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81-489: A memorandum of understanding between AREVA and MHI effectively creating the entity was signed 19 October 2006 and the name of the joint venture was announced on 3 September 2007. The European Commission cleared the joint venture in October 2007 on the grounds that the activities of Areva and MHI were geographically complementary and Atmea was unlikely to strengthen the competitiveness of each parent company. The completion of

162-532: A 60-year service life and a load-following capability. The reactor can be set to a 12- to 24 month operational cycle. The ATMEA1 reactor's systems and components were previously developed by AREVA and MHI for the EPR and APWR respectively, including steam generators with axial economizer and TT690 tubes, advanced accumulators and reactor internals with Heavy Neutron Reflector. The ATMEA1 safety features include three redundant trains of emergency core cooling systems and

243-503: A LOC incident. However, when a team was sent to investigate the status of the RCIC of unit 2 the following morning (02:55), they confirmed that the RCIC was operating with the PCV pressure well below design limits. Based on this information, efforts were focused on unit 1. However, the condensate storage tank from which the RCIC draws water was nearly depleted by the early morning, and so the RCIC

324-445: A causal relationship between radiation and the cancer. Six other persons have been reported as having developed cancer or leukemia . Two workers were hospitalized because of radiation burns , and several other people sustained physical injuries as a consequence of the accident. Criticisms have been made about the public perception of radiological hazards resulting from accidents and the implementation of evacuations (similar to

405-403: A closed coolant loop from the pressure vessel with a heat exchanger in a dedicated condenser tank. Steam would be forced into the heat exchanger by the reactor pressure, and the condensed coolant would be fed back into the vessel by gravity. Each reactor was initially designed to be equipped with two redundant ICs which were each capable of cooling the reactor for at least 8 hours (at which point,

486-405: A closed-loop system which draws coolant from the suppression chamber (SC) instead of the storage tank, should the storage tank be depleted. Although this system could function autonomously without an external energy source (besides the steam from the reactor), direct current (DC) was needed to remotely control it and receive parameters and indications and alternating current (AC) was required to power

567-546: A core-melt retention system. With a power output of about 1200 Mwe, the ATMEA1, was targeted to attract new-entry countries looking to develop nuclear power. In comparison, Mitsubishi's APWR was slated to have a power of 1700 MWe while Areva's European Pressurized Reactor has an output of 1600 Mwe. In 2013, the Canadian Nuclear Safety Commission (CNSC) released a pre-project design review of

648-466: A document constitutes a binding contract depends only on the presence or absence of well-defined legal elements in the text proper of the document (the so-called " four corners "). The required elements are offer and acceptance , consideration , and the intention to be legally bound ( animus contrahendi ). In the US, the specifics can differ slightly depending on whether the contract is for goods (falls under

729-462: A formal, legally enforceable contract (though an MoU is often a first step towards the development of a formal contract). In the United Kingdom , the term MoU is commonly used to refer to an agreement between parts of The Crown . The term is often used in the context of devolution , for example the 1999 concordat between the central Department for Environment, Food and Rural Affairs and

810-418: A matter of law, the title of MoU does not necessarily mean the document is binding or not binding under international law . To determine whether a particular MoU is meant to be a legally binding document (i.e., a treaty), one needs to examine the parties’ intent as well as the signatories' position (e.g., Minister of Foreign Affairs vs. Minister of Environment). A careful analysis of the wording will also clarify

891-420: Is a type of agreement between two ( bilateral ) or more ( multilateral ) parties. It expresses a convergence of will between the parties, indicating an intended common line of action. It is often used either in cases where parties do not imply a legal commitment or in situations where the parties cannot create a legally enforceable agreement. It is a more formal alternative to a gentlemen's agreement . Whether

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972-663: Is determined by the parties' internal law and depends to a large degree on the subject agreed upon. MoUs that are kept confidential (i.e., not registered with the UN) cannot be enforced before any UN organ, and it may be concluded that no obligations under international law have been created. Although MoUs in the multilateral field are seldom seen, the transnational aviation agreements are actually MoUs. Examples include: Examples from U.S. law include: Examples from international development contexts include: Fukushima Daiichi nuclear disaster The Fukushima nuclear accident

