THE BEHAVIORAL APPROACH TO SECURITY SYSTEMS PROVIDES A METHODOLOGY BY WHICH PHYSICAL SECURITY IS EXAMINED ACROSS A BROAD RANGE OF SUBJECTS THAT AFFECT THE SYSTEMS' SUCCESS OR FAILURE. COMBINING SYSTEMS ANALYSIS AND BEHAVIORAL APPROACHES, INTERESTED PERSONS CAN INVESTIGATE SECURITY SYSTEMS, SECURITY REQUIREMENTS, AND SYSTEM IMPLEMENTATION. THE APPROACH DEVELOPED FOR THE NUCLEAR REGULATORY COMMISSION'S SPECIAL SAFEGUARDS STUDY PROVIDED A THREAT ASSESSMENT BY ANSWERING QUESTIONS CONCERNING THE CHARACTERISTICS OF GROUPS VIEWING NUCLEAR INSTALLATIONS AS TARGETS. BECAUSE OF THE LIMITED EXPERIENCE WITH NUCLEAR TERRORISM, ANALYSIS OF THREATS TO NUCLEAR FACILITIES HAS CONSIDERED ANALOGOUS SITUATIONS SUCH AS BOMBINGS OF MICROWAVE TOWERS IN THE 1960'S AND 5,000 OTHER MALEVOLENT ACTS RECORDED IN A DATA BASE. THE FORMATION OF THE TERRORIST ACTIVITY DATA BASE PROVIDED EMPIRICAL SUPPORT TO THE THREAT ASSESSMENT, REMOVING MUCH OF THE SUBJECTIVITY FROM THE ANALYSIS. INQUIRY INTO THE TACTICS OF POSSIBLE NUCLEAR TERRORISM REVEALED THAT ATTACKS ON CRITICAL AREAS OF NUCLEAR PLANTS WOULD BE QUITE DIFFICULT, EVEN FOR DEDICATED PERSONNEL. AS THE OBJECTIVE OF A TERRORIST GROUP BECOMES MORE SEVERE IN TERMS OF SOCIAL CONSEQUENCES, THE TARGETING MOVES FROM DISCRIMINATE TO INDISCRIMINATE RANDOM VIOLENCE. ALTHOUGH VERY FEW GROUPS HAVE THE CAPABILITY TO SUCCESSFULLY ATTACK A NUCLEAR INSTALLATION, SIGNIFICANT THREATS COULD BE POSED BY ORGANIZED CRIMINALS AND PROFESSIONAL MILITARY PERSONNEL. REPETITIVE SECURITY MEASURES AND ELABORATE EQUIPMENT CONTROLS CAN HELP DETER NUCLEAR TERRORISM. TABULAR DATA ARE PROVIDED. (TWK)