Shinn-Adolph Melissa #0482558
417.782.2822 [e-mail] Thomas Edison State College November 2011 Global Environmental Change ENS-314-GS
Final Project - Nuclear Power
The Question: Is nuclear power a clean, safe, energy choice that could be the predominant source of electricity in 2020?
I definitely believe that nuclear power is a clean, safe, feasible, energy choice that could be the predominant source of electricity in 2020, if the planning and implementing is done carefully and properly. In this paper, I will show you how. Nuclear Power Nuclear power is a clean energy choice. Taken from an Assignment 7 source, "Nuclear power is a clean energy source as it does not put CO2 back into the atmosphere. Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. Today it is almost all uranium. The basic energy fact is that the fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal." (McCarthy, 1995) There have been 2 major nuclear accidents, one at Three Mile Island in 1979 near Middleton, PA, USA, and one at Chernobyl in 1986 in Ukraine. There has also been a new incident this past year, in March, 2011, in Fukushima, Japan, that has the world wondering about the safety and feasibility of nuclear power. Three Mile Island After the accident at Three Mile Island in 1979, there were major safety rules implemented for nuclear power. At each unfortunate incident we gain knowledge of betterment for all nuclear projects. Scientists find the cause of what went wrong and find solutions to make sure the same occurrence doesn't happen again. "From its restart in 1985, Three Mile Island Unit 1 has operated at very high levels of safety and reliability. Application of the lessons of the TMI-2 accident has been a key factor in the plant's outstanding performance. In 1997, TMI-1 completed the longest operating run of any light water reactor in the history of nuclear power worldwide - 616 days and 23 hours of uninterrupted operation. (That run was also the longest at any steam-driven plant in the U.S., including plants powered by fossil fuels.) And in October 1998, TMI employees completed three million hours of work without a lost-work day accident. At the time of the TMI-2 accident, TMI-1 was shut down for refueling. It was kept shut down during lengthy proceedings by the Nuclear Regulatory Commission. During the shutdown, the plant was modified and training and operating procedures were revamped in light of the lessons of TMI-2. When TMI-1 restarted in October 1985, General Public Utilities pledged that the plant would be operated safely and efficiently and would become a leader in the nuclear power industry. Those pledges have been kept." (World Nuclear Association, 2001) Chernobyl "The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel. The resulting steam explosion and fires released at least 5% of the radioactive reactor core into the atmosphere and downwind. Two Chernobyl plant workers died on the night of the accident, and a further 28 people died within a few weeks as a result of acute radiation poisoning. UNSCEAR says 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." Resettlement of areas from which people were relocated is ongoing." (World Nuclear Association, updated 2011)
The outcome of these incidents has been positive in the future of the use of nuclear power as an energy source. Chernobyl was a horrific accident, but the Soviet design of that facility is different than those of western design. The US has learned a great deal from Chernobyl. Chernobyl has been the only incident in history with casualties. Then, less than one year ago, Japan had a terrible disaster. It started with an earthquake "centered just off Japan's east coast, near Honshu. The added horror of the tsunami quickly followed." (Mirsky, 2011) As a consequence of these terrible events, there was an explosion at the Fukushima Daichi nuclear reactor affecting the housing structure. "Two workers died inside the plant. Some scientists predict that one million lives will be lost to cancer." (McNeill, 2011) I think the sources I found were great sources and I do agree with their standing on the subject of Nuclear Power. They were very informative and forthcoming with their information. The source articles covered all aspects of the subject and didn't leave out information in an attempt to cover up or dismiss any part of the claim of nuclear accidents. They didn't blame or point fingers but instead reported the facts as a great news piece should do. Nuclear Power Process Again, I don't like to use Wikipedia as a source very often, but this is what it had to say about the process of Nuclear Power. "In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), and releasing a tremendous amount of energy. The two nuclei produced are most often of comparable size, typically with a mass ratio around 3:2 for common fissile isotopes. Most fissions are binary fissions, but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced in a ternary fission. The smallest of these range in size from a proton to an argon nucleus. Fission is usually an energetic nuclear reaction induced by a neutron, although it is occasionally seen as a form of spontaneous radioactive decay, especially in very high-mass-number isotopes. The unpredictable composition of the products (which vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from purely quantumtunneling processes such as proton emission, alpha decay and cluster decay, which give the same products every time. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). In order for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very dense source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons may counterbalance the desirable qualities of fission as an energy source, and give rise to ongoing political debate over nuclear power." (Wikipedia) Some Advantages "The basic energy fact is that the fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal. Present reactors that use only the U-235 in natural uranium are very likely good for some hundreds of years. Bernard Cohen has shown that with breeder reactors, we can have plenty of energy for some billions of years." (McCarthy, 1995) Some Disadvantages One disadvantage is the minute possibility of an explosion and nuclear particles getting into the air or taking numerous surrounding businesses and homes with it. Another is the dilemma of how to expose of the rods properly. I think that transporting objects with radiation