1053-696: The Scottish Environment Directorate . MoUs can also be used between a government agency and a non-commercial, non-governmental organization. In international relations, MoUs fall under the broad category of treaties and should be registered in the United Nations treaty collection. In practice and in spite of the United Nations Office of Legal Affairs ' insistence that registration be done to avoid 'secret diplomacy', MoUs are sometimes kept confidential. As

1134-540: The Uniform Commercial Code ) or services (falls under the common law of the state). Many companies and government agencies use MoUs to define a relationship between departments, agencies or closely held companies. In business , an MoU is typically a legally non-binding agreement between two (or more) parties, outlining terms and details of a mutual understanding or agreement, noting each party's requirements and responsibilities—but without establishing

1215-476: The disposal of treated wastewater once used to cool the reactor , resulting in numerous protests in neighboring countries. The Fukushima Daiichi Nuclear Power Plant consisted of six General Electric (GE) light water boiling water reactors (BWRs). Unit 1 was a GE type 3 BWR. Units 2–5 were type 4. Unit 6 was a type 5. At the time of the Tōhoku earthquake on 11 March 2011 , units 1–3 were operating. However,

1296-456: The reactor pressure vessel (RPV) and embedded itself into the concrete at the base of the PCV. Although at the time it was difficult to determine how far the fuel had eroded and diffused into the concrete, it was estimated that the fuel remained within the PCV. Computer simulations, from 2013, suggest "the melted fuel in Unit 1, whose core damage was the most extensive, has breached the bottom of

1377-500: The spent fuel pools of all units still required cooling. Many of the internal components and fuel assembly cladding are made from a zirconium alloy (Zircaloy) for its low neutron cross section . At normal operating temperatures (~300 °C (572 °F)), it is inert. However, above 1,200 °C (2,190 °F), Zircaloy can be oxidized by steam to form hydrogen gas or by uranium dioxide to form uranium metal . Both of these reactions are exothermic . In combination with

1458-492: The 13 EDGs, 10 were water-cooled and placed in the basements about 7–8 m below the ground level. The coolant water for the EDGs was carried by several seawater pumps placed on the shoreline which also provide water for the main condenser. These components were unhoused and only protected by the seawall. The other three EDGs were air-cooled and were connected to units 2, 4, and 6. The air-cooled EDGs for units 2 and 4 were placed on

1539-573: The 20th. Unit 6 was not operating, and its decay heat was low. All but one EDG was disabled by the tsunami, allowing unit 6 to retain AC-powered safety functions throughout the incident. However, because the RHR was damaged, workers activated the make-up water condensate system to maintain the reactor water level until the RHR was restored on the 20th. Cold shutdown was achieved on the 20th, less than an hour after unit 5. On 21 March, temperatures in

1620-477: The 4400 MWe plant were ratified by Turkey's government in April 2015. Ownership of the plant would be split between a consortium of Japan's Mitsubishi Heavy Industries (MHI) and Itochu , and France's Areva and GDF Suez with 51%, and Turkey's state-run power producer EUAS with 49%. The plant would comprise four ATMEA1 reactors. As of 2015, subject to final agreement, construction was planned to begin in 2017, with

1701-666: The ATMEA1 reactor and found the design compliant with CNSC regulatory requirements and expectations for new nuclear power plants in Canada. In 2012 the French Nuclear Safety Authority, ( Autorité de sûreté nucléaire or ASN), released a report finding the safety options and design choice of the ATMEA1 satisfactory and in compliance with French regulations. On 7 July 2008 the International Atomic Energy Agency (IAEA) completed

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1782-567: The Chernobyl nuclear accident), as they were accused of causing more harm than they prevented. Following the accident, at least 164,000 residents of the surrounding area were permanently or temporarily displaced (either voluntarily or by evacuation order). The displacements resulted in at least 51 deaths as well as stress and fear of radiological hazards. Investigations faulted lapses in safety and oversight, namely failures in risk assessment and evacuation planning. Controversy surrounds

1863-462: The FP injection port was hidden under debris. The next morning (12 March, 04:00), approximately 12 hours after the loss of power, freshwater injection into the reactor vessel began, later replaced by a water line at 09:15 leading directly from the water storage tank to the injection port to allow for continuous operation (the fire engine had to be periodically refilled). This continued into the afternoon until

