Executive Summary: Fukushima Dai-ichi Disaster

Transcription

1 Executive Summary: Fukushima Dai-ichi Disaster April 22, 2011 The Fukushima Dai-ichi nuclear power disaster has exposed specific design flaws asssociated with the Mark I Boiling Water Reactor. An in depth analysis of these design flaws, as well as a critique of the on-site waste storage facilities at Fukushima I, is presented in this paper, and possible improvements are disscussed. It is believed that understanding these design flaws will prevent future nuclear catastrophes. Fukushima Dai-ichi used General Electric Mark I Boiling Water Reactors to generate steam. By investigated the design plans, as well as the accident reports, the following defects can be found. First, boiling water reactors generate steam directly in their cores, making them susceptible to overheating and pressure buildup in a loss of coolant/flow situation. This situation occurred at Fukushima Dai-ichi, and the workers were forced to vent the steam in the core to the secondary containment structure. The suppressor, installed as a fail safe in emergency situations, inadequately controlled the amount of steam within the secondary containment structure. Consequently, the core overheated and the zirconium fuel rods cracked, catalyzing the hydrogen-oxygen dissociation process. The resulting buildup of hydrogen gas within the secondary containment structure led to hydrogen explosions at three of the six units at Fukushima Dai-ichi. These explosions exposed the environment to unsafe radiation levels. Further flaws with the placement of the spent fuel pools were found. Fuel pools hold nuclear waste, a byproduct of nuclear fission. This waste is intended to be held at a permanent storage facility, but few such facilities exist. Consequently, nuclear waste is kept on site, endangering workers and the environment in the event of a catastrophe. The damage done to the spent fuel pools at Fukushima Dai-ichi is partially responsible for further radiation contamination. Due to the half lifes of the radioactive materials released, clean up at Fukushima will take years. In order to avoid future incidences of this kind, scientists must learn from Fukushima. Mark I Boiling Water Reactors should be designed to handle a loss of flow/coolant under these conditions. Also, spent fuel rods should be moved to permanent storage facilities. However, even if these actions are taken, it is uncertain what role nuclear energy will play in the future. A few speculations can be made though. Given that Japan is an island nation, it cannot afford to eliminate nuclear energy, which until recently met 30% of Japan s energy demand. Furthermore, rising oil prices mandate that countries, such as the U.S., begin aggressively pursuing alternative fuels. Nuclear energy is an extremely safe and effective alternative fuel source, despite this accident, and it should therefore be taken seriously by these countries. 1

2 Electrical Power: Transmission, Conversion, and Generation Preprint typeset using L A TEX style emulateapj v. 11/10/09 An Analysis of the Fukushima Dai-ichi Nuclear Disaster Jacob A. Tutmaher 1 1. INTRODUCTION Nuclear energy provides a clean, non-co 2 emitting, alternative to hydrocarbon sources. Its ability to generate large amounts of energy from small amounts of mass make it especially desirable for electrical generation. Despite its environmentally friendly background, popular opinion often views it with skepticism. This is for two reasons. First, nuclear energy, produced by a process known as fission, produces a radioactive byproduct called nuclear waste. This waste is hazardous to the public, and adequate storage is extremely difficult to find. Second, a few specific incidences, such as Three Mile Island, Chernobyl, and now Fukushima Dai-ichi, have caused weariness among the populace. Though some of this concern is legitimate, some of it can be attributed to misunderstanding. By studying the incidences at Fukushima I, specific design flaws can be identified; and understanding these flaws is essential to preventing similar incidences. Though a single flaw is not responsible for the accident at Fukushima, inadequacies with the reactor s design, especially the suppressor, can be held partially responsible. The suppressor s inability to effectively maintain safe steam levels led to a buildup of hydrogen gas, thereby causing hydrogen explosions which breached the secondary containment structure. This breach released radiation into the environment, leading to a 20 kilometer evacuation zone around the plant. Some solace can be found within this catastrophe though. By understanding why these units failed, future scientist will be able to create safer reactors, ensuring that accidents of this magnitude do not happen again. 