As authorities work to avoid a full meltdown at the Fukushima Daiichi power plant, where a second explosion occurred this morning and where three of four nuclear reactors are now experiencing severe cooling problems, potentially harmful radiation has already been introduced to the surrounding environment. There's still a good deal that's uncertain about how the situation will play out, but here's where things stand now.
What's causing the radiation leak?
Friday's tsunami easily overcame sea walls at the Fukushima Daiichi power plant and flooded the diesel generators that power the plant's cooling systems. Operators have been using sea water to cool the nuclear fuel, though this has resulted in a build-up of pressure that's required operators to vent the reactors' cooling vessels by releasing radioactive steam into the atmosphere. The radioactive material in the steam is, at this point, relatively modest, and the most highly radioactive material remains contained in the reactors' cores. The two explosions at the Fukushima Daiichi plant were the byproduct of hydrogen build-up, and neither is thought to have released significant amounts of radiation into the atmosphere.
Who's currently at risk?
Some 140,000 people were evacuated from the areas surrounding the troubled plants over the weekend - about 110,000 in the 20km surrounding the Fukushima Daiichi plant and 30,000 in a 10km radius around the Fukushima Daini plant. Evacuations will continue as authorities gather more evidence on where and how the radioactive material is spreading. Those most at risk, however, are the plant operators themselves. Re-establsihing the cooling system at the Daiichi plant for example will likely require plant technicians to access areas that have already been highly contaminated.
How serious is the problem?
While it could get really bad really fast if one of the reactors themselves were to crack open - a full meltdown would release significant amounts of radioactive elements like iodine-131 that disperse rapidly in air and water, greatly increasing the chances for birth defects, thyroid cancer and other problems - health experts are currently cautiously optimistic. As of this weekend, radiation levels in the plant's control room were 1000 times higher than normal but only eight times above normal in areas surrounding the plant. According to Ron Chesser, director of the centre for Environmental Radiation Studies at Texas Tech University, both of those levels are technically safe for humans, who absorb an average of 360 millirems of radiation per year from cosmic rays and manmade sources. Still, three elements in particular - iodine-131, strontium-90 and cesium-137 - are worrisome because they mimic substances found naturally in the body.
What happens to those who have been exposed?
The combination of the modest levels of radioactive material in the steam that has been vented and the swift evacuation of the areas surrounding the concerned plants means that harmful exposure, at this point, has likely been limited. Exposure to moderate levels of radiation can result in radiation sickness, causing nausea, vomiting, and fever, though potassium iodine tablets can be taken to offset these symptoms, preventing the body from absorbing the radioactive iodine originating from the reactors.
Where is the radiation spreading?
The hope is that the modest amounts of radioactive steam that have already been introduced to the environment will blow out to sea, though a shift in winds could direct it back toward Japanese cities. Still, there are signs that the material is spreading more quickly than initially thought; helicopters equipped with radioactive counters have detected small amounts of radioactive material up to 100km offshore from the Fukushima Daiichi plant.
How close are we to being in the clear?
That remains to be seen. While Tokyo Electric Power Co, the plants' operator, remains confident (at least publicly) that a full meltdown can be avoided, the nuclear cores are continuing to heat up and the pressure-relieving steam releases could be necessary for weeks or even months, likely preventing evacuees from returning to their homes anytime soon. Still, according to the WSJ, radiation levels are already receding from their weekend highs, which is a good sign.
Is this the next Chernobyl?
Almost certainly not. While radioactive material has indeed leaked, the contamination to the areas surrounding the plants has thus far been limited. Moreover, the reactors at the Fukushima plants are fundamentally safer than those used at Chernobyl, housed in steel containment vessels and employing water instead of carbon to slow down neutrons, eliminating the possibility of quick-spreading radioactive soot as was seen after the Chernobyl disaster. Still, despite the seawater cooling and steam blasts, the cores at Fukushima Daiichi are continuing to heat up, and if one them were to explode, then the crisis would become much more serious. [NYT, BBC, NPR, WSJ 1, 2]