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Nuclear Plant's Tough Floor Coating Minimizes Spread of Radioactive Contaminants

Mon, 07/09/2001 - 6:31am
Keeping concrete floors clean, is always an important maintenance function. In nuclear power plants, however, this function is especially important because it helps stop the spread of radioactive particles generated during maintenance on systems containing radioactive contamination. These contaminants accumulate and spread in nuclear facilities in much the same way dirt and dust spread through other industrial plants.

All nuclear plants have radiation safety programs established and monitored by the federal government. A thorough and detailed housekeeping program -including the use of materials and procedures to keep the floors clean - is a part of this program. When the floors in nuclear power plants are kept free of radioactive contamination, workers may freely access all areas of the plant without undergoing time-consuming decontamination procedures. As a result, keeping the main access area of the plant free of this low-level radioactive material is important for efficient plant operation and maintenance.

The Duane Arnold Energy Center (DAEC) in Palo, IA, is a 26-year-old nuclear facility utilizing one boiling-water reactor, rated at 535 mW. At full power, it produces enough electricity to serve 200,000 average homes. At the DAEC, both the turbine building and the reactor building are considered radiation exposure areas. Workers or visitors to these areas must walk through monitors upon leaving. When higher-than-acceptable levels of radiation are detected, individuals are required to follow decontamination procedures. The key to decontamination is to shower with tepid water so pores don't open or close. This allows radioactive particles to be rinsed off without being absorbed by the body.

Because contamination, like dirt, can be picked up by shoes and tracked, keeping floors clean is one of the ways radiation exposure, and the need for decontamination, are minimized at the DAEC. As in any industrial facility, however, floor maintenance is complicated by the damage caused when tools and equipment are dropped on the floor or dragged across it. At the DAEC, the reactor floor must also withstand the effects of steel-wheeled vehicles and the abrasion that results when forklifts transport heavy metal boxes containing items such as lead brackets, often weighing up to 6,000 lbs. Dirt and dust that lodges in chips, breaks or cracks in floor coatings may contain small amounts of radioactive contamination.

As a result, a properly specified concrete floor coating system is necessary to protect the underlying concrete substrate and to provide a smooth surface that is easy to clean. When the DAEC decided to refinish its floors five years ago, it chose two-part epoxy coating products for the reactor building, turbine building and pump house floors: AromorSeal 33 Primer Sealer and AromorSeal 650 Self-Leveling Recoatable Epoxy, both manufactured by Cleveland, OH-based Sherwin-Williams Co. The coatings provide a high-gloss, hygienic surface that is hard-wearing and durable. The abrasion-resistant topcoat offers self-leveling properties as well as chemical- and impact-resistance.

Because the 5,000-sq.-ft reactor building could not be coated at one time, the floor was divided into 500-sq.-ft. patches. Seams resulted where one pour butted up to another pour, which were feathered to ensure a smooth transition, says Eilers. "Rough edges were ground out," says Dave Eilers, decontamination coordinator at DAEC, "then a second thin coat of ArmorSeal 650 was applied to the seam. We've become quite experienced at pouring seams." The floor was painted by DAEC's in-house maintenance staff.

Regular floor maintenance includes mopping with water once a week, "then dry mopping using oil-impregnated wipes twice a week," says Eilers. During scheduled plant shutdowns or "outages," Eilers says the entire 5,000 sq. ft. of the first floor of the reactor building is wet-mopped at least twice a day, and dry mopping with the oil-impregnated wipes occurs four or five times daily. No harsh abrasives are used on the floor and all water is recycled for re-use by the plant. Eilers says the ArmorSeal floor-coating system has proven easy to clean. "Our plant housekeeping work force said maintaining the floors was significantly easier than during previous outages."

The coating system is now being used at the DAEC for the turbine building, the reactor building and the pump house. Historically, these areas are repainted every 18 to 36 months. "We are satisfied that with this coating system, we will not have to recoat these areas for many years," says Eilers.

The Sherwin-Williams Co., 101-T Prospect Ave. N.W., Cleveland, OH 44115; 216-566-2000.

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