1 Dept. of Physics and Astronomy, University of Rochester, Rochester, NY FUKUSHIMA NUCLEAR PLANT DESIGN 2.1. Steam Generators Nuclear fission was first discovered in 1939, and it was soon used to generate large amounts of electricity. The first nuclear plants were constructed in the United States in the late 1950s, and since then many more have been created.(7) Nuclear fission generators also became prominant abroad, with plants being constructed in Europe and Asia. Fukushima Dai-ichi (Fukushima I) was constructed on the north east coast of Japan and was fully operational by It used a General Electric Mark I Boiling Water Reactor (BWR) system to produce 4.7GW of power to the surrounding area.(11) The entire plant is still governed by the Tokyo Electric Power Company (TEPCO).(13) It is important to note that nuclear power plants, in general, operate much like coal or gas burning power plants. They differ only in how they heat the boiler. In order to understand nuclear plants one must first understand steam generation plants in general. A typical steam generation plant follows a Rankine Cycle. A Rankine Cycle is a thermodynamic process, and is most easily explained using a visual reference. Figure 1 demonstrates a typical Rankine Cycle. The highest points on the graph correspond to the points of highest enthalpy. Enthalpy is defined as the total energy available in a system. Something known as the Gibbs free energy and the entropic energy compose enthalpy. A basic formulation is: H = G + T S, where H is the enthalpy, G is the Gibbs free energy, and TS represents the temperature multiplied by the entropy

3 2 Fig. 1. The point at position 1 represents the superheated steam entering the turbine. It drops to position 2 after the energy is extracted out of it and moves through the condenser to the pump. It then reaches the boiler at position 4 and is superheated back to position 1. Image obtained from: Steam Power Cycle, Updated: June, 2009 (entropic energy). In a typical power plant, water is circulated through a few distinct points-shown in Figure 2. Starting at the pump, which is the force behind the circulation, water travels to the boiler. The boiler boils the water at a given pressure and then sends it to a superheater. superheater is essential to the system for several reason; one, it assures that the steam maintains a high quality (low fluid to vapor ratio); and two, it optimizes the energy in the steam in order to achieve a high energy transfer to the turbine. Once the steam passes through the turbine it goes to a condenser. A condenser converts a gaseous state to a liquid state, lowering the entropy of the substance in the process. The remaining water is run back through the cycle.(10) It is also important to note that the points labeled in Figure 1 correspond to the points labeled in Figure 2. This should give the reader a feel for the amount of Enthalpy available at each stage in the cycle. Many modern plants also use something known as a reheat, which basically adds an extra step to the cycle. The steam, after leaving the turbine, is superheated again and sent back through another (low pressure) turbine. The addition of a reheat further optimizes the process because the plant can extract even more energy from the steam without adding more energy to the boiler. A Fig. 2. This diagram shows the typical path of water in a steam/water in a generation system. Image obtained from: Steam Power Cycle, Updated: June, Nuclear Fission: Theory As stated before, nuclear reactors differ from other plants, such as coal burning plants, primarily in how they heat the boiler. Nuclear reactors undergo a process know as fission. Fission is the release of energy through atomic nuclei splitting. Einstein theorized that every particle, when at rest, had an energy equal to the particle s mass times the speed of light-indicating that mass was directly related to energy. E = mc 2. It was also theorized that some of this mass was converted to energy when nucleons collected (or binded) in the nucleus. If this nucleus was ever split, then the energy required to bind the nucleons