Tailoring the response of Autonomous Reactivity Control (ARC) systems

Abstract

The Autonomous Reactivity Control (ARC) system was developed to ensure inherent safety of Generation-IV reactors while having a minimal impact on reactor performance and economic viability. In this study we present the transient response of fast reactor cores to postulated accident scenarios with and without ARC systems installed. Using a combination of analytical methods and numerical simulation, the principles of ARC system design that assure stability and avoids oscillatory behavior have been identified. A comprehensive transient analysis study for ARC-equipped cores, including a series of Unprotected Loss of Flow (ULOF) and Unprotected Loss of Heat Sink (ULOHS) simulations, were performed for Argonne National Laboratory (ANL) Advanced Burner Reactor (ABR) designs. With carefully designed ARCsystems installed in the fuel assemblies, the cores exhibit a smooth non-oscillatory transition to stabilization at acceptable temperatures following all postulated transients. To avoid oscillations in power and temperature, the reactivity introduced per degree of temperature change in the ARC system needs to be kept below a certain threshold the value of which is system dependent, the temperature span of actuation needs to be as large as possible.

Reducing Irradiation Damage in a Long-Life Fast Reactor with Spectral Softening

“…These types of control devices were successfully demonstrated at the Fast Flux Test Facility [12]. A similar approach using a lithium injection device was proposed for reactivity control in breed-burn fast reactors [14], and transient analyses showed that this type of device could enable fast reactors with large positive coolant temperature reactivity coefficients to operate safely [15]. Additionally, mechanisms such as grid-plate expansion and axial fuel expansion could help reduce the large coolant temperature reactivity coefficient in both metal-and oxide-fueled cores.…”

FY2017 Updates to the SAS4A/SASSYS-1 Safety Analysis Code

“…In response to needs identified by a Nuclear Energy University Partnership project, new mathematical operations were required to represent the reactivity feedback characteristics of an Autonomous Reactivity Control device. [11] The behavior of an ARC device can be represented by a variable lag compensator. A variable lag compensator is similar to a lag compensator except that the delay time parameter can vary during the Control System simulation.…”