Following the cue from Nuclear and Industrial Safety Agency, who finally admitted that the fuel pellets may have melted, TEPCO now says the fuel rods may have melted in the Reactor 1.
Even the inept Japanese government already admitted, through the Prime Minister's advisor, that they knew the core had melted but they didn't feel like announcing it.
But don't worry, says TEPCO, chlorine-38 wasn't detected after all (as we now interpret the data according to the advice of the experts under the government guidance), so there is no "re-criticality" as some have alleged happening.
(Expect the admission of re-criticality in about 3 weeks.)
From Yomiuri Shinbun (4/20/2011):
And this is the new and improved data on water in the Reactor 1 turbine room from March 24 that have been re-evaluated for accuracy, and the proof that there is no re-criticality (no chlorine-38; on the table it says "below detectable range"). The second column from the left is the new and improved interpretation, the third column from the left is the original announcement on March 25. The column on the right indicates reasons for change (if any), and in the case of chlorine-38, the reason was "Based on the guideline from NISA to avoid misinterpretation of the data, the nuclides were identified and the level of radiation determined by the main peaks."
Junichi Matsumoto of TEPCO admitted on April 20 [in the press conference] that there was a possibility that the fuel rods have melted in the Reactor 1, where about 70% of the fuel rods may have been damaged". Matsumoto said "the melted fuels may be stuck in the middle of the Pressure Vessel and hasn't dropped to the bottom."He cited the lower temperature at the bottom of the Pressure Vessel than at the top as the reason for his assumption. So far, TEPCO has described the damage of the fuel rods as probably "holes on the surface, or the cracked cladding", and has avoided commenting on the fuel melt.
To browse through the charts, go here and click on the PDF files at the bottom. They are in Japanese. No English version has been posted yet.