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Control Rod Drop Surveillance Using Two Friction Coefficients

J. Blázquez, I. Vallejo, A. García-Berrocal, M. Balbás

Nuclear Technology / Volume 176 / Number 2 / November 2011 / Pages 284-289

Technical Paper / Nuclear Plant Operations and Control

In the case of large burnup, a control rod (CR) guide tube in the pressurized water reactor of a commercial nuclear power plant might bend. As a consequence, a CR drop experiment may indicate an event of a CR partially inserted and whether the CR should be deemed inoperable. Early prevention of such an event can be achieved by measuring two friction coefficients: the hydraulic coefficient and the sliding coefficient. The hydraulic coefficient hardly changes, so that the curvature of the guide tube can only be detected thanks to a variation of the sliding coefficient. A simple model for the CR drop is established and validated with CR drop experiments. If tmx denotes the instant of CR maximum velocity, a linear relationship between (tmx)-2 and the sliding coefficient is found.

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