Why is meltdown dangerous

Plagued by design flaws and operator errors, the plant experienced fires, explosions, and radiation leakage. As a result, 30 people died of acute radiation syndrome, and thousands of cases of fatal cancers and birth defects have been reported in the following years.

Today, limited access is allowed inside a km mile exclusion zone surrounding the area. In , a minor cooling system malfunction led to a series of events that caused a partial meltdown that damaged one of the reactors. However, very little radiation was released into the environment due to the surrounding primary containment vessel. Although the accident caused public concern, no deaths or adverse health effects have been officially attributed to the meltdown.

In Japan, the current nuclear crisis at the Fukushima Daiichi power plant lies somewhere in between Three Mile Island and Chernobyl , according to recent news reports.

Although employees at the plant have been risking their lives to try to keep the reactors cool, the chance of a serious meltdown seems to be increasing. Inside the core of a nuclear reactor are thousands of long, thin fuel rods made of zirconium alloy that contain uranium. When a reactor is turned on, the uranium nuclei undergo nuclear fission , splitting into lighter nuclei and producing heat and neutrons. The neutrons can create a self-sustaining chain reaction by causing nearby uranium nuclei to split, too.

Fresh water flows around the fuel rods, keeping the fuel rods from overheating and also producing steam for a turbine. Even when the reactor is turned off so nuclear reactions no longer occur, the fuel rods remain extremely radioactive and hot and need to be cooled by water for an extended period of time.

Without enough water, the fuel rods get so hot that they melt. If they begin to melt the nuclear reactor core and the steel containment vessel, and release radiation into the environment, nuclear meltdown occurs.

When the earthquake struck Japan, three of the six reactors Reactors 4, 5, and 6 at the Fukushima power plant were already off for routine inspections. Earthquake tremors triggered the automatic shutdown of the other three reactors, Reactors 1, 2, and 3 along with eight other nuclear reactors at other power plants. To stop the chain reaction, control rods that absorb neutrons were inserted in between the fuel rods.

But the fuel rods are still hot, since radioactive byproducts of past fission reactions continue to produce heat. As a backup measure, diesel generators turned on to spray the fuel rods with coolant. The next backup measure for cooling the fuel rods was a battery system, but the batteries lasted only a few hours. Later, technicians brought in mobile generators and also attempted to inject seawater into the nuclear reactors, which makes them permanently unusable but could help prevent a complete meltdown.

While the nuclear technicians searched for better cooling options, the water levels continued to decrease, exposing the tops of the fuel rods. Pressure also began building in some of the reactors.

So far, at least three explosions have occurred in Reactors 1, 2, and 3. This does not mean any or every country will do this, but historically some have and the risk is high, as noted by IPCC. To date, 1. The nuclear industry has proposed new reactor designs that they suggest are safer.

However, these designs are generally untested, and there is no guarantee that the reactors will be designed, built and operated correctly or that a natural disaster or act of terrorism, such as an airplane flown into a reactor, will not cause the reactor to fail, resulting in a major disaster.

Uranium mining causes lung cancer in large numbers of miners because uranium mines contain natural radon gas, some of whose decay products are carcinogenic. A study of 4, uranium miners between and found that 10 percent died of lung cancer, a rate six times that expected based on smoking rates alone.

Clean, renewable energy does not have this risk because a it does not require the continuous mining of any material, only one-time mining to produce the energy generators; and b the mining does not carry the same lung cancer risk that uranium mining does. There is no such thing as a zero- or close-to-zero emission nuclear power plant.

Even existing plants emit due to the continuous mining and refining of uranium needed for the plant. In addition, all nuclear plants emit 4. This contrasts with solar panels and wind turbines, which reduce heat or water vapor fluxes to the air by about 2. The resulting difference in air pollution emissions may have caused 69, additional air pollution deaths in China in alone, with additional deaths in years prior and since.

Last but not least, consumed fuel rods from nuclear plants are radioactive waste. Most fuel rods are stored at the same site as the reactor that consumed them. This has given rise to hundreds of radioactive waste sites in many countries that must be maintained and funded for at least , years, far beyond the lifetimes of any nuclear power plant. The more nuclear waste that accumulates, the greater the risk of radioactive leaks, which can damage water supply, crops, animals, and humans.

To recap, new nuclear power costs about 5 times more than onshore wind power per kWh between 2. Nuclear takes 5 to 17 years longer between planning and operation and produces on average 23 times the emissions per unit electricity generated between 9 to 37 times depending upon plant size and construction schedule.

Nuclear advocates claim nuclear is still needed because renewables are intermittent and need natural gas for backup. However, nuclear itself never matches power demand so it needs backup. Today, in fact, batteries are beating natural gas for wind and solar backup needs throughout the world.

A dozen independent scientific groups have further found that it is possible to match intermittent power demand with clean, renewable energy supply and storage, without nuclear, at low cost.

Meltdown can also occur in the pools containing spent fuel rods. Overheating of the spent fuel pools could cause the water containing and cooling the rods to evaporate.

Without coolant, the fuel rods become highly vulnerable to catching fire and spontaneously combusting, releasing dangerous levels of radiation into the atmosphere. Since spent fuel is less radioactive than fuel in the reactor core, these pools are easier to control, said Peter Caracappa, a professor and radiation safety officer at Rensselaer Polytechnic Institute.

Most of the problems with the backup generators were caused by the tsunami flooding them. But Makhijani suspects that unseen damage from the earthquake may be adding another challenge. Yesterday, they had trouble releasing a valve. If you have a question on science or technology for Just Ask , send an e-mail to science newshour. Support Provided By: Learn more. Wednesday, Nov Nuclear power Research update How to stop a nuclear meltdown by leavening the reactor core like a loaf of bread 11 Oct Cooling corium: Sandia National Laboratories researchers Jessica Kruichak and William Chavez pour a granulated material onto hot lead oxide.

Courtesy: Randy Montoya A new way of cooling and containing the radioactive, lava-like mass that forms in the core of a nuclear reactor during a catastrophic meltdown has been developed by researchers in the US. Want to read more? Register to unlock all the content on the site. E-mail Address. Ian Randall is a science writer based in the UK. Physics World Jobs Take the next step in your career and find your perfect job. Read previous Climate Research update Water stress rises as more wells run dry.