After a once-in-300-years earthquake, the Japanese have been keeping cool amid the chaos, organizing an enormous relief and rescue operation, and generally earning the world's admiration. We wish we could say the same for the reaction in the U.S., where the troubles at Japan's nuclear reactors have produced an overreaction about the risks of modern life and technology. 
 
 Part of the problem is the lack of media proportion about the disaster itself. The quake and tsunami have killed hundreds, and probably thousands, with tens of billions of dollars in damage. The energy released by the quake off Sendei is equivalent to about 336 megatons of TNT, or 100 more megatons than last year's quake in Chile and thousands of times the yield of the nuclear explosion at Hiroshima. The scale of the tragedy is epic. 
 
 Yet the bulk of U.S. media coverage has focused on a nuclear accident whose damage has so far been limited and contained to the plant sites. In simple human terms, the natural destruction of Earth and sea have far surpassed any errors committed by man. 
 
 Editorial Board Member Mary Kissel explains the Japanese response to the quake. 
 
 Given the incomplete news reports, it is impossible to say how much worse the nuclear damage will be. Unlike the Soviets at Chernobyl, the Japanese have been taking sensible precautions like evacuating people near the plants and handing out iodine pills even if they may never be needed. These precautions increase public worry, but better to take them even if they prove to be unnecessary. 
 
 We will have plenty of time to dissect events at the reactors and the safety lessons going forward. William Tucker provides some useful context nearby, and one crucial point is that the containment walls seem to have held. These walls are designed to withstand quakes and explosions, and it is good news if they have done so. The crisis seems to have been triggered by the failure of diesel generators that provided electricity to cool the reactors once they were shut down. Mr. Tucker explains that this weakness has been corrected in new nuclear plant designs. 
 
 We have no special brief for nuclear power over any other energy source. Our view is that it should compete with other sources on a market basis, without subsidies or government loan guarantees. Every energy source has risks and economic externalities, whether they are noise and bird kills (wind), huge land requirements (solar), rig explosions and tanker spills (oil), or mining accidents (coal). 
 
 But more than other energy sources, nuclear plants have had their costs increased by artificial political obstacles and delay. The U.S. hasn't built a new nuclear plant since 1979, after the Three Mile Island meltdown, even as older nuclear plants continue to provide 20% of the nation's electricity. 
 
 Enlarge Image Close JIJI PRESS/AFP/Getty Images An aerial photo shows the quake-damaged Fukushima Dai-Ni nuclear power plant. 
 
 The Tennessee Valley Authority is a couple of years away from completing a reactor at Watts Bar after years of effort. Proposals for 20 new reactors to be built over the next 15 to 20 years are in various stages of review in the multiyear approval process at the Nuclear Regulatory Commission, with two each in Georgia and South Carolina at the front of the line. But the much-ballyhooed "nuclear renaissance" is a long way off, and it will be longer after events in Japan. 
 
 Our larger point is less about nuclear power than how we react as a society to inevitable disasters, both natural and man-made. Because a plane crashes, we don't stop flying. Because an oil rig explodes in the Gulf, we don't (or at least we shouldn't) stop drilling for oil. And because the Challenger space shuttle blew up, we didn't stop shuttle flights—though we do seem to have lost much of our national will for further manned space exploration. We should learn from the Japanese nuclear crisis, not let it feed a political panic over nuclear power in general. 
 
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 The paradox of material and technological progress is that we seem to become more risk-averse the safer it makes us. The more comfortable we become, the less eager we are to take the risks that are the only route to future progress. The irony is that one reason Japan has survived this catastrophic event as well as it has is its great material development and wealth. 
 
 Modern civilization is in the daily business of measuring and mitigating risk, but its advance requires that we continue to take risk. It would compound Japan's tragedy if the lesson America learns is that we should pursue the illusory and counterproductive goal of eliminating all risk. ||||| Even while thousands of people are reported dead or missing, whole neighborhoods lie in ruins, and gas and oil fires rage out of control, press coverage of the Japanese earthquake has quickly settled on the troubles at two nuclear reactors as the center of the catastrophe. 
 
 Rep. Ed Markey (D., Mass.), a longtime opponent of nuclear power, has warned of "another Chernobyl" and predicted "the same thing could happen here." In response, he has called for an immediate suspension of licensing procedures for the Westinghouse AP1000, a "Generation III" reactor that has been laboring through design review at the Nuclear Regulatory Commission for seven years. 
 
