From the Introduction: "In recent years, increases both in the total volume of terrorist incidents worldwide and the casualties resulting from such incidents have prompted renewed concern that terrorists might attack a nuclear facility. Among the reasons cited to explain the likelihood of such an attack is that as terrorism has become more frequent, public attention is not so readily claimed as it once was. Terrorists, therefore, have been forced to undertake more spectacular and, unfortunately, bloodier deeds. Accordingly, actions involving nuclear material or weapons may have become more attractive to some terrorist groups. In addition, state-sponsorship of terrorism, that is, support of terrorist organizations by foreign governments, has also increased significantly, providing terrorists with far greater capabilities than they have had in the past, while eliminating some of their constraints. As a result of these developments, in 1986 the Department of Energy (DOE) reviewed its adversary characterization and threat definition guidelines then in force and decided to place greater emphasis on guard weaponry, training, and tactical response exercises and to upgrade some physical security measures."
Defense Technical Information Center (DTIC): https://discover.dtic.mil/