Executive SummaryThe safeguards system of the International Atomic Energy Agency (IAEA) is intended to provide the international community with credible assurance that a State is fulfilling its safeguards obligations. Effective and cost-efficient IAEA safeguards at the facility level are, and will remain, an important element of IAEA safeguards as those safeguards evolve towards a "State-Level approach." The Safeguards by Design (SBD) concept can facilitate the implementation of these effective and costefficient facility-level safeguards (Bjornard, et al. 2009a(Bjornard, et al. , 2009b IAEA, 1998;Wonder & Hockert, 2011). This report, sponsored by the National Nuclear Security Administration's Office of Nuclear Safeguards and Security, introduces a methodology intended to ensure that the diverse approaches to Safeguards by Design can be effectively integrated and consistently used to cost effectively enhance the application of international safeguards.The Facility Safeguardability Assessment (FSA) methodology introduced here supports SBD in three areas:1. It supports effective operator/designer engagement in the necessary interactions between the IAEA, the State regulator, and the owner/designer of a new or modified facility at the stages where the designer's SBD efforts can be applied most productively.2. It presents a screening tool intended to help the designer identify potential safeguard issues for a) design changes to existing facilities, b) new facilities similar to existing facilities with established IAEA safeguards approaches, and c) new designs.3. It provides a structured framework for the application of the SBD tools such as SBD good practice guides, design guidance, and safeguardability evaluation methods (called here the FSA toolkit). This toolkit can be used by the owner/designer to both identify potential safeguards issues and to develop solutions for potential safeguards issues during the interactions with the State regulator and IAEA.The majority of new facilities are expected to reflect modest design evolution from existing safeguarded facilities. Therefore, a major focus of the FSA process is efficiently assessing the impact of such an evolution in facility or process design upon required safeguards-related design features. The more a design evolves or differs from the design of similar-type facilities, the greater the probability that new safeguards issues will be introduced, and the more challenging SBD becomes. FSA can help the designer anticipate where new safeguards challenges are posed, and the size of the gap between established safeguards approaches and safeguards tools and measures at existing facilities of the same type and what the IAEA might require for the new design. For first-of-a-kind facilities or research facilities that involve previously unused processes or technologies, comparison with previously required safeguard design features may not be sufficient. Accordingly, a comprehensive vulnerability or path assessment may be required to adequately identify and assess new safeg...