TEPCO failed to report possible hydrogen explosion
Tokyo Electric Power Co. knew there could be an explosion at the No. 3
reactor at the Fukushima No. 1 nuclear power plant the day before it
happened, but didn’t report the possibility to authorities.
The failure to notify the central and local governments was revealed in
reports submitted by TEPCO to the Nuclear and Industrial Safety Agency
(NISA) of the Ministry of Economy, Trade and Industry (METI).
The reports were made available on NISA’s website June 24.
>From March 11 to May 31, TEPCO provided 11,000 documents to NISA and
neighboring local governments by fax based on Article 10 of the special
measures law on nuclear disasters.
According to the documents, a hydrogen explosion took place at the No. 3
reactor building around 11 a.m. on March 14, blowing off the upper part
of the building.
Before the explosion, however, TEPCO did not submit to NISA data it had
showing that an explosion was possible.
According to the data, 300 millisieverts of radiation per hour were
detected in the No. 3 reactor building at 1:17 p.m. on March 13, a day
before the explosion.
A report written at 2:07 p.m. also stated there was a strong possibility
that hydrogen had accumulated in the No. 3 reactor building.
At 5:20 a.m. on March 14, TEPCO’s head office ordered officials at the
nuclear power plant to again check hydrogen concentrations in the No. 3
reactor building, a document revealed.
The documents indicate hydrogen was being produced because the fuel rods
were exposed to air after the earthquake and tsunami destroyed the
cooling system.
However, TEPCO did not report these findings to NISA or local governments.
At a news conference in May, NISA spokesman Hidehiko Nishiyama said: "If
we had understood the situation in the No. 3 reactor building before the
explosion, we would have notified the public. We will look at TEPCO’s
failure to report the facts to NISA in the course of the full
investigation into the explosion."
Regarding the dumping of seawater into the pressure vessel of the No. 1
reactor to cool it, officials at the plant started the injection at 7:04
p.m. on March 12 and continued it without suspension.
However, TEPCO incorrectly told NISA it had suspended the operation for
a short time before restarting at 8:20 p.m.
This report was also included in the documents made available on NISA’s
website.
Based on the inaccurate report, lawmakers held heated discussions in the
Diet on whether the suspension was a good idea when in reality the
effort to cool the reactor with seawater had never stopped.
Takashi Sugimoto and Eisuke Sasaki, Asahi Shimbun, June 26, 2011
http://www.asahi.com/english/TKY201106250160.html
TEPCO likely failed to vent No. 1 reactor at tsunami-hit nuclear plant
Tokyo Electric Power Co. (TEPCO) likely failed in its attempt to vent the No. 1 reactor of its tsunami-hit Fukushima No. 1 Nuclear Power Plant in mid-March shortly before a hydrogen explosion, despite its claim that it successfully vented the reactor, it has emerged.
TEPCO insiders said the valves for venting the reactor did not sufficiently open, and TEPCO’s headquarters admitted that it has not confirmed whether the valves opened.
Experts have pointed out that data released by the utility suggests that one of the valves closed after it briefly opened. However, it still remains unclear whether the hydrogen explosion in the reactor building was caused by a venting failure, as experts say it is possible that hydrogen was accumulating even before the venting attempt.
Shortly after noon on March 12, the pressure inside the containment vessel in the plant’s No. 1 reactor surged to 600 kilopascals — far above the upper designated limit of 427 kilopascals — prompting the plant manager to instruct workers to vent the reactor building.
At 6:50 a.m., the government ordered TEPCO to vent the reactor building under the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors. Plant workers began to vent the reactor at around 9 a.m.
In venting a reactor, steam and hydrogen in its containment vessel are sent through pipes from the suppression pool at the bottom of the vessel. This passes through the AO valve unit that is driven by air on the basement of the reactor building and the MO valve on the second floor that is driven by electric power, before being released out of the building through a duct.
The AO valve unit consists of a small valve and a big valve, and if one of them functions, steam can be led into the duct.
TEPCO workers operated the emergency lever to manually open the MO valve by 25 percent at around 9:15 a.m. About 15 minutes later, they attempted to manually open the small valve in the AO unit, but abandoned it because radiation levels around the unit were extremely high. At 10:17 a.m., the workers tried to open the small valve by remote control from the central control room.
