A U.S. Energy Dept. facility in Idaho that has stored melted fuel from the Three Mile Island nuclear plant since 1999 has not done enough to address crumbling concrete modules encasing radioactive material, says the U.S. Nuclear Regulatory Commission. The facility holds damaged fuel from TMI unit 2, whose partial meltdown in 1979 resulted in the worst nuclear accident in U.S. history. The concrete modules are “showing significant cracking and degradation,” though they were built to last 50 years, NRC says. DOE has determined the problem is worsening, NRC says. The cracks have no impact on the safe storage of the spent fuel, says DOE.