Fukushima Daini Nuclear Power Plant
|Fukushima Daini Nuclear Power Plant|
The Fukushima II NPP
|Status||Out of service|
|Construction began||March 16, 1976|
|Commission date||April 20, 1982|
|Operator(s)||Tokyo Electric Power Company|
|Nuclear power station|
|Units operational||4 x 1,100 MW|
The Fukushima Daini Nuclear Power Plant (福島第二原子力発電所 Fukushima Daini ( pronunciation) Genshiryoku Hatsudensho?, Fukushima II NPP, 2F), is a nuclear power plant located on a 150 ha (370-acre) site in the town of Naraha and Tomioka in the Futaba District of Fukushima Prefecture, Japan. The Tokyo Electric Power Company (TEPCO) runs the plant.
The reactors for units 1 and 3 were supplied by Toshiba, and for units 2 and 4 by Hitachi. Units 1–3 were built by Kajima while the unit 4 was built by Shimizu and Takenaka. The design basis accident for an earthquake was between 0.42 g (4.15 m/s2) and 0.52 g (5.12 m/s2) and for a tsunami was 5.2 m.
|Unit||First criticality||Installation costs (yen/MW)||Reactor supplier||Architecture||Construction||Containment|
|2||23/06/1983||230,000,000||Hitachi||Hitachi||Kajima||Mark 2 advanced|
|3||14/12/1984||290,000,000||Toshiba||Toshiba||Kajima||Mark 2 advanced|
|Mark 2 advanced|
The Fukushima Daini plant is connected to the rest of the power grid by the Tomioka Line (富岡線) to the Shin-Fukushima (New Fukushima) substation.
In January 1989, an impeller blade on one of the reactor coolant pumps in Unit 3 broke at a weld, causing a large amount of metal debris to flow throughout the primary loop. As a result, the reactor was shut down for a considerable length of time.
2011 earthquake and tsunami
On March 11, 2011, a 9-meter-high tsunami struck the No. 2 plant, while the No. 1 plant was hit by a 13-meter-high tsunami. The tsunami caused the No. 2 plant's seawater pumps, used to cool reactors, to fail. Of the plant's four reactors, three were in danger of meltdown. One external high-voltage power line still functioned, allowing plant staff in the central control room to monitor data on internal reactor temperatures and water levels. 2,000 employees of the No. 2 plant worked to stabilize the reactors. Some employees connected 200-meter sections of cable, each weighing more than a ton, over a distance of 9 kilometres. It is pointed out only 40 employees would have been at the plant if the earthquake had occurred in the evening or on a weekend. According to the head of the plant, the plant was near meltdown.
The March 11, 2011 Tōhoku earthquake resulted in maximum horizontal ground accelerations of 0.21 g (2.10 m/s2) to 0.28 (2.77 m/s2) at the plant site, which is well below the design basis. All four units were automatically shut down immediately after the earthquake, according to Nuclear Engineering International, and the diesel engines were started to power the reactor cooling. TEPCO estimated that the tsunami that followed the earthquake and inundated the plant was 14 meters high which is more than twice the designed height. This flooded the pump rooms used for the essential service water system transferring heat to the sea, the ultimate heat sink of the reactors. In unit 3, one seawater pump remained operational. The steam powered reactor core isolation cooling system (RCIC) in all 4 units was activated and ran as needed to maintain water level. At the same time, operators utilized the safety relief valve systems to keep the reactor pressures from getting too high by dumping the heat to the suppression pools. In unit 3, the residual heat removal system (RHR) was started to cool the suppression pool and later brought the reactor to cold shutdown on March 12, but in units 1, 2, and 4 heat removal was unavailable, so the suppression pools began heating up and on March 12, the water temperature in the pools of units 1, 2, and 4 topped 100 °C between 05:30 and 06:10 JST, removing the ability to remove pressure from the reactor and drywell. Also, operators had to prepare an alternate injection line for each unit, as the RCIC can run indefinitely only while there is sufficient pressure and steam in the reactor to drive its turbine; once reactor pressure drops below a certain level, the RCIC shuts down automatically. Operators prepared for this and set up an alternate injection line using a non-emergency system known as the Makeup Water Condensate System to maintain water level which was an accident mitigation method TEPCO put in place at all its nuclear plants. The system was started and stopped in all 4 units, including unit 3, as needed to maintain the water level. The RCICs in each unit later shut down due to low reactor pressure. Operators had to also use the MUWC and the makeup water purification and filtering (MUPF) system to try to cool the suppression pool and drywell in addition to the reactor to prevent the drywell pressure from getting too high. Water injection into unit 4 was later switched from the MUWC to the High Pressure Core Spray (HPCS) system, part of the Emergency Core Cooling System. While the water level was maintained in the three units using emergency water injection, pressures in the containment vessel continued to rise and the operators prepared to vent the containments making restoration of heat removal urgent. Unit 1 was prioritized as it had the highest drywell pressure.
