Abstract The fundamental aim of an efficient regulatory emergency preparedness and response system is to provide sustained emergency readiness and to prevent emergency situations and accidents. But when an event occurs, the regulatory mission is to mitigate consequences and to protect people and the environment against nuclear and radiological damage. The regulatory emergency response system, which would be activated in the case of a nuclear and/or radiological emergency and release of radioactivity to the environment, is an important element of a comprehensive national regulatory system of nuclear and radiation safety. In the past, national emergency systems explicitly did not include vulnerability assessments of the critical nuclear infrastructure as an important part of a comprehensive preparedness framework. But after the huge terrorist attack on 11/09/2001, decision-makers became aware that critical nuclear infrastructure could also be an attractive target to terrorism, with the purpose of using the physical and radioactive properties of the nuclear material to cause mass casualties, property damage, and detrimental economic and/or environmental impacts. The necessity to evaluate critical nuclear infrastructure vulnerability to threats like human errors, terrorist attacks and natural disasters, as well as preparation of emergency response plans with estimation of optimized costs, are of vital importance for assurance of safe nuclear facilities operation and national security. In this paper presented new methodology and solution methods for vulnerability assessment can help the overall national energy sector to identify and understand the terrorist threats to and vulnerabilities of its critical infrastructure. Moreover, adopted methodology could help national regulators and agencies to develop and implement a vulnerability awareness and education programs for their critical assets to enhance the security and a safe operation of the entire energy infrastructure. New methods can also assist nuclear power plants to develop, validate, and disseminate assessment and surveys of new efficient countermeasures. Consequently, concise description of developed new quantitative method and adapted new methodology for nuclear regulatory vulnerability assessment of nuclear power plants are presented.