A 2003 study, led by Robert Alvarez, a former official at the United States Department of Energy, estimated that a worse-case terrorist attack could drain cooling pools, resulting in spent fuel rods heating up and possibly combusting. That, in turn, would cause substantial amounts of radioactive material to be released if containment structures are breached, potentially resulting in an area of contamination greater than that caused by the Chernobyl accident in 1986.