Summary: Pursuant to a congressional request, GAO reviewed the Department of Energy's (DOE) efforts to comply with the 1991 National Defense Authorization Act's requirements governing radioactive waste tank storage and safety. GAO noted that: (1) some of the act's provisions have been difficult to implement; (2) DOE has prepared safety plans for problem tanks, reported its tank safety improvement plans to Congress, and implemented procedures to prohibit the addition of further wastes to tanks, but identification and monitoring of problem tanks continues to be difficult; (3) other day-to-day tank facility operations problems make DOE application of safety controls difficult; (4) one problem of particular concern is that tank flammability safety standards have not been enforced; (5) in 1995, DOE reported 25 safety-related incidents involving tank facility operations; (6) DOE facility managers have directed the contractor to take steps to improve the conduct of facility operations; and (7) it is too soon to determine whether DOE and contractor efforts will be successful.