1944-642: The French nuclear industry reorganisation under EDF leadership in 2018 also led to a renewed partnership within ATMEA. ATMEA was initially formed as a joint venture between AREVA NP and MHI to develop the next-generation AT-MEA1 reactor. Under the new structure, there was a fifty-fifty ownership of ATMEA between EDF and MHI, along with a special share owned by Framatome. This would reinforce the Franco/Japanese new nuclear power offering to many countries recognizing

2025-487: The Fukushima coast. In response to the station blackout during the initial hours of the accident and the ongoing uncertainty regarding the cooling status of units 1 and 2, a 2 km radius evacuation of 1,900 residents was ordered at 20:50. However, due to difficulty coordinating with the national government, a 3 km evacuation order of ~6,000 residents and a 10 km shelter-in-place order for 45,000 residents

2106-523: The HPCI and RCIC systems, but both failed to restart. Following this loss of cooling, workers established a water line from the valve pit to inject seawater into the reactor alongside unit 2. However, water could not be injected due to RPV pressures exceeding the pump capability. Similarly, preparations were also made to vent the unit 3 PCV, but PCV pressure was not sufficient to burst the rupture disk. Later that morning (9:08), workers were able to depressurize

2187-539: The HPCI system showed signs of malfunction. The HPCI isolation valve failed to activate automatically upon achieving a certain pressure. In response, the workers switched off HPCI and began injection of water via the lower-pressure firefighting equipment. However, the workers found that the SRVs did not operate to relieve pressure from the reactor vessel to allow water injection by the DDFP. In response, workers attempted to restart

2268-707: The International Nuclear Event Scale. According to the United Nations Scientific Committee on the Effects of Atomic Radiation , "no adverse health effects among Fukushima residents have been documented that are directly attributable to radiation exposure from the Fukushima Daiichi nuclear plant accident". Insurance compensation was paid for one death from lung cancer , but this does not prove

2349-435: The PCV was completed later that afternoon at 14:00. At the same time, pressure in the reactor vessel had been decreasing to equalize with the PCV, and the workers prepared to inject water into the reactor vessel using the DDFP once the pressure had decreased below the 0.8 MPa limit. Unfortunately, the DDFP was found to be inoperable and a fire truck had to be connected to the FP system. This process took about 4 hours, as

2430-473: The RCIC system failed. In response, the high-pressure coolant injection (HPCI) system was activated to alleviate the lack of cooling while workers continued to attempt to restart the RCIC. Additionally, the FP system was used to spray the PCV (mainly the SC) with water in order to slow the climbing temperatures and pressures of the PCV. On the morning of the 13th (02:42), after DC power was restored by new batteries,

2511-422: The RCIC system was continuing to cool the reactor. However, knowing that their DC supply was limited, the workers managed to extend the backup DC supply to about 2 days by disconnecting nonessential equipment, until replacement batteries were brought from a neighboring power station on the morning of the 13th (with 7 hours between loss and restoration of DC power). At 11:36 the next day, after 20.5 hours of operation,

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2592-436: The atmosphere, those which remain in a gaseous phase will simply be diluted by the atmosphere, but some which precipitate will eventually settle on land or in the ocean. Approximately 40–80% of the atmospheric caesium-137 was deposited in the ocean. Thus, the majority (90~99%) of the radionuclides which are deposited are isotopes of iodine and caesium, with a small portion of tellurium , which are almost fully vaporized out of

2673-410: The blackout, the RCIC was functioning as designed without the need for operator intervention. The safety relief valves (SRVs) would intermittently release steam directly into the PCV suppression torus at its design pressure and the RCIC properly replenished lost coolant. However, following the total blackout of Unit 2, the plant operators (similar to Unit 1) assumed the worst-case scenario and prepared for

2754-459: The condenser tank would have to be refilled). However, it was possible for the IC system to cool the reactor too rapidly shortly after shutdown which could result in undesirable thermal stress on the containment structures. To avoid this, the protocol called for reactor operators to manually open and close the condenser loop using electrically operated control valves. After the construction of Unit 1,

2835-708: The contaminated waters far into the Pacific Ocean, dispersing the radioactivity. As of late 2011, measurements of both the seawater and the coastal sediments suggested that the consequences for marine life would be minor. Significant pollution along the coast near the plant might persist, because of the continuing arrival of radioactive material transported to the sea by surface water crossing contaminated soil. The possible presence of other radioactive substances, such as strontium-90 or plutonium , had not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along