across countries to store is asinine. The Three Mile Island Accident The accident at the Three Mile Island Unit 2 (TMI2) nuclear power plant near Middletown, Pa., on March 28, 1979, was the most serious in U.S. commercial nuclear power plant operating history, even though it led to no deaths or injuries to plant workers or members of the nearby community. But it brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the U.S. Nuclear Regulatory Commission to tighten and heighten its regulatory oversight. Resultant changes in the nuclear power industry and at the NRC had the effect of enhancing safety. The sequence of certain events equipment malfunctions, design-related problems and worker errors led to a partial meltdown of the TMI2 reactor core but only very small offsite releases of radioactivity. Summary of Events The accident began about 4:00 a.m. on March 28, 1979, when the plant experienced a failure in the secondary, non nuclear section of the plant. The main feed water pumps stopped running, caused by either a mechanical or electrical failure, which prevented the steam generators from removing heat. First the turbine, then the reactor automatically shut down. Immediately, the pressure in the primary system (the nuclear portion of the plant) began to increase. In order to prevent that pressure from becoming excessive, the pilot-operated relief valve (a valve located at the top of the pressurizer) opened. The valve should have closed when the pressure decreased by a certain amount, but it did not. Signals available to the operator failed to show that the valve was still open. As a result, cooling water poured out of the stuck-open valve and caused the core of the reactor to overheat. As coolant flowed from the core through the pressurizer, the instruments available to reactor operators provided confusing information. There was no instrument that showed the level of coolant in the core. Instead, the operators judged the level of water in the core by the level in the pressurizer, and since it was high, they assumed that the core was properly covered with coolant. In addition, there was no clear signal that the pilot-operated relief valve was open. As a result, as alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident. They took a series of actions that made conditions worse by simply reducing the flow of coolant through the core. Because adequate cooling was not available, the nuclear fuel overheated to the point at which the zirconium cladding (the long metal tubes which hold the nuclear fuel pellets) ruptured and the fuel pellets began to melt. It was later found that about one-half of the core melted during the early stages of the accident. Although the TMI-2 plant suffered a severe core meltdown, the most dangerous kind of nuclear power accident, it did not produce the worst-case consequences that reactor experts had long feared. In a worst-case accident, the melting of nuclear fuel would lead to a breach of the walls of the containment building and release massive quantities of radiation to the environment. But this did not occur as a result of the three Mile Island accident. The accident caught federal and state authorities off-guard. They were concerned about the small releases of radioactive gases that were measured off-site by the late morning of March 28 and even more concerned about the potential threat that the reactor posed to the surrounding population. They did not know that the core had melted, but they immediately took steps to try to gain control of the reactor and ensure adequate cooling to the core. The NRC=s regional office in King of Prussia, Pa., was notified at 7:45 a.m. on March 28. By 8:00, NRC Headquarters in Washington, D.C., was alerted and the NRC Operations Center in Bethesda, Md., was activated. The regional office promptly dispatched the first team of inspectors to the site and other agencies, such as the Department of Energy and the Environmental Protection Agency, also mobilized their response teams. Helicopters hired by TMI's owner, General Public Utilities Nuclear, and the Department of Energy were sampling radioactivity in the atmosphere above the plant by midday. A team from the Brookhaven National Laboratory was also sent to assist in radiation monitoring. At 9:15 a.m., the White House was notified and at 11:00 a.m., all nonessential personnel were ordered off the plant's premises. By the evening of March 28, the core appeared to be adequately cooled and the reactor appeared to be stable. But new concerns arose by the morning of Friday, March 30. A significant release of radiation from the plants auxiliary building, performed to relieve pressure on the primary system and avoid curtailing the flow of coolant to the core, caused a great deal of confusion and consternation. In an atmosphere of growing uncertainty about the condition of the plant, the governor of Pa., Richard L. Thornburgh, consulted with the NRC about evacuating the population near the plant. Eventually, he and NRC Chairman Joseph Hendrie agreed that it would be prudent for those members of society most vulnerable to radiation to evacuate the area. Thornburgh announced that he was advising pregnant women and pre-school-age children within a 5-mile radius of the plant to leave the area. Within a short time, the presence of a large hydrogen bubble in the dome of the pressure vessel, the container that holds the reactor core, stirred new worries. The concern was that the hydrogen bubble might burn or even explode and rupture the pressure vessel. In that event, the core would fall into the containment building and perhaps cause a breach of containment. The hydrogen bubble was a source of intense scrutiny and great anxiety, both among government authorities and the population, throughout the day on Saturday, March 31. The crisis ended when experts determined on Sunday, April 1, that the
bubble could not burn or explode because of the absence of oxygen in the pressure vessel. Further, by that time, the utility had succeeded in greatly reducing the size of the bubble. Health Effects Detailed studies of the radiological consequences of the accident have been conducted by the NRC, the Environmental Protection Agency, the Department of Health, Education and Welfare (now Health and Human Services), the Department of Energy, and the State of Pa.. Several independent studies have also been conducted. Estimates are that the average dose to about 2 million people in the area was only about 1 millirem. To put this into context, exposure from a chest xray is about 6 millirem. Compared to the natural radioactive background dose of about 100125 millirem per year for the area, the collective dose to the community from the accident was very small. The maximum dose to a person at the site boundary would have been less than 100 millirem. In the months following the accident, although questions were raised about possible adverse effects from radiation on human, animal, and plant life in the TMI area, none could be directly correlated to the accident. Thousands of environmental samples of air, water, milk, vegetation, soil, and foodstuffs were collected by various groups monitoring the area. Very low levels of radionuclides could be attributed to releases from the accident. However, comprehensive investigations and assessments by several wellrespected organizations have concluded that in spite of serious damage to the reactor, most of the radiation was contained and that the actual release had negligible effects on the physical health of individuals or the environment. Impact of the Accident The accident was caused by a combination of personnel error, design deficiencies, and component failures. There is no doubt that the accident at Three Mile Island permanently changed both the nuclear industry and the NRC. Public fear and distrust increased, NRC's regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully. The problems identified from careful analysis of the events during those days have led to permanent and sweeping changes in how NRC regulates its licensees which, in turn, has reduced the risk to public health and safety. Here are some of the major changes which have occurred since the accident: Upgrading and strengthening of plant design and equipment requirements. This includes fire protection, piping systems, auxiliary feed water systems, containment building isolation, reliability of individual components (pressure relief valves and electrical circuit breakers), and the ability of plants to shut down automatically; Identifying human performance as a critical part of plant safety, revamping