Workers on Pennsylvania State University’s main campus were continuing efforts today to find and plug a leak discovered last week in the cooling pool of the university’s Breazeale Nuclear Reactor, which is used for research. The university and state health officials have said the water possesses a very slight radioactivity and poses no safety threat.

The university shut down the reactor after staff members determined that the 71,000-gallon pool was losing about 10 gallons per hour, the university said in a statement. The water is flowing into the ground beneath the reactor building, said a university spokeswoman, A’ndrea Elyse Messer.

The concentration of radioactivity in the water is 0.03 microcuries per liter, she said. That level is well below the Nuclear Regulatory Commission’s maximum permissible amount that can be released. If that level occurred in drinking water, it would add minimally to the background amount of radiation to which people living in central Pennsylvania are normally exposed from a variety of sources, Ms. Messer said.

The university has so far failed to find the source of the leak with detection devices, she said. Workers have walled off and drained half of the pool, using an existing dividing barrier, and will apply epoxy to the pool’s walls to try to plug the leak, she said.

The university’s 1,000-kilowatt reactor uses low-grade uranium, unlike some college facilities that use high-grade fuel. —Jeffrey Brainard