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Division Spotlight
Thermal Hydraulics
The division provides a forum for focused technical dialogue on thermal hydraulic technology in the nuclear industry. Specifically, this will include heat transfer and fluid mechanics involved in the utilization of nuclear energy. It is intended to attract the highest quality of theoretical and experimental work to ANS, including research on basic phenomena and application to nuclear system design.
Meeting Spotlight
Utility Working Conference and Vendor Technology Expo (UWC 2024)
August 4–7, 2024
Marco Island, FL|JW Marriott Marco Island
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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Latest News
Vogtle-3 shuts down for valve issue
One of the new Vogtle units in Georgia was shut down unexpectedly on Monday last week for a valve issue that has since been investigated and repaired. According to multiple local news outlets, Georgia Power reported on July 17 that Unit 3 was back in service.
Southern Company spokesperson Jacob Hawkins confirmed that Vogtle-3 went off line at 9:25 p.m. local time on July 8 “due to lowering water levels in the steam generators caused by a valve issue on one of the three main feedwater pumps.”
Yue Guan, Fei Li, Mohammad Modarres
Nuclear Technology | Volume 133 | Number 3 | March 2001 | Pages 290-309
Technical Paper | Reactor Safety | doi.org/10.13182/NT01-A3175
Articles are hosted by Taylor and Francis Online.
A method of integrating traditional thermal-hydraulic (TH) analysis with probabilistic assessment (PA) (called the TH-PA method) has been developed. This method allows for an exhaustive search through a set of individually developed but subsequently linked logic models to screen and identify accident scenarios. The logic models consist of a probabilistic risk assessment (PRA) used for probabilistic screening purpose and an ensemble of integrated behavior logic diagrams (IBLDs). The PRA model represents the functional/logical relationships of the components and accident scenarios, the same way as is modeled in the conventional PRAs. The IBLDs hierarchically represent system interactions/dependencies due to TH phenomena and human actions. This hierarchy also shows causal factors and consequences of plant states, and identifies induced system failures. The TH-PA method relies on two types of scenario screening: probabilistic screening (PA screening) and TH screening. The PA screening eliminates scenarios with low frequencies (e.g., <10-10/reactor-yr). The traditional frequency-based screening method used in the PRAs has been adopted for PA screening. The TH screening eliminates scenarios that do not expect to result in core uncovery. For the TH screening, a simple accident trajectory approach has been devised. A trajectory represents the collapsed liquid volume fraction in the reactor primary system as a function of primary pressure. The trajectories are based on simple mass and energy conservation equations (if the TH-PA method is applied to a system where mechanical energy transfer is important, momentum conservation should also be considered). The roles of each plant system are then identified by indicating whether the system is a "source" or a "sink" for mass and energy at a given time during accident progression. Based on an input set that represents the plant system failures and the stage of the transient, the accident trajectory is developed. The accident trajectory allows for the evaluation of safety significance of scenarios. The trajectory also determines whether the core becomes uncovered, should the input conditions (i.e., conditions described by the input set) remain unchanged.