operator training and staffing requirements, followed by improved instrumentation and controls for operating the plant, and establishment of fitness-for-duty programs for plant workers to guard against alcohol or drug abuse; Improved instruction to avoid the confusing signals that plagued operations during the accident; Enhancement of emergency preparedness to include immediate NRC notification requirements for plant events and an NRC operations center that is staffed 24 hours a day. Drills and response plans are now tested by licensees several times a year, and state and local agencies participate in drills with the Federal Emergency Management Agency and NRC; Establishment of a program to integrate NRC observations, findings, and conclusions about licensee performance and management effectiveness into a periodic, public report; Regular analysis of plant performance by senior NRC managers who identify those plants needing additional regulatory attention; Expansion of NRC's resident inspector program first authorized in 1977 whereby at least two inspectors live nearby and work exclusively at each plant in the U.S. to provide daily surveillance of licensee adherence to NRC regulations; Expansion of performanceoriented as well as safetyoriented inspections, and the use of risk assessment to identify vulnerabilities of any plant to severe accidents; Strengthening and reorganization of enforcement as a separate office within the NRC; The establishment of the Institute of Nuclear Power Operations (INPO), the industry's own "policing" group, and formation of what is now the Nuclear Energy Institute to provide a unified industry approach to generic nuclear regulatory issues, and interaction with NRC and other government agencies; The installing of additional equipment by licensees to mitigate accident conditions, and monitor radiation levels and plant status; Employment of major initiatives by licensees in early identification of important safetyrelated problems, and in collecting and assessing relevant data so lessons of experience can be shared and quickly acted upon; and Expansion of NRC's international activities to share enhanced knowledge of nuclear safety with other countries in a number of important technical areas.
Current Status Today, the TMI2 reactor is permanently shut down and defueled, with the reactor coolant system drained, the radioactive water decontaminated and evaporated, radioactive waste shipped offsite to an appropriate disposal site, reactor fuel and core debris shipped offsite to a Department of Energy facility, and the remainder of the site being monitored. In 2001, FirstEnergy acquired TMI-2 from GPU. FirstEnergy has contracted the monitoring of TMI-2 to Exelon, the current owner and operator of TMI-1. The companies plan to keep the TMI-2 facility in longterm, monitored storage until the operating license for the TMI1 plant expires, at which time both plants will be decommissioned. The Chernobyl Disaster The April 1986 disaster at the Chernobyl nuclear power plant in Ukraine was the product of a flawed Soviet reactor design coupled with serious mistakes made by the plant operators. It was a direct consequence of Cold War isolation and the resulting lack of any safety culture. The accident destroyed the Chernobyl 4 reactor, killing 30 operators and firemen within three months and several further deaths later. One person was killed immediately and a second died in hospital soon after as a result of injuries received. Another person is reported to have died at the time from a coronary thrombosis. Acute radiation syndrome (ARS) was originally diagnosed in 237 people on-site and involved with the clean-up and it was later confirmed in 134 cases. Of these, 28 people died as a result of ARS within a few weeks of the accident. Nineteen more subsequently died between 1987 and 2004 but their deaths cannot necessarily be attributed to radiation exposure. Nobody off-site suffered from acute radiation effects although a large proportion of childhood thyroid cancers diagnosed since the accident is likely to be due to intake of radioactive iodine fallout. Furthermore, large areas of Belarus, Ukraine, Russia and beyond were contaminated in varying degrees. "The Chernobyl disaster was a unique event and the only accident in the history of commercial nuclear power where radiation-related fatalities occurred. However, the design of the reactor is unique and the accident is thus of little relevance to the rest of the nuclear industry outside the then Eastern Bloc. The Chernobyl site and plant The Chernobyl Power Complex consisted of four nuclear reactors of the RBMK-1000, units 1 and 2 being constructed between 1970 and 1977, while units 3 and 4 of the same design were completed in 1983. To the southeast of the plant, an artificial lake of some 22 square kilometers, situated beside the river Pripyat, a tributary of the Dniepr, was constructed to provide cooling water for the reactors. This area of Ukraine is described as Belarussian-type woodland with a low population density. About 3 km away from the reactor, in the new city, Pripyat, there were 49,000 inhabitants. The old town of Chornobyl, which had a population of 12,500, is about 15 km to the southeast of the complex. Within a 30 km radius of the power plant, the total population was between 115,000 and 135,000. The RBMK-1000 is a Soviet-designed and built graphite moderated pressure tube type reactor, using slightly enriched (2% U-235) uranium dioxide fuel. It is a boiling light water reactor, with two loops feeding steam directly to the turbines, without an intervening heat exchanger. Water pumped to the bottom of the fuel channels boils as it progresses up the pressure tubes, producing steam which feeds two 500 MWe turbines. The water acts as a coolant and also provides the steam used to drive the turbines. The vertical pressure tubes contain the zirconium alloy clad uranium dioxide fuel around which the cooling water flows. The extensions of the fuel channels penetrate the lower plate and the cover plate of the core and are welded to each. A specially designed refuelling machine allows fuel bundles to be changed without shutting down the reactor. The moderator, whose function is to slow down neutrons to make them more efficient in producing fission in the fuel, is graphite, surrounding the pressure tubes. A mixture of nitrogen and helium is circulated between the graphite blocks to prevent oxidation of the graphite and to improve the transmission of the heat produced by neutron interactions in the graphite to the fuel channel. The core itself is about 7 m high and about 12 m in diameter. In each of the two loops, there are four main coolant circulating pumps, one of which is always on standby. The reactivity or power of the reactor is controlled by raising or lowering 211 control rods, which, when lowered into the moderator, absorb neutrons and reduce the fission rate. The power output of this reactor is 3200 MW thermal, or 1000 MWe. Various safety systems, such as an emergency core cooling system, were incorporated into the reactor design. The 1986 Chernobyl accident On 25 April, prior to a routine shutdown, the reactor crew at Chernobyl 4 began preparing for a test to determine how long turbines would spin and supply power to the main circulating pumps following a loss of main electrical power supply. This test had been carried out at Chernobyl the previous year, but the power from the turbine ran down too rapidly, so new voltage regulator designs were to be tested.
