During a routine recirculation of the Spent Resin Tank contents a spill of unknown origin occurred. It was clear that robots would be required for any recovery effort. However, Waterford 3 did not own a robot nor did it have any experience in this area.
The clean-up job was finally completed with the help of the contractor Remote Operating Vehicles (ROV) Technologies and the use of two robots: Scavenger and Scarab.
In trying to determine the cause of the tank spill, it was unclear if a pump seal or flange gasket had failed, a pipe had ruptured, or a valve was mispositioned. Approximately 30-40 ft3 of resin had spilled into the pump room. A sample of the resin indicated that dose rates at the floor would exceed 100 rem/hr.
A multi-disciplined team was assembled to determine the most efficient method of removing the material from the room. The team decided to process the resin near room access, reducing the need for long runs of hose through the Reactor Auxiliary Building. A suitable shielded transportation cask and High Integrity Container was obtained meeting the size and load limits.
The next obstacle was to determine which robotic device would be an effective delivery platform for the waste transfer line.
The Big Rock Point and Brunswick stations had experienced similar events, but there was a noticeable difference with Waterford’s situation. In particular, Waterford’s Spent Resin Tank Pump Room is extremely congested with many near floor obstacles. Placing a berm in the doorway and flooding the room with 4-6 inches of water (and pumping out the liquid) was deemed unacceptable. While this produced successful conditions at Big Rock Point, the Waterford team had three objections.
First, because of the many near floor obstacles, there was concern that resin would be moved and deposited in areas that were previously not affected. Secondly, the obstacles would limit mobility of the preferred robot, SCAVENGER. Thirdly, standing water may cause the introduction of moisture into low lying conduits causing insulation breakdown of the conductors inside.
To develop a different approach, a meeting was arranged with ROV.
ROV recommended using SCARAB units in conjunction with SCAVENGER to control the amount of water used to slurry the resin to the low point of the room. This involved mounting a spray nozzle to SCARAB’s z-axis boom. With its climbing capabilities this unit was able to access the south side of the room and move resin to SCAVENGER. To ensure a consistent slurry, SCAVENGER was equipped with a front mounted spray bar and placed near the room floor drain.
Commonwealth Edison’s Byron Station supplied two SCARAB robots. ROV supplied two operators to setup, perform maintenance, and operate the robots in the tight confines of the room. ROV setup the spray wand and camera on a special bracket of SCARAB 2 that provided a continuous picture of the wand action. The wand nozzle limited the maximum flow of water into the room to five gallons per minute.
The wand was attached to a heavy duty tilt fixture and a standard elbow for panning motion.
The small size of SCARAB 2 allowed the robot to gain access over, behind and between the obstacles in the room. The wand could be positioned to maximise the slurry while minimising the amount of water into the room. An adjustable pitch plough blade was attached to the front track axle. With this plough the more powerful 2A was able to clear a pathway into the room through the four inch deep resin. The blade was also useful in positioning the waste transfer hose, robot umbilicals, and assisting SCAVENGER into initial position.
SCAVENGER acted as the delivery platform for the waste transfer line. Its onboard lights and camera gave the operators a good indication of when a proper slurry was obtained. The waste transfer line was connected to an M-15 diaphragm pump which carried the slurry to the fillhead on top of the High Integrity Container.
A robot control station and resin process station were setup outside the temporary lead shield wall in a concrete shielded valve gallery. The High Integrity Container was placed inside the processing area.
The robots were driven into the room and a four inch berm was installed in the doorway. The berm was a precautionary measure to prevent resin from spilling outside of the room. Each robot was equipped with a Merlin Gerin telemetry dosimeter which monitored dose rate fields and the robots’ cumulative exposure.
The 2A entered the room first using its plough blade to move resin to the low point in the room. Once a path was cleared, SCAVENGER and SCARAB 2 entered and began transfer operations. With SCAVENGER near the floor drain, water was introduced to the room. The resin slowly began to take a more fluid form and flow toward SCAVENGER. As the resin level decreased, SCARAB 2 used its spray wand to “sweep” the resin toward SCAVENGER.
A successful robotic clean-up operation was completed. However a number of problems had to be solved along the way: SCARAB 2 lost the use of some tracks (in one case due to binding of resin in the drive mechanism) and its rear tilt function failed while climbing over a conduit; 2A experienced track problems; and SCAVENGER’s motor had to be replaced.
Overhead obstructions in one section prevented the SCARAB 2 robot from performing its task. As there was only a small amount of resin in that section, the team entered and with a hose washed the resin to the SCAVENGER.
The robots adsorbed 104.051 rem of exposure while personnel exposure was limited to 0.775 rem. The job was a success and a testament to technology and teamwork. During this process three different NRC inspections indicated no concerns or findings on the methodology.