2916-431: The core due to their high vapor pressure. The remaining fraction of deposited radionuclides are of less volatile elements such as barium , antimony , and niobium , of which less than a percent is evaporated from the fuel. In addition to atmospheric deposition, there was also a significant quantity of direct releases into groundwater (and eventually the ocean) through leaks of coolant which had been in direct contact with

2997-399: The critical parts of the reactor was found. In 2006, the design of the reactors was reevaluated with new standards requiring the reactors to withstand accelerations ranging up to 450 Gal. In the event of an emergency, operators planned to pump water into the reactors to keep them cool. This would inevitably create steam which should not be very radioactive because the fuel would still be in

3078-574: The exact nature of the document. The International Court of Justice has provided some insight into the determination of the legal status of a document in the landmark case of Qatar v. Bahrain , 1 July 1994. One advantage of MoUs over more formal instruments is that, because obligations under international law may be avoided, they can often be put into effect without requiring legislative approval. Hence, MoUs are often used to modify and adapt existing treaties, in which case these MoUs have factual treaty status. The decision concerning ratification, however,

3159-473: The exothermic reaction of boron carbide with stainless steel , these reactions can contribute to the overheating of a reactor. In the event of an emergency, reactor pressure vessels (RPV) are automatically isolated from the turbines and main condenser and are instead switched to a secondary condenser system which is designed to cool the reactor without the need for pumps powered by external power or generators. The isolation condenser (IC) system involved

3240-443: The explosion. The debris produced by the explosion damaged the mobile emergency power generator and the seawater injection lines. The seawater injection lines were repaired and put back into operation at 19:04 until the valve pit was nearly depleted of seawater at 01:10 on the 14th. The seawater injection was temporarily stopped in order to refill the valve pit with seawater using a variety of emergency service and JSDF vehicles. However,

3321-409: The final 20 km evacuation zone. 20% of residents who were within the initial 2 km radius had to evacuate more than six times. Additionally, a 30 km shelter in place order was communicated on the 15th, although some municipalities within this zone had already decided to evacuate their residents. This order was followed by a voluntary evacuation recommendation on the 25th, although

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3402-559: The first unit to be in operation by 2023. In 2018 an Environmental Impact Assessment application was submitted to the Environment and Urban Planning Ministry. Location and construction licenses were still to be obtained from the Turkey Atomic Energy Agency. In April 2018, Nikkei reported that Itochu would withdraw from the project, while MHI and other investors were continuing the feasibility study through

3483-400: The following numbers of fuel assemblies: The original design basis was a zero-point ground acceleration of 250 Gal and a static acceleration of 470 Gal, based on the 1952 Kern County earthquake (0.18 g , 1.4 m/s , 4.6 ft/s ). After the 1978 Miyagi earthquake , when the ground acceleration reached 0.125 g (1.22 m/s , 4.0 ft/s ) for 30 seconds, no damage to

3564-475: The following units were designed with new open-cycle reactor core isolation cooling (RCIC) systems. This new system used the steam from the reactor vessel to drive a turbine which would power a pump to inject water into the pressure vessel from an external storage tank to maintain the water level in the reactor vessel and was designed to operate for at least 4 hours (until the depletion of coolant or mechanical failure). Additionally, this system could be converted into

3645-455: The freshwater tank was nearly depleted. In response, injection stopped at 14:53 and the injection of seawater, which had collected in a nearby valve pit (the only other source of water), began. Power was restored to units 1 (and 2) using a mobile generator at 15:30 on 12 March. At 15:36, a hydrogen explosion damaged the secondary confinement structure (the RB). The workers evacuated shortly after

3726-542: The fuel pond had risen slightly, to 61 °C (142 °F), and water was sprayed over the pool. Power was restored to cooling systems on 24 March and by 28 March, temperatures were reported down to 35 °C (95 °F). Quantities of the released material are expressed in terms of the three predominant products released: caesium-137 , iodine-131 , and xenon-133 . Estimates for atmospheric releases range from 7–20  PBq for Cs-137, 100–400 PBq for I-131, and 6,000–12,000 PBq for Xe-133. Once released into

3807-496: The fuel. Estimates for this release vary from 1 to 5.5 PBq caesium-137 and 10-20 PBq iodine-131 . According to the French Institute for Radiological Protection and Nuclear Safety , the release from the accident represents the most important individual oceanic emissions of artificial radioactivity ever observed. The Fukushima coast has one of the world's strongest currents ( Kuroshio Current ). It transported

