On the Aspect of Evaluation of Critical Channel Power and Associated Uncertainty in CANDU Slow Loss of Regulation Event Analysis

Abstract of the technical paper presented at:
16^th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH16)
Chicago, Illinois, USA,
August 30 – September 4, 2015

Prepared by:
Y. Guo and N. Hammouda
Canadian Nuclear Safety Commission
Ottawa, Ontario, Canada

Abstract

Critical channel power is an important figure-of-merit parameter in safety analysis of CANDU slow loss of regulation events. Evaluation of critical channel power and associated uncertainty for such events is complex; it has entailed significant analytical and experimental effort and numerous discussions within the CANDU Industry. Critical heat flux and dryout power are two other important parameters that are closely related to critical channel power and to each other. Unfortunately, in many occasions, particularly in the context of uncertainty analysis, the relationship of the critical heat flux and dryout power with critical channel power is very much confused.

This paper clearly defines the terms of critical heat flux, dryout power, and critical channel power that are frequently referenced in CANDU slow loss of regulation event analysis, and clarifies their inter-relationship and the associated proper uncertainty propagation formulation. The inter-relationship of the critical heat flux, dryout power and critical channel power is demonstrated based on their definitions and through mathematical relations of these parameters. A method for estimating uncertainties in dryout power and critical channel power is illustrated, which comprises identification of uncertainty sources, propagation of the source uncertainties, and consideration of sensitivity of each of the uncertainty sources in the propagation process. The information presented in this paper should provide better understanding of the sensitivity of critical channel power to the critical heat flux parameter, and better understanding on how to properly quantify the uncertainty in critical channel power due to uncertainty in critical heat flux.

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