would be released in a process called fission. In the mid 1900s, when scientists learned how to harness this energy, an 80% conversion to thermal energy was achieved. This conversion rate meant that nuclear fission produced 3 million times as much energy as coal! 2 (1) In order to achieve stable fission however, only certain elements can be used. Since a high nucleon count often results in unstable atoms with intrinsically high repulsive forces, atoms with high mass numbers are almost exclusively used. The most famous element used is Uranium, though other elements such as Plutonium and Thorium may be used. Uranium 238 is mined naturally, 3 and 2 On a per atom basis. 3 the 238 indicates the mass number, or the number of total

4 Fukushima Dai-ichi Nuclear Power Plant 3 TABLE 1 Reactor Types at Fukushima I Reactor Design Size Date of Operation Fukushima I-1 General Electric Mark I BWR 439MW March 1971 Fukushima I-2 General Electric Mark I BWR 760MW July 1974 Fukushima I-3 General Electric Mark I BWR 760MW March 1976 Fukushima I-4 General Electric Mark I BWR 760MW October 1978 Fukushima I-5 General Electric Mark I BWR 760MW April 1978 Fukushima I-6 General Electric Mark II BWR 1067 MW October 1979 contains trace amounts of Uranium These trace in a fission reaction, a wide array of neutron energies are amounts of U 235 will be shown to be important later. Uranium is especially desirable for the fission process because of its relatively long half life. Since atomic decay follows an exponential decay, the time required for half of the element to decay is found by setting this exponential produced. Few of these neutrons, though, have enough energy to split a U 238 nucleus. 5 The moral of the story is this: U 238 is not unstable enough to produce a stable fission reaction alone because more neutrons are absorbed than released. Thus, U 238 must be enriched with U 235 equal to 1 2 and taking the natural logarithm of both sides. if stabilized fission is to be achieved. 6 U 235 is far more Thus, and ln( 1 2 )= λt 1 2, t 1 = λ unstable, and therefore provides the extra neutrons required to produce stable fission. The resulting neutron density in enriched uranium is known as critical mass, and traditionally hovers around 1 neutron per atom for stable reactions.(1) 7 Here λ represents the decay constant, and is different for every element. The half life for U 238 and U 235 is years and years respectively.(3) This long half life means that scientists don t have to worry about the element rapidly decaying. When elements, like uranium 238, are subjected to high energy neutrons, a nuclear fission reaction occurs. A nuclear fission reaction typically follows this pattern: first, a neutron penetrates a U 238 or U 235 nucleus. Depending on the speed it will yield a symmetric or nonsymmetric split. Slow moving neutrons typically yield a non-symmetric split, but this is only in more unstable U 235 atoms. U 238 atoms require higher energy neutron penetration in order to split; therefore, slow moving neutrons usually do not result in atomic splitting in pure U 238. (1) The need for high energy neutrons complicates the stabilization process for fission reactions. This is because, neutrons and protons in the nucleus. 4 About 0.7% In a nuclear reactor, the splitting of the uranium nuclei releases the atom s binding energy. This energy, at an 80% thermal conversion rate, heats the water near the core to a boiling temperature. This produces steam which is transported to the turbines. Electrical energy is generated by the spinning turbines and transported to the surrounding areas using high voltage transmission lines Boiling Water Reactors As stated before, Fukushima Dai-ichi uses boiling water reactors. At the time it was built there were two competing boiler designs for nuclear reactors. One was known as a Pressurized Water Reactor (PWR), and the other was known as a Boiling Water Reactor (BWR). To 5 Even neutrons with an energy value of 1 MeV cannot split the nucleus. An ev is an electron volt. It is defined as the amount of energy required to move an electron through a one volt potential 6 The enrichment process is something that occurs in a laboratroy. It requires the manual seperation of U 235 from U At this point I would like to address the age old question: Can a nuclear reactor ever produce a nuclear explosion? No. Even with enriched uranium one can not achieve the neutron density required to go supercritical.