A series of operator actions, including the disabling of automatic shutdown mechanisms, preceded the attempted test early on 26 April. By the time that the operator moved to shut down the reactor, the reactor was in an extremely unstable condition. A peculiarity of the design of the control rods caused a dramatic power surge as they were inserted into the reactor. The interaction of very hot fuel with the cooling water led to fuel fragmentation along with rapid steam production and an increase in pressure. The design characteristics of the reactor were such that substantial damage to even three or four fuel assemblies can and did result in the destruction of the reactor. The overpressure caused the 1000 t cover plate of the reactor to become partially detached, rupturing the fuel channels and jamming all the control rods, which by that time were only halfway down. Intense steam generation then spread throughout the whole core (fed by water dumped into the core due to the rupture of the emergency cooling circuit) causing a steam explosion and releasing fission products to the atmosphere. About two to three seconds later, a second explosion threw out fragments from the fuel channels and hot graphite. There is some dispute among experts about the character of this second explosion, but it is likely to have been caused by the production of hydrogen from zirconium-steam reactions. Two workers died as a result of these explosions. Immediate impact of the Chernobyl accident The accident caused the largest uncontrolled radioactive release into the environment ever recorded for any civilian operation, and large quantities of radioactive substances were released into the air for about 10 days. This caused serious social and economic disruption for large populations in Belarus, Russia and Ukraine. Most of the released material was deposited close by as dust and debris, but the lighter material was carried by wind over the Ukraine, Belarus, Russia and to some extent over Scandinavia and Europe. The casualties included firefighters who attended the initial fires on the roof of the turbine building. All these were put out in a few hours, but radiation doses on the first day were estimated to range up to 20,000 millisieverts (mSv), causing 28 deaths six of which were firemen by the end of July 1986. The next task was cleaning up the radioactivity at the site so that the remaining three reactors could be restarted, and the damaged reactor shielded more permanently. About 200,000 people ('liquidators') from all over the Soviet Union were involved in the recovery and clean-up during 1986 and 1987. They received high doses of radiation, averaging around 100 millisieverts. Some 20,000 of them received about 250 mSv and a few received 500 mSv. Later, the number of liquidators swelled to over 600,000 but most of these received only low radiation doses. The highest doses were received by about 1000 emergency workers and on-site personnel during the first day of the accident. Initial radiation exposure in contaminated areas was due to short-lived iodine-131; later caesium-137 was the main hazard. (Both are fission products dispersed from the reactor core, with half lives of 8 days and 30 years, respectively. About five million people lived in areas contaminated and about 400,000 lived in more contaminated areas of strict control by authorities. Environmental and health effects of the Chernobyl accident Several organizations have reported on the impacts of the Chernobyl accident, but all have had problems assessing the significance of their observations because of the lack of reliable public health information before 1986. In 1989, the World Health Organization (WHO) first raised concerns that local medical scientists had incorrectly attributed various biological and health effects to radiation exposure. Following this, the Government of the USSR requested the International Atomic Energy Agency (IAEA) to coordinate an international experts' assessment of accident's radiological, environmental and health consequences in selected towns of the most heavily contaminated areas in Belarus, Russia, and Ukraine. Between March 1990 and June 1991, a total of 50 field missions were conducted by 200 experts from 25 countries (including the USSR), seven organizations, and 11 laboratories. In the absence of pre-1986 data, it compared a control population with those exposed to radiation. Significant health disorders were evident in both control and exposed groups, but, at that stage, none was radiation related. Paths of radiation exposure Subsequent studies in the Ukraine, Russia and Belarus were based on national registers of over one million people possibly affected by radiation. By 2000, about 4000 cases of thyroid cancer had been diagnosed in exposed children. However, the rapid increase in thyroid cancers detected suggests that some of it at least is an artifact of the screening process. Thyroid cancer is usually not fatal if diagnosed and treated early. In February 2003, the IAEA established the Chernobyl Forum, in cooperation with seven other UN organizations as well as the competent authorities of Belarus, the Russian Federation and Ukraine . In April 2005, the reports prepared by two expert
