Florida Power and Light said that in 1982 it had mistakenly made a shipment to a landfill, but the documents appear to show numerous shipments to multiple locations. In addition, while the company conducted a survey and cleanup in the one known location, it found only one kind of radioactive material, and nuclear experts involved in the lawsuits say there must have been other isotopes for which no tests were conducted. The overall level of contamination is difficult to determine.

Plant workers used a sink to wash mops, rags and other heavily contaminated materials, believing that the drain was connected to the plant's radioactive waste system, but instead it drained into a sanitary sewage system, according to the documents. The contaminants were then hauled away with sludge. According to documents cited by the plaintiffs, at one point the plant in St. Lucie County was shipping to regular landfills materials that were 10 times as radioactive as what it was shipping to a low-level waste dump.

A spokeswoman for Florida Power and Light said the company had mistakenly made two such shipments in the early 80's, but had disclosed it at the time and removed the waste afterward.

"It's a 23-year-old event," said Rachel Scott, the spokeswoman. "It was thoroughly investigated at the time by both the Nuclear Regulatory Commission and the Florida Department of Health, who determined that there was no health issue."

Samples were tested in a lab and only one isotope, cobalt-60, was found, Ms. Scott said. Cobalt-60 is a material that becomes radioactive when neutrons from the reactor core are captured by atoms of metal. But the plaintiffs say records show that at the time St. Lucie's fuel was leaking fission products, like strontium and cesium, into the cooling water and thus contaminating the plant. Such contaminants would have been present in the mops and similar materials, they argue.

According to documents obtained by the plaintiffs, however, a week after the cleanup was completed at a dump site the company found contamination at a level 20 times what was proposed by the State of Florida, and thousands of times higher than what the Environmental Protection Agency allowed for agricultural land; the surrounding area is used for cattle and citrus.

A state document quoted by the plaintiffs says that some contaminated material was transported to a "cow pasture." Another state document refers to daily sludge being "removed by Portolet to unknown site."

The company has concealed the shipments from the Nuclear Regulatory Commission, according to the lawsuits.

The parents of Zachary Finestone, an 11-year-old who grew up in the area and was diagnosed with cancer in March 2000, filed suit in Federal District Court for the Southern District of Florida in 2003. The case is scheduled to go to trial in January.

The parents of Ashton Lowe, who had brain cancer when he died at age 13 in May 2001, filed suit in 2003 in the same court. That case is scheduled for trial early next year.

The parents' lawyer, Nancy La Vista, said she planned to argue that tests of the boys' baby teeth showed abnormally high levels of radioactive strontium, which is produced when atoms are split and that when ingested binds to human bones. Older people have strontium in their bones that was created from atmospheric nuclear testing. But, Ms. La Vista said, "These kids were all born after Chernobyl, after Three Mile Island, and after atmospheric testing."