5 4 Fig. 3. A cross section of a typical General Electric boiling water reactor is shown above. It is important to not that the entire cylindrical core is filled with these square cross sections penetrated with uranium oxide fuel rods. The cruciform control rods are inserted upwards from the bottom of the reactor. (12) be honest, boiling water reactors vary little from pressurized water reactors. As one could have guessed, the fundamental difference is that pressurized water reactors operate at higher pressures. 8 For this paper, we will be concerned with the specifics of a boiling water reactor since Fukushima I used them. Refer to Table 1 to view specific information regarding the Fukushima reactors. (11) A boiling water reactor consists of a core, which contains the fuel rods, the moderators, and (occassionally) the control rods. The core is surrounded by a secondary containment unit which houses a suppressor. A typical core is 3.8 meters in height and 4.8 meters in diameter. It s cylindrical volume contains hundreds of fuel rods and control rods, indicating that these elements are relatively small. (3) A cross sectional area of the GE core design 8 They also require a constant enrichment percentage for all of the fuel rods and operate under an indirect cycle. In this type of cycle the primary system is completely isolated from the turbine.(6) is presented in Figure 3. The fuel rods are the heat source. They contain pellets of Uranium Oxide in zirconium alloy tubes, and are evenly spaced within the cylindrical cell.(6) Due to the cruciform shaped control rods and the unevenly spaced moderator tubes within the core, different fuel rods have different enrichment factors within the core. Rods closer to the moderators and control rods, particularly rods on the outer edges, have higher enrichment factors; usually between 2.5% and 3.0%. Rods in the interior of the core, where a higher neutron density is typically found, have a lower enrichment factor between 1.7% and 2.1%. These different enrichment factors compensate for the uneven neutron distribution and help create a more even fission process.(2) The control rods are stainless steel cruciform tubes packed with Boron Carbide powder. This substance is effective at absorbing neutrons; thereby lower the neutron density in a fission reaction. Lowering the neutron density enough will stop the fission process altogether.(4) The control rods are present primarily for emergency purposes. The core also contains tubes through which a moderator passes. A moderator basically controls small fluctuations in neutron density, scattering them if need be. In a BWR, the moderator is usually water (H 2 0). Water is pumped through the core via a pump in BWRs.(3) Water is also used as a coolant. Coolants work by absorbing energy and neutrons produced by the nuclear reaction. In a BWR, water (injected with a neutron poison of Gadolinium Oxide) absorbs neutrons and controls the reaction. Coolants are usually used to control fission reactions (on a daily basis) rather than control rods. If a fission reaction gets too high, the water is injected with larger amounts of Gadolinium Oxide. If it s too low, the amount of Gadolinium Oxide is reduced. In emergency situations the water is injected with Sodium Pentaborate or Boron and the control rods are completely inserted

6 Fukushima Dai-ichi Nuclear Power Plant 5 into the core.(4) In a BWR the core basically is the boiler. Water is circulated from the bottom of the reactor to the top via a pump, and the steam is generated directly in the core. This is desirable because extra room at the top of the core can be allotted for steam separation. 9 This required room at the top also mandates that the control rods are placed at the bottom of the reactor. In an emergency, hydraulic pumps push the control rods up into the core.(5) Outside the core, within the secondary containment unit, is a toroid shaped (doughnut shaped) device known as a suppressor. Its purpose is to remove heat from the system in the event that a large amount of steam is generated. The core rests on top of the suppressor.(16) This entire system is surrounded by a large secondary containment wall, which provides protection to the facility in case the core ruptures. In modern BWRs a steam vent is added to the core. In case of a high pressure meltdown, the vent is open and steam can escape into the secondary containment unit. The suppressor can then control this excess steam. This helps control the pressure inside the core.(18) During (stable) nuclear fission, the steam is sent from the core to the turbine, and the left over water is cycled back through the reactor. Since only about 14% of the water introduced to the boiler is converted to gas, little new water is introduced to the system. The output power can be controlled by adjusting the flowrate specified by the pump. A higher flowrate usually generates a larger power output. Typical BWR s can produce 3830 MW of thermal power and 1330MW of electrical power. (5) This is the equivalent power output of 33 large offshore windmills Nuclear Waste When uranium nuclei split two separate nuclei are generated. Furthermore, sometimes a free neutron does not 9 Steam needs to be separated (e.g. vapor separated from dry steam) via a seperator in order to protect the turbines from decay and ensure a high energy transfer. split a uranium nuclei but rather is absorbed by it, changing the properties of the atom in the process. In a nuclear reactor, after a sufficient number of reactions take place within the core, the number of usable uranium nuclei will inevitably decrease. Eventually, such a small number of uranium nuclei are present in the core that stable fission is impossible. When this happens the fuel rods must be replaced with fresh-uranium rich-fuel rods. The spent fuel rods are not benign though. They contain radioactive waste, sometimes referred to as daughter products, which are toxic to the public. Managing these radioactive materials is a huge concern, one worth discussing. The daughter products are usually classified as either high-level or low-level wastes. If a product is a high level waste it is extremely radioactive, and therefore dangerous to the environment. These elements will remain dangerous until atomic stability is reached. This process takes time, and is governed by the various half-lifes of the products. Common waste products produced by a nuclear fission reaction are Plutonium 239 (half life of 24,000 years) and Americium 241 (half life of 400 years).(8) Since the fuel rods are still hot when they are removed from a reactor core they are placed in a pool of boric acid, temporarily, in order to cool down. 10 They are kept there until a permanent storage facility is located. As of yet, few storage facilities exists, so much of this toxic waste is kept on site until a permanent solution is obtained.(9) Another source of radiation is the reactor itself. Being that the reactor is exposed to high levels of radiation every day, it is inevitable that it will become radioactive itself. This usually is not a problem until the plant is decommissioned. Once decommissioned all elements in the plant are disassembled. This results in dismantling the core and exposing the environment to high levels of radiation. The decommissioning process can be quite 10 Boric acid is a good absorber of radiation.

