Study of the Open Loop and Closed Loop Oscillator Techniques

Dr. George Imel
Department of Nuclear Engineering and Health Physics
Idaho State University

In the years 2008-2014 we undertook a careful study of the theory and operation of absorbing samples of very low reactivity worth oscillated in our AGN-201 reactor. In this study both the open loop and closed loop techniques were directly compared, with the objective being to prove that the open loop technique (no feedback control) can achieve the same low degree of uncertainty as the technically more complicated closed loop system (requiring reactor control of power via a low worth control rod as well as a feedback control system). That is, the lower limit of uncertainty in either method is limited by reactor noise.

During the years 2008 and 2009 undergraduates at Idaho State University completed two senior design projects: the first to design and build a simple open loop oscillator, and the second to design and build a simple closed loop oscillator (capable of maintaining reactor power constant through a small worth experimental rod using feedback control).

Through the years 2010 to 2013 our team refined the two oscillators regarding actuator control and data acquisition. Additionally through this period the important reactor parameters (λi, βi, generation time) were quantified and uncertainties carefully studied. This phase is extremely crucial to the success of the open loop system which relies on inverse kinetics to unfold the reactivity of a small worth sample. Finally in this phase a controlling “pilot rod” of low worth (to provide reactivity resolution) had to be designed, fabricated, and calibrated.

In the last years of this project, which officially ended December, 2014, many experiments were performed, and the prime objectives were met: a clear demonstration of the equivalency of the open and closed loop techniques as well as showing that both were only limited by reactor noise regarding achievable uncertainties.

Finally, two simple designs were produced to implement the open loop system in a thermal reactor (a TRIGA) and a generic fast reactor.

In summary, we will present all of the important steps that we had to make in order to successfully meet our objectives. We will present some of the surprises, as well as some of the mistakes we made along the way. We do this in the hopes that the simpler open loop technique will be implemented elsewhere in support of measurements for the advanced reactor research.