The Fukushima nuclear plant is a disabled power plant located in Japan. The plant consists of 6 boiling water reactors (BWR). The plant was first commissioned in 1971 and generated a combined power of 4.7 GWe making Fukushima one of the largest nuclear reactors in the world. On March 11, 2011 the nuclear plant suffered crippling damage during a 9.0 earthquake and subsequent tsunami. The damage was severe and the plant is not expected to reopen. Nine days after the accident Japanese authorities quarantined the reactors and a 20 km radius around them. The consequences of the reactor meltdown are great, but it is also beneficial to weigh the costs with the benefits of nuclear power.
A BWR uses de-mineralized water as a coolant and neutron moderator. Fission in the reactor core heats up the water producing steam. Nuclear fission is a revolutionary and complicated chemical reaction that splits the nucleus of an atom into smaller parts. This process produces free neutrons and photons. Fission of heavy elements, like those used in nuclear power plants, creates a highly energetic exothermic reaction. The energy released is both electromagnetic radiation and kinetic energy of the fragments. In order the fission process to produce energy to be captured the binding energy of the products must be greater than the energy of the starting element. This results in a product that is not the same as the starting material. This process is called nuclear transmutation.
Nuclear fuels undergo fission when struck by fission neutrons. The neutrons emitted when they break apart create a self-sustaining nuclear reaction, which releases energy at a controlled rate. The steam previously mentioned is vital in the harnessing of nuclear energy into usable electrical energy. The steam is used to drive a turbine, which is part of the reactor unit. The turbines spin, which in turn powers an electrical generator that is connected to power lines.
The nuclear fuel cycle is not always a one-way system. The fuel can either be disposed of safely at the end of a cycle, or re-purposed and added back into the cycle. The problem arises when the fuel is no longer viable and needs to safely disposed of. The fuel discharged at this time is stored either in a spent fuel pool on site, or at a facility off-site. In cases where the fuel rods themselves are spent they are then stored in either water or boric acid. Disposal of the spent nuclear fuel and fuel rods is vital in protecting the biosphere from radiation. Controversy arises over storage concerns and safety of future generations.
Spent nuclear fuel and fuel rods must be stored safely from the biosphere until the radioactivity is diminished to safe levels. While the storage itself is not that difficult, the time that radiation is present within the fuel is a huge problem. Nuclear radiation can stay present in spent fuel for up to 10,000 years or more. We have a responsibility to future generations to protect them the nuclear radiation we store. No man-made structure has ever lasted 10,000 years. So the question arises, “How do we let future generations know?” This isn’t the only problem. Storage in a geological structure is relatively simple, but the geological structure must be stable for 10,000 years or more. Typically this involves storage deep within the Earth, mountains (Yucca mountains USA), deep ocean trenches, etc.
During the earthquake and subsequent tsunami power went out at Fukushima leading to a shutdown of the reactor and emergency cooling units. Seven weeks later the crisis has substantially subsided relative to week one, but serious problems remain. While specific details of the damage to the reactors in Japan are unknown it is clear that the fuel damage during this event was larger than all other previous nuclear power plant accidents.
Nuclear fuel is stored in metal zirconium casing called cladding. When the fuel heats up, due to lack of cooling, the cladding will rupture. Once the cladding ruptures radioactive gases escape and the cladding burns resulting in flammable hydrogen. Eventually, as the temperature inside the reactor continues to increase, the cladding will start to melt and further issues can arise including greater radiation release and melting through the reactor floor.
Using this information researchers can accurately estimate what components failed in the earthquake and subsequent tsunami despite lack of Japanese cooperation. The hydrogen explosions at Fukushima are evidence of the cladding burning and rupturing as well as spent fuel pools. While fuel melting is speculated it cannot yet be confirmed. Of the six BWR’s all were severely damaged. At the time of the earthquake reactors 4, 5, and 6 were in various stages of shut down while the first 3 shut down automatically following the incident. A little less than an hour after the earthquake a tsunami wave breached the levee and flooded the reactors and the electrical generators for cooling the reactor core.
