Possibly it's ongoing and concealed. All along, Japanese and Tokyo Electric (TEPCO) officials downplayed or lied about the severity of the crisis. Virtually nothing they say can be believed. 
 

Nor from the Obama administration, budgeting loan guarantees for new reactor construction instead of decommissioning all 104 nuclear plants because operating them risks full core meltdowns.
 

Partial or full ones gravely harm earth, air, water and food. Three hazardous Fukushima radioactive isotopes are especially problematic. University of Rochester Professor Jacqueline Williams, a radiation expert, says ingesting radioactive iodine-131 causes thyroid and other cancers. So does hazardous beta and gamma radiation from Cesium-137. Released Strontium 90 also causes leukemia and other cancers. Large amounts of all three are spewing daily.
 

Under a worst case scenario, millions of Japanese, Pacific rim and northern hemisphere people will be harmed, many gravely. Millions of deaths may result. The dangers of nuclear power can't be overstated. Potentially, all planetary life is threatened. What better reason to end all commercial and military use now.
 

Wikipedia calls a nuclear meltdown "an informal term for a severe nuclear reactor accident that results in core damage from overheating." Partial or full meltdowns result, releasing toxic atmospheric radiation. 
 

Through nuclear fission, reactors generate high heat to produce electricity - essentially boiling water to create steam, used to run turbines and generate power. Unless controlled, dangerously high heat results. 
 

Core meltdowns occur when heat generated exceeds what cooling systems remove, causing uranium and plutonium fuel to melt. At fault may be coolant problems, including accidents, fires, loss of coolant pressure, low coolant flow, or none at all from high heat causing evaporation. In other words, insufficient cooling elevates temperatures high enough to trigger melting and toxic atmospheric radiation releases.
 

Measured in rems (roentgen equivalent in man or mammal), it represents the amount needed to damage living tissue. All radiation is harmful, cumulative, permanent, and unforgiving. The more gotten, the greater the danger, especially doses over 100 rems, producing radiation sickness, including nausea, vomiting, headaches, white blood cell loss, and susceptibility to infection.
 

Doses above 200 rems cause hair loss and other harm. Above 300, significant internal harm, including damaged nerve cells, others lining the digestive track, the reproductive system, DNA and RNA. Severe white blood cell loss also results, the body's main defense against infection, causing vulnerability to cancer and other diseases.
 

Moreover, radiation reduces blood platelets production, making hemorrhaging more likely. Doses above 450 rems kill half of those exposed. Above 800 assures death in days, weeks, or longer-term after painful illnesses, including leukemia and other cancers.

High atmospheric radiation levels threaten life over the short or longer-term. The more ingested, absorbed or inhaled, the greater the risk. Fukushima is spreading large amounts. If unstoppable, all bets are off.
 

On March 17, New York Times writers Norimitsu Onishi, David Sanger and Matthew Wald headlined, "High Radiation Severely Hinders Emergency Work to Cool Japanese Plant," saying:
 

"Amid widening (global alarm), military fire trucks began spraying cooling water on (Fukushima's) spent fuel rods." Earlier, high radiation levels forced back police water cannon trucks. Japan's Self-Defense Forces dumped tons of seawater on Unit 3, saying later it was ineffective. Unknown is whether anything can work. In day six, everything tried failed, raising grave doubts, a frightening prospect if true.
 

Panic throughout Japan is increasing. Some Toyko residents are fleeing. Everyone is scared. Radiation levels are spreading and rising. People are jamming airports to leave. Some embassies and companies are evacuating their personnel. Inbound flights are being cancelled. 
 

An anonymous nuclear industry official told The Times of India that TEPCO management is "in a full-scale panic, (not) know(ing) what to do." On March 16, European Union Energy Commissioner Guenther Oettinger told an EU parliamentary committee:
 

Fukushima "is effectively out of control. In the coming hours, there could be further catastrophic events, which could pose a threat to the lives of people on the island," and beyond. 
 

In fact, global contamination is threatened. Obama said radioactivity wouldn't reach America. He lied. It will reach California by weekend and spread east across the entire country and North America. The industry-controlled World Nuclear News warned of a "dramatic escalation in Japan."
 

Compounding the threat, around 600,000 exposed Fukushima spent fuel rods are stored unprotected near the top of reactors, making them extremely vulnerable to melting. Nuclear engineer Arnie Gundersen said if they catch fire, it "would be like Chernobyl on steroids." 
 

Several fires, in fact, erupted. Others could ignite any time. If one or more containment vessels ruptures, all bets are off. Fears are it already happened, making a bad situation far worse. Fukushima is an unprecedented disaster, in unchartered territory. Understating the potential catastrophic risk is irresponsible and criminal.
 

On Wednesday, US Nuclear Regulatory Commission (NRC) chairman, Gregory Jaczko, told a congressional committee that thousands of Unit 4 spent fuel rods have little or no protective water, meaning they're exposed, melting, and spreading toxic atmospheric radiation. He added:
 

"We believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures."
 

Fukushima has six reactors. All risk meltdown. Experts believe a full plant evacuation may be necessary, leaving reactor and spent fuel rods to melt down, a potential worst case unstoppable "China syndrome."
 

Late Wednesday night, the US State Department announced a "voluntary" evacuation of government personnel dependents and other US citizens from northeastern Japan down to Tokyo and Yokohama.  Charter flights will be provided. Numerous other nations are urging their nationals to leave.