N.C. State University officials say they have patched up a leak that shut down the campus nuclear reactor nearly three weeks ago.

The small research reactor had been leaking about 10 gallons of water an hour from a 15,600-gallon pool used to cool the superheated reactor core and radioactive fuel rods. Total leakage came to about 3,500 gallons.

The leaking water was tainted with radioactivity but posed no public health risk, university officials said. The water was presumed to flow through the Burlington Nuclear Engineering Laboratory on campus and into the ground below.

North Carolina, which relies on nuclear power for nearly half its electricity, is home to some of the nation's highest concentrations of radioactive waste taken from nuclear plants and kept in pools to prevent overheating.

This state's accumulated nuclear waste ranks fourth in the nation by volume, according to a report issued today by the Institute for Policy Studies, a left-leaning advocacy group in Washington, D.C.

The waste has been stored for decades at Progress Energy's Shearon Harris nuclear plant in southwestern Wake County, Brunswick plant near Wilmington and Duke Energy's McGuire plant near Charlotte.

Shearon Harris, less than 25 miles from Raleigh, stores overflow waste from the company's Brunswick plant and H.B. Robinson plant in South Carolina. The Harris plant ranks 22nd nationwide for total nuclear waste.

The first air samples collected by state authorities show that radiation wafting from Japan is at barely detectible levels and poses no threat to public safety in North Carolina.

Officials at the Radiation Protection Section expected infinitesimal increases in background radiation after Progress Energy and Duke Energy reported slight increases last week during routine monitoring at their nuclear plants in the Carolinas and in Florida.

State officials said today that initial air sampling confirms their expectations. The Radiation Protection Section, within the N.C. Department of Environmental and Natural Resources, analyzed four air samples taken Sunday and Tuesday.

The radioactive fallout is the result of malfunctioning Japanese reactors that were damaged by a tsunami earlier this month. The Japanese plants have lost emergency cooling equipment, resulting in melted nuclear fuel and radioactive releases from several reactors and spent fuel pools.

Local health officials in a four-county area near the Shearon Harris nuclear power plant will be distributing potassium iodide pills to residents living within 10 miles of the nuclear plant.

Potassium iodide pills, known as KI pills, are an over-the-counter medication that can reduce the risk of thyroid cancer from radioactive exposure. The pills are being distributed free of charge to help prevent health risks during a nuclear accident.

The pills are not to be ingested unless residents are directed to take the pills during an emergency. Officials warn that the KI pills are not an alternative for evacuation during a nuclear accident.

Officials in Wake, Chatham, Harnett and Lee counties will be giving away the pills at local public schools and other locations on May 15. Some will also distribute the pills on May 22.

Local health officials began distributing the pills in 2002 within the nuclear plant's 10-mile Emergency Planning Zone. The cost of the pills is covered by the U.S. Nuclear Regulatory Commission.

About 74,000 people live within 10 miles of the nuclear plant, up from about 15,000 when the plant began operating in 1986.