When a reactor loses cooling power, such as Fukushima, then the natural decay (due to fission) results in overheating. In reactors 1-3 there was evidence of partial core meltdown and in reactors 1, 3 and 4 hydrogen explosions perforated the upper cladding. Meanwhile, despite being shutdown, reactors five and six also began to overheat. Furthermore, spent fuel rods in the cooling pool also began to overheat. This had severe and nearly catastrophic consequences for workers, locals, and a wider radius of Japanese residents.
Workers of the Fukushima facility received the majority of radiation poisoning. The workers, at the time of the meltdown, were exposed to the radiation in shifts and evacuated afterward. Radiation concerns extend, unfortunately, far beyond the radiation directly applicable to the workers. Radiation was released into the atmosphere by deliberate venting of the reactors to reduce pressure. There was also pumping of coolant water (contaminated) into the sea. It was reported that radiation levels reached 30,000 to 110,000 TBq of iodine-131. Due to the high levels of radiation a 20km radius around Fukushima was immediately evacuated.
In order for workers to continue work at the plant the maximum radiation dose they could receive was increased to 250mSV/year. This has put TEPCO, the company in charge of the power plant, under severe scrutiny. It has been claimed that they did not provide sufficient safety equipment for the workers and proper monitoring equipment.
Radiation levels to locals became a greater concern at the end of March. Milk produced near Fukushima and the local water supply showed radiation levels above the safe limits. A very recent article published in Science News used Chernobyl as a model for possible cancer outcomes. Thirty years after the Chernobyl incident there was a marked 30% increase in thyroid cancer. Thyroid cancer is especially prevalent because of the use of Iodine in nuclear reactors. Unfortunately the distribution of prophylactic iodine tablets does not have a significant affect on the number of people who obtain thyroid cancer later in life. We are left with the problem: what is the cancer risk at Fukushima?
Using the Tondel method, developed by Martin Tondel, researchers were able to estimate the amount of cancers directly related to Fukushima by the year 2061 (Tondel, 2006). This method states that 417,000 extra cancers will arise in a 200km radius by 2061. Other methods, such as the ICRP method, 6158 cancer cases in a 100km radius in the next 50 years.
Safety measures are being put in place to both repair the nuclear plant and decrease radiation emission. TEPCO has returned to the site since plugs have been put in place to clear the tunnel systems and repair the cooling units. Highly radioactive water took about 40 hours to pump from the trenches into the turbine condenser. While the efforts to clear the contaminated water initially decreased water levels, they began to increase again after plugs to the ocean increased again. Japanese officials are now pumping the water into waste treatment plants to reduce the contaminated water levels.
Since the accident nuclear facilities worldwide are being scrutinized for potential risks and are being rigorously tested to avoid future nuclear disasters. The risk assessment for nuclear facilities based on Fukushima will result in a steep increase in the price of running and building nuclear power plants.
According to Selena Ng, “ there was a sort of complacency before now with regards to nuclear power, we don’t have that luxury anymore.” What Selena is ultimately saying is that the world is now awakened to the benefits and consequences of nuclear power. Regulations must be stiffer and more safety measures in place. Many scientists are saying that the IEAE needs to police nuclear plants much closer to push the new safety regulations.
Countries across the world are considering shutdowns of reactors in areas of seismic activity. In the United States, however, the Obama administration has openly stated support for the advancement of nuclear science and energy. Despite the support for nuclear energy by the government the nuclear reactors currently under construction in Texas have been shut down. The shutdown of the two projects is largely due to the loss of financial support from TEPCO and other energy companies.
Nuclear energy seems like a good alternative to our dwindling supply of fossil fuels, but upon closer examination it is clear that our safety measures are not sufficient. Nuclear energy provides a cheap form of energy, after the initial building process, but is not cleaner or safer than fossil fuels or renewable energy resources. It ultimately becomes a debate of ethics and science. To what degree do we owe our future generations a clean and safe environment? Is it ethical to sacrifice the health of a few lives to make living cheaper and easier for thousands? As a communal whole we do not have the right to sacrifice a few lives or even a single life to make the communities lives easier. Not only that, but science has not yet caught up with the potential hazards of nuclear reactors. Without complete understanding of the reactions taking place and the radiations aftermath we cannot say with certainty that nuclear energy is both safe and viable.
