| Fukushima II Nuclear Power Plant | |
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The Fukushima II NPP |
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| Country | Japan |
| Location | Naraha |
| Coordinates | |
| Status | Out of service |
| Construction began | March 16, 1976 |
| Commission date | April 20, 1982 |
| Operator(s) | Tokyo Electric Power Company |
| Constructor(s) | Kajima Takenaka |
| Reactor information | |
| Reactors operational | 4 x 1,100 MW |
| Reactor type(s) | BWR |
| Reactor supplier(s) | Toshiba Hitachi |
| Power generation information | |
| Installed capacity | 4,400 MW |
| Website Home page, Real time monitoring |
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| As of March 14, 2011 | |
The Fukushima II Nuclear Power Plant (福島第二原子力発電所 Fukushima Dai-Ni () Genshiryoku Hatsudensho, Fukushima II NPP, 2F), or Fukushima Dai-ni (dai-ni means "number two"), is a nuclear power plant located on a 1,500,000-square-metre (370-acre) site[1] in the town of Naraha and Tomioka in the Futaba District of Fukushima Prefecture, Japan. The Tokyo Electric Power Company (TEPCO) runs the plant.
After the 2011 Tōhoku earthquake and tsunami, the four reactors at Fukushima II automatically shut down.[2]
Japan's worst nuclear incident occurred at TEPCO's Fukushima Daiichi Nuclear Power Plant, a 11.5 kilometres (7.1 mi) boundary to boundary road journey to the north,[3] after the same March 11 earthquake.
Contents |
All reactors in the Fukushima II Nuclear Power Plant are BWR-5 type[4] with electric power of 1,100 MW each (net output: 1,067 MW each).[5]
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.[5] 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.[6]
| Unit | First criticality | Installation costs (yen/MW) | Reactor supplier | Architecture | Construction | Containment[7] |
|---|---|---|---|---|---|---|
| 1 | 31/07/1981 | 250,000,000 | Toshiba | Toshiba | Kajima | Mark 2 |
| 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 |
| 4 | 17/12/1986 | 250,000,000[8] | Hitachi | Hitachi | Shimizu Takenaka |
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.[9]
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 considerably long time.[10]
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.[6][11] All four units were automatically shut down immediately after the earthquake, according to Nuclear Engineering International,[2] and the diesel engines were started to power the reactor cooling.[12] 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.[6] This flooded the pump rooms used for the essential service water system transferring heat to the sea, the ultimate heat sink of the reactors.[12] 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.[12]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,[13][14][15] removing the ability to remove pressure from the reactor and drywell.[12] Also, operators had to prepare an alternate injection line for each unit as the RCIC cannot 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 setup 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.[16]
The service seawater system pumps in the pump room were repaired in units 1, 2 and 4 starting March 13th 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. [13] 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.[13] Reactors 1 and 3 followed at 1:24 and 3:52 on March 14 and Reactor 4 at 7:00 on March 15.[17] 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.[18][19][20]
Officials made preparations for release of pressure from the plant on March 12.[21][22] As of March 20, however, no pressure release had been reported.[13][23]
An evacuation order was issued to people living within 3 kilometres (1.9 mi) of the plant,[24] subsequently expanded to 10 km (6.2 mi).[25][26] Air traffic was restricted in a 10 km (6.2 mi) radius around the plant, according to a NOTAM.[27] These zones were 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 p.m. and confirmed dead at 5:17 p.m.[25][28][29][30][31]
Smoke was escaping from one of the buildings on 30 March 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.[26]
By March 15, all four reactors of Fukushima II reached cold shutdown which remained non-threatening through April.[32]
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.[33]
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.
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