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LFR plant assessment against a Fukushima-like scenario

LFR plant assessment against a Fukushima-like scenario. Technical Workshop to Review Safety and Design Aspects of European LFR Demonstrator (ALFRED), European LFR Industrial Plant (ELFR), and European Lead Cooled Training Reactor (ELECTRA)

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LFR plant assessment against a Fukushima-like scenario

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  1. LFR plant assessment against a Fukushima-like scenario Technical Workshop to Review Safety and Design Aspects of European LFR Demonstrator (ALFRED), European LFR Industrial Plant (ELFR), and European Lead Cooled Training Reactor (ELECTRA) Joint Research Centre, Institute for Energy and Transport, Petten, the Netherlands, 27–28 February 2013 Luigi Mansani Luigi.mansani@ann.ansaldo.it

  2. Definition of a Fukushima-like scenario • Seismic event • Fukushima Peak Ground  0.52g • Tsunami • 30 min after seismic events* • Assumed peak tsunami height of 9.0 m • Sustained flood level ≤ 5.2 m • Water steadily recedes over 5 hours * Fukushima was impacted by the tsunami 56 minutes after the initial seismic event.

  3. Seismic Design Basis and Seismic Margins • LFR designed for a Safe Shutdown Earthquake (SSE) of 0.3g (as requested by EUR) • 2D seismic isolators under the primary building adopted (application to LFR System is on going in SILER project) • All equipment required to mitigate accident for first 72 hours located within the Primary Building • A Seismic Margin Assessment (SMA) will be performed to evaluate, for each relevant System Structure and Component (SSC), sequence-level High Confidence, Low Probability of Failures (HCLPFs) • This analysis has been already performed for GEN III plants (AP1000, EPR), showing that the SSCs required for safe shutdown have a HCLPF > 0.50g

  4. Flooding Design Basis and Margins • LFR designed for a probable maximum flood level up to site grade elevation  flooding not exceeding plant grade would not affect safe shutdown components • In case of extreme events with flood greatly exceeding the basis: • Containment would remain unaffected  core protected • 24-hour & 72-Hour Safety-Related Batteries will be located in the Auxiliary Building at elevation above the plant grad with watertight doors  1E DC actuation power and 1E DC display power available • Even with a postulated loss of all AC and DC power, fail-safe nature of passive safety features results in their automatic actuation for decay heat removal

  5. Effect of Seismic Event • Impact on Structures and Components • All major site buildings remain structurally intact • 1E electrical / I&C equipment remains functional • Passive safety equipment remains functional • Immediate Effects • Loss of Offsite Power: Switchyard/Transmission Failures • Trip of Main Turbine/Generator: High Vibration • Conservatively assumed • All active systems fail • Standby Diesel Generators fail to start ( not necessary for safety systems and accident mitigation)

  6. Tsunami Effect • Containment Area  unaffected • Radwaste, Auxiliary, Turbine, Annex, and Diesel Buildings • Elevations below grade completely inundated • External tanks (water and fuel oil) not available • Standby Diesel Generators inoperable

  7. Accident Mitigation Short‐Term  prior to Tsunami (0‐30 minutes) • Reactor tripped • Due to LOOP, the coupling electromagnet is switch off and the absorber assemblies are free to rise up • Decay heat removal • DHR (Isolation Condenser) would be actuated by PMS • DC power for valves actuation provided by the Class 1E batteries • If the valves are not yet actuated before tsunami, the Air Operated Valves “fail open” on loss of DC power • After Tsunami • Operation of DHR not impacted by the flood for 72 hours

  8. Accident Mitigation • Long-Term Shutdown (Post-72 Hours Operation) • Supplemental resources required at 72 hours from prearranged sources, connected to built-in hook-ups • Small portable AC power units for ancillary loads only, to power portable pumps and PAMS I&C • Fire trucks or portable pumps, used to transfer water to Isolation Condenser tanks • Alternate water sources available at plant: Misc water tanks; dirty water / sea water permissible

  9. Ultimate Mitigation Measures • In the very unlikely scenario leading to the loss of all heat sinks with unavailability of both DHR systems, the heat can be extracted injecting water in the reactor cavity, between the reactor and safety vessels • In case of reactor vessel breach, the decay heat can still be removed by the same system that cools the concrete of cavity walls • Such very ultimate provisions are possible because Lead is chemically inert with air and water so that fire fighters or dedicated rescue troops can flood the reactor with water

  10. ALFRED Thank you for your attention

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