Nuclear Safety Analysis

Our nationally recognized experts perform specialized nuclear safety analysis work. We are capable of clarifying the relationships among related design basis analyses to identify and remove excessive margin brought about by combining single failures and redundant conservatisms. We have successfully performed safety analysis projects requiring both thermal-hydraulic and radiation protection analysis capability. One of our strengths is in solving problems that couple thermal-hydraulic and radiation protection analysis; e.g., problems involving BWR secondary containment drawdown time and PWR containment spray performance (flowrate, coverage, and NPSH concerns).

Another example of such a “coupled” analysis applicable to both BWRs and PWRs is the degree of air exchange between the environment and structures such as the Turbine Building when non-Safety Related ventilation systems are assumed to fail. Knowledge of the environmental exchange behavior enabled Polestar to assist one of our clients in defining release points and the associated volumetric flows in support of an atmospheric dispersion analysis using the NRC’s ARCON96 modeling.

Finally, Polestar has experience in radiochemistry related to post-accident pH control of PWR sumps and BWR suppression pools and associated radioiodine re-evolution which has permitted us to successfully reduce ESF leakage radioiodine releases for PWRs, an important contributor to offsite and control room dose.

Alternative Source Term
Polestar was influential in the development of Alternative Source Term (AST) regulations following the TMI accident, and we are industry leaders in successfully applying these regulations with numerous clients to avoid or reduce major capital cost additions and to add significant design and operating margins. Effective application of this technology can significantly improve plant reliability while at the same time reducing operating costs.

As examples, Polestar made the first application of AST to an operating plant enabling deletion of the Main Steam Isolation Valve Leakage Control System (MSIV-LCS) and a simultaneous increase in MSIV allowable leakage. Polestar was also selected to perform AST analysis for the only two BWRs in the US without control room filtration enabling these plants to continue to operate and, in one case, to increase MSIV allowable leakage while also implementing extended power uprate.

The Polestar team has performed AST analysis for 13 US facilities and was asked to peer-review the applications of four additional facilities. Our unique expertise with AST is integrated closely with our specialized nuclear safety analysis work.


Control Room Habitability
Polestar has been a major contributor to the NEI Control Room Habitability (CRH) Task Force and to the interaction with the NRC to develop Regulatory Guides 1.194 through 1.197 dealing with CRH assessments. Polestar has a thorough understanding of CRH tracer gas testing and uncertainty analysis and has peer-reviewed tracer gas test plans, data collection, and analysis with substantial improvements in the results (reduction in unfiltered inleakage by a factor of two). We have applied our thorough understanding of tracer gas testing and uncertainty analysis to achieve more margin in CRH dose analysis results.

Probabilistic Risk Assessment
Polestar staff have extensive experience in Probabilistic Risk Assessment, having been responsible for both management and technical performance of the Big Rock Point PRA, one the the earliest plant PRA studies, and the Oconee PRA, a benchmark industry study that pioneered standard methods and was throughly documented in EPRI's NSAC-60 report. Polestar has also performed expert reviews for clients for PRA Level 1 and Level 2 models, and has developed and exercised PRA Level 3 models including their application to Emergency Planning.


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For more information contact:
Jim Metcalf
(603) 380-3938