More than 10 minutes afterward, radiation levels outside the No. 1 reactor building rose sharply, indicating that radioactive substances were being released from the structure. However, the levels returned to normal just 30 minutes later.
The pressure inside the containment vessel failed to decline, and TEPCO was unable to confirm whether its attempt to vent the reactor was effective.
At around 2 p.m., TEPCO used an air compressor borrowed from another company to send compressed air into the big valve in an attempt to open it.
The pressure inside the containment vessel subsequently decreased from 755 kilopascals recorded shortly before the work commenced to 530 kilopascals.
However, TEPCO insiders have admitted that the valves were not sufficiently opened. Specifically, the air compressor did not sufficiently compress the air to fully open the big valve, according to the insiders. Moreover, an indicator in the reactor did not show that the valves had opened.
The pressure inside the containment vessels stopped decreasing at around 3 p.m. and then continued to rise until the hydrogen explosion occurred at 3:36 p.m.
“We concluded that we successfully vented the reactor because the pressure inside its containment vessel declined. We haven’t confirmed whether the big valve opened,” a TEPCO official said.
NISA denied that it had determined TEPCO was successful in venting the reactor.
“It was TEPCO that judged that it had successfully vented the reactor, but the government hasn’t mentioned whether the attempt was successful,” a NISA representative said.
In a report submitted to the International Atomic Energy Agency, the government clearly stated that TEPCO had concluded that it was successful in venting the reactor, which is expected to stir controversy during discussions of the government’s fact-finding panel.
Mainichi Shimbun , June 24, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/06/24/20110624p2a00m0na011000c.html
Suspected failure to vent Fukushima reactor casts doubt on accountability standards
Revelations that Tokyo Electric Power Co. (TEPCO) highly likely failed to vent a crippled reactor at its tsunami-hit Fukushima No. 1 Nuclear Power Plant have raised doubts about the utility’s and government’s accountability standards.
TEPCO had claimed that it had successfully vented the plant’s No. 1 reactor to decrease pressure inside it prior to a hydrogen explosion, and the government had supported the power supplier’s claim.
The power company attempted to vent the reactor on March 12, the day after the tsunami triggered by the Great East Japan Earthquake hit the plant. After confirming that the pressure inside the containment vessel of the reactor had declined, TEPCO announced at around 3 p.m. that it had succeeded in venting the reactor.
However, the pressure still remained above the designated upper limit of 427 kilopascals and rose moderately after the announcement. Moreover, the monitoring post on its premises showed no signs of radioactive materials being released out of the reactor following the venting attempt. TEPCO insiders say they were unable to confirm that the valve for venting had opened.
Both TEPCO and the government could have checked whether the venting was successful on many occasions. Nevertheless, the government simply mimicked TEPCO’s comments on the matter in a report it submitted to the International Atomic Energy Agency (IAEA) on June 7, without scrutinizing the utility’s view for nearly three months.
In 1992, the International Trade and Industry Ministry (the predecessor of the Ministry of Economy, Trade and Industry) urged power suppliers to equip all reactors at their nuclear power plants with valves and other venting devices as part of their accident management efforts.
TEPCO increased the pressure capacity of the reactors at the Fukushima No. 1 plant and finished equipping them with valves for venting by 2001.
However, the power company has now admitted that it cannot confirm whether it was successful in venting not only its No. 1 reactor but also its No. 2 reactor.
The apparent failure to vent the reactor, which the government viewed as an effective way to respond to a serious nuclear power accident, has raised questions about government regulatory bodies’ safety measures for nuclear power plants.
The government’s fact-finding panel is urged to closely scrutinize whether the utility was sufficiently prepared for a possible serious accident at its nuclear power stations as well, as it assumed that the plant could be hit by a massive tsunami like the one triggered by the March 11 quake. (By Naritake Machida and Shusaku Sugimoto, Tokyo City News Department)
Mainichi Shimbun , June 24, 2011
http://mdn.mainichi.jp/perspectives/column/news/20110624p2a00m0na006000c.html