Fukushima No. 4 unit explosion caused by hydrogen leak from No. 3
TOKYO (Kyodo) — Tokyo Electric Power Co. has found evidence that the March 15 explosion at its Fukushima Daiichi nuclear power plant’s No. 4 reactor unit was caused by hydrogen that had flown from the adjacent No. 3 unit, officials said recently.
When it measured on Thursday the radiation levels of filters of exhaust pipes from the No. 4 and the No. 3 unit before a common exhaust stack, the utility found evidence indicating radioactive steam and hydrogen had flown into the No. 4 reactor building, in an opposite flow from usual, the utility officials said.
The radiation was 6.7 millisieverts per hour near the junction but fell to 0.5 millisievert and 0.1 millisievert at the approach to the building, they said.
The plant operator known as TEPCO initially believed the explosion at the No. 4 unit was caused by hydrogen gas produced by the exposure of fuel stored under water in a pool in that building. But TEPCO officials said the new evidence points to the possibility, first suspected in May, that hydrogen gas had flown from the No. 3 unit as the fuel was not particularly damaged.
Kyodo, August 29, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/29/20110829p2g00m0dm006000c.html
PM’s office failed to use data predicting Fukushima power loss, meltdowns
In the hours after the March 11 earthquake and tsunami, the Prime Minister’s Office failed to take advantage of up-to-date analysis of the Fukushima No. 1 nuclear plant that projected both power failures and subsequent core meltdowns, according to the Nuclear and Industrial Safety Agency (NISA).
NISA released the results of analysis on the Fukushima nuclear reactors using the Emergency Report Support System (ERSS) on Sept. 2 — about six months after the analysis was conducted right after the magnitude-9 earthquake struck. The analysis predicted the loss of power and subsequent nuclear meltdowns at the No. 1, 2 and 3 reactors at the plant before they occurred.
NISA sent the analysis on the No. 2 and 3 reactors to the Prime Minister’s Office, but the office did not use the information either to help plot containment measures or to initiate a swift evacuation of local communities. The agency did not send the results of the No. 1 reactor analysis.
According to NISA, the Japan Nuclear Energy Safety Organization (JNES), which developed the ERSS, activated the system just after the quake. Based on the assumption of a complete loss of power at the plant, JNES predicted how the water levels, pressure and temperatures would change at the No. 1, 2 and 3 reactors.
The JNES sent the data on the No. 2 reactor to NISA around 9:30 p.m. on March 11. Based on the data, NISA officials projected a chain of events remarkably true to those that were to unfold at the plant, such as, “At 22:50, reactor cores will be exposed; At 24:50, fuel meltdown.” NISA handed the predictions to the Prime Minister’s Office at around 10:45 p.m. on March 11 and again shortly after midnight. NISA sent the data on the No. 3 reactor to the Prime Minister’s Office about 20 minutes after receiving it from JNES around 6:30 a.m. on March 13.
However, the government did not use the data in its disaster response measures. Yoshinori Moriyama, NISA deputy director-general for nuclear accident measures, told a news conference on Sept. 2, “The data were not used because they were not based on facts.”
Based on assumed amounts of radioactive substances inferred from the predictions for the No. 1 reactor, NISA also projected the diffusion of nuclear substances using a system known as SPEEDI, or the System for Prediction of Environmental Emergency Dose Information. The agency did not, however, release the predictions immediately, and were in the end not used at all. NISA had previously said that SPEEDI was not functioning after the quake because of a complete loss of power.
Mainichi Shimbun , September 3, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/09/03/20110903p2a00m0na012000c.html
Gov’t nuclear watchdog criticizes TEPCO for delayed release of tsunami estimate
A government nuclear watchdog has criticized the Tokyo Electric Power Co. (TEPCO) for not releasing an estimate it put together years ago that a tsunami over 10 meters high could hit the Fukushima No. 1 Nuclear Power Plant.
The estimate was put together in 2008 but not reported until March 7 this year — only four days before the Great East Japan Earthquake.
“Even if it was only an estimate, TEPCO should have released the data earlier and explained it before experts because it far exceeded the previous estimate (that a tsunami of up to 5.7 meters could hit the No. 1 through No. 4 reactors),” said Yoshinori Moriyama, an official of the watchdog, the Nuclear and Industrial Safety Agency (NISA), during a press conference on Aug. 25.
TEPCO, however, refuted the criticism.
“We think that rather than relying on TEPCO to make its own estimations and evaluate the safety of the nuclear power plant, it was more rational to have the Japan Society of Civil Engineers (JSCE, which decides tsunami-prevention measures for nuclear plants) make an evaluation, and TEPCO’s report (to NISA) should come after that,” said Junichi Matsumoto, deputy chief of TEPCO’s nuclear power division.
Furthermore, while NISA maintains that its official in charge of earthquake-proof safety screening told TEPCO on March 7 after receiving the report that it needed to “take measures to safeguard the plant’s equipment,” TEPCO’s Matsumoto denied this, saying, “That is not true.”
TEPCO also revealed on Aug. 25 that the 2008 tsunami estimate was known about by its management. It says that in October 2008 it requested to the JSCE that it revise its guidelines for evaluating nuclear plants’ tsunami-readiness, and that request was reported to Sakae Muto, then vice chief of TEPCO’s nuclear power division. Muto later became TEPCO vice president and currently serves as an advisor to the utility.
Mainichi Shimbun , August 26, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/26/20110826p2a00m0na010000c.html
3/7: Tepco gave NISA high-wave scenarios
Tokyo Electric Power Co. was aware 10-meter-plus tsunami could hit the Fukushima No. 1 nuclear power station as early as in 2008, reporting the results of simulations for the first time to the Nuclear and Industrial Safety Agency on March 7 Å\ four days before 13-meter waves knocked out the plant, leading to three meltdowns, it was learned Wednesday.
The government and Tepco repeatedly had claimed they never imagined tsunami of such heights could hit the Fukushima plant.
But Tepco in fact conducted the simulations, from April to May 2008, assuming 10-meter-plus tsunami, officials of the utility said. The utility, however, never attempted to bolster the wave defenses of the Fukushima plant.
“That was only one of the research activities,” a Tepco official said, playing down the significance of the simulations.
Tepco conducted the simulations after the government revised quake resistance standards for nuclear plants in 2006.
The simulations were based on 10.2-meter-high tsunami hitting reactors 5 and 6 of the Fukushima plant, 9.3-meter waves hitting unit 2 and 8.7- to 8.4-meter waves hitting reactors 1, 3 and 4.
A Tepco section chief reported the results to NISA on March 7. NISA officials had pointed out “countermeasures are urgently needed,” calling for modifications.
The simulations assumed the occurence of an 8.2-magnitude quake hitting the ocean trench along the Tohoku region to the Boso Peninsula of Chiba Prefecture. The March 11 temblor was 9.0-magnitude.
“We need to examine how and what measures were taken” after the simulation results were submitted to NISA, said Yoshinori Moriyama, a senior NISA official in charge of measures against nuclear disasters.
Kyodo, August 25, 2011
http://search.japantimes.co.jp/cgi-bin/nn20110825a1.html