MOX fuel that was believed to have been kept cool at the bottom of one of the reactors at the crippled Fukushima No. 1 nuclear plant after its core melted is believed to have breached the vessel after melting again, a study said Monday.

The study by Fumiya Tanabe, an expert in nuclear safety, said most of reactor 3’s mixed uranium-plutonium oxide fuel may have dribbled into the containment vessel underneath, and if so, the current method being used to cool the reactor will have to be rethought. This could force Tokyo Electric Power Co. to revise its schedule for containing the five-month-old disaster.

Tepco earlier said that the cores of reactors 1 to 3 are assumed to have suffered meltdowns, although the melted fuel was believed to have been kept at cool enough to solidify at the bottom of each pressure vessel after water was injected.

After analyzing data made public by Tepco, Tanabe argues it became difficult to inject coolant water into the pressure vessel after the pressure rose early March 21. He says the fuel at the bottom overheated and melted again over a four-day period.

Kyodo, August 9, 2011

* http://search.japantimes.co.jp/cgi-bin/nn20110809a3.html

Outgoing nuclear agency chief was aware of possible meltdown at Fukushima plant

Nobuaki Terasaka, outgoing director general of the Nuclear and Industrial Safety Agency (NISA), said Aug. 10 that he was aware of the possibility of a meltdown at the Fukushima No. 1 Nuclear Power Plant due to the detection of cesium on March 12, a day after the Great East Japan Earthquake and tsunami crippled the plant.

“I thought the possibility (of a meltdown) cannot be ruled out,” Terasaka said at a news conference. His comment drew close attention because a NISA spokesman in March was replaced shortly after he admitted such a possibility.

The government said in June that the No. 1 to 3 reactor cores experienced meltdowns shortly after the March 11 natural disasters.

Mainichi Shimbun , August 11, 2011

* http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/11/20110811p2a00m0na005000c.html

Japan Nuclear Panel to Disclose All Documents

Tokyo, Aug. 8 (Jiji Press)—The Nuclear Safety Commission of Japan said Monday it will disclose all documents on its meetings before December 1996 in the wake of the nuclear crisis at Tokyo Electric Co.’ Fukushima No. 1 power plant.

The agency, which started to disclose information in that month, decided to open all the materials and minutes of the meetings to the public. It started the information disclosure following a sodium leak accident at the Monju fast breeder reactor in Tsuruga, Fukui Prefecture, central Japan, in December 1995.

There has been no clear standard for the disclosure of information compiled before December 1996.

Thousands of files will be disclosed, including some from about 30 years ago. The agency will upload the files to its Web site.

In 1993, a working group of the commission warned about the risk of damage to reactor cores at nuclear plants from loss of all AC power.

Jiji Press, August 8, 2011

* http://jen.jiji.com/jc/eng?g=eco&k=2011080800877