The first photographs of the inside of a reactor at the Fukushima No. 1 nuclear power plant taken since the March 11 earthquake show that the water level in the containment vessel may be lower than previously thought.
The first photographs of the inside of a reactor at the Fukushima No. 1 nuclear power plant taken since the March 11 earthquake show that the water level in the containment vessel may be lower than previously thought.Seven still images taken using an industrial endoscope in the No. 2 reactor were released on Jan. 19 by the plant’s operator, Tokyo Electric Power Co.Steam in the containment vessel of the reactor and high radiation levels limited the clarity of the images, but they raise the possibility that melted fuel at the bottom of the vessel may not be adequately covered by water, according to one nuclear expert.TEPCO officials had calculated that the water level in the No. 2 reactor was about 4.5 meters, but the endoscope was lowered to scaffolding used for inspection work within the reactor about 4 meters from the vessel bottom, and the water level could not be confirmed. TEPCO officials said it appeared likely that the water level was less than 4 meters from the bottom.TEPCO had stated that it believed some of the nuclear fuel in the reactor had melted and fallen to the bottom of the containment vessel, but the endoscope did not capture images of it.A thermometer was attached to the endoscope and recorded a gas temperature near the lower half of the containment vessel of 44.7 degrees. A temperature reading from a thermometer attached to the outside of the vessel was 42.6 degrees, indicating that the thermometer was giving accurate readings.White dots found on the images were likely the result of radiation, according to TEPCO officials. There did not appear to be damage to the piping in the images, but there were signs of rust. The peeling of paint on the inner wall of the containment vessel was likely the result of the sudden increase in the temperature soon after the accident, TEPCO said.There were also signs of water droplets on the lenses of the endoscope. The high temperature within the containment vessel has likely caused condensation similar to the interior of a steamy bathroom.TEPCO must determine the water level and whether its nuclear fuel has been adequately cooled before any work can begin to decommission the reactor.The endoscope used was manufactured by Olympus Corp. and has a diameter of 8.5 millimeters and a length of 10 meters. It was inserted through piping on the side of the containment vessel and placed about two meters into the containment vessel.The No. 2 reactor was chosen for the first endoscope survey because radiation levels were comparatively low and the location of the piping used to insert the endoscope was known.A total of 34 workers were involved in the operation, which took about 70 minutes. The maximum radiation exposure to the workers was 3.07 millisieverts.Experts said the still photos left many unanswered questions.Tadahiro Katsuta, associate professor of nuclear engineering at Meiji University, said: "While an inside look was provided much sooner than I expected, it is still too early to rest assured. The water level is lower than estimated, so there is the possibility that the melted fuel that fell to the bottom of the vessel is not being adequately covered by water."Keiji Miyazaki, professor emeritus of nuclear reactor engineering at Osaka University, said nothing definitive could be concluded about the state of the reactor because only part of the inside of the vessel was shown in the images. However, he said the damage did appear to be less than initially thought.He added that more work would have to be done to get a better view."What are needed for decommissioning work are images of the bottom of the reactor core, where damaged nuclear fuel is believed to have settled," he said.TEPCO officials said more detailed analysis and video images would be released after Jan. 20.After further analysis, TEPCO officials will consider how to survey the No. 1 and No. 3 reactors, including whether to insert industrial robots through larger openings.The road map for decommissioning the reactors that was released toward the end of last year by the central government and TEPCO said the removal of melted nuclear fuel would begin after about 10 years. A more detailed survey of the inside of the containment vessel is set for about 2017, and a similar survey of the pressure vessel has been set for about 2019.