There have been a couple of news stories that seem to indicate that both governments have decided to move past this potential breach. From Reuters:
U.S. Nuclear Regulatory Commission chairman Gregory Jaczko said the United States was working to provide ideas and possibly equipment to help Japan cool its overheating Daiichi nuclear power plant about 240 km (150 miles) north of Tokyo.From the New York Times:
He stressed that it could take weeks to succeed in cooling the reactor down.
"This is something that will likely take some time to work through, possibly weeks, as eventually you remove the majority of the heat from the reactors and then the spent fuel pool," Jaczko told a briefing at the White House.
His agency will carry out the U.S. review Obama requested. The commission will meet on Monday to begin discussions about it, a NRC spokesman said.
“There was a slight delay conveying to the U.S. side the information about whether or not there is water,” the government spokesman, Yukio Edano, said about the No. 4 reactor. Mr. Edano was responding to a question asked by a Japanese journalist at a morning news conference — the single one that dealt with Mr. Jaczko’s comments.I'm reading those two statements as Jaczko's pulling back and Japan's gracefully allowing him to do so.
Unfortunately, neither gives much information about what the status really is. I'm speculating, but the lack of unexpected events since the helicopter water drops and the water-cannon cooling suggests that those interventions were effective and that the containment, both of the reactors and of the water in the spent fuel pools, is reasonably intact.
Another note on the Jaczko incident. The Nuclear Energy Institute update for 5 pm Thursday, March 17:
Dan Poneman, the deputy secretary of energy, said today that two U.S. flights to Japan collected information on radiation levels. These readings informed the decision to recommend that Americans evacuate an area 50 miles from the Fukushima Daiichi nuclear energy facility.I would expect them also to collect air samples. The US has been doing this since the first Soviet nuclear test in 1949. The isotopes collected give a great deal of information about what's happening.