CONTROVERSES NUCLEAIRES !
SEISMES ET ENERGIE NUCLEAIRE
JAPON, le 16 juillet 2007
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20 juillet
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Nuclear plant's transformer likely caught fire due to land subsidence

07/19/2007
THE ASAHI SHIMBUN

     A fire at a nuclear power plant in Niigata Prefecture after Monday's earthquake was likely caused by land subsidence, exposing yet another danger in the anti-temblor design of the facility, officials said.
     A bridge column supporting a transformer and electric cables sank into the ground, causing an electrically-charged copper bar to make contact with covering metal, according to Niigata prefectural government officials. The contact could have caused a short-circuit or overheating.
     The officials also said the fire-fighting system at the Kashiwazaki-Kariwa Nuclear Power Plant may have been damaged by the land sinkage, possibly preventing plant workers from extinguishing the fire by themselves. The local fire department had to douse the fire.
     The latest finding raised the possibility that even a small fire could lead to unexpected damage at a nuclear plant if the fire-fighting system is inadequate or disabled in an earthquake.
     The Niigata prefectural government has conducted on-site inspections based on a safety agreement with Tokyo Electric Power Co., operator of the plant.
     Under government guidelines, buildings that house nuclear reactors and turbines must be constructed on solid ground.
     But auxiliary facilities, such as transformers, are not required to have a quake-resistance strength equivalent to that of the primary structures. That is because ensuring safety of reactors is given the highest priority in the event of an earthquake, rather than repairing damage or taking fire-fighting measures for auxiliary facilities such as transformers.
     According to prefectural government officials, the soil around the No. 3 reactor building was removed when it was built directly on bedrock. The soil was returned after the building was erected.
     The bridge column, which stands on the soft ground around the reactor building, sank into the ground during Monday's quake.
     Seismometers installed at the plant registered a shaking at least twice as strong as the level that the plant was designed to withstand.
     The bridge column supports the transformer and power cables, which transmit electricity generated inside the reactor building to the transformer.
     The prefectural officials said a copper belt that conducts electricity and the metal covering the belt, both inside the transformer, might have come in contact when the cables were tilted.
     That may have led to a short-circuit that generated sparks causing the fire. Another possibility is that the metal became so overheated that oil inside the transformer ignited.
     The officials also said a water pipe connected to a hydrant might have been damaged under the weight of the bridge column that sank into the ground.
     The pipe was located under the bridge column, and the officials said the damage possibly crippled fire-fighting activities by plant workers in the early stages.(IHT/Asahi: July 19,2007)


N-plant seismic data lost; more radiation emitted
The Yomiuri Shimbun (Jul. 20, 2007)

     Tokyo Electric Power Co. said Thursday that data was lost from 63 seismometers at the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture following the Niigata Prefecture Chuetsu Offshore Earthquake that hit the facility Monday.
     The company also said air containing radioactive substances was emitted from one of the reactors for two days.
     These new revelations came after TEPCO was found to have committed various errors in its initial efforts to deal with problems arising from the effects of Monday's earthquake. Among 97 seismometers at the power plant, TEPCO lost parts of data from 63 older types of seismometers, the company said.
     The seismometers were supposed to constantly transmit data to Tokyo over phone lines, but the lines became overwhelmed immediately after the quake, and data were overwritten with a series of aftershocks before the previous transmissions were completed, it said. Up to 1-1/2 hours of data were lost from some of the devices.
     Although data from 30 newer seismometers were transmitted during the initial quake, the loss of the other raw data may impact the investigation of the quake resistance security check, observers said.
     Meanwhile, TEPCO said Thursday radioactive iodine had been emitted for two days until noon Wednesday from an exhaust fan at the plant's No. 7 reactor.
     After the plant stopped reactor operations, it failed to stop the fan on the turbine that generates electric power, and air containing radioactive substances was emitted from the turbine area, the company said.
     There were no filters to eliminate radioactive substances in the pathway that connects the fan and the exhaust pipe, it said.
     But the amount of the radiation was small and there is no danger to the environment or the residents in the area, it added.
     The power plant stopped the fan on Wednesday, but it will not be known until Friday if the emission of the radioactive iodine was fully stopped.
     TEPCO said it did not detect radiation around the plant, but the government said it will keep a closer watch on the facility.
     The company also confirmed that water leaked again from a damaged part of an fire-extinguishing duct. The total number of problems and instances of damages has so far increased to 63, TEPCO said.
     The Nuclear Safety Commission and the Nuclear and Industrial Safety Agency, an organization under the Economy, Trade and Industry Ministry, said Thursday they found the government's preparedness against disasters and preventive measures insufficient after the officials investigated the plant.
     They said the plant's failure to learn from mistakes at other plants was a problem.
Hokuriku Electric Power Co. had a similar problem at its Shika nuclear power plant when a temblor hit the Noto Peninsula in Ishikawa Prefecture in March.

suite:
Plants told to speed up checks

     Chief Cabinet Secretary Yasuhisa Shiozaki told Vice Economy, Trade and Industry Minister Takao Kitabata on Thursday to ensure electric power companies complete checking safety levels at the nation's nuclear power plants ahead of schedule, government officials said.
     The Nuclear and Industrial Safety Agency revised the seismic resistance guideline for nuclear plants in September and requested electric power companies use the new guideline to check their safety levels by the end of December 2007.
     The government, however, decided to push up safety checks and take immediate preventive measures in the wake of Monday's earthquake.
     "We want [electric companies] to check [their levels of safety] as soon as possible," Shiozaki said during a press conference.