7 6 safe if the proper precautions are taken; however, if an accident does occur, miscellaneous pieces of the reactor can become exposed and leak radiation at an unchecked rate.(8) 3. FUKUSHIMA I NUCLEAR DISASTER 3.1. Events On March 11, 2011 an 8.9 magnitude earthquake occurred off the northern coast of Japan. Shortly thereafter electric power provided by TEPCO was cut off to many areas-including the Fukushima I nuclear power plant. The plant now relied on the diesel backup generators to circulate the coolant through the reactors. Fortunately, loss of power automatically caused the control rods to be inserted into the reactor s core. According to Japan s Nuclear and Industrial Safety Agency (NISA), the reactors at the Fukushima Dai-ichi plant were properly shut down, but continued to heat up since the fission process still released energy.(14) Unfortunately, the subsequent tsunami later destroyed the back up generators, disabled the cooling system. With the cooling system disabled, the nuclear reactors (especially unit 1) began to overheat.(13) This core generated unsafe amounts of steam and pressure inside the reactor. Steam vents leading to the secondary containment unit were opened, but the suppressor failed to effectively control the excess steam. In order to prevent further pressure build up, and to prevent the buildup of hydrogen gas, 11 preparations to vent the secondary containment system of unit 1 began. On March 12, a hydrogen explosion occurred at unit 1. A hydrogen explosion later occurred at unit 3 two days later and unit 2 three days later. The explosion at unit 1 damaged the secondary containment vessel, though the core remained intact. Units 2 and 3 were not quite as lucky, with significant damage to both the core and the secondary containment structure occurring at both sites. Unit 4, though damaged, remained fairly 11 See next footnote. stable through the turmoil. Units 5, and 6 remained stable since they had been shut down before the earthquake for maintenance.(14) On March 22 the International Atomic Energy Agency reported that the fuel rods in all three reactors were only half covered with coolant. Due to these explosions, and the low coolant level, radioactive cesium and iodine were being released into the environment. Furthermore, the spent fuel rod pools that lie adjacent to the reactors were also disturbed. Efforts were made to deliver coolant to the spent fuel rods via a cement truck. 12 (15)(14) A partial meltdown had now occurred at Fukushima I, and the Japanese workers now faced the task of venting the steam to reduce the pressure in the core; while, at the same time, preventing radiation release. If the pressure was not vented, a second explosion could be generated, setting fire to the plant. This fire would result in a total meltdown, and enormous quantities of radiation would be released into the environment.(15) Unfortunately, venting steam from the reactors would consequently release radiation into the environment. The Japanese workers were forced to choose the lesser of two evils. Workers at the plant began to vent the steam from the secondary containment units, and pumps were brought in to circulate ocean water through the core. Though ocean water will act as a suitable coolant, it is highly corrosive, thereby destroying the reactors at Fukushima. The use of seawater also has another downside. Once 12 Before I continue, I must clarify something. Hydrogen explosions are not nuclear explosions. Hydrogen explosion in BWRs are due to a buildup of hydrogen gas, largely attributed to radiolysis and dissociation. Radiolysis occurs when alpha radiation emitted by the fuel rods separate the hydrogen and oxygen from each other. Dissociation of the hydrogen and oxygen bonds is due to extremely high temperatures. Dissociation becomes especially common when hot zirconium encased fuel rods fail to be cooled. When this happens, cracks in the zirconium fuel rods release uranium oxide (and its daughter products) into the boiler. These products cause radiolysis in water. Furthermore, once the rods reach a temperature above 1200 degrees Celsius, the zirconium (which acts as the catalyst in this reaction) will strip the hydrogen from the oxygen. This buildup of hydrogen gas within the core or the secondary containment vessel can explode if the concentration exceeds 4%. This is what happened at Units 1, 2, and 3 at Fukushima Daiichi. Any cracks generated by this explosion can subsequently release uranium oxide and other various daughter products into the environment.(15)

