Nuclear Power

Disaster at Three Mile Island

How it Happened?

On March 28, 1979, a cooling circuit pump in the non-nuclear section of Three Mile Island's second station (TMI-2) malfunctioned, causing the reactor's primary coolant to heat and internal pressure to rise. Within seconds, the automated response mechanism thrust control rods went into the reactor and shut down the core. An escape valve opened to release pressure but failed to close properly. Control room operators only saw that a "close" command was sent to the relief valve, but nothing displayed the valve's actual position. With the valve open, coolant escaped through the pressurizer, sending misinformation to operators that there was too much pressure in the coolant system.

Operators then shut down the water pumps to relieve the "pressure." Operators allowed coolant levels inside the reactor to fall, leaving the uranium core exposed, dry, and intensely hot. Even though inserting control rods halted the fission process, the TMI-2 reactor core continued to generate about 160 megawatts of "decay" heat, declining over the next three hours to 20 megawatts.

Approximately one-third of the TMI-2 reactor was exposed and began to melt. By the time operators discovered what was happening, superheated and partially radioactive steam built up in auxiliary tanks, which operators then moved to waste tanks through compressors and pipes. The compressors leaked. The steam leakage released a radiation dose equivalent to that of a chest X-ray scan, about one-third of the radiation humans absorb in one year from naturally occurring background radiation. No damage to any person, animal, or plant was ever found.

The Outcome and Lessons Learned

The local population of 2 million people received an average estimated dose of about 1 millirem--miniscule compared to the 100-125 millirems that each person receives annually from naturally occurring background radiation in the area. Nationally, the average person receives 360 millirems per year. No significant radiation effects on humans, animals, or plants were found.

A number of technological and procedural changes have been implemented by industry and the Nuclear Regulatory Commission (NRC) to considerably reduce the risk of a meltdown since the 1979 incident. These include:

                                        Plant design and equipment upgrades, including fire protection, auxiliary feed water systems, containment building isolation, and automatic plant shut down capabilities.

                                        Enhanced emergency preparedness, including closer coordination between federal, state, and local agencies.

                                        Regular plant performance analysis by senior NRC managers who identify plants that require additional regulatory attention.

                                        Expanded performance- and safety-oriented inspections.

                                        Establishment of the Institute for Nuclear Power Operators, an industry-created non-profit organization that evaluates plants, promotes training and information sharing, and      helps individual plants overcome technical issues.

Disaster at Chernobyl

What Exactly Happened at the Chernobyl Nuclear Power Plant?

Aftermath of Chernobyl

On April 26th, 1986, disaster struck in the form of a nuclear accident at a power plant in the Ukraine. Large quantities of radioactive contamination were released and spread to Western USSR and as far as Europe. This accident was, and still is today, considered to be the worst nuclear accident in the history of mankind.

The whole catastrophe began on the 26th during a typical systems test on reactor number four of the plant. Once a sudden power outage occurred, workers at the plant sensed immediate danger. Because of this, they initiated an emergency shutdown, thinking that this could only help the situation. They were indeed wrong. The emergency attempt only spiked the power outage. Due to this lack of power one of the reactors burst open, leading to several violent explosions. A fire soon ignited (because of the chemicals) and smoke started to leave the plant, carrying radioactive material with it into the air supply. The polluted air traveled great distances, contaminating areas mostly in Western USSR but also making it to parts of Europe. Out of all the affected areas, no one saw worse than Belarus, Russia, and the Ukraine.

Because of this detrimental accident many began questioning how capable the Soviet was in terms of running nuclear power plants. This disaster put a definitive halt on nuclear advancement for the Soviet, and even worldwide as critics examined just how safe these plants were.

What was the Aftermath like at Chernobyl?

The Red Forest

The accident at Chernobyl left nearly 250 people with acute radiation sickness, or ARS. Out of those many almost 30 died a few months later because of the ARS diagnosis. Though many still believe that the exposure can lead to radiation induced cancer, no studies have revealed this to be absolutely the case. Some also connect the radiation exposure to serious mutations, both in animals and in the children of those who have been in contact with the radioactive materials.