3888-412: The ground floor of the spent fuel building, but the switches and various other components were located below, in the basement. The third air-cooled EDG was in a separate building placed inland and at higher elevations. Although these EDGs are intended to be used with their respective reactors, switchable interconnections between unit pairs (1 and 2, 3 and 4, and 5 and 6) allowed reactors to share EDGs should

3969-440: The ground or basement levels at approximately 15:41. The switching stations that provided power from the three EDGs located higher on the hillside also failed when the building that housed them flooded. One air-cooled EDG, that of unit 6, was unaffected by the flooding and continued to operate. The DC batteries for units 1, 2, and 4 were also inoperable shortly after flooding. As a result, units 1–5 lost AC power and DC power

4050-415: The isolation valves. In an emergency where backup on-site power was partially damaged or insufficient to last until a grid connection to off-site power could be restored, these cooling systems could no longer be relied upon to reliably cool the reactor. In such a case, the expected procedure was to vent both the reactor vessel and primary containment using electrically or pneumatically operated valves using

4131-560: The key role of nuclear energy in the transition towards low-carbon power generation. The joint development was abandoned in 2019, following the similar fate of the French-Japanese ASTRID fast reactor design the same year. The ATMEA1 reactor design was an about 1200 MWe generation III+ pressurized water reactor with three coolant loops and a thermal power level of 3,150 MWth. The design has high thermal efficiency (typically 10% higher than currently operating reactors),

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4212-437: The majority of residents had evacuated from the 30 km zone by then. The shelter in place order was lifted on April 22, but the evacuation recommendation remained. Of an estimated 2,220 patients and elderly who resided within hospitals and nursing homes within the 20 km evacuation zone, 51 fatalities are attributed to the evacuation. There was one suspected death due to radiation, as one person died 4 years later of

4293-455: The need arise. The power station was also equipped with backup DC batteries kept charged by AC power at all times, designed to be able to power the station for approximately 8 hours without EDGs. In units 1, 2, and 4, the batteries were located in the basements alongside the EDGs. In units 3, 5, and 6, the batteries were located in the turbine building where they were raised above ground level. The units and central storage facility contained

4374-406: The ocean began two hours later, and cooling of unit 3 resumed in the afternoon (approximately 16:00) and continued until cooling was lost once more as a result of site evacuation on the 15th. Unit 4 was not fueled at the time, but the unit 4 spent fuel pool (SFP) contained a number of fuel rods. On 15 March, an explosion was observed at unit 4 RB during site evacuation. A team later returned to

4455-463: The power station to inspect unit 4, but were unable to do so due to the present radiological hazard. The explosion damaged the fourth-floor rooftop area of Unit 4, creating two large holes in a wall of the RB. The explosion was likely caused by hydrogen passing to unit 4 from unit 3 through shared pipes. The following day, on the 16th, an aerial inspection was performed by helicopter which confirmed there

4536-410: The primary containment vessel and even partially eaten into its concrete foundation, coming within about 30 cm (1 ft) of leaking into the ground". A Kyoto University nuclear engineer said with regard to these estimates: "We just can't be sure until we actually see the inside of the reactors." Unit 2 was the only other operating reactor which experienced a total loss of AC and DC power. Before

4617-496: The primary containment vessel. Therefore, the steam would manually be released by venting valves to prevent a high pressure explosion. The 9.0 M W earthquake occurred at 14:46 on Friday, 11 March 2011, with the epicenter off of the east coast of the Tōhoku region . It produced maximum ground g-force of 560 Gal , 520 Gal, 560 Gal at units 2, 3, and 5 respectively. This exceeded the seismic reactor design tolerances of 450 Gal, 450 Gal, and 460 Gal for continued operation, but

4698-496: The process of restarting seawater injection was interrupted by another explosion in unit 3 RB at 11:01 which damaged water lines and prompted another evacuation. Injection of seawater into unit 1 would not resume until that evening, after 18 hours without cooling. Subsequent analysis in November 2011 suggested that this extended period without cooling resulted in the melting of the fuel in unit 1, most of which would have escaped

