RELAP5 Model of a CANDU-6 (Embalse) Nuclear Power Plant: Application to a Turbine Trip Event (NUREG/IA-0489)

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Publication Information

Manuscript Completed: May 2017
Date Published: January 2019

Prepared by:
A. I. Lazarte and M. V. Guala

Autoridad Regulatoria Nuclear (ARN)
Av. Del libertador 8250, CABA C1429PNB

Kirk Tien, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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As part of the Embalse Nuclear Power Plant (CANDU-6) refurbishment, the Nuclear Regulatory Authority of Argentina (ARN) has developed a full plant thermo-hydraulic model with point kinetics. Using the RELAP5 mod.3.3 Patch4 thermal-hydraulic code, the model simulates accidents within the design basis. This model is being used to perform an independent review of the safety analysis submitted by the designer and operator to the regulatory body. It would also be used as a tool for understanding plant dynamic behavior. The model developed by the ARN includes most of the hydraulic systems and control logic from the original design; the planned design changes for refurbishment are implemented in a more recent version of the model. To validate the model regarding its response to transients, a postulated initiating event (PIE) was modeled and simulated, and the results obtained were compared with recorded data of that particular event which took place in the NPP in 2007. The event consists of a spurious turbine trip leading to a rapid power reduction (stepback) to 49% of full power. This reduction was the only boundary condition imposed to the model. The purpose of this comparison is to verify consistency between important plant parameters, thermal-hydraulic model predictions and recorded data. Only the first 15 minutes of the transient were simulated. It is shown that the evolutions of some given variables are similar to those observed in the NPP. Also, the results obtained indicated that modifications should be performed to improve the model, especially regarding control components for getting better adjustment of plant data.

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