THE OPERATOR of Japan’s beleaguered Fukushima nuclear plant has said for the first time that uranium fuel in at least one of its six reactors has melted.
The admission effectively torpedoes a plan to flood the overheating fuel with water and bring a quick end to the world’s worst nuclear crisis since Chernobyl, say critics.
Tokyo Electric Power Company (Tepco) said water levels have fallen at least one metre below fuel rods inside reactor 1 and that melted fuel has dropped to the bottom of the reactor’s containment vessel.
Engineers are working inside the reactor building for the first time since the crisis began when a hydrogen explosion blew its roof off following the March 11th quake and tsunami.
Tepco general manager Junichi Matsumoto told reporters in Tokyo that the discovery means its timetable to entomb the containment reactor vessel in water may have to be scrapped. “The plan needs to be revised,” Mr Matsumoto said. “We can’t deny the possibility that a hole in the pressure vessel caused water to leak.”
Observers fear that reactor 3 which contains Mox fuel may have also suffered a meltdown, while the situation inside reactor 2 remains shrouded in mystery. Mox fuel, or mixed oxide fuel, consists of plutonium blended with natural uranium, reprocessed uranium or depleted uranium.
Tepco and Japan’s Nuclear Industrial Safety Agency had been arguing since last month that the crisis inside the Fukushima plant was stabilising and moving towards a controlled shutdown some time later this year.
“The situation is clearly far more serious than previously reported, and could escalate rapidly if the lava melts through the reactor vessel,” warned Jan Beránek of Greenpeace International. “As the fuel rods were fully exposed and subsequently melted, it is highly likely that the core’s integrity is compromised and that there is a larger amount of melted fuel at the bottom of the reactor pressure vessel.”
The Fukushima plant has been leaking radiation for two months as Tepco workers struggle to shut down reactors 1,2 and 3. Engineers have pumped 10,000 tons of water into the reactor 1 so far, more than enough to fill the reactor vessel and the containment building that surrounds it.
The fact that its fuel rods are still exposed suggests that the uranium could have melted a hole in the reactor vessel, Tepco admitted.
Seawater samples from near the plant showed levels of caesium-134 at 18,000 times safe levels following another spill, Tepco said. The fresh leak forced Japan’s government spokesman Yukio Edano into making another apology to South Korea and other neighbouring countries. Tepco says it has since stopped the leak.
Tepco critics say flooding the containment vessel and its exposed fuel with water risks an explosion that could destroy reactor 1. Japan’s nuclear and safety agency says that the temperature of the fuel suggests it is being cooled by water already inside the container, and that the water can be reused to achieve cold shutdown.