Obama says it is unlikely that radiation will harm anyone in USA and update on Fukushima from NEI and BraveNewClimate

It is unlikely that radiation released from the nuclear reactors in Japan will harm anyone in the United States, President Obama said in a press briefing this afternoon.

In Japan, engineers have laid a power line that can connect reactor 2 of the Daiichi facility to the off-site power grid, the International Atomic Energy Agency reported. Workers are working to reconnect the power to reactor 2 after they complete spraying water into the reactor 3 complex to provide additional cooling to the used fuel pool. Reconnecting to the power grid is expected to enhance efforts to prevent further damage at the plant.

Japan's Nuclear and Industrial Safety Agency reported on Thursday that the backup diesel generator for reactor 6 is working and supplying electricity to reactors 5 and 6. TEPCO is preparing to add water to the storage pools that house used nuclear fuel rods at those two reactors.

UPDATE AS OF 1:30 P.M. EDT, THURSDAY, MARCH 17

Radiation readings at the Fukushima Daiichi site boundary were measured today at a lower level, between 2 and 3 millirem per hour.

Brave New Climate analysis from Barry Brook

Are the spent fuel in the pools in Units 3 and 4 are now uncovered? The big concern here is that unlike the releases from damaged fuel in the reactor cores of Units 1, 2, and 3, which were largely filtered by scrubbing in the containment suppression pools (wetwell torus), releases of volatile fission products (e.g., cesium and iodine) from these spent fuel pools have direct pathways to the environment, if they remain dry for an extended period.

Efforts to deliver water to these pools have proven to be very difficult, and fuel damage may be occurring. If they are exposed, then the use of the evaporation of salt water as a heat sink over periods of more than a few days is not viable because the quantities of salt deposited as the water evaporates becomes large in volume and plugs the flow paths through the fuel, degrading heat removal. Everything that is cooled becomes a heat sink to condense anything volatilized. Unfortunately, a fresh water supply seems difficult to come by.

In sum, this accident is now significantly more severe than Three Mile Island in 1979. It resulted from a unique combination of failures to plant systems caused by the tsunami, and the broad destruction of infrastructure for water and electricity supply which would normally be reestablished within a day or two following a reactor accident. My initial estimates of the extent of the problem, on March 12, did not anticipate the cascading problems that arose from the extended loss of externally sourced AC power to the site, and my prediction that ‘there is no credible risk of a serious accident‘ has been proven quite wrong as a result. It remains to be seen whether my forecast on the possibility of containment breaches and the very low level of danger to the public as a result of this tragic chain of circumstances will be proven correct. For the sake of the people there, I sure hope it does stand the test of time.

So it is now generally agreed that this is an International nuclear and radiological event scale 6 event. Worse than Three mile island (5) but not yet to Chernobyl (7).