Safety focuses on unintended conditions or events leading to radiological releases from authorized activities. It relates mainly to intrinsic problems or hazards.
Security focuses on the intentional misuse of nuclear or other radioactive materials by non-state elements to cause harm. It relates mainly to external threats to materials or facilities.
Safeguards focus on restraining activities by states that could lead to acquisition of nuclear weapons. It concerns mainly materials and equipment in relation to rogue governments.