Cold Shutdown … or Escape of Hot Fuel?
I noted last month in connection with Tepco’s announcement of “cold shutdown” of the Fukushima reactors:
If the reactors are “cold”, it may be because most of the hot radioactive fuel has leaked out.
The New York Times pointed out last month:
A former nuclear engineer with three decades of experience at a major engineering firm … who has worked at all three nuclear power complexes operated by Tokyo Electric [said] “If the fuel is still inside the reactor core, that’s one thing” …. But if the fuel has been dispersed more widely, then we are far from any stable shutdown.”
Indeed, if the center of the reactors are in fact relatively “cold”, it may be because most of the hot radioactive fuel has leaked out of the containment vessels and escaped into areas where it can do damage to the environment.
After drilling a hole in the containment vessel of Fukushima reactor 2, Tepco cannot find the fuel. As AP notes:
The steam-blurred photos taken by remote control Thursday found none of the reactor’s melted fuel ….
The photos also showed inner wall of the container heavily deteriorated after 10 months of exposure to high temperature and humidity, Matsumoto said.
TEPCO workers inserted the endoscope — an industrial version of the kind of endoscope doctors use — through a hole in the beaker-shaped container at the Fukushima Dai-ichi plant’s No. 2 reactor ….
The probe failed to find the water surface, which indicate the water sits at lower-than-expected levels inside the primary containment vessel and questions the accuracy of the current water monitors, Matsumoto said.
And while cold shutdown means that the water inside the reactors is below the boiling point, CNN reports:
Massive steam and water drops made it difficult to get a clear vision….
Given that steam forms when water boils, this is an indication that the reactor is not in cold shutdown.
Asahi Shimbun reports:
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.”
The Daily Yomiuri notes that even Tepco has gone from 100% confident that water was covering the fuel to saying it is “quite unlikely” that there is any problem:
Drops of water fall like rain in the video, which was shot using an industrial endoscope. The drops were apparently the result of vapor–created by the heat from melted nuclear fuel–that cooled inside the upper part of the reactor containment vessel.
“It’s quite unlikely nuclear fuel was exposed, as liquid from condensation is dripping down,” a TEPCO official said.
Mainchi points out that reactors 1 and 3 are probably in no better shape:
The fuel inside the Nos. 1 to 3 reactors is believed to have melted through the pressure vessels and been accumulating in the outer primary containers after the Fukushima plant lost its key functions to cool the reactors in the wake of the earthquake and tsunami on March 11 last year.