By Brian Schimmoller, Contributing Editor
Safe, effective nuclear plant operation and maintenance depends on thousands of little things going right. Sustained high performance depends on the united actions of scores of people, processes, and equipment. Sure, big things come along once in a while that can have an outsized impact – condition-based maintenance and digital instrumentation and control, for example – but it’s the little things that add up to keep nuclear plant reliability and capacity factors high.
Entergy recently adapted a little thing (with a celestial moniker) from another industry to enhance safety, reduce dose, and reduce the time needed for certain maintenance tasks. During recent refueling outages at Units 1 and 2 of its Arkansas Nuclear One nuclear plant, Entergy deployed portable, lightweight construction platforms called Angel Wings to support various inspection, repair, and “hot work” activities such as welding and cutting.
Used in the construction industry, Angel Wings provide a portable work platform that can be installed in minutes without special tools, eliminating or dramatically reducing the amount of scaffolding required. Each Angel Wing unit is made from an aluminum alloy, weighs about 40 pounds, and can support a 440-pound load with a 4:1 safety factor. Moreover, the platforms have been approved for industrial use by the Occupational Safety and Health Administration.
The Angel Wings that Entergy employed at Arkansas Unit One attach to I-beams using a hook and wing nut assembly, but other versions are available, such as for attaching to concrete walls. For easy handling and transportation, the units fold flat and include a support bar that can be used as a handle. At Arkansas Nuclear One, the Angel Wings supported a reactor coolant pump and motor replacement project. One example of its efficiency involved the removal and installation of the whip restraint girder, which had to be removed to access the pump. The whip restraint girder provides structural support to keep the reactor coolant pumps secure and in place in the event of a loss-of-coolant accident.
A traditional scaffolding approach would have involved erecting scaffold structures on both ends of the girder to access the bolting. After removing the bolts, Entergy would then have had to dismantle the scaffolding so the girder could be removed, and then the process would have been reversed to reinstall the girder. “We would have had to install, remove, and re-install about 40 feet of scaffolding to perform this task,” said Troy Hollowoa, Entergy project manager and team lead. “With the Angel Wings, the workers lowered the Angel Wings to the girder, where they were able to secure the platforms and get to work removing the bolts.”
Entergy realized significant benefits from the Angel Wings platforms. By eliminating 40 scaffolding tasks – and the time and dose associated with erecting, inspecting, and dismantling the scaffolding – Arkansas Nuclear One required 1400 fewer man-hours in the reactor building and achieved an 800 mRem savings in dose. Entergy calculated one-time economic savings of $52,000, based on an $8,000 capital cost for the Angel Wings units and $60,000 in avoided labor costs. Recurring economic savings are estimated at about $30,000 per outage, or $450,000 over the remaining years of the plant license.
The maintenance workers also have acknowledged benefits from the Angel Wings. Welders, for example, have indicated that they feel more comfortable working 30 to 40 feet off the ground on the Angel Wings platform than on conventional scaffolding.
Entergy currently has eight Angel Wings platforms to support maintenance activities at Arkansas Nuclear One. Six have been used to date inside containment, with two in reserve. In between uses, the units are stored in special SeaLand containers designed to store contaminated tooling and equipment in compliance with safety and quality standards.
As a new type of work platform for nuclear plant applications, Entergy had to complete a Job Safety Hazard Analysis to ensure the Angel Wings were compliant with nuclear industry safety standards. “The use of such platform systems was not envisioned or addressed in our industrial safety manuals,” said Hollowoa, “so we had to obtain approval for a deviation from our safety manual. That was successful, but to ensure all parties were comfortable with their use, we also bought one Angel Wing unit in advance and conducted a demonstration outside of containment.”
Entergy is broadening the use of Angel Wings across its fleet. The Waterford Plant will be employing several of the portable work platforms during its fall outage to support a reactor coolant pump motor change-out project and the steam generator replacement.