The service seawater system pumps in the pump room were repaired in units 1, 2 and 4 starting March 13 and cooling was switched to the Residual Heat Removal System (RHR). The RHR systems were first activated to cool down the suppression pools (torus) and drywells, and water injections were made to the reactors using the Low Pressure Coolant Injection (LPCI) mode as needed. When the suppression pool was cooled down to below 100 degrees, the RHR was switched to the shutdown cooling mode and brought the reactors to a cold shutdown. Coolant temperatures below 100 °C (cold shutdown) were reached in reactor 2 about 34 hours after the emergency shut down (SCRAM) restoring the ability to lower the pressure of the reactor via the torus. Reactors 1 and 3 followed at 1:24 and 3:52 on March 14 and Reactor 4 at 7:00 on March 15. The loss of cooling water at reactors 1, 2 and 4 was classified a level 3 on the International Nuclear Event Scale (serious incident) by Japanese authorities as of March 18.
An evacuation order was issued to the people living within 3 kilometres (1.9 mi) of the plant, subsequently expanded to 10 km (6.2 mi). Air traffic was restricted in a 10 km (6.2 mi) radius around the plant, according to a NOTAM. These zones were later superseded by the 20 km evacuation and 30 km no-fly zones around Fukushima I on March 12 and 15, respectively.
TEPCO announced that a worker who had been seriously injured by the earthquake and trapped in the crane operating console of the exhaust stack was transported to the ground at 5:13 pm and confirmed dead at 5:17 pm.
By March 15, all four reactors of Fukushima II reached cold shutdown, which remained non-threatening.
Smoke was escaping from one of the buildings on March 30, 2011. It was emitted from equipment which supplies electrical power to a motor pump that collects outdoor water. The smoke stopped after workers disconnected the motor.
As of June 2011, 7,000 tons of seawater from the tsunami remained in the plant. The plant planned to release it all back into the ocean, as the tanks and structures holding the water were beginning to corrode. Approximately 3,000 tons of the water was found to contain radioactive substances, and Japan's Fisheries Agency refused permission to release that water back into the ocean.
On December 26, 2011, the Prime Minister officially cancelled the nuclear emergency declaration for the Fukushima Daini plant officially ending the incident. However, the emergency situation continues at the much more heavily damaged Fukushima Daiichi plant. On February 8, 2012, the plant was opened to news media for the first time since the 2011 Tōhoku earthquake and tsunami.
The evacuation order was partly rescinded for Daini evacuees in August 2012. Some of the residents, such as the 7200 at Naraha town, were permitted to return but others were ordered to remain away. The area did not become contaminated and was safe to visit without protective clothing.
- Nuclear power in Japan
- 2011 Japanese nuclear accidents
- List of boiling water reactors
- Lists of nuclear disasters and radioactive incidents
- List of civilian nuclear accidents
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