What is the first action taken after a nuclear security breach is detected?

The first action taken after a nuclear security breach is the immediate lockdown of the facility. Locking down the facility serves as a critical initial measure to ensure the safety and security of the nuclear assets, personnel, and surrounding community. This action helps to prevent further unauthorized access and allows for the establishment of control over the situation.

By securing the facility, response teams can assess the situation more effectively, manage any potential threats, and initiate emergency protocols. This immediate response is vital as it sets the stage for subsequent actions, such as investigations and assessments, while ensuring that no additional risk is posed to sensitive areas or materials.

Other options, such as investigating potential damage, notifying the media, or assessing personnel response, are essential actions in the overall response plan but are not the first measures taken after a breach is detected. They typically follow the lockdown, which prioritizes immediate containment and security.