8 Fukushima Dai-ichi Nuclear Power Plant 7 seawater is pumped into the reactor, it must be pumped out. Consequently, this contaminated seawater will now be re-introduced into the ocean, exposing more life forms to high radiation levels. This was a necessary risk, because a total nuclear meltdown would release even more radiation into the environment. 13 On March 12, after the first hydrogen explosion, anyone living within a ten kilometer radius was evacuated due to radiation.(14) By the end of March each unit had obtained AC power, enabling the coolant to be pumped through the reactors; however, as of April 15, 2011, Units 1, 2, and 3 remained above cold shutdown status (indicating that their cores were still above 100 degrees Celsius). Currently, fresh water, laced with boron, is continually pumped through these reactors, and each day yields a lower temperature value. Unit 1 is also pumped with nitrogen gas (an inert gas) in order to reduce the possibility of a second hydrogen explosion.(14) At the present time the Japanese government has increased the evacuation zone to twenty kilometers.(13) Officials are optimistic that the worst is behind them, though complete recovery will take years. This long term recovering can be attributed to the long half lifes of the radioactive elements released by the plant. 4. IMPLICATIONS AND FUTURE IMPACT 4.1. Known BWR Deficiencies Even before the Fukushima I nuclear disaster, design flaws regarding the suppression system in the GE designed BWR were identified. Critics claimed that the BWR piping was particularly susceptible to hydrogen explosions, and that the toroid shaped suppressor was ineffective at handling large amounts of steam.(18) The Nuclear Resource and Information Service, a group against nuclear power, cite a statement made by Harold Denton, the top official at the Nuclear Regulatory Commission in 1986, claiming that, Mark I containment, especially 13 A total nuclear meltdown means that the fuel rods within the reactors actually melt. They get so hot that they penetrate the core, then the secondary containment unit, then the bottom of the plant. Once beneath the plant they expose the environment to massive amounts of radiation being smaller with lower design pressure, in spite of the suppression pool, if you look at the WASH 1400 safety study, [has] something like a 90% probability of containment failure.(17)(18) Containment fails because hydrogen gas can collect (usually within the secondary containment after excess steam is vented from the core) in BWRs because the suppressor can not effectively remove heat from the steam, thus forcing workers to manually vent the secondary containment structure in order to avoid an explosion. Critics, such as the Nuclear Resource and Information Service, claim that this is an inadequate fix and that it further exposes the environment to radioactive steam.(18) General Electric maintains that no known design flaws were present in the Mark I BWR.(20) Citing a quote on General Electric s website, GE s containment systems utilize pressure suppression technology, where a pool of water is available to condense steam in the event of an accident and reduce the pressures on the containment vessel. Units are built to withstand predicted peak containment pressures based upon their design under accident guidelines. GE also claims that the BWR is not susceptible to hydrogen gas buildup.(20) Regardless, Fukushima I did overheat. This led to a buildup of steam and hydrogen gas in the secondary containment vessel which led to an explosion. Damage to these containment vessel consequently led to radiation exposure. It would seem as if, under the circumstances of March 11, 2011, the BWR Mark I reactor did not perform adequately. Whether this is due to a design flaw or negligence on the part of the Japanese workers is presently unknown. Another known problem is the location of the spent fuel rods.(18)(14) Since long term storage facilities are rare, many plants are forced to hold nuclear waste on site. During an emergency this fuel is especially dangerous due to its radioactivity and lack of protection. At Fukushima, the cooling system was disabled to the spent

