September-October 2017 NPJ

44 NuclearPlantJournal.com Nuclear Plant Journal, September-October 2017 High-pressure washing is typically done from the pool edge using a high pressure(i.e.3000psi)handheldgunorwand which is held close to the decontamination surface. This method is quite widespread throughout the US nuclear industry, but it has disadvantages: the addition of water in the reactor cavity has the potential to alter chemistry, particularly impacting boron concentration in PWR plants, and has the potential to spread contaminants or create airborne activity. Similar to high-pressure washing, hydrolasing also uses water to blast the cavity surfaces, except with much greater force. Using the greater force of the water jet, hydrolasing delivers decontamination results using less water, yet it still has the potential to impact boron concentrations in PWRs. The powerful jet can also cause personnel injury if used improperly. Most automated decontamination systems perform reliable decontamination and require fewer staff resources than manual methods, resulting in greatly reduced personnel dose exposure. However, these tools only work on flat surfaces or require the constant use of an auxiliary hook, boom, rail, or primary overhead crane while performing decontamination. These tools also provide inconsistent decon results. Some of the tools require modifying the tool outside of the pool in order to switch from cleaning the floor to walls, and vice versa, and the brush change- out can be time consuming as well. The underwater robotic decon solution developed by Diakont presents a substantial improvement over historical cavity decon methods because it can reduce personnel dose exposure, reduce radwaste, doesn’t impact plant chemistry, doesn’t risk inadvertently spreading contamination, and eliminates the risk of personnel injury and component damage associated with hydrolasing. Most importantly, by performing decontamination robotically while the cavities are flooded and in parallel with fuel movement and other activities, critical path schedule duration can be reduced. The self-propelled Remotely Operated Vehicle (ROV) -crawler solution does not require the constant use of bridge or crane after deployment. Unlike other robotic decon tools, this system is simple to use and plant personnel can be trained to operate it without the need to bring in outside vendors. Remotely Operated, Self-Propelled Solution The robotic decontamination tool deployed for FENOC is a hybrid ROV- crawler platform equipped with an integrated cleaning system. It operates and transitions freely between ROV “flying” mode, and “crawler” mode (for any orientation) with no physical adjustments required to the system. To accomplish this, the tool utilizes a flow- less vortex generator on its chassis that creates up to 60 pounds of suction force to adhere to flat and curved, horizontal and vertical surfaces, including interferences and seams. The crawler system is driven in a simple tank-like “skid steer” fashion and has 26 pounds of traction drive force that provides full control in flow conditions, as well as appropriate umbilical movement. When in ROV mode, six (6) identical brushless DC vectored and vertical thrusters provide versatile maneuverability and positioning. The tool’s cleaning system is comprised of a shroud enclosing an integrated, fixed-force rotating cylindrical brush assembly connected to an existing vacuum submerged in the cavity, which filters the contaminated particulates dislodged by the brush. Rotational speed and downforce are adjustable for optimal performance. The system uses off-the- shelf brushes to keep costs down and the brushes can be exchanged for various abrasive grit sizes depending on the surface and level of cleaning required. The decon tool also includes independent lighting and multiple camera systems for appropriate situational awareness and navigation. The entire tool utilizes mature, nuclear-proven, and foreign material exclusion (FME)- compliant subassemblies. Robotic Underwater Decontamination Procedure Before entering containment, the Diakont field engineer team completed an FME pre-check on the decon tooling and cables in a staging area. Once completed, the team set up the ROV-crawler control station on the refueling floor away from the edge of the refueling cavity, in a lower-dose space separate from other outage operations. After a complete system function check, the decon tool was connected to the vacuum pump in the cavity. The tool was then deployed into the water using the overhead crane, taking precaution to minimize disruption to the water surface. The team then cleared the shroud cavity of air bubbles by cycling the vacuum pump power, such that the vehicle buoyancy was appropriately balanced. The final step was the deployment of a high definition camera into the cavity to monitor decon operations and umbilical location from a bird’s eye perspective, to support the operator’s situational awareness. The robotics operator navigated the decon tool in “flying” mode close to the wall and positioned the tool so either the port or starboard sidewas close to thewall. Then the operator rotated the tool until the track wheels touched the cavity wall and activated the flow-less vortex generator to adhere to the wall. The robotics operator next initiated the brush operation and performed surface cleaning by traversing Reducing Dose... ( Continued from page 43) Tool in swim mode, travelling to the next area for decontamination.