One of the most startling findings announced Thursday was that water levels in the reactor vessel, which houses the fuel rods, appeared to be about three feet below where the bottom of the fuel rods would normally stand. Ever since the reactor shut down, workers’ primary task has been to keep pouring water into the reactors to ensure the nuclear fuel remained covered so that it would not melt. But the new information suggests the fuel was uncovered for at least some time, probably early in the crisis.
That indicated that the exposed fuel has probably melted and slumped to the bottom of the vessel in little pellets, Junichi Matsumoto, a Tepco spokesman, said Thursday at a news conference.
David Lochbaum of the Union of Concerned Scientists, a nonprofit group usually critical of the nuclear industry, agreed that the temperature readings were a good sign.
He said he believed that the damage to the fuel at Reactor No. 1 was already finished, and that even if some fuel rods were still standing — and therefore exposed — they were no longer hot enough to keep melting.
“As bad as things are,” Mr. Lochbaum said, “they’re getting better.”
At the Nuclear Regulatory Commission in Washington, R. William Borchardt, the top staff official, briefed the five members of the commission on Thursday morning about the new disclosures, but did not describe them as major developments. Over all, he described the status of the Fukushima complex as “not exactly stable, but you might say that they’re static.”
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