Date: 11/1/2011
by: Catherine Kobayashi
Part 1 from http://www3.nhk.or.jp/daily/english/02_10.html
The operator of the Fukushima Daiichi nuclear plant has poured water containing boric acid into the No. 2 reactor.
The move followed the detection of a radioactive substance, xenon, in the reactor's containment vessel, indicating that nuclear fission may have resumed.
Tokyo Electric Power Company poured boric acid solution into the No. 2 reactor for one hour from shortly before 3 AM on Wednesday.
Last Friday, TEPCO began operating equipment to remove radioactive substances from the No. 2 reactor.
The device sucks out gas from the containment vessel and filters out radioactive materials. The company has been analyzing the types of radioactive substances and their density near the outlet of the device.
On Tuesday, TEPCO detected xenon-133 and xenon-135, substances that are produced during the nuclear fission of uranium-235. The company says the possibility of nuclear fission inside the reactor cannot be excluded.
TEPCO says even if nuclear fission has resumed, it should be on a small scale as there have been no major changes in the temperature or pressure of the reactor, or radiation levels at monitoring posts around the compound.
The government's Nuclear and Industrial Safety Agency says it is unlikely that nuclear fuel has begun melting again as the density of the xenon is low and there has been no change in the reactor temperatures. The agency says it will continue to monitor the xenon in the reactor.
Wednesday, November 02, 2011 07:27 +0900 (JST)
Part 2 from http://www3.nhk.or.jp/daily/english/02_13.html
A nuclear energy expert says the presence of xenon in the No.2 reactor leaves open the possibility that localized and temporary fission could still occur.
Professor Koji Okamoto of the University of Tokyo Graduate School says substances from melted fuel that could undergo fission are probably scattered around, but are unlikely to react.
He says, however, that neutrons from radioactive materials could react with the uranium fuel and other substances.
Okamoto says a self-sustaining chain reaction that creates criticality is unlikely to happen because huge amounts of boric acid have been poured into the reactor.
He adds that these neutrons must be closely monitored to make sure fission does not take place.
The professor also referred to a plan by the government and TEPCO to achieve a state of cold shutdown by the end of the year. He says that if fission reactions are not under control, it would not be a cold shutdown.
Okamoto says TEPCO must locate the melted fuel inside and outside the reactor in order to prevent further reactions.
Wednesday, November 02, 2011 10:24 +0900 (JST)