Rivers, including the Pripyat and Dnipro, seemed to become immediately contaminated after the disaster. Because of this, strict attention was placed on safety levels of the drinking water, as well as the contamination in the fish population.

In addition, several trees, located relatively close to the Chernobyl plant, turned a reddish color and died soon after. This area has been titled the “Red Forest.” Also, animals whose habitat was indeed this forest suffered as well. A serious amount of radiation was found in those that were hunted (also a problem for the food source of the population), some of which even stopped reproducing.

Japanese Nuclear Disater at Fukushima

What Exactly Happened at Fukushima?

Crisis at Fukushima

On March 11th, 2011, a 9.0 magnitude earthquake and tsunami named Tohoku hit Japan. The chain of events that followed immediately changed the feelings on nuclear power. After the earthquake occurred, there was a release of radioactive material along with a series of equipment failures at the Fukushima Nuclear Power Plant. This plant consisted of six boiling water reactors preserved by the Tokyo Electric Power Company. This was indeed the largest nuclear accident in Japanese history, and theorists believe it to even be the second largest in the history of the world, behind only Chernobyl.

What Went Wrong at the Plant?

Reactor at Fukushima

When the earthquake began two of the reactors, five and six, were in “cold shutdown” mode because of necessary maintenance concerns. Reactor four had even been de-fueled. However, the remaining reactors were only capable of shutting down automatically after the earthquake. After the shutdown the emergency generators began to run a very essential electronic control system as well as a reactor cooling procedure, or at least attempted to do so. The Fukushima plant was meant to have top notch security, as a “seawall” capable of withstanding a 5.7m tsunami bordered the facility. The only problem was that when the waves arrived at the plant, they were measured at heights of 14m, leading to a seawall failure, and a flooded nuclear plant. This flood annihilated the entire electrical control system, meaning, all power needed to cool down the reactors was lost. Thus, the lack of cooling triggered an extreme case of overheating of reactors due to the decaying of fission products left remaining pre-accident. From there on reactor after reactor began to face either core meltdowns or containment damage. Even those reactors, 5 and 6, that were in “cold shutdown” began to overheat. Eventually, after predictions of radiation leakage, workers and those located close to the plant were ordered to keep a 12 mile distance from the plant. Though many eventually escaped to safety without damage, others suffered radiation exposure. After the phenomenon was somewhat “over” generators were restarted to cool reactors five and six (those that were still overheating but manageable to contain). However, due to excessive damage (through floods, fires, and explosions) the machinery used to cool reactors one through four remained unusable. Radioactive leaking into the water made it impossible for any imaginable repairs to be made on these four reactors.

Environmental Effects

The samples (from different sources, food, water, etc) from up to 50km away from the plant were tested by science officials and the results were extremely alarming. What the radiation levels told the science ministry of Japan was that the releases of radioactive material found from Fukushima were at the same alarming magnitude of Chernobyl. Immediately after these tests were found to be inconclusive the food supply grown within the radius of determined radiation was banned and kept from consumers. In addition, officials recommended that the intake of tap water be limited (if used at all). Though this accident at Fukushima was ranked at a level of 4 on the International Nuclear Event Scale, it was done so by Japanese officials which some believe to be hiding the truths. Critics believe that this accident should be measured closer to the level of Chernobyl.

Whats Being Done to Fix the Situation

Immediately following the disaster, the Tokyo Electric Power Company made little efforts in coming up with a strategy, more specifically, how to stop the overheating reactors and how to make sure this problem remains contained. However, after a few weeks following the disaster TEPCO issued a plan for the future. The plan included a few key elements. First, in about nine months they planned to get back to the “cold shutdown” stage for some of the reactors. Next, in about three months they planned to indeed fix the cooling machinery. In addition to these two “promises”, TEPCO stated that they would create special covers for some of the more damaged reactors, create more containment units for radioactive water, and also build fences that would limit ocean contamination.