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Monju Nuclear Power Plant
Monju (もんじゅ) was a Japanese sodium-cooled fast reactor, located near the Tsuruga Nuclear Power Plant, Fukui Prefecture. Its name is a reference to Manjusri. Construction started in 1986 and the reactor achieved criticality for the first time in April 1994. The reactor has been inoperative for most of the time since it was originally built. It was last operated in 2010 and is now closed.
Monju was a sodium cooled, MOX-fueled, loop-type reactor with three primary coolant loops, designed to produce 280 MWe from 714 MWt. It had a breeding ratio of approximately 1.2. The plant is located on a site that spans 1.08 km2 (267 acres), the buildings occupy 28,678 m2 (7 acres), and it has 104,680 m2 of floor space.
An accident in December 1995, in which a sodium leak caused a major fire, forced a shutdown. A subsequent scandal involving a cover-up of the scope of the accident delayed its restart until May 6, 2010, with renewed criticality reached on May 8, 2010. In August 2010 another accident, involving dropped machinery, shut down the reactor again. As of June 2011, the reactor had only generated electricity for one hour since its first testing two decades prior. As of the end of 2010, total funds spent on the reactor amounted to ¥1.08 trillion. An estimated ¥160–170 billion would be needed to continue to operate the reactor for another 10 years. As of 2014, the plant had cost ¥1 trillion ($9.8 billion).
A final decision on the project (e.g. to decommission or extend funding) was due by end 2016, and a decision to close the facility was made in December 2016. In December 2017 the Japan Atomic Energy Agency applied for approval of its decommissioning plan by the Nuclear Regulation Authority. Decommissioning and dismantling are planned to be completed by 2047 and is expected to cost ¥375 billion.
On December 8, 1995, the reactor suffered an accident rated level 1 on the International Nuclear Event Scale (INES). Intense vibration caused a thermowell inside a pipe carrying sodium coolant to break, possibly at a defective weld point, allowing several hundred kilograms of sodium to leak out onto the floor below the pipe. Upon contact with air, the liquid sodium reacted with oxygen and moisture in the air, filling the room with caustic fumes and producing temperatures of several hundred degrees Celsius. The heat was so intense that it warped several steel structures in the room. An alarm sounded around 7:30 p.m., switching the system over to manual operations, but a full operational shutdown was not ordered until around 9:00 p.m., after the fumes were detected. When investigators located the source of the spill they found as much as three tons of solidified sodium.
The leak occurred in the plant's secondary cooling system, so the sodium was not radioactive. However, there was massive public outrage in Japan when it was revealed that Power Reactor and Nuclear Fuel Development Corporation (PNC), the semi-governmental agency then in charge of Monju, had tried to cover up the extent of the accident and resulting damage. This coverup included falsifying reports and the editing of a videotape taken immediately after the accident, as well as issuing a gag order that aimed to stop employees revealing that tapes had been edited.
The official in charge of investigating the coverup, Shigeo Nishimura, committed suicide by leaping from the roof of a Tokyo hotel. Nishimura was deputy general manager of the general affairs department of the Power Reactor and the Nuclear Fuel Development Corporation, the Government concern that ran the country's prototype fast-breeder reactor. Officials said Nishimura was not involved in the cover-up but was distressed by evidence he had unearthed.
On November 24, 2000, Japan Atomic Energy Agency announced their intention to restart the Monju reactor. This decision was met with resistance by the public, resulting in a series of court battles. On January 27, 2003, the Nagoya High Court's Kanazawa branch made a ruling reversing its earlier 1983 approval to build the reactor, but then on May 30, 2005, Japan's Supreme Court gave the green light to reopen the Monju reactor.
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Monju Nuclear Power Plant
Monju (もんじゅ) was a Japanese sodium-cooled fast reactor, located near the Tsuruga Nuclear Power Plant, Fukui Prefecture. Its name is a reference to Manjusri. Construction started in 1986 and the reactor achieved criticality for the first time in April 1994. The reactor has been inoperative for most of the time since it was originally built. It was last operated in 2010 and is now closed.
Monju was a sodium cooled, MOX-fueled, loop-type reactor with three primary coolant loops, designed to produce 280 MWe from 714 MWt. It had a breeding ratio of approximately 1.2. The plant is located on a site that spans 1.08 km2 (267 acres), the buildings occupy 28,678 m2 (7 acres), and it has 104,680 m2 of floor space.
An accident in December 1995, in which a sodium leak caused a major fire, forced a shutdown. A subsequent scandal involving a cover-up of the scope of the accident delayed its restart until May 6, 2010, with renewed criticality reached on May 8, 2010. In August 2010 another accident, involving dropped machinery, shut down the reactor again. As of June 2011, the reactor had only generated electricity for one hour since its first testing two decades prior. As of the end of 2010, total funds spent on the reactor amounted to ¥1.08 trillion. An estimated ¥160–170 billion would be needed to continue to operate the reactor for another 10 years. As of 2014, the plant had cost ¥1 trillion ($9.8 billion).
A final decision on the project (e.g. to decommission or extend funding) was due by end 2016, and a decision to close the facility was made in December 2016. In December 2017 the Japan Atomic Energy Agency applied for approval of its decommissioning plan by the Nuclear Regulation Authority. Decommissioning and dismantling are planned to be completed by 2047 and is expected to cost ¥375 billion.
On December 8, 1995, the reactor suffered an accident rated level 1 on the International Nuclear Event Scale (INES). Intense vibration caused a thermowell inside a pipe carrying sodium coolant to break, possibly at a defective weld point, allowing several hundred kilograms of sodium to leak out onto the floor below the pipe. Upon contact with air, the liquid sodium reacted with oxygen and moisture in the air, filling the room with caustic fumes and producing temperatures of several hundred degrees Celsius. The heat was so intense that it warped several steel structures in the room. An alarm sounded around 7:30 p.m., switching the system over to manual operations, but a full operational shutdown was not ordered until around 9:00 p.m., after the fumes were detected. When investigators located the source of the spill they found as much as three tons of solidified sodium.
The leak occurred in the plant's secondary cooling system, so the sodium was not radioactive. However, there was massive public outrage in Japan when it was revealed that Power Reactor and Nuclear Fuel Development Corporation (PNC), the semi-governmental agency then in charge of Monju, had tried to cover up the extent of the accident and resulting damage. This coverup included falsifying reports and the editing of a videotape taken immediately after the accident, as well as issuing a gag order that aimed to stop employees revealing that tapes had been edited.
The official in charge of investigating the coverup, Shigeo Nishimura, committed suicide by leaping from the roof of a Tokyo hotel. Nishimura was deputy general manager of the general affairs department of the Power Reactor and the Nuclear Fuel Development Corporation, the Government concern that ran the country's prototype fast-breeder reactor. Officials said Nishimura was not involved in the cover-up but was distressed by evidence he had unearthed.
On November 24, 2000, Japan Atomic Energy Agency announced their intention to restart the Monju reactor. This decision was met with resistance by the public, resulting in a series of court battles. On January 27, 2003, the Nagoya High Court's Kanazawa branch made a ruling reversing its earlier 1983 approval to build the reactor, but then on May 30, 2005, Japan's Supreme Court gave the green light to reopen the Monju reactor.