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Level II Probabilistic Risk Assessments (PRA) for Nuclear Safety

Posted by The Fauske Team on 03.11.14

In the wake of the Fukushima Daiichi accident in Japan, nuclear power safety is under heightened scrutiny throughout the United States and worldwide. Fauske & Associates, LLC (FAI) utilizes Probabilistic Risk Assessments (PRA) to gauge the probability of risk by using calculations to determine the potential, probability and possible severity of an unwanted phenomena occurring in a nuclear power plant. FAI developed extensive capabilities and experience in performance of NRC classified Level II risk analysis specifically focused on the potential for accidents that could release radioactivity from a nuclear facility.

In the late 1980’s, FAI supported the nuclear industry response to the NRC’s Generic Letter 88-20 requirement that all nuclear facilities undergo a risk assessment for severe accident vulnerabilities termed as an Individual Plant Examination (IPE), assisting a large percentage of US utilities in the process. IPE updates included improvements to Level I success criteria, assessments of Large Early Release Frequencies (LERF), determination of Level II source term releases and assessments of plant vulnerabilities to severe accident phenomena. FAI also performed a number of key experiments to expand the understanding of severe accidents related to:PWR Containment Cross Sectional View

• Direct containment heating
• Drywell shell core debris interaction (liner melt-through)
• External cooling of the RPV
• Lower plenum penetration response
• Rapid pressurization due to steaming (steam explosions)
• In-vessel cooling
• Hydrogen control and management

The extensive Level II work performed by FAI is indicative of both a strong knowledge base and a high-quality organization," states Martin Plys, ScD, Vice President, Waste Technology & Post Fukushima Services, FAI. "Both in-house experiments and knowledge of experiments performed elsewhere have provided FAI professionals with an in-depth understanding of the broad technical basis developed for accident analyses including those focused on severe accident phenomena. This understanding is communicated through phenomenological position papers which become part of the living documentation. This, coupled with a staff of experienced engineers with hands-on nuclear power plant experience, positions FAI as the ideal choice for performing or assisting in Level II risk analysis."

The Modular Accident Analysis Program (MAAP4 and MAAP5) an Electric Power Research Institute (EPRI) owned and licensed computer software have been used to perform severe accident analysis and associated severe accident phenomena such as: hydrogen generation and combustion, direct-containment heating, rapid pressurization due to steaming, core concrete interactions, fission product releases, transport and deposition, for many decades. These codes are also used extensively in the probabilistic risk/safety assessment (PRA/PSA) arena as well as for applications including success criteria evaluations, human reliability analyses (HRA) and Level II source term evaluations.

FAI was also the principal author of the original Severe Accident Management (SAM) Technical Basis Report (TBR - EPRI TR-101869). This report provided the technical bases upon which the PWR (Pressurized-Water Reactor) Owners Groups at the time (Westinghouse, Combustion Engineering and Babcock & Wilcox) developed generic severe accident management guidance SAMG) support material, which served as a framework for each utility’s plant-specific SAMG program. In the aftermath of the Fukushima accident, EPRI commissioned an update to the original TBR, and FAI was once again a principal author of this update. In addition to the immediate insights from the Fukushima accident, the TBR update also incorporates a significant amount of research and experimental information that post-dated the original TBR.

While FAI leveraged its severe accident technical basis experience within the SAM TBR in its post-TMI and post-Fukushima evolutions, Westinghouse Electric Company, LLC (In 1986, FAI became a wholly owned subsidiary), focused on implementation of the TBR into the actual plant-specific SAMG implementation programs for customer sites. Thus, FAI and Westinghouse have maintained complementary SAMG capabilities which can be utilized to assist customers with preparing for NRC inspections. Due to the diversity of skills across FAI’s engineering staff, the company specializes in many functional areas within the nuclear power and decontamination/decommissioning industries including:

Corium Pool• General Thermal Hydraulics Analysis
• Fluid System-Specific Transient Analysis
• Two-Phase Critical Flow
• Waterhammer and Related Hydrodynamics
• High-Pressure Subcooled Jet Depressurization and Jet Impingement
• One-Phase Plume and Jet Mixing Analysis
• Building Analysis (Primary Containment, Reactor Building, Auxiliary Building)
• Software Development
• NRC Regulations and FAI Supporting Skill Set
• Industry Flexible and Diverse (FLEX) Strategy for Extended SBO
• BWR High-Reliability Hardened Vent Support
• Spent Fuel Pool Monitoring (SFPIS)
• Containment Filtered Vent Support
• Hydrogen Generation, Monitoring and Control
• Severe Accident Management
• Probabilistic Risk Assessment (PRA)

Founded in 1980 by Drs. Hans Fauske, Robert Henry and Michael Grolmes, FAI is a world leader in nuclear, industrial and chemical process safety. For more information on PRA, MAAP, severe accident analysis or other nuclear power safety concerns, please contact Dr. Martin Plys: or 630-887-5207

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Topics: severe accident, MAAP, nuclear safety, nuclear power, PWR Owners Group, Probabilistic Safety Assessment, nuclear


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