groups "Environment", coordinated by the IAEA, and "Health", coordinated by WHO were intensively discussed by the Forum and eventually approved by consensus. The conclusions of this 2005 Chernobyl Forum study (revised version published 2006) are in line with earlier expert studies, notably the UNSCEAR 2000 report which said that "apart from this [thyroid cancer] increase, there is no evidence of a major public health impact attributable to radiation exposure 14 years after the accident. There is no scientific evidence of increases in overall cancer incidence or mortality or in non-malignant disorders that could be related to radiation exposure." As yet there is little evidence of any increase in leukemia, even among clean-up workers where it might be most expected. However, these workers where high doses may have been received remain at increased risk of cancer in the long term. Apart from these, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) says that "the great majority of the population is not likely to experience serious health consequences as a result of radiation from the Chernobyl accident. Many other health problems have been noted in the populations that are not related to radiation exposure." The Chernobyl Forum report says that people in the area have suffered a paralyzing fatalism due to myths and misperceptions about the threat of radiation, which has contributed to a culture of chronic dependency. Some "took on the role of invalids." Mental health coupled with smoking and alcohol abuse is a very much greater problem than radiation, but worst of all at the time was the underlying level of health and nutrition. Apart from the initial 116,000, relocations of people were very traumatic and did little to reduce radiation exposure, which was low anyway. Psycho-social effects among those affected by the accident are similar to those arising from other major disasters such as earthquakes, floods and fires. According to the most up-to-date estimate of UNSCEAR, the average radiation dose due to the accident received by inhabitants of 'strict radiation control' areas (population 216,000) in the years 1986 to 2005 was 31 mSv (over the 20-year period), and in the 'contaminated' areas (population 6.4 million) it averaged 9 mSv, a minor increase over the dose due to background radiation over the same period (about 50 mSv). UNSCEAR in 2011 concludes: In summary, the effects of the Chernobyl accident are many and varied. Early deterministic effects can be attributed to radiation with a high degree of certainty, while for other medical conditions; radiation almost certainly was not the cause. In between, there was a wide spectrum of conditions. It is necessary to evaluate carefully each specific condition and the surrounding circumstances before attributing a cause. Progressive closure of the Chernobyl plant In the early 1990s, some US$400 million was spent on improvements to the remaining reactors at Chernobyl, considerably enhancing their safety. Energy shortages necessitated the continued operation of one of them (unit 3) until December 2000. (Unit 2 was shut down after a turbine hall fire in 1991, and unit 1 at the end of 1997.) Almost 6000 people worked at the plant every day, and their radiation dose has been within internationally accepted limits. A small team of scientists works within the wrecked reactor building itself, inside the shelter. Workers and their families now live in a new town, Slavutich, 30 km from the plant. This was built following the evacuation of Pripyat, which was just 3 km away. Ukraine depends upon, and is deeply in debt to, Russia for energy supplies, particularly oil and gas, but also nuclear fuel. Although this dependence is gradually being reduced, continued operation of nuclear power stations, which supply half of total electricity, is now even more important than in 1986. When it was announced in 1995 that the two operating reactors at Chernobyl would be closed by 2000, a memorandum of understanding was signed by Ukraine and G7 nations to progress this, but its implementation was conspicuously delayed. Alternative generating capacity was needed, either gas-fired, has which ongoing fuel cost and supply implications, or nuclear, by completing Khmelnitski unit 2 and Rovno unit 4 ('K2R4') in Ukraine. Construction of these was halted in 1989 but then resumed, and both reactors came on line late in 2004, financed by Ukraine rather than international grants as expected on the basis of Chernobyl's closure. Chernobyl today Chernobyl unit 4 is now enclosed in a large concrete shelter which was erected quickly (by October 1986) to allow continuing operation of the other reactors at the plant. However, the structure is neither strong nor durable. Some 200 tonnes of highly radioactive material remains deep within it, and this poses an environmental hazard until it is better contained. A New Safe Confinement structure is due to be completed in 2014, being built adjacent and then will be moved into place on rails. It is to be an 18,000 tonne metal arch 110 metres high, 200 metres long and spanning 257 metres, to cover both unit 4 and the hastily-built 1986 structure. Holtec International became the contractor in 2007 for new interim spent fuel storage facility (ISF-2) now being completed by mid-2014. Design approval and funding from EBRD's Nuclear Safety Account was confirmed in October 2010. The facility will accommodate 21,217 fuel assemblies in dry storage for a 100-year service life. Most of these are straightforward to handle, but about 50 are damaged and require special handling.
