*2.2. Installation of Acoustic Emission Systems*

Prior to the installation at the Savannah River Site (SRS), the consistency of the sensor readings was checked using pencil lead breaks on an acrylic rod [24,25]. Six pencil lead breaks were performed for each sensor. An appropriate sensor response was demonstrated as the average amplitude response of a sensor type that was within ±6 dB of the average amplitude of the sensor group. A threshold of 40 dB was used for data collection. An analog filter was used to collect signals with a frequency between 1 kHz and 1 MHz. The waveform sampling rate was 1 million samples per second (MSPS) with 256 micro-seconds pre-trigger and 1 kilobyte length. Peak definition time (PDT), hit definition time (HDT), and hit lock-out time (HLT) were set to 200, 400, and 200 micro-seconds, respectively. Each AE system was connected to a cellular modem to allow for remote monitoring and each system was remotely controlled through appropriate software. This allowed for altering system settings and saving data at the University of South Carolina.

## 2.2.1. Crane Maintenance Area

The wired AE system was installed to monitor the activity in this area of building 105-C with ten sensors including five resonant sensors (type R6I) and five broadband sensors (type WDI). The sensors were installed at three different locations. The first location was near a column to roof interface (referred to as the 'vertical column to roof interface location'). This area had been visually assessed by the Savannah River Nuclear Solutions/Savannah River National Laboratory (SRNS/SRNL) personnel and is known to have deteriorated in comparison to the majority of the structural system comprising the 105-C reactor building. Spalling occurred in this area in the recent past and ongoing corrosion activity was suspected. The area has undergone at least one repair activity in the past. A total of six sensors (three resonant and three broadband) were installed at this location, which is shown in Figure 2. The locations of the sensors were chosen to be near the exposed reinforcing bars showing visual signs of corrosion damage. The locations of the sensors with respect to the red dot shown in Figure 2 are provided in Table 1.

The second location was chosen on a horizontal beam that forms the connection with the previously described column (referred to as the 'horizontal beam location'). Two sensors (one resonant and one broadband) were installed at a distance of 12 inches below the beam to roof interface where signs of deterioration were visually observed (Figure 3a). The spacing between the sensors was 6 inches. The third location was chosen at an area where no signs of damage were observed (referred to as the 'control location'). Two sensors (one resonant and one broadband) were installed at this location, which is shown in Figure 3b. The horizontal distance between the two sensors is 6 inches. The data collected from the control location was used to evaluate the effectiveness of data reduction approaches.


**Table 1.** Location of sensors shown in Figure 2.

\* Positive dimension indicates below the red dot are shown in Figure 2. Negative dimension indicates above the red dot are shown in Figure 2.

**Figure 2.** Photographs of the crane maintenance area: (**a**) Main sensor grid, (**b**) close-up of sensor on side of column, and (**c**) view of main grid from the floor level (red dot is at corner).

**Figure 3.** Photograph of: (**a**) Horizontal beam location and (**b**) control location.
