Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants (2014) / Chapter Skim
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3 Great East Japan Earthquake and Tsunami and Impacts on Japanese Nuclear Plants
3 Great East Japan Earthquake and Tsunami and Impacts on Japanese Nuclear Plants
Pages 72-100
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From page 72... ...
This chapter is organized into five sections. • Section 3.1 describes the Great East Japan Earthquake and tsunami.
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. When the seismic moment is known from the analysis of seismic and geodetic data, the calculation of a moment magnitude is straightforward.6 Estimates of the moment magnitude were largely 9.0 (e.g., Lay and Kanamori, 2011; Frankel, 2013b; Maeda et al., 2013; Satake et al., 2013; Sugawara et al., 2013; Yamazaki et al., 2013)
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74 LESSONS LEARNED FROM THE FUKUSHIMA NUCLEAR ACCIDENT Tsugaru Sea of kaikyo Japan Tokyo t ai tr S fe rry ea or K Philippine Sea Higashidori NPS N Aomori Akita Iwate Onagawa NPS Miyagi Yamagata Fukushima Fukushima Daiichi NPS Fukushima Daini NPS Ibaraki Tokai Daini PS Tokyo km 0 100 200 miles 0 100 200 FIGURE 3.1 Map of the Tohoku region of Japan (shaded area in inset) showing the hypocenter of the Great East Japan Earthquake and the locations of the five nuclear plants discussed in this chapter.
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Yue and Lay (2013) inverted teleseismic P-wave, shortperiod Rayleigh waves, permanent GPS stations on Japan, and seafloor displacements to find that the peak slip at the trench was 60 m and slip at the hypocenter was 25 m (Lay et al., 2013)
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. The earthquake was accompanied by large crustal displacements of onshore regions in northern Japan (Figure 3.4)
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in cm/s2 for the Great East Japan Earthquake and tsunami (divide by 100 to obtain accelerations in m/s2, where g = 9.8 m/s2)
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displacements of the crust resulting from the March 11, 2011, Great East Japan Earthquake. The movements shown are relative to a reference point located at Ishinomaki City (Miyagi Prefecture)
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3.1.5 Discussion The magnitude of the Great East Japan Earthquake exceeded the thenexisting maximum estimated earthquake magnitude for the Tohoku Region (Kagan and Jackson, 2013)
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The approximate locations of the five nuclear plants are shown on the figure. SOURCE: 2011 Tohoku Earthquake Tsunami Joint Survey Group.
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noted that the 2009 seismic hazard map for Japan (March 2009) reported a 30-40 percent chance of a rupture in the region where the Great East Japan Earthquake occurred in the next decade and a 60-70 percent chance in the next 20 years.
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at Plant of Earthquake Higashidori Nuclear Power Station 300 1 0 Onagawa Nuclear Power Station 80 3 3 Fukushima Daiichi Nuclear Power 150 6 3 Station Fukushima Daini Nuclear Power 160 4 4 Station Tokai Daini Power Station 260 1 1 NOTE: Distances estimated from U.S. Geological Survey–determined location for earthquake epicenter (38.297°N, 142.372°E)
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Four of the five offsite AC power lines were tripped by the earthquake, cutting most offsite AC power. Emergency diesel generators started up after the loss of offsite power, but two of the five operating generators tripped after the tsunami flooded their cooling-water pumps.
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3 (Units 1-4) 4 Tokai Daini 5.4 8 6.1 8 NOTE: Elevations are relative to the Onahama Peil (Onahama Port Construction Standard Surface)
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Figure 3-6 Among the more significant damage reported was an electrical short in a switchgear panel, which caused a fire, the toppling of an oil tank, and flooding in the basement of the Unit 2 reactor building, which submerged a heat exchanger, flooded cooling-water pumps, and resulted in the loss of function of two emergency diesel generators, as noted previously. 3.2.3 Fukushima Daiichi Nuclear Power Station The Fukushima Daiichi Nuclear Power Station is located in east-central Fukushima Prefecture (Figure 3.1; see also Figure 1.2 in Chapter 1)
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The floodwater damaged pumps, electrical distribution panels, backup batteries, and diesel generators, causing loss of most plant power and ultimate heat sink.17 In the 72 hours following loss of power, the Unit 1, 2, and 3 reactors melted down, releasing hydrogen and radioactive materials. Hydrogen explosions in the Unit 1, 3, and 4 reactor buildings caused severe structural damage (Figure 3.9)
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. FIGURE 3.8 Photo showing flooding at the Fukushima Daiichi plant on the north side of Radiation Waste Treatment Facility on March 11, 2011.
