ALBUQUERQUE, N.M. (AP) — Thirteen employees who were exposed to radiation during a leak at the nation’s only underground nuclear waste dump aren’t likely to experience any health effects, federal officials said Wednesday.

The U.S. Department of Energy confirmed last week that 13 workers were exposed when radiation leaked from the Waste Isolation Pilot Plant. Testing on follow-up samples taken from the employees came back negative for plutonium and americium, the two radioactive isotopes that were detected in preliminary tests.