4779-468: The reactor by operating the safety relief valves using batteries collected from nearby automobiles. This was shortly followed by the bursting of the venting line rupture disk and the depressurization of the PCV. Unfortunately, venting was quickly stopped by a pneumatic isolation valve which closed on the vent path due to a lack of compressed air, and venting was not resumed until over 6 hours later once an external air compressor could be installed. Despite this,

4860-414: The reactor operators began planning to lower the PCV pressure by venting. The PCV reached its maximum pressure of 0.84 MPa at 02:30 on 12 March, after which it stabilized around 0.8 MPa. The decrease in pressure was due to an uncontrolled vent via an unknown pathway. The plant was notified Okuma town completed evacuation at 9:02 on 12 March. The staff subsequently began controlled venting. Venting of

4941-399: The reactor pressure was immediately low enough to allow for water injection (borated freshwater, as ordered by TEPCO) using the FP system until the freshwater FP tanks were depleted, at which point the injected coolant was switched to seawater from the valve pit. Cooling was lost once the valve pit was depleted but was resumed two hours later (unit 1 cooling was postponed until the valve pit

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5022-426: The reactor vessel. However, the reactor pressure had already increased to many times greater than the limit of the DDFP. Additionally, the team detected high levels of radiation within the secondary confinement structure, indicating damage to the reactor core, and found that the primary containment vessel (PCV) pressure (0.6  MPa ) exceeded design specifications (0.528 MPa). In response to this new information,

5103-603: The release of radioactive contaminants into the surrounding environment. The accident was rated seven (the maximum severity) on the International Nuclear Event Scale by Nuclear and Industrial Safety Agency, following a report by the JNES (Japan Nuclear Energy Safety Organization). It is regarded as the worst nuclear incident since the Chernobyl disaster in 1986, which was also rated a seven on

5184-506: The remaining electricity on site. This would lower the reactor pressure sufficiently to allow for low-pressure injection of water into the reactor using the fire protection system to replenish water lost to evaporation. Station operators switched the reactor control to off-site power for shutdown, but the system was damaged by the earthquake. Emergency diesel generators (EDG) then automatically started to provide AC power. Two EDGs were available for each of units 1–5 and three for unit 6. Of

5265-626: The review of the conceptual safety design features for the ATMEA1. The report concluded that the ATMEA1 conceptual design addresses the IAEA's fundamental safety principles and key design and safety assessment requirements. On 3 May 2013, Turkish prime minister Recep Tayyip Erdoğan and his Japanese counterpart Shinzo Abe , signed an outline US$ 22 billion deal for the construction of the Sinop Nuclear Power Plant in Turkey. Plans for

5346-455: The seismic values were within the design tolerances of unit 6. Upon detecting the earthquake, all three operating reactors (units 1, 2, and 3) automatically shut down. Due to expected grid failure and damage to the switch station as a result of the earthquake, the power station automatically started up the EDGs, isolated the reactor from the primary coolant loops, and activated the emergency shutdown cooling systems. The largest tsunami wave

5427-648: The summer of 2018. The remaining members of the Japanese consortium abandoned the project in December 2018 after a failure to reach agreement with the Turkish government on financing terms. Construction costs had almost doubled to about $ 44 billion, because of post-Fukushima safety improvements and the fall in the value of the Turkish lira . Memorandum of understanding A memorandum of understanding ( MoU )

5508-625: The televised news media. Citizens were informed by radio, trucks with megaphones, and door to door visits. Many municipalities independently ordered evacuations ahead of orders from the national government due to loss of communication with authorities; at the time of the 3 km evacuation order, the majority of residents within the zone had already evacuated. Due to the multiple overlapping evacuation orders, many residents had evacuated to areas which would shortly be designated as evacuation areas. This resulted in many residents having to move multiple times until they reached an area outside of

5589-412: The tsunami, operators attempted to manually open the IC control valve, but the IC failed to function, suggesting that the isolation valves were closed. Although they were kept open during IC operation, the loss of DC power in unit 1 (which occurred shortly before the loss of AC power) automatically closed the AC-powered isolation valves to prevent uncontrolled cooling or a potential LOC. Although this status

5670-462: The tsunami. The isolation condenser (IC) was functioning prior to the tsunami, but the DC-operated control valve outside of the primary containment had been in the closed position at the time to prevent thermal stresses on the reactor components. Some indications in the control room stopped functioning and operators correctly assumed loss of coolant (LOC). At 18:18 on 11 March, a few hours after