9 8 fuel rod pools as well as the reactors. Much like the reactors, the old fuel rods are radioactive; and, if the pool sustains sufficient damage, radiation can be leaked. In order to avoid this catastrophe long term storage facilities should be located, and spent fuel rods should be moved out of the plant once sufficiently cooled. This flaw is shared among nearly all nuclear power plants, and many scientists have identified this as a primary concern.(19) 4.2. Future Implications The Fukushima disaster will have a profound impact on nuclear policy both domestic and abroad. Already in the United States, top officials of the Natural Resources Defense Council s Nuclear Program have been question by members of Congress regarding nuclear energy s future. Thomas Cochran, the senior scientist of the Natural Resources Defense Council s Nuclear Program, stressed learning from the Fukushima incident rather than using it as a scapegoat for nuclear elimination.(19) Specifically, Dr. Cochran wants to readdress issues concerning the BWRs containment problems. He also wants the NRDC to look into improving the Mark I s handling of hydrogen interactions, and reassess its ability to deal with power losses. Finally, Dr. Cochran wants to move spent fuel rods to long term storage facilities. He hopes that these actions will put America s nuclear energy fears to rest. Indeed, President Barack Obama has expressed interest in pursuing nuclear energy since the Fukushima disaster. At a energy talk at Georgetown University on March 30, 2011, the President apparently embraced nuclear power as part of America s energy future, despite increased safety concerns following the earthquake and tsunami in Japan that severely damaged a nuclear power plant there.(21) Nuclear power will certainly be an integral part of the Obama Administrations plan to cut U.S. oil imports by one-third by 2025.(21) It would seem that in order to transition from an energy importer to a self-sustaining power, the U.S. will have to embrace alternative fuel sources-including nuclear energy. The Fukushima nuclear disaster will also have a dramatic impact on Japanese nuclear policy. Although it is still too early to find significant changes in Japan s nuclear policies, some speculations can be made. Japan first began to embrace nuclear energy in the 1970s, when oil prices spiked.(22) The earthquake on March 11 significantly damaged units 1-4 at Fukushima I, removing about 2.7 GW from the grid. This number only represents a fraction of the total energy generated from nuclear fission though. Currently, nuclear energy makes up about 30% of Japan s energy system (which is about 1085 billion kwh a year), with plans to increase this number to 50% by There are also systems in place to recycle spent fuel rods, making Japan s nuclear program one of the most economical in the world. Since these guidelines are already in place, it would seem almost impractical for Japan to eliminate nuclear energy completely. Furthermore, given that Japan is an island, and that it does not possess an abundant stash of raw materials, nuclear energy seems almost essential to its survival.(22) Despite the incident at Fukushima I, nuclear power will remain prominent in Japan for years to come. 5. CONCLUSION Since nuclear fission s advent in 1939, fission has proven to be one of the most efficient energy sources ever used. However, accidents such as Chernobyl, Three Mile Island, and now Fukushima have generated a negative stigma towards nuclear energy. Instead of eliminating nuclear energy though, many countries have used these incidences as learning experiences. Indeed, understanding the specifics that led to the tragedy at Fukushima will increase safety and efficiency amongst all nuclear energy plants. Consequently, the lessons learned from Fukushima will create a more energy efficient future for all nuclear users. The lessons learned from the Fukushima specifically relate to design inadequacies with the Mark I Boiling