Resettlement of contaminated areas In the last two decades there has been some resettlement of the areas evacuated in 1986 and subsequently. Recently the main resettlement project has been in Belarus. In July 2010, the Belarus government announced that it had decided to settle back thousands of people in the 'contaminated areas' covered by the Chernobyl fallout, from which 24 years ago they and their forbears were hastily relocated. The main priority is agriculture and forestry, together with attracting qualified people and housing them. Initial infrastructure requirements will mean the refurbishment of gas, potable water and power supplies, while the use of local wood will be banned. Schools and housing will be provided for specialist workers and their families ahead of wider socio-economic development. Overall, some 21,484 dwellings are slated for connection to gas networks in the period 2011-2015, while about 5600 contaminated or broken down buildings are demolished. Over 1300 kilometres of road will be laid, and ten new sewerage works and 15 pumping stations are planned. The cost of the work was put at BYR 6.6 trillion ($2.2 billion), split fairly evenly across the years 2011 to 2015 inclusive. The feasibility of agriculture will be examined in areas where the presence of caesium-137 and strontium-90 is low, "to acquire new knowledge in the fields of radiobiology and radioecology in order to clarify the principles of safe life in the contaminated territories." Land found to have too high a concentration of radionuclides will be reforested and managed. A suite of protective measures is to be set up to allow a new forestry industry whose products would meet national and international safety standards. In April 2009, specialists in Belarus stressed that it is safe to eat all foods cultivated in the contaminated territories, though intake of some wild food was restricted. What has been learnt from the Chernobyl disaster? Leaving aside the verdict of history on its role in melting the Soviet 'Iron Curtain', some very tangible practical benefits have resulted from the Chernobyl accident. The main ones concern reactor safety, notably in Eastern Europe. (The US Three Mile Island accident in 1979 had a significant effect on Western reactor design and operating procedures. While that reactor was destroyed, all radioactivity was contained as designed and there were no deaths or injuries.) While no-one in the West was under any illusion about the safety of early Soviet reactor designs, some lessons learned have also been applicable to Western plants. Certainly the safety of all Soviet-designed reactors has improved vastly. This is due largely to the development of a culture of safety encouraged by increased collaboration between East and West, and substantial investment in improving the reactors. Since 1989, over 1000 nuclear engineers from the former Soviet Union have visited Western nuclear power plants and there have been many reciprocal visits. Over 50 twinning arrangements between East and West nuclear plants have been put in place. Most of this has been under the auspices of the World Association of Nuclear Operators (WANO), a body formed in 1989 which links 130 operators of nuclear power plants in more than 30. Many other international programs were initiated following Chernobyl. The International Atomic Energy Agency (IAEA) safety review projects for each particular type of Soviet reactor are noteworthy, bringing together operators and Western engineers to focus on safety improvements. The Nuclear Safety Assistance Coordination Centre database lists Western aid totaling almost US$1 billion for more than 700 safety-related projects in former Eastern Bloc countries. The Convention on Nuclear Safety adopted in Vienna in June 1994 is another outcome. The Chernobyl Forum report said that some seven million people are now receiving or eligible for benefits as 'Chernobyl victims', which means that resources are not targeting the needy few percent of them. Remedying this presents daunting political problems however. Fukushima "TOKYO--Public confidence in Japan's scientists and engineers took a major hit from the 11 March earthquake, tsunami, and subsequent Fukushima nuclear power plant disaster. How to regain it was a major theme of a recent symposium held here to explore the role of scientists in the accident, and their responsibilities both before and after. The Fukushima accident exposed troubling issues, speakers noted. Despite the resources poured into analyzing crustal movements and having expert committees determine earthquake risk, for instance, researchers never considered the possibility of a magnitude-9 earthquake followed by a massive tsunami. The failure of multiple safety features on nuclear power plants has raised questions about the nation's engineering prowess. Government flip-flopping on acceptable levels of radiation exposure confused the public, and health professionals provided little guidance. Facing a dearth of reliable information on radiation levels, citizens armed themselves with dosimeters, pooled data, and together produced radiological contamination maps far more detailed than anything the government or official scientific sources ever provided.
Such developments suggest scientists and engineers "need to reposition ourselves in relation to the governmental administration and the general public [so that] the scientific community can play a useful role in providing scientific advice," said Science Council President Takashi Onishi, an urban planner at the University of Tokyo. Several speakers blasted their own fields. "There must have been complacency" about safety among nuclear experts, said Satoru Tanaka, a nuclear engineer at the University of Tokyo and president of the Atomic Energy Society of Japan. He noted that nuclear regulators did not incorporate the latest thinking on nuclear safety and warnings from Japanese seismologists and tsunami experts into evaluations of existing plants. During the crisis, Tanaka said, his society was "not able to fulfill our stated mission" of being the most reliable source of information on nuclear power. The society is studying how to rebuild its credibility while trying to help the government and Tokyo Electric Power Co. wrestle with the thorny issues of disposing of damaged fuel and demolishing the four damaged reactors. Japan faces hard choices in recovering from the triple disaster, other speakers said. Disposing of the "tens of millions of cubic meters of contaminated soil [would] surpass the total capacity of all disposal sites in Japan," noted Kyoto University civil engineer Minoru Yoneda. Stripping soil and vegetation could increase flooding and landslides. Finding the right balance between decontamination and risk is a gray area. "The question of how much [low dose radiation] is tolerable is open," said radiation health expert Tomoko Kusama, president of Oita University of Nursing and Health Sciences. Resolving such issues will require reliable scientific advice, but many speakers argued that paths for scientific input into public policy in Japan are underdeveloped. During the crisis, "scientists acted separately and disparately, so accurate information was not being given to policy makers," said Yoshikawa, who called on scientists to develop "a coherent voice." In the end, although