tional changes to reduce vulnerabilities to and the consequences of attacks. Some possible changes are listed in the classified annex. This list is by no means exhaustive, and an effective remedy can be applied at a particular reactor only after a careful analysis of risks and benefits, taking into account the comparative risk reduction that could be achieved by devoting resources to hardening nuclear plants versus other large industrial facilities.

Although the damage potential of RDDs is far less than that of stolen nuclear weapons, improvised nuclear explosives, or successful attacks on reactors, the terror/panic potential of RDDs warrants increased attention to the control and use of radiological sources by regulatory agencies and materials licensees.

Recommendation 2.11: The U.S. Nuclear Regulatory Commission and the states with agreements with that agency should tighten regulations for obtaining and possessing radiological sources that could be used in terrorist attacks (i.e., large sources containing long-lived isotopes), including requirements for securing and tracking these sources. Additionally, licensees possessing large sources should be encouraged to substitute nonradioactive sources (compact accelerators, electron beams, and x-ray generators) when economically feasible.

Other important counters to RDDs are public education, emergency responder training, and preparation of leaders to deal quickly and effectively with terrorist acts. As noted above, the likely aim of an RDD attack would be to spread fear and panic and cause disruption. Recovery would therefore depend on how such an attack is handled by first responders, political leaders, the media, and general members of the public.

In general, public fear of radiation and radioactive materials appears to be disproportionate to the actual hazards. Although hazardous at high doses, ionizing radiation is a weak carcinogen, and its effects on biological systems are better known than those of most, if not all, toxic chemicals. Federal standards that limit human exposure to environmental ionizing radiation, which are based on the linear, nonthreshold dose-response relationship,¹⁴ are conservative and protec-