Comparative Study of Transfer Functions for NRAD and AGN-201 Reactor Systems

Abstract

The project is about building an infrastructure for an open loop technique and implementing this technique to measure the reactivity worth of small samples. The reactivity samples are allowed to oscillate back and forth in the reactor system to cause perturbations and the corresponding reactor response is measured in the form of the transfer function. The transfer function obtained is used to determine stability characteristics along with other kinetic parameters such as delayed neutron fraction, prompt neutron lifetime, shutdown margins, and absolute power. This paper compares transfer functions for reactors like Neutron Radiography (NRAD) and Aerojet General Nuclear (AGN-201). The magnitude of the transfer function correlates with the reactivity of the sample that caused the perturbation. In addition, the transfer function allows one to determine whether the reactor is a stable system or not. In other words, the reactor’s response to the change in neutron population in the reactor can be easily described. Moreover, a transfer function measurement is useful to extract important kinetic parameters of the reactor system, such as instance prompt neutron generation lifetime, reactivity shutdown margin, absolute power, etc. The transfer function plots presented in the results section correlate the reactivity of the sample that caused perturbations. NRAD was found to have a higher break frequency than that AGN-201. This was an expected result since break frequency is inversely proportional to neutron generation time. With this relation, break frequency was found to be around 306 Hertz. So, the reactor cannot respond beyond this frequency but passes the low frequencies. The corresponding analysis and comparative transfer function plots using MATLAB for these two reactor systems are presented in the results section. Many reactivity measurements have been already in practice however if the transfer function technique can give reactivity measurements with similar or better precision and accuracy, it could be a great benefit. Moreover, this can be installed in those facilities where more complex systems cannot be incorporated easily.