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The NRC staff is developing a proposed rule to amend the Commission's regulations to revise the acceptance criteria for the emergency core cooling system (ECCS) for light-water nuclear power reactors. The proposed ECCS acceptance criteria would be performance-based, and reflect recent research findings which identified new embrittlement mechanisms for fuel rods with zirconium alloy cladding under loss-of-coolant accident conditions. The proposed rule would also address two petitions for rulemaking by establishing requirements applicable to all fuel types and cladding materials, and requiring the consideration of crud, oxide deposits, and hydrogen content in zirconium-based alloy fuel cladding. Further, the proposed rule would contain a provision allowing entities to use a risk-informed alternative to address the effects of debris during the long-term period.