Nuclear Power Plants, Risk Assessment, Nuclear Reactors, Safety Measures, Industrial Safety, Probabilistic Safety Assessment, PSA, Multi Unit Perspective, Lessons Learned, Fukushima Daiichi Accident, Multiple Reactor Units, Methodology, Multi Unit PSA, MUPSA, Site Level Risk Metrics, Technical Approach, External Events, Tsunami Vulnerability, Seismic, Fire, Floods, Site Evaluation, Single Reactor Unit, External Hazards, Internal Hazards, Deterministic Evaluation Models, Good Practices, System Models, Event Sequence Analysis, Radiological Consequences, Results, Documentation, Core Damage Frequency, CDF, Loss of Off-Site Power, OECD, Model, Terminology, Initiating Events, Human Errors, Frequency Quantification, Risk Integration, Multi Unit Sites, Deterministic Safety Analyses, System Models, Risk Assessment, Correlation