 Author William Tucker explains why the danger is limited at Japan's nuclear reactors. 
 
 Before we respond with such panic, though, it would be useful to review exactly what is happening in Japan and what we have to fear from it. 
 
 The core of a nuclear reactor operates at about 550 degrees Fahrenheit, well below the temperature of a coal furnace and only slightly hotter than a kitchen oven. If anything unusual occurs, the control rods immediately drop, shutting off the nuclear reaction. You can't have a "runaway reactor," nor can a reactor explode like a nuclear bomb. A commercial reactor is to a bomb what Vaseline is to napalm. Although both are made from petroleum jelly, only one of them has potentially explosive material. 
 
 Once the reactor has shut down, there remains "decay heat" from traces of other radioactive isotopes. This can take more than a week to cool down, and the rods must be continually bathed in cooling waters to keep them from overheating. 
 
 On all Generation II reactors—the ones currently in operation—the cooling water is circulated by electric pumps. The new Generation III reactors such as the AP1000 have a simplified "passive" cooling system where the water circulates by natural convection with no pumping required. 
 
 If the pumps are knocked out in a Generation II reactor—as they were at Fukushima Daiichi by the tsunami—the water in the cooling system can overheat and evaporate. The resulting steam increases internal pressure that must be vented. There was a small release of radioactive steam at Three Mile Island in 1979, and there have also been a few releases at Fukushima Daiichi. These produce radiation at about the level of one dental X-ray in the immediate vicinity and quickly dissipate. 
 
 Editorial Board Member Mary Kissel explains the Japanese response to the quake. 
 
 If the coolant continues to evaporate, the water level can fall below the level of the fuel rods, exposing them. This will cause a meltdown, meaning the fuel rods melt to the bottom of the steel pressure vessel. 
 
 Early speculation was that in a case like this the fuel might continue melting right through the steel and perhaps even through the concrete containment structure—the so-called China syndrome, where the fuel would melt all the way to China. But Three Mile Island proved this doesn't happen. The melted fuel rods simply aren't hot enough to melt steel or concrete. 
 
 The decay heat must still be absorbed, however, and as a last-ditch effort the emergency core cooling system can be activated to flood the entire containment structure with water. This will do considerable damage to the reactor but will prevent any further steam releases. The Japanese have now reportedly done this using seawater in at least two of the troubled reactors. These reactors will never be restarted. 
 
 None of this amounts to "another Chernobyl." The Chernobyl reactor had two crucial design flaws. First, it used graphite (carbon) instead of water to "moderate" the neutrons, which makes possible the nuclear reaction. The graphite caught fire in April 1986 and burned for four days. Water does not catch fire. 
 
 Second, Chernobyl had no containment structure. When the graphite caught fire, it spouted a plume of radioactive smoke that spread across the globe. A containment structure would have both smothered the fire and contained the radioactivity. 
 
 If a meltdown does occur in Japan, it will be a disaster for the Tokyo Electric Power Company but not for the general public. Whatever steam releases occur will have a negligible impact. Researchers have spent 30 years trying to find health effects from the steam releases at Three Mile Island and have come up with nothing. With all the death, devastation and disease now threatening tens of thousands in Japan, it is trivializing and almost obscene to spend so much time worrying about damage to a nuclear reactor. 
 
 What the Japanese earthquake has proved is that even the oldest containment structures can withstand the impact of one of the largest earthquakes in recorded history. The problem has been with the electrical pumps required to operate the cooling system. It would be tragic if the result of the Japanese accident were to prevent development of Generation III reactors, which eliminate this design flaw. 
 
 Mr. Tucker is author of "Terrestrial Energy: How Nuclear Power Will Lead the Green Revolution and End America's Energy Odyssey" (Bartleby Press, 2010). ||||| (See Correction & Amplification item below.) 
 
 TOKYO—The Japanese government raised its assessment of the monthlong crisis at its Fukushima Daiichi nuclear power plant to the highest severity level by international standards—a rating only conferred so far upon the Chernobyl accident. 
 
 Japanese officials raised its nuclear crisis to the level of Chernobyl. WSJ's Yumiko Ono reports. Also Jerry Seib reports on a new era of dialogue in Washington as debt ceiling and budget talks heat up again. And Donald Trump gets serious about 2012. 
 
