Thursday, April 7, 2011


Incident at Chernobyl

How the Nuclear Reactor Works-
·         First, uranium fuel is loaded up into the reactor—a giant concrete dome that's reinforced in case it explodes. In the heart of the reactor (the core), atoms split apart and release heat energy, producing neutrons and splitting other atoms in a chain reaction.
·         Control rods made of materials such as cadmium and boron can be raised or lowered into the reactor to soak up neutrons and slow down or speed up the chain reaction.
·         Water is pumped through the reactor to collect the heat energy that the chain reaction produces. It constantly flows around a closed loop linking the reactor with a heat exchanger.
·         Inside the heat exchanger, the water from the reactor gives up its energy to cooler water flowing in another closed loop, turning it into steam. Using two unconnected loops of water and the heat exchanger helps to keep water contaminated with radioactivity safely contained in one place and well away from most of the equipment in the plant.
·         The steam from the heat exchanger is piped to a turbine. As the steam blows past the turbine's vanes, they spin around at high speed.
·         The spinning turbine is connected to an electricity generator and makes that spin too.
·         The generator produces electricity that flows out to the power grid—and to our homes, shops, offices, and factories.
What Went Wrong at Chernobyl
The Chernobyl accident in 1986 was the result of a corrupted reactor design that was not operated by fully trained personnel. It resulted in a steam explosion and fires released at least 5% of the radioactive reactor core into the atmosphere. It started when engineers at Chernobyl conducted an experiment to find out if low power from the reactor could be used to support the cooling pump system in case the supply of auxiliary electricity is cut off. The control rods of the reactor were lowered to bring output level down to 20% of the normal output, but the engineers lowered too many rods, and this caused output to decrease too rapidly. Then, the reactor was very close to shutting down. So, they started to raise the control rods to bring the reactor back to normal. They kept raising rods until the power reached about 12%, and then, the power suddenly shot up to extremely high levels. Soon, overheating occurred and the water coolant began to evaporate. The engineers pressed the shutdown button, but the reinsertion of control rods increased the concentration of reactivity in the lower part of the reactor. Now, the power level of the reactor was 100 times higher than regular, and then the reactor began to explode and it blew off the upper radiation shield. The contents from the reactor core erupted outwards, and air from the outside reacted with the carbon monoxide gas in the reactor to start a fire which lasted for nine days. 

How They Fixed It and Some Lasting Effects
The damaged reactor was sealed off and 200 cubic meters of concrete was placed between the disaster site and the operational buildings. They let three of the six reactors run because there would be an energy shortage in the country. Then one of the reactors had a fire, and it was declared the reactor was damaged beyond repair. Chernobyl is now enclosed by a large concrete sarcophagus, which was built quickly to allow the continuation of the operation of the other reactors at the plant. Since this structure was built very quickly they did not build it very well so they are now trying to build a New Safe Confinement which was supposed to be built by 2005. Delays kept on happening since 2010 and now they are projected to finish it by 2013. The nuclear reactor in a power plant exploded and it spread nuclear radiation throughout Europe and some lasting effects. It caused many health problems for many people and many plantations had been contaminated. Two Chernobyl plant workers died on the night of the accident, and 28 other people died within a few weeks as a result of radiation poisoning. UNSCEAR said that apart from increased thyroid cancers, "there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident." The building of the reactor was badly damaged and 31 people were killed. The accident could have been prevented if a concrete shell was constructed to around the reactor, which is the way nuclear reactors are built in other countries. An estimated 6500 people may contract cancer because of the Chernobyl nuclear accident. In fact, many children in the regions around Chernobyl are suffering from thyroid cancer today. About 200 people were hospitalized because of exposure to the radiation. It is believed that the medical effects of exposure to nuclear radiation will only start to show many years after the incident, and some of the health problems that are associated with radiation exposure are skin diseases, birth defects, and cancer. 

Explosion at Japan
Relating Chernobyl to Japan Incident
“Nuclear experts have repeatedly stated that the Japanese situation cannot get as bad as Chernobyl,” says Michael Marshall. In Japan the name of the reactor that was damaged is Fukushima Daiichi. The major difference between the incident at Fukushima Daiichi and Chernobyl is that at Chernobyl it was caused by untrained personnel and it was caused by people trying to do an experiment. At Fukushima Daiichi there was an earthquake which caused the nuclear reactor to be damaged. The nuclear reactors at Fukushima Daiichi automatically shut down which was supposed to happen. But the cooling systems have repeatedly failed, which caused the cores of some of the reactors to overheat. This has led to explosions damaging the outer buildings and parts of the containment systems which prevents radioactive material from escaping the reactor. Staff at Fukushima Daiichi were running tests to find out how well they could cope with a temporary shutdown of the reactor's cooling system. The test went bad and there was a power surge. They tried to shut the reactor down before anything happen but they were unsuccessful. "For a few seconds it was generating thousands of times the normal power output," says Michael Bluck of Imperial College London. The heat from the nuclear reaction caused an explosion, which blew off the roof of the reactor vessel and the building that contained it. This exposed radioactive material into the atmosphere. Many fires started but these fires were put out in the next few hours, but one of the reactors burned for a couple more days and it spread even more radioactive material. Another difference is that the Chernobyl reactor was running, but at Fukushima Daiichi the reactors were automatically shut down when the earthquake hit. Some people say that we shouldn’t be worried and some people say that we should only be worried a little bit. I think we shouldn’t be worried because at Chernobyl the International Nuclear Event Scale, scaled it at a level 7, and at Fukushima Daiichi a French Nuclear Agency predict it to be a level 5 or 6. I think that Chernobyl will always be worse because it wasn’t caused by a earthquake or something it was caused by some scientists trying to do an experiment, and at Fukushima Daiichi it was caused by a natural disaster.