10 Fukushima Dai-ichi Nuclear Power Plant 9 Water Reactor. Since the steam is generated directly in the core, dangerous pressure levels can be reached during an emaregency. A safety vent, leading from the core to the secondary containment structure, was put in place to relieve this burden in the 1980s. Unfortunately, the suppressor inside the secondary containment structure cannot adequately handle a large steam buidup if the coolant/flow is lost. This buildup leads to overheating, resulting in hydrogen gas buildup and combustion. These events occured at Fukushima I on March 11, 2011, resulting in radiation leakage. Critics have claimed that the suppressor s inadequacies were known before the incident at Fukushima I. General Electric, on the other hand, claims that their Mark I BWRs are very safe, implying that circumstances relating to the tsunami, such as back up generator failure, are directly responsible for the radiation leaks. To be fair, there are few things on this earth that can withstand an 8.9 magnitude earthquake, but this should not be used as an excuse. Certainly, the loss of coolant was devasting to the reactors at Fukushima; however, perhaps these reactors should be designed to withstand a loss of coolant/flow incident. Many U.S. scientist believe this to be the case, and intend on implementing precautions based on the incidences at Fukushima before pursuing nuclear power more vigorously in the future. Japan, understandably so, will also increase caution; however, their island nation cannot afford to erase nuclear energy completely. Though this incident at Fukushima I was catastrophic, the correct safety protocols were followed, and many citizens were saved in the process. Just as a single plane crash should not erase air travel forever, a single nuclear accident should not erase nuclear energy forever. Nuclear energy should still be viewed as a ligitimate alternate fuel source for years to come. REFERENCES [1]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Design Basics Vol. 1, 4th edition, Chapman and Hall, Inc. 1994, [2]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Systems Engineering Vol. 2, 4th edition, Chapman and Hall, Inc. 1994, [3]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Design Basics Vol. 1, 4th edition, Chapman and Hall, Inc. 1994, [4]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Design Basics Vol. 1, 4th edition, Chapman and Hall, Inc. 1994, [5]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Systems Engineering Vol. 2, 4th edition, Chapman and Hall, Inc. 1994, [6]Weisman, Joel, Elements of Nuclear Reactor Design. 2nd Edition, Robert E. Krieger Publishing Company, Inc., 1983, 5-8 [7]Glasstone, Samuel and Sesonske, Alexander, Nuclear Reactor Engineering: Reactor Design Basics Vol. 1, 4th edition, Chapman and Hall, Inc. 1994, 1-2 [8] Types of Nuclear Waste, waste types - /nuclear waste types.html, Accessed: April 15, [9] Nuclear Waste Storage, waste types - /nuclear waste types.html, Accessed: April 15, [10]Jones, T. B., Department of Electrical and Computer Engineering,University of Rochester, Class Leture Notes: Rankine Cycle and Steam Generators. Updated April 2011 [11]Nuclear Information and Resource Service, Fact Sheet on Fukushima Nuclear Power Plant, Updated: March 11, 2011 [12]World Nuclear Association, Nuclear Fuel Fabrication, fuel fabricationinf127.html, Updated: March, 2010 [13]Nuclear Energy Institute, Resources and Stats: Events at the Fukushim Daiichi Nuclear Power Plant in Japan, - reports/events-at-the-fukushima-daiichi-nuclear-power-plantin-japan-/?page=1, Updated: March 12, [14]International Atomic Energy Agency, Fukushima Nuclear Accident Update Log, Updated: April 15, 2011, Accessed April 16, [15]Scientific American, Partial Meltdowns Led to Hydrogen Explosions at Fukushima Nuclear Power Plant, partialmeltdowns-hydrogen-explosions-at-fukushima-nuclear-powerplant, Updated March 14, 2011 [16] Boiling Water Reactor, Updated: February [17]The Gazette, 23 US reactors share design with failed Japan nukes, mark-failed.html, Updated: March [18]Nuclear Information and Resource Service, Hazards of Boiling Water Reactors in the United States, Updated: March [19]Federal News Service Inc. Capitol Hill Hearing: Review of the Nuclear Emergency in Japan and Implications for the U.S. - UserDisplayFullDocument&orgId 574&topicId 25151docId l: &isRss true, Updated: April 12, 2011 [20]General Electric Reports, Setting the Record Straight on Mark I Containment History, Updated: March 2011.

11 10 [21]Associated Press, Obama Sets Ambitious Goals to Reduce U.S. Oil Imports, US-Obama-Energy/id e12461c883ba30af34e777e, Updated: March 30, [22]World Nuclear Association, Nuclear Power in Japan, Updated: March 30, 2011.