TEPCO may have hoped that it was one of those vent pipes from the dry well to the suppression chamber in Reactor 2 that was leaking the water injected into the RPV, but the awkward 4-legged Robot by Toshiba couldn't find any leak. So the conclusion is that the suppression chamber is probably leaking.
I would think it will be much harder (near impossible) to plug, because the suppression chamber is submerged in highly contaminated water.
From Jiji Tsushin (3/15/2013; part):
TEPCO says leak may be from the Reactor 2 suppression chamber
TEPCO announced on March 15 that there was no leak after examining the "vent pipes" that connect to the suppression chamber of Reactor 2 containment vessel at Fukushima I Nuclear Power Plant. The water leaked into the basement of the reactor building was likely to be coming from the suppression chamber.
In that press conference on March 15, TEPCO's spokesman (no longer Mr. Matsumoto, I don't know the name of this young person who croaks when he speaks) didn't explicitly admit that the leak was from the suppression chamber; instead, he said, in response to a question by the reporter from Tokyo Shinbun on how TEPCO felt about the discovery (after 27 minutes):
Since the leak is not from the PCV (primary containment vessel), it will be easier to plug the leak.
How could a repair job in an inaccessible part of the suppression chamber (lower half) be easier?
His reasoning was that the PCV was closer to higher contamination, so any repair work away from the PCV would be easier. He tried to spin it as a positive discovery. "The PCV is sound, and it's a good thing", he said. The only problem was how to find the leak in the lower half (submerged part) of the suppression chamber, or other locations, he said.
It didn't seem like an answer to me, but as usual, the reporter said "OK, I got it", and that was the end of his questions.
(I miss the previous spokesman Matsumoto, who looked like Doraemon. He didn't try to spin, like the current one does.)
One of the photos taken by Toshiba's robot, released on March 15, 2013. Lots of white noise (click to enlarge):
The radiation levels inside the Reactor 2 torus room is not known. TEPCO couldn't lower the camera and dosimeter through the hole drilled on the 1st floor when they found out there were unexpected pipes blocking the way.