participants appeared to share a general sense that the scientific community needs to regain public trust and take a more active role in proffering advice, they put forward no concrete proposals for reform. Onishi promised a report on how the community and the council should respond by the first anniversary of the 11 March disaster. " (Normite, 2011) "Ever since Japan's battered Fukushima Daiichi reactor complex began emitting radiation in March, calls to abandon nuclear power have risen in the U.S. and Germany, among other countries. If only it were so simple. Nuclear contributes 20 percent of the U.S. power supply and a significant share in other developed countries. If we gave it up, what would replace it? Pollution from fossil-fueled power plants shortens the life span of as many as 30,000 Americans a year. Coal companies lop off mountaintops, hydraulic fracturing for natural gas threatens water supplies, and oil dependence undermines the nation's energy security. Then there is the small matter of greenhouse gas emissions. Clean renewable technologies will take years to reach the scale needed to replace the power we get from splitting atoms. Nuclear power's benefits for climate and security are clear. But still the public worries about safety--and no wonder. The industry and the U.S. Nuclear Regulatory Commission (NRC) claim that nuclear power is safe, but their lack of transparency does not inspire confidence. For example, an Associated Press investigation in March revealed 24 cases from December 2009 to September 2010 in which plant operators did not report equipment defects to the NRC. The industry and regulators must regain the public's trust. That does not necessarily mean more regulations. Plenty of safety rules have been put in place since the 1979 Three Mile Island accident. The trouble is that regulations are not being enforced rigorously. The NRC has to mete out stiff penalties for violations and make every action transparent to us all. It will have a chance to demonstrate its resolve when it submits its review of all 104 commercial reactors to the White House, due this month. A crucial test will be what the review says about several plants that are already on the agency's watch list for safety issues. Evacuation plans are a sore point for many citizens. The agency advised Americans in Japan to stay 50 miles away from Fukushima, yet within the U.S. the emergency evacuation radius is only 10 miles. What is the proper limit? Are evacuation plans subjected to serious tests? If exercises showed that residents around a plant could not leave quickly enough, the NRC should consider shutting it down. A good test case is the Indian Point plant 38 miles north of New York City. Evacuating the 20 million people who live within 50 miles staggers belief. To its credit, the NRC will work with New York governor Andrew Cuomo to review the plant's safety ahead of the scheduled relicensing review in 2013. The NRC must also be scrupulous about licensing new plants. If an operator proposes a site that is too close to an earthquake fault, or too close to oceanfront that is vulnerable to a tsunami or hurricane storm surge, or downriver from a huge dam that could burst, then the NRC should reject the bid. Similarly, if the utility could not protect spent fuel pools or casks from being breached during a severe accident, which happened in Japan, the NRC should not license it. Saying no to a suspect plant would do more than anything else to restore public confidence. The industry argues that advanced technology will ensure safety. The 22 new reactors proposed in the U.S. use socalled Gen III+ designs that are safer than today's reactors, which date to the 1970s or earlier. Building them could
displace new coal plants or relieve the pressure to extend the life of old reactors that should instead be retired. Yet, as the article "Planning for the Black Swan," by Adam Piore, on page 48 notes, the new plants may have weaknesses. Manufacturers should pursue even safer, meltdown-proof designs that they have experimented with but shelved, such as liquid fluoride thorium reactors and pebble bed reactors. China is developing both. In the end, however, no technology is 100 percent safe, and better designs cannot eliminate the need for careful siting and emergency planning. Americans need clarity from the federal government, too. Reactors across the country have accumulated 72,000 tons of spent fuel. Some utilities have packed four times as many spent fuel rods into temporary holding pools than the structures were designed to contain. The government poured $9 billion and decades of effort into the planned permanent repository at Yucca Mountain in Nevada, with little to show for it. Then President Barack Obama scuttled the project. The waste continues to pile up. At some point, officials will have to face down the citizen refrain of "not in my backyard." Nuclear power has a good safety record, but when it fails it can fail catastrophically. Now is the time to make tough, transparent decisions that could regain public trust. Otherwise, the public might make the ultimate call: "no more nukes." (Scientific America, 2011) "The Japanese quake and tsunami have thrown a spotlight on the safety of North American shores. Last week, the White House asked the Nuclear Regulatory Commission to conduct a comprehensive safety review of all 104 US nuclear reactors, and state senators held hearings on the safety of California's nuclear plants on Monday 21 March. All US nuclear plants are designed to withstand earthquakes and tsunamis, on the basis of risk assessments for each site. But experts are posing questions about the possibility of bigger than expected quakes, and of large tsunamis created by underwater landslides. Eyes have turned to California in particular -- it is in a seismically active area and has the only two nuclear facilities on the US Pacific coast: Diablo Canyon and San Onofre. But the fault lines off the Californian coast are expected to produce smaller tremors, up to the magnitude-7 range, and horizontal movements that don't usually create tsunamis. The main North American tsunami-generating fault, the Cascadia subduction zone, lays further north, offshore Oregon, Washington, and British Columbia in Canada. "Are the nuke plants in California safe from the maximum earthquake? I don't think anyone knows." As in Japan, though, those fault lines could hold surprises. The record of known earthquakes is too short to produce reliable estimates, says Chris Goldfinger, a geophysicist at Oregon State University in Corvallis. "The construction standards are set for a 'maximum credible earthquake', which in many regions is little more than a guess." "Are the nuke plants in California safe from the maximum earthquake that could occur on nearby faults? I don't think anyone knows," says Goldfinger. One fault line near the Diablo Canyon plant was discovered only in 2008, and in-depth studies are ongoing. Some have expressed concerns that a quake could destroy roads, making it impossible to flee any subsequent nuclear accident. Extreme conditions Harry Yeh, a civil engineer at Oregon State University who has been researching tsunamis since 1993, worked at the Diablo Canyon plant in the 1980s. He says that the plant was built to defend against extreme conditions, including