Mark Willacy reported this story on Thursday, May 12, 2011 18:10:00

MARK COLVIN: The company that owns the Fukushima nuclear plant, Tepco, has finally admitted what many have long suspected, that one of their reactors underwent a full meltdown after the tsunami that hit Japan's east Coast.



They say the fuel rods in the number one reactor at the Fukushima Daiichi plant are exposed.



We begin with our Tokyo correspondent Mark Willacy.



Mark this has, as I say, been long suspected, but what are they saying today?



MARK WILLACY: Well what they're saying Mark is that these fuel rods, which are about four metres long each, have been exposed, in other words, the water has not been covering them and keeping them cool.



The exposed area of the rods is about 1.5 to 1.7 metres long and that a large part of this fuel has now melted and that it's probably dripped down to the bottom of the containment vessel.



Now the Tepco operator had estimated earlier that about 55 per cent of the reactor core at number one had been damaged.



We assume this will make them obviously have a re-evaluation; this could really push things up a notch or two because this is talking about meltdowns.



Now, the one thing the company is saying is that the temperature inside that reactor, the number one reactor is stable and it is cool, so that is one piece of good news coming from Tepco at least.



MARK COLVIN: I think it was just last week I read a piece saying that the radiation levels in the number one reactor had dropped enough for them to be able to get people in there for the first time in some time. Now, is it just because of that, that they've been able to get in there, that they've discovered this?



MARK WILLACY: We believe so. We were told that the reactors one, two and three as you mentioned were stabilising. We've now been told that in reactor one at least these fuel rods have been exposed, that some of them have melted and that they are potentially at the bottom of the containment vessel, which is a major issue.



And we've had a statement just in the last little while from Greenpeace saying, look this situation is clearly far more serious than previously reported and could escalate rapidly if "the lava melts through the reactor vessel".



So that's the worst case scenario but what we're hearing from Tepco at least is that everything is cool inside the reactor there's no overheating at this stage, although there has been some meltdown.



MARK COLVIN: So we know that it is still inside the metal vessel.



MARK WILLACY: That's right, that's what we understand. We understand there's been no breach of that metal containment vessel.



MARK COLVIN: See I asked the nuclear regulator in that first week about what was under that vessel in reactor number one because I had been told that there wasn't necessarily anything; there wasn't a proper containment vessel, a concrete containment vessel under the metal containment vessel.



He didn't know and I've never seen a satisfactory answer to that; do we know what's underneath?



MARK WILLACY: I think you're not the only one who hasn't seen a satisfactory answer; the Japanese people certainly haven't been told. Obviously Tepco has now squashed it's obviously three or four press conferences a day into one. The Japanese media get all the questions and I don't believe that that question, either it hasn't been asked or it hasn't been answered.



So it's a very good question and it's one that Tepco hasn't provided an answer on at least at this stage.



MARK COLVIN: Because the significance is whether this meltdown just drops down into a concrete vessel underneath as I say, or whether it drops down into the earth below, with the possibility of contaminating the water table and basically drilling down a lot further.



MARK WILLACY: That's right and the assumption is and obviously assumption's a very dangerous thing when you're dealing with nuclear power plants, like ones that crippled at Fukushima, that there is some sort of concrete containment vessel under the main metal vessel that holds the fuel rods in. Because if that, as you say, escapes out of the initial vessel, nothing's going to stop it if there's no concrete containment there.



And we're getting more worrying news from the Government here as well I have to say we've had the chief cabinet secretary, Yukio Edano today again apologise and this time again it's over reactor number three, which we obviously have heard is leaking more radioactive water into the sea. He said this is a very "deplorable issue".



So the news, after not getting much news for a while, we've heard that the three nuclear reactors have stabilised; now that people are going back in to have a look around, the bad news seems to be leaching out.



MARK COLVIN: Well we'll see what happens in number two and number three.



Mark Willacy is our Tokyo correspondent. Thanks Mark.