Impact of Active Control on Passive Safety Response Characteristics of Sodium-Cooled Fast Reactors: I—Theoretical Background

Abstract

The interaction of the active control system with passive safety behavior is investigated for sodium-cooled fast reactors. A claim often made of advanced reactors is that they are passively safe against unprotected upset events. In practice, such upset events are not analyzed in the context of the plant control system, but rather the analyses are performed without considering the normally programmed response of the control system (open-loop approach). This represents an oversimplification of the safety case. The issue of passive safety override arises since the control system commands actuators whose motions have safety consequences. Depending on the upset involving the control system (operator error, active control system failure, or inadvertent control system override), an actuator does not necessarily go in the same direction as needed for safety. So neglecting to account for control system action during an unprotected upset is nonconservative from a safety standpoint. It is important then, during the design of the plant, to consider the potential for the control system to work against the inherent and safe regulating effects of purposefully engineered temperature feedbacks.

Keywords:

• Sodium-cooled fast reactors
• active controllers
• passive safety

Acknowledgments

This paper was created by UChicago Argonne, LLC, operator of Argonne National Laboratory (Argonne). Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory, is operated under contract DE-AC02-06CH11357. This work was supported by the DOE Office of Nuclear Energy, under contract DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.