How long before meltdown

The Fukushima Daiichi station, which has been hit hard by the March 11 earthquake, houses six of those reactors, all of which came online in the s. Worldwide, nuclear energy accounts for about 15 percent of electricity generation; Japan gets nearly 30 percent of its electricity from its nuclear plants.

The U. About 20 percent of U. What fuels a nuclear reactor? Most nuclear reactors use uranium fuel that has been "enriched" in uranium , an isotope of uranium that fissions readily. Isotopes are variants of elements with different atomic masses.

Uranium is much more common in nature than uranium but does not fission well, so fuel manufacturers boost the uranium content to a few percent, which is enough to maintain a continuous fission reaction and generate electricity.

Enriched uranium is manufactured into fuel rods that are encased in metal cladding made of alloys such as zirconium. Reactor No. How do you turn off a nuclear reaction?

Sustained nuclear fission reactions rely on the passing of neutrons from one atom to another—the neutrons released in one atom's fissioning trigger the fissioning of the next atom. The way to cut off a fission chain reaction, then, is to intercept the neutrons. Nuclear reactors utilize control rods made from elements such as cadmium, boron or hafnium, all of which are efficient neutron absorbers.

When the reactor malfunctions or when operators need to shut off the reactor for any other reason technicians can remotely plunge control rods into the reactor core to soak up neutrons and shut down the nuclear reaction. Can a reactor melt down once the nuclear reaction is stopped? Even after the control rods have done their job and arrested the fission reaction the fuel rods retain a great deal of heat. What is more, the uranium atoms that have already split in two produce radioactive by-products that themselves give off a great deal of heat.

So the reactor core continues to produce heat in the absence of fissioning. If the rest of the reactor is operating normally, pumps will continue to circulate coolant usually water to carry away the reactor core's heat. In Japan the March 11 earthquake and tsunami caused blackouts that cut off the externally sourced AC power for the reactors' cooling system.

According to published reports, backup diesel generators at the power plant failed shortly thereafter, leaving the reactors uncooled and in serious danger of overheating.

From the perspective of safety, these are highly important pieces of equipment. Cracks were found in the Fukushima Daiichi Power Plant, reactor one, reactor two, reactor three, reactor four, reactor five. The report is not confirmed to have been filed as of this time. The problems were not only with the piping. Gas tanks at the site also exploded after the earthquake. The outside of the reactor building suffered structural damage.

There was some chaos. There was no one really qualified to assess the radioactive leakage because, as the Nuclear Industrial Safety Agency admits, after the accident all the on-site inspectors fled the site.

And the quake and tsunami broke most of the monitoring equipment so there was little information available on radiation afterwards. Before the dawn on March 12, the water levels at the reactor began to plummet and the radiation began rising. Meltdown was taking place. According to The Chunichi Shinbun and other sources, a few hours after the earthquake extremely high levels of radiation were being measured within the reactor one building.

The levels were so high that if you spent a full day exposed to them it would be fatal. The water levels of the reactor were already sinking. After the Japanese government forced TEPCO to release hundreds of pages of documents relating to the accident in May, Bloomberg reported on May 19 that a radiation alarm went off 1.

TEPCO would not deny the possibility that there was significant radiation leakage before the power went out. They did assert that the alarm might have simply malfunctioned. On March 11, at p. Around 11 p. The meltdown was already underway.

Oddly enough, while TEPCO later insisted that the cause of the meltdown was the tsunami knocking out emergency power systems, at the p. TEPCO press conference the same day, the spokesman in response to questions from the press about the cooling systems stated that the emergency water circulation equipment and reactor core isolation time cooling systems would work even without electricity.

Sometime between 4 and 6 a. Seawater was not pumped in until hours after a hydrogen explosion occurred, roughly p. By then, it was probably already too late. As Burnie points out, TEPCO also admitted massive fuel melt hours after loss of coolant, and hours before the explosion in unit 1. Walls and equipment collapse, and dozens of fires start up, including one on top of the neighboring reactor. Despite all evidence to the contrary, the nuclear engineer in charge of the test insists that reactor No.

He later dies of radiation poisoning. They have no knowledge of the radiation and wear no protective clothing. Police officers assisting with the roadblock likewise have no knowledge of the radiation and wear no protective clothing. April 26, , 5 a. They are re-opened months later. April 27, , 10 a. The Elephants Foot of the Chernobyl disaster in the immediate aftermath of the meltdown. April 27, 2 p.

Residents are informed it will be temporary and that they should pack only vital documents and belongings, plus some food. Soon after, however, an exclusion zone is set up around Chernobyl that prevents their return. April 28, Swedish air monitors detect a large amount of radiation in the atmosphere, which is traced back to the USSR. April 29, Spy satellite photos provide U. May 1, Soviet officials refuse to cancel the May Day festivities in Kiev, even as radiation continues to be released unabated.