 Past Nuclear Incidents See a timeline of how the Fukushima nuclear incident compares to other nuclear incidents. View Interactive More photos and interactive graphics 
 
 Japan's nuclear regulators said the plant has likely released so much radiation into the environment that it must boost the accident's severity rating on the International Nuclear Event scale to a 7 from 5 currently. That is the same level reached by the Chernobyl nuclear disaster in the former Soviet Union, which struck almost exactly 25 years ago, on April 26, 1986. 
 
 "Based on the cumulative data we've gathered, we can finally give an estimate of total radioactive materials emitted,'' Hidehiko Nishiyama, spokesman for Japan's Nuclear and Industrial Safety Agency, said at a press conference Tuesday. 
 
 Even as they upgraded their assessment of the situation, Japanese officials went to lengths to say that the problem they are struggling to contain isn't anywhere near the disaster of Chernobyl. 
 
 "It is quite different from Chernobyl," said Mr. Nishiyama. "First, the amount of released radiation is about a tenth of Chernobyl," he said, adding that while there were 29 deaths resulting from short-term exposure to high doses of radiation at Chernobyl, there were no such deaths at Fukushima. 
 
 Enlarge Image Close ZUMAPRESS.com Japanese police searched for victims inside the deserted evacuation zone in Minamisoma in Fukushima Prefecture. 
 
 "At Chernobyl, the nuclear reactor itself exploded," he said, adding that at the Fukushima plant, the pressure vessel and the containment vessel were largely intact. 
 
 Still, Fukushima Daiichi operator Tokyo Electric Power Co. warned Tuesday that since the Fukushima Daiichi plant is still releasing radioactive materials, the total level of radiation released could eventually exceed that of Chernobyl, a spokesman said. 
 
 The new assessment comes as Japan admits that the effects of the Fukushima Daiichi nuclear accident—which has already caused the evacuation of tens of thousands of people and spread radiation through groundwater and farms over a broad section of eastern Japan—are likely to be long-lasting and grave. The accident was precipitated by the massive March 11 earthquake and tsunami, which knocked out Fukushima Daiichi's power and cooling systems, causing several of the reactors to overheat. 
 
 The International Nuclear Event scale, whose development is coordinated by the International Atomic Energy Agency, measures the severity of accidents based on how much radiation is released, the degree of damage to the nuclear cores and how widespread and long-lasting the effects are likely to be. 
 
 Level 5—the previous level given the Fukushima Daiichi accident—indicates a "limited release'' of radioactive materials requiring "some planned countermeasures.'' The 1979 Three Mile Island accident in Pennsylvania was rated a 5. 
 
 Enlarge Image Close European Pressphoto Agency The reactor building of Unit 1-2 at Fukushima Daiichi Nuclear Power Station on Sunday. 
 
 Enlarge Image Close ZUMAPRESS.com Houses collapsed by the earthquake and tsunami in Minamisoma. 
 
 Level 7 labels this "a major accident," the most serious on the international scale. It means high levels of radiation have been released, and that the amount of time needed to bring the plant under control will require an extended period. But not all "major accidents" are equal in severity. 
 
 The decision to upgrade formally the severity of the accident came a day after Japan broadened the 12-mile nuclear evacuation zone around the plant to include all or part of five towns and villages that housed tens of thousands of people before the disaster, a sign that officials now see the long-term risks as far higher than originally estimated. 
 
 And the crisis appears far from over, with constant reminders that efforts to bring the crippled reactors under control are far from complete. Operator Tepco scrambled to keep reactors stable in the wake of another big earthquake Monday and a battery fire Tuesday morning, signs of how vulnerable the plant remains a month after the quake. 
 
 Experts have predicted it could take months for Tepco to bring Fukushima Daiichi's reactors truly under control, and years to clean up the plant itself. 
 
 Japanese nuclear regulators determined that after the accident, the plant has likely released tens of thousands of terabecquerels—or a mind-boggling tens of thousands of trillions of becquerels—of radiation in the immediate area. That's a level that's been recorded only during the Chernobyl accident. 
 
 While the new assessment puts Fukushima on a par with Chernobyl, there are key differences between the two, suggesting the Ukraine disaster was still far more serious. 
 
 The Japanese government said the monthlong crisis at its Fukushima Daiichi nuclear power plant is on par with Chernobyl in terms of severity. WSJ's Mariko Sanchanta and Yumiko Ono discuss the public's reaction to the news. 
 
