyses using RADTRAD-NAI including development of the full set of radiological analysis for the Chapter 15 accident analyses. Usually, the AST analysis also includes a complete replacement, evaluation, and validation of raw meteorological data in accordance with METD program (NUREG-0917) screening and validation requirements. RADTRAD-NAI models of the Technical Support Center (TSC) and Emergency Operations Facility (EOF) were also developed and used to evaluate radiological consequences at those locations. The projects usually included development of draft Technical Specification and UFSAR changes, draft License Amendment Request and support for the pre-submittal meeting with the NRC.

To support our clients, NAS provides guidance and analyses to demonstrate safe continued operation of power plants and resolve NRC findings. Our staff has evaluated modifications needed to meet NRC requirements, support resolutions to GL-2008-01, demonstrate that radiological doses for all events are within regulatory limits and analyze hydrodynamic loads on spent fuel pool level instrumentation associated with seismic events.

NAS has experience supporting Generic Issue resolutions, including GSI-191 and GL 2008-01.

RELAP5-3D was utilized to support LOCA methods development and analyses as well as GSI-191 issue resolutions. GOTHIC models for containment analyses have been used to predict containment atmosphere pressure and temperature results, sump temperature results, containment liner temperature results and net positive suction head (NPSH) results. We also developed modeling guidelines to support this effort and the associated licensing submittal. In addition, NAS's personnel completed development of multiple GOTHIC containment models, including benchmarks against the current models. These models included the appropriate components and inputs need to model the long-term mass and energy release in order to support GSI-191 issues.

NAS has also performed numerous GOTHIC gas transport analyses for several nuclear power plants. The analyses were utilized for several purposes including: past operability, future acceptance criteria and resolution of Generic Letter 2008-01 (Managing Gas Accumulation Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems) issues. Our experience includes the identification of voids (location and size), validation and benchmarking, voids upstream of pumps (entrainment), voids downstream of pumps (water hammer), acceptance criteria and determining allowable void size.

Our analytical methods include best estimate plus uncertainty (BEPU) applying EMDAP (Evaluation Model Development and Assessment Process) in accordance with Regulatory Guide 1.203 (Transient and Accident Analysis Methods). Prior analytical methods work has included more traditional deterministic analyses, particularly for events where margin is not an issue. NAS has experience in developing and obtaining NRC acceptance of several computer codes as part of analytical methods, including GOTHIC, RETRAN, VIPRE, RELAP, COBRA and RADTRAD-NAI. All development of computer codes and the resultant analysis methodologies supporting licensing basis safety analysis is performed under Numerical Advisory Solutions's 10 CFR 50 Appendix B and NQA-1 quality assurance program. Other computer codes where NAS has supported analytical methods include CASMO/SIMULATE and several fuel performance codes. These analytical methods and computer codes support increased margin, fuel vendor independence and operations and maintenance flexibility.