## 2 AE Monitoring at the 105-C Reactor Facility
### Results and Discussion
#### 2.3.3 Damage Classification Using Acoustic Emission
Figures 10 and 11 are plots of Intensity Analysis results from the period beginning 10 September 2014 and ending 25 August 2015 for data recorded from resonant and broadband sensors, respectively. For the majority of field applications, only resonant sensors would be utilized due to the increased sensitivity of this sensor type in comparison to broadband sensors. The use of resonant sensors, therefore, reduces the number of sensors needed for a given application. However, resonant sensors do not provide high fidelity representations of the frequency content in comparison to broadband sensors. One purpose of using the two different sensor types is to investigate the associated differences in the results. The limits of the Intensity Analysis chart were developed based on data from resonant sensors [2]. Thus, it is expected that data collected from broadband sensors may yield underestimated damage classification if the same limits are used. Figure 10: Intensity Analysis results for resonant sensors: (**a**) roof to column interface, (**b**) horizontal beam location, and (**c**) control location. The preliminary estimation of damage was based on visual inspection during the initial visit to 105-C and was located near the border between the 'no damage' and the 'depassivation' regions of  
Figure 11: Intensity Analysis results for broadband sensors: (**a**) roof to column interface, (**b**) horizontal beam location, and (**c**) control location. the chart (severity = 300,000 and historic index = 2.0) for both the vertical column to roof interface location and the horizontal beam location. This assumed level of damage underestimated the actual condition of the structures since these areas are known to have ongoing corrosion damage. Ideally, this initial point would be established through a combination of methods including visual inspection and electrochemical methods. Electrochemical methods, however, were not collected during this part of the study. For the control location, no damage was assumed and, therefore, the initial point was located at the left corner in the 'no corrosion' region of the chart. Acoustic emission activity during the monitoring period (approximately one year) at the vertical column to the roof interface location indicated a progression from the initial state to the severe damage state for both sensor types. It is noted that the results of IA after approximately 2 months of monitoring (1 November 2014) showed that corrosion is ongoing at this location. On 1 December 2014, Intensity Analysis results indicated that severe damage occurred. For monitoring over this relatively short duration, such a progression from the initial state to the'severe' damage state is indicative of a relatively high level of ongoing damage growth in the monitored areas. For this plot, the term 'cracking' refers to micro-cracking that is generally non-visible while'severe damage' refers to visible cracking that may be accompanied by spalling. This result is supported by the spalling that occurred at this location during the monitoring period. Acoustic emission data from the resonant sensor and the broadband sensor at the horizontal beam location progressed from the initial state to the cracking state over the duration of the monitoring period. This result is also an indication of ongoing damage growth at this location when the relatively short monitoring period is considered. The broadband sensor results (Figure 11b) indicated less damage than the resonant sensor results (Figure 10b) especially during the first 3 months of monitoring. This can be attributed to the lower sensitivity of the broadband sensors. In contrast to the roof interface location and the horizontal beam location, the intensity analysis results for the control location indicate no damage progression during the monitoring period and, therefore, the initial state and final state coincide (plot on top of one another) for the control location.