 In the case of Chernobyl, a graphite fire burned uncontrolled for days, spewing out radioactive smoke that spread around the world. Fukushima, unlike Chernobyl, has a containment structure, which, even if damaged, has meant that the Japanese accident has shown "much, much, much lower'' traces of far-flung radiation, Wolfgang Weiss, chair of the United Nations Scientific Committee on the Effects of Atomic Radiation, said in Vienna last week. 
 
 The release from Fukushima of tens of thousands of terabecquerels of iodine-131, while huge, appears to be smaller than the 5.2 million terabecquerels released from Chernobyl. Japanese government officials said the radiation release was between 370,000 and 630,000 terabecquerels so far from Fukushima. The permissible level of iodine-131 for vegetables and fish is 2,000 becquerels per kilogram, or just a tiny fraction of what has been released. 
 
 A 2005 United Nations study said up to 4,000 people could eventually die from radiation exposure to Chernobyl. 
 
 In Japan, so far, a handful of workers have been hospitalized, but they were released a few days later, and regulators said they showed no signs of lasting injury. 
 
 Japanese suppliers impacted by last month's quake are struggling to hang onto their business amid shortages of key components and electricity. Companies that rely on that hard-hit supply network are also rethinking their exposure to Japan. 
 
 On Edge | Worries over Fukushima Daiichi Enlarge Image Close 
 
 Earthquake in Japan View Interactive 
 
 There are, however, regular reports in the Japanese press of elevated radiation exposure for the workers trying to contain Fukushima, and it could be months, or years, before the real impact is known. The same is true for the population in and around the plant. 
 
 Officials said they expanded the original evacuation zone because the accident had lasted longer than expected. 
 
 "Japan has been doing drills for possible nuclear accidents, but they assumed that the accidents would be resolved in about 10 days," said Mr. Nishiyama, the spokesman. "We are now dealing with a crisis of a historic proportion. This has necessitated different kinds of responses than initially planned." 
 
 Even in announcing the expanded evacuation zone, Japanese officials said residents of the affected areas weren't in danger of surpassing government exposure limits anytime soon and that they have about a month to move. 
 
 Testing by Japanese, U.S. and IAEA officials shows that the radioactive contamination is spreading unevenly from the plant, creating what are known as hot spots due to wind, topography and other natural conditions that show a higher density of radioactive material compared with some areas closer to the plant. 
 
 The move will present major logistical hurdles for communities already battered by the March 11 earthquake and tsunami that damaged the plant as well as much of the surrounding countryside. The area includes towns and villages with a population totaling about 115,000 people before the crisis, though the number of people affected is likely to be far less because the government's order applies only to particular hot spots believed to have higher radiation levels, not a set radius from the plant. 
 
 Meanwhile, efforts to stabilize reactors at Fukushima Daiichi continue to be dogged by setbacks and scares, in a sign of how fragile the situation on the ground remains. On Tuesday morning, Tepco said there was a small fire at a battery unit outside reactor No. 4, which was put out shortly after being reported. 
 
 On Monday, a 7.1 magnitude quake centered in coastal Fukushima temporarily shut down power supply and makeshift cooling systems to three reactors at the plant, causing the evacuation of workers to the compound's command center. The systems remained down for nearly an hour while the evacuation remained in effect, keeping workers from switching to emergency power generators. 
 
 Tepco said the suspension didn't appear to have caused significant safety issues. But the scramble to restore power served as a reminder of how aftershocks and the risk of tsunami could upset the delicate efforts to stabilize the problems at the plant. 
 
 —Mitsuru Obe contributed to this article. 
 
 Correction & Amplification: 
 
 The Three Mile Island accident occurred in 1979. An earlier version of this article incorrectly said it happened in 1978.
– America is positively freaking out over the state of Japan’s nuclear reactors, with some calling for a halt to the development of new nuclear plants. But that’s a wild overreaction, opines a Wall Street Journal editorial. The media’s done a poor job of putting the tragedy in Japan in proportion: The quake killed hundreds, and released a thousand times more energy than the nuclear explosion at Hiroshima. “In simple human terms, the natural destruction of Earth and sea have far surpassed any errors committed by man.” In a separate piece, William Tucker breaks down the technical workings of the reactors, and concludes that there’s little danger. “None of this amounts to ‘another Chernobyl,’” he says. Chernobyl had massive design flaws that these Generation II reactors don’t; their containment structures have held. “If a meltdown does occur,” he concludes, “it will be a disaster for the Tokyo Electric Power Company, but not for the general public.” For another (paywall-free) dose of realism, click here.