Air samples taken before and after the repair showed no toxic hydrogen fluoride at the Paducah plant.
By Joe Walker email@example.com
"There was some material in the plug hole and on the ground near the plug, but we don't have any reason to believe there was any significant release to the atmosphere," said Greg Cook, spokesman for plant environmental contractor Bechtel Jacobs. "We think the threads of the plug hole corroded over time. We believe what is missing from the cylinder can be measured in grams."
During routine inspections at 12:30 p.m., four Bechtel Jacobs employees discovered the plug lying on the ground directly below the hole. The area was evacuated, and a response team wearing protective equipment was sent to patch the opening, which may have existed for several months.
Air samples taken before and after the repair showed no toxic hydrogen fluoride, formed when the cylinder contents contact air and moisture, Cook said. The material, resembling green rock salt, contains low-level radiation and toxins.
He said he was unaware if radiation samples were taken at the cylinder, but urine tests were run on the inspection workers for toxins and radiation. Test results on the personnel, who were not wearing protective equipment, were pending, Cook said.
The cylinder, originally containing about 284 pounds of spent uranium hexafluoride, or UF6, is about 50 years old and among 58 smaller cylinders stored outside on racks a few inches high. Cook said the cylinders are a foot in diameter and 53 inches long, much smaller than the roughly 37,000 large depleted UF6 cylinders stored at the plant.
Although the small cylinders are nickel and "in good condition" considering their age, their plugs and holes are made of corrosive metal, Cook said. Inspectors believe the plug gradually loosened from rusty threads and fell to the ground.
"There is no indication the plug blew out," Cook said. "It's directly where you would have expected to see it if it had simply dropped to the ground."
Cook said inspectors think air gradually seeped around the loosened plug, causing the cylinder's contents to solidify.
"So it tends to heal itself. It creates almost a scab of UF6 where air penetrates," he said. "That helps to retard very slow leakage."
Cook said the small cylinders are inspected every four years, the last being in June 1996, when the plug was intact. He said metal skirts on the ends of the cylinders were cleaned in September.
"We don't believe the plug was missing at that point," Cook said. "It's highly unlikely they could have cleaned the skirt ends and not noticed the plug was missing. We believe this to have occurred since the skirts were cleaned in September 1999."
On Friday, inspectors raised concerns that a second small cylinder, containing about 11 pounds of UF6, had a hole on each side of a valve on the opposite end from the plug. Cook said the holes appeared to have been machined and were completely through the metal, but inspectors saw no leakage or material outside the cylinder.
Cook said the second cylinder, whose holes were patched, had the same inspection and maintenance schedule as the one that leaked. The overall inspection was completed Friday, and no other cylinders showed problems, he said.
"The release of the whole quantity of 11 pounds would not create a health and safety hazard off-site," Cook said. "But the obvious question is, what happened? Either it wasn't noticed previously or it wasn't open previously. We don't have the answer to that."
Asked if the trouble would prompt more frequent and rigorous inspections, Cook said, "We haven't gotten that far yet. We've been following up with this and completing the inspections."
The age, condition and safety of the thousands of cylinders have come under increasing scrutiny by Congress, citizens' groups and the atomic workers' union. Federal lawmakers from Kentucky have demanded that the U.S. Department of Energy, which owns the plant, move faster with a congressionally mandated plan to build a facility to convert the contents into something safer that might be commercially used.
Recently, DOE officials blamed the delay on determining how many of the cylinders are contaminated with plutonium and other highly radioactive substances. The contamination came from uranium in spent reactor fuel recycled at the plant during the Cold War years.
Although DOE first said the contamination was limited to cylinders stored before 1980, recent findings show some cylinders stored in the ’80s and ’90s have traces of highly radioactive substances called transuranics. If ingested in high enough amounts, the material can be deadly.
Asked if the small cylinders have transuranics, Cook said, "We don't know. This cylinder was used more than one time. We have a history, but we haven't had an opportunity to put that together."
He said transuranics will be included in a chemical and radiological analysis of the material on the ground below the cylinder that leaked.