The Nuclear Regulatory Commission thinks the reactor in unit 2 of Japan’s disabled power plant got so hot it “probably melted through the reactor pressure vessel,” U.S. Representative Edward Markey said. Martin Virgilio, the agency’s deputy director for reactor and preparedness programs, told reporters after a House hearing today that the commission doesn’t think the “core has breached,” which would let radiation escape. The commission gets reports several times a day from agency staff in Japan and none mentioned a breach, he said. The pressure vessel is one line of defense preventing a larger radiation leak from Fukushima Dai-Ichi’s crippled reactors, where workers have sought to reconnect power to provide a steady supply of water. “After you lose the vessel, then you are down to one final barrier, that’s the containment,” Virgilio told reporters.