Two challenges to increase the efficiency in nuclear energy production are the ability to enhance the fundamental understanding of reactor operation and developing improved approaches for diagnostic and prognostic techniques. Traditionally, radiation-hardened sensors and their associated signal-conditioning electronics are used to study key process parameters inside the nuclear reactor core. However, traditional approaches have limitations such as the requirement of at least two wires to provide power, communicating information from inside to outside the nuclear reactor vessel, and the degradation of the performance of sensors along with their instrumentation/electronics over time. These limitations can have an adverse effect on measurement accuracy and model predictions. Conventional process sensors generally monitor quasi-static variations and tend to filter dynamic events that may be critical to diagnosing issues. A new approach to process monitoring is being developed to address some of the shortcomings of traditional process monitoring techniques in nuclear reactors. This paper describes a methodology that uses intrinsic reactor processes, an Acoustic Measurement Infrastructure and a novel data processing method to determine abnormal reactor operation. The resulting data from the Advanced Test Reactor is used to identify reactor state changes which will enable diagnostic and prognostic capabilities. The use of intrinsic reactor processes and the acoustic transmission of signals for process monitoring address the limitations of traditional process sensing.