5751-489: Was 13–14 m (43–46 feet) high and hit approximately 50 minutes after the initial earthquake, overtopping the seawall and exceeding the plant's ground level, which was 10 m (33 ft) above sea level. The waves first damaged the seawater pumps along the shoreline, 10 of the plant's 13 cooling systems for the emergency diesel generators (EDG). The waves then flooded all turbine and reactor buildings, damaging EDGs and other electrical components and connections located on

5832-514: Was a major nuclear accident at the Fukushima Daiichi nuclear power plant in Ōkuma, Fukushima , Japan which began on 11 March 2011. The proximate cause of the accident was the 2011 Tōhoku earthquake and tsunami , which resulted in electrical grid failure and damaged nearly all of the power plant's backup energy sources . The subsequent inability to sufficiently cool reactors after shutdown compromised containment and resulted in

5913-457: Was damaged and the isolation valve for the PCV vent was found to be closed and inoperable. At 13:00 on the 14th, the RCIC pump for unit 2 failed after 68 hours of continuous operation. With no way to vent the PCV, in response, a plan was devised to delay containment failure by venting the reactor vessel into the PCV using the SRVs to allow for seawater injection into the reactor vessel. The following morning (March 15, 06:15), another explosion

5994-416: Was established nearly simultaneously at 21:23. The evacuation radius was expanded to 10 km at 5:44, and was then revised to 20 km at 18:25. The size of these evacuation zones was set for arbitrary reasons at the discretion of bureaucrats rather than nuclear experts. Communication between different authorities was scattered and at several times the local governments learned the status of evacuation via

6075-639: Was filled). However, despite being cooled, PCV pressure continued to rise and the RPV water level continued to drop until the fuel became uncovered on the morning of the 14th (6:20), as indicated by a water level gauge, which was followed by workers evacuating the area out of concerns about a possible second hydrogen explosion similar to unit 1. Shortly after work resumed to reestablish coolant lines, an explosion occurred in unit 3 RB at 11:01 on March 14, which further delayed unit 1 cooling and damaged unit 3's coolant lines. Work to reestablish seawater cooling directly from

6156-533: Was heard on site coinciding with a rapid drop of suppression chamber pressure to atmospheric pressure, interpreted as a malfunction of suppression chamber pressure measurement. Due to concerns about the growing radiological hazard on site, almost all workers evacuated to the Fukushima Daini Nuclear Power Plant . Although AC power was lost, some DC power was still available in unit 3 and the workers were able to remotely confirm that

6237-412: Was lost in units 1, 2, and 4. In response, the operators assumed a loss of coolant in units 1 and 2 and developed a plan in which they would vent the primary containment and inject water into the reactor vessels with firefighting equipment. Tokyo Electric Power Company ( TEPCO ), the utility operator and owner, notified authorities of a "first-level emergency". Two workers were killed by the impact of

6318-424: Was manually reconfigured at 05:00 to recirculate water from the suppression chamber instead. On the 13th, unit 2 was configured to vent the PCV automatically (manually opening all valves, leaving only the rupture disk) and preparations were made to inject seawater from the valve pit via the FP system should the need arise. However, as a result of the explosion in unit 3 the following day, the seawater injection setup

6399-404: Was not possible, as the reactor was not producing sufficient steam. However, the water within the RPV proved sufficient to cool the fuel, with the SRVs venting into the PCV, until AC power was restored on March 13 using the unit 6 interconnection, allowing the use of the low-pressure pumps of the residual heat removal (RHR) system. Unit 5 was the first to achieve a cold shutdown in the afternoon on

6480-448: Was sufficient water remaining in the SFP. On the 20th, water was sprayed into the uncovered SFP, later replaced by a concrete pump truck with a boom on the 22nd. Unit 5 was fueled and was undergoing an RPV pressure test at the time of the accident, but the pressure was maintained by an external air compressor and the reactor was not otherwise operating. Removal of decay heat using the RCIC

6561-435: Was unknown to the plant operators, they correctly interpreted the loss of function in the IC system and manually closed the control valves. The plant operators would continue to periodically attempt to restart the IC in the following hours and days, but it did not function. The plant operators then attempted to use the building's fire protection (FP) equipment, operated by a diesel-driven fire pump (DDFP), to inject water into

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