Second quake-linked radiation leak probed
Tepco reports 50 cases of malfunctions
The Japan Times 2007.7.18 Compiled from AP, Kyodo
     Authorities Tuesday were investigating if Tokyo Electric Power Co.'s huge nuclear plant in Kashiwazaki, Niigata Prefecture, had suffered another radiation leak from the previous day's powerful earthquake, after finding 100 drums of low-level atomic waste had fallen over and some had broken open.
     This followed Tepco's revelation Monday, 12 hours after the magnitude-6.8 temblor hit, that 1,200 liters of water containing radioactive materials spilled from a tank at one of the plant's seven reactors, flowing into the Sea of Japan. Tepco denied the leak posed an environmental risk.
     Tepco also said Tuesday a total of 50 cases of malfunctions and other trouble had been found at seven reactors at the Kashiwazaki-Kariwa nuclear plant since the quake. The utility said it was still inspecting the plant and that it may find further problems.
     The cases included minor fires, broken pipes and water leaks containing radioactive material, as well as detection of a small quantity of radiation from a ventilation filter.
     In five of the reactors, major exhaust pipes were knocked out of place and Tepco was investigating whether they had leaked radioactive materials, it said in a statement.
     The company also said a small amount of the radioactive materials cobalt-60 and chromium-51 were emitted into the atmosphere from an exhaust stack.
     The quake left some 13,000 people homeless, and thousands crowded into shelters Tuesday, including schools and other secure structures, the Fire and Disaster Management Agency said.

RELATED STORIES

Temblor topped reactor design premise

The Japan Times: Friday, July 20, 2007
Kyodo News
     More data were released Thursday showing the Kashiwazaki-Kariwa nuclear power plant was not built to withstand a powerful earthquake like the tough one that hit the Niigata Prefecture complex earlier in the week, causing what the operator claims have been minor radiation leaks.
     Operator Tokyo Electric Power Co. said the seismic acceleration recorded at the plant was much greater than the levels predicted for that location. Asia's largest electric utility had built the reactors at the world's largest nuclear plant to government standards that only require a resistance to epicentral earthquakes of a magnitude 6.5.
     Monday's earthquake had a recorded magnitude of 6.8 and its epicenter was located 16 km from the compound, which stretches along the coast from the city of Kashiwazaki to the village of Kariwa.
     Meteorological Agency aftershock data also appear to show that the fault line where Monday's quake took place extends beneath the plant.
     Seismologists and construction experts said Thursday's data are yet another indication the quake resistance level the government sets for nuclear reactors is insufficient.
     Data from seismometers at the power plant show that the east-west acceleration during Monday's quake was greater than the north-south acceleration, Tepco said.
     A north-south acceleration of 267-311 gals was recorded, compared with the predicted maximum level of 167-274 gals, while an east-west acceleration of 322-680 gals was logged, much larger than the anticipated top range of 167-273 gals, it said. A metric gal is 1 cm per second squared. The No. 1 rector recorded the largest accelerations — 311 gals north-south and 322 gals east-west.
     A vertical acceleration of 205-488 gals was recorded at the seven-reactor compound, with six of the seven reactors topping the anticipated 273 gals, the utility said.
     Meanwhile, the Nuclear and Industrial Safety Agency, an organization under the Ministry of Economy, Trade and Industry, said Thursday that radioactive iodine had been detected again in the filter of an exhaust pipe of one of the seven reactors at the complex.
     But the agency said there is no danger of any impact on the environment or possible damage to nuclear fuel. Radioactive iodine and other radioactive substances were also detected in the filter Monday after the quake.
     Tepco also said data recorded by 63 seismometers installed at the reactors were lost because the machines recorded the aftershocks over the top of the data from the first earthquake.
     However, the company said data from 30 other seismometers installed after a 2004 quake are intact and it was continuing to analyze them.
     At the time of the earthquake, four of the seven reactors at the power station were operating or preparing to begin operating. They all automatically shut down when sensors picked up the strong temblor.
     The quake caused at least 100 drums containing low-level radioactive waste to topple over and open, and, separately, water containing radioactive material also leaked into the Sea of Japan. There was also a minor blaze at an electric transformer outside one of the reactors.
     The Kashiwazaki Municipal Government ordered Tepco on Wednesday not to restart the power plant until its safety is confirmed — raising the prospect of a prolonged shutdown and a possible energy supply shortage.