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3.2.4 Fukushima Daini Nuclear Power Station The Fukushima Daini Nuclear Power Station is also located in eastcentral Fukushima Prefecture, about 12 km south of the Fukushima Daiichi
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It shut down automatically. The earthquake cut all offsite AC power, but emergency diesel generators supplied backup power until offsite power was restored on March 13.
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However, the main area of the site was not flooded. 3.3 DIFFERENCES IN PLANT IMPACTS The March 11, 2011, earthquake and tsunami had markedly different impacts on the five nuclear plants located along the northeast coast of Japan.
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The Japanese Prime Minister is responsible for notifying prefecture governors, mayors of municipalities, and the public that a nuclear emergency has occurred. but their emergency diesel generators operated as designed to provide the backup power needed to bring the reactors to cold shutdown.
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FIGURE 3.11 Photo showing flooding of the Fukushima Daini plant adjacent to Unit 1 during the March 11, 2011, tsunami. Flooding depth was between 2-3 m.
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• Seawater pump motors, which are used to move decay heat from the reactors to the Pacific Ocean, were not elevated sufficiently to protect them from flooding. As noted previously, the tsunami flooded emergency diesel generators, batteries, pumps, and electrical distribution equipment, resulting in a cascade of failures: loss of electrical power, severe damage to the Unit 1-3 reactor cores, and severe structural damage to the Unit 1, 3, and 4 reactor buildings.
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3.4 TSUNAMI HAZARDS AT JAPANESE NUCLEAR PLANTS The importance of protecting nuclear plants from large tsunamis was well understood when the Fukushima Daiichi and Daini nuclear plants were designed and constructed.20 At the time these plants were constructed it was common practice to use records of past tsunamis to estimate expected maximum tsunami wave heights. In the case of Fukushima Daiichi and Daini, TEPCO used the tsunami from the May 22, 1960 earthquake near Valdivia, Chile,21 as an estimate of the maximum tsunami wave heights that would be expected at these plants.
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+ 5.7 m, over 2.5 m higher than the estimate in the plant's original permit. The maximum tsunami wave height at Fukushima Daini was estimated to be O.P.
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TEPCO revised its maximum tsunami wave height estimates in 2009 using the JSCE (2006) methodology with updated bathymetric and tidal data.
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3.5 DISCUSSION AND FINDING It should be clear from the descriptions in the preceding section that TEPCO actively implemented countermeasures to protect critical equipment and infrastructure at its Fukushima Daiichi and Daini plants in response to new information about tsunami hazards. Consequently, it is puzzling to the committee why TEPCO appeared to lack a sense of urgency to act after its 2008 trial calculations yielded tsunami wave estimates that were substantially higher than previous estimates (Table 3.3)
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might have required extensive modifications to the harbor front at the plant, for example, augmentation of the existing seawall,27 construction of a new harbor wall in front of the plant, and/or reconfiguration of the seawater intakes and outfalls. However, other types of countermeasures might have been implemented through less disruptive modifications: • Moving seawater pumps to protect them from flooding; • Raising the elevations of emergency diesel generators, batteries, and electrical switching equipment; • Implementing other means to protect this equipment from flooding, for example, by sealing entryways into buildings against water intrusion; and/or • Installing additional backup equipment at higher elevations on the plant site.
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FINDING 3.1: The overarching lesson learned from the Fukushima Daiichi accident is that nuclear plant licensees and their regulators must actively seek out and act on new information about hazards that have the potential to affect the safety of nuclear plants. Specifically, 1.
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29 Several of the gauges were located near the epicenter of the Great East Japan Earthquake. 30 http://oceanobservatories.org.
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