This report provides an update on the materials performance criteria and methodology relevant to liquid metal reactors (LMRs), in particular, sodium cooled fast reactors. The report is the first deliverable (Level 3) in FY11 (M3A11AN04030303) under the work package A-11AN040303 "Materials Performance Criteria and Methodology" as part of Advanced Structural Materials Program for the Advanced Reactor Concepts.The overall objective of the Advanced Materials Performance Criteria and Methodology project is to evaluate the key requirements for the ASME Code qualification and the Nuclear Regulatory Commission (NRC) approval of advanced structural materials in support of the design and licensing of the liquid metal fast reactors. Advanced materials are a critical element in the development of fast reactor technologies. Enhanced materials performance not only improves safety margins and provides design flexibility but also is essential for the economics of future advanced fast reactors. Qualification and licensing of advanced materials are prominent needs for the development and implementation of advanced fast reactor technologies. Nuclear structural component designs in the U.S. comply with the ASME Boiler and Pressure Vessel (B&PV) Code Section III (Rules for Construction of Nuclear Facility Components) and the NRC grants licensing. As the LMR will operate at higher temperatures than the current light water reactors (LWRs), the design of elevated-temperature components must comply with ASME Section III Subsection NH (Class 1 Components in Elevated Temperature Service). A number of technical issues relevant to materials performance criteria and high temperature design methodology in the LMR were identified and presented in earlier reports [Natesan et al. 2008[Natesan et al. , 2009. A viable approach to resolve these issues and the R&D priority were also recommended. The development of mechanistically based creep-fatigue interaction models for life prediction and reliable data extrapolation was chosen to be the central focus in near-term efforts.Our current efforts focus on the creep-fatigue damage issue in high-strength ferriticmartensitic steels for two primary reasons. First, the current ASME design rule of bilinear damage summation puts severe limits of fatigue and creep loads for mod.9Cr-1Mo (G91) ferriticmartensitic steel, the lead structural material for fast reactors; secondly, the ferritic-martensitic steels behave fundamentally differently from austenitic stainless steels, for which the current ASME creep-fatigue design rules were developed. The unique deformation and damage characteristics in G91 steel, e.g. cyclic softening, degradation of creep and rupture strength during cyclic service, demands a new creep-fatigue design procedure that explicitly accounts for the material's unique creep-fatigue behavior. To support the development of predictive models and to resolve the over-conservative issue with the ASME design rule for G91 steel, we recovered stress relaxation data from thirteen creep-fatigue te...