subsidence of 2 metres from a strong earthquake, the largest historical hurricane-force storm plus 20%, and a tsunami -- all at the same time. "The philosophy was to look at those kinds of conditions, to ensure that the equipment would work no matter what. However, apparently the same philosophy applied in Japan," he says. The operators of the Diablo Canyon plant say that it was built to withstand an earthquake of magnitude-7.5, and is sat at the top of a cliff providing nearly 11 metres of protection from the 'largest credible tsunami' of just 2 metres. The San Onofre plant was built to withstand a peak ground acceleration of 6.7 metres per second -- the peak ground acceleration in Fukushima, Japan, was estimated at 5.1 metres per second -- and it lies behind a 10-metre-high wall. The 2009 California tsunami inundation map, which shows predicted impacts of modelled tsunami waves, indicates a maximum wave height of less than 7 metres. Costas Synolakis, director of the Tsunami Research Center at the University of Southern California in Los Angeles, says that California is "prepared in terms of tsunamis that come in from far away like Japan or Chile. But it is not properly prepared against tsunamis generated close to shore." Even small earthquakes can cause huge underwater landslides that cause tsunamis, he says -- as happened to a small degree in Haiti last year (see Haiti earthquake produced deadly tsunami). The risk of large underwater landslides near California is unknown, because most of the sea floor remains unmapped, he says. Vasily Titov, director of the National Oceanic and Atmospheric Administration's Center for Tsunami
Research in Seattle, Washington agrees, but says that large landslide tsunamis are very, very rare. "Most are prehistoric," he says. Slip and slide Submarine landslide tsunamis are also a rare but important concern for the east coast of the United States, says Uri ten Brink, a US Geological Survey geophysicist at the Woods Hole Field Center in Massachusetts. There are many more reactors on this coast. In 1929, says ten Brink, a magnitude-7.2 quake off the coast of Newfoundland in Canada, caused a 22,000-kilometre-square landslide in the Grand Banks area, creating a wave as high as 13 metres. There's no reason why that couldn't happen further south in the United States, he says. Ten Brink says the east coast is better mapped than the west: a few hundred historic submarine landslides have been identified. But only a handful has been dated, making it impossible to know how often they occur. It is also unclear whether an area that had a big slip in the past is immune from future slips, or more likely to experience them, he says. The question for policy-makers is whether these extreme cases need to be accounted for. "You can't protect against everything," says Titov. But the Japanese tsunami, he says, did not seem to be an impossible event like an asteroid strike or a massive submarine landslide right next to a power plant. "I'm surprised it wasn't taken into account." (Jones, 2011) The future of nuclear reactor designs As noted above, new designs of generators are safer than what we are running today. "Approximately 441 Gen II reactors in 31 countries produce nearly 17 % of the world's electricity. Nearly all of these reactors are thermal reactors, i.e. they use slow neutrons to induce fission. Thus, these reactors must have a moderator to slow the initial fast neutrons produced by fission. Over the last fifty years, a number of different GEN II reactor designs have been deployed. The designs reflect different answers to three primary design decisions: moderator: light-water, heavy-water, graphite fuel: enriched uranium, natural uranium, mixed (plutonium + uranium) coolant: how heat is extracted from the reactor core to cool it and convert water to steam, which drives the turbinegenerator Generation III reactors are those designs that have evolved from improvements in Gen II reactors. These improvements have resulted from extensive operating experience with the earlier reactor designs. They included improve fuel technology, passive safety features and standardized designs. All of these features are expected to produce reactors that are cheaper and quicker to build and safer than current reactors. Some GEN III reactors have already been built whereas others are still on the drawing broad. In the United States, GEN III reactors have not been built yet, but many have received approval from the NRC for standardized designs. Generation IV nuclear power refers to the next generation of nuclear power systems currently under development around the world. These systems are in the design stage and will not be deployed before 2030. They will represent a fundamental change in reactor design and nuclear fuel cycle. GEN IV systems are designed to be sustainable, environmentally responsible, economical and proliferation-resistant. They will require major technological advances in a wide range of fields, e.g. engineering, metallurgy, etc, if they are to become economically viable". (Myers, 2010) Smarter use of nuclear waste Despite long-standing public concern about the safety of nuclear energy, more and more people are realizing that it may be the most environmentally friendly way to generate large amounts of electricity. Several nations, including Brazil, China, Egypt, Finland, India, Japan, Pakistan, Russia, South Korea and Vietnam, are building or planning nuclear plants. But this global trend has not as yet extended to the U.S., where work on the last such facility began some 30 years ago. If developed sensibly, nuclear power could be truly sustainable and essentially inexhaustible and could operate without contributing to climate change. In particular, a relatively new form of nuclear technology could overcome the principal drawbacks of current methods--namely, worries about reactor accidents, the potential for diversion of nuclear fuel into highly destructive weapons, the management of dangerous, long-lived radioactive waste, and the depletion of global reserves of economically available uranium. This nuclear fuel cycle would combine two innovations: pyrometallurgical processing (a high-temperature method of recycling reactor waste into fuel) and advanced fast-neutron reactors capable of burning that fuel. With this approach, the radioactivity from the generated waste could drop to safe levels in a few hundred years, thereby eliminating the need to segregate waste for tens of thousands of years.
For neutrons to cause nuclear fission efficiently, they must be traveling either slowly or very quickly. Most existing nuclear power plants contain what are called thermal reactors, which are driven by neutrons of relatively low speed (or energy) ricocheting within their cores. Although thermal reactors generate heat and thus electricity quite efficiently, they cannot minimize the output of radioactive waste. All reactors produce energy by splitting the nuclei of heavy metal (high-atomic-weight) atoms, mainly uranium or elements derived from uranium. In nature, uranium occurs as a mixture of two isotopes, the easily fissionable uranium 235 (which is said to be "fissile") and the much more stable uranium 238. The uranium fire in an atomic reactor is both ignited and sustained by neutrons. When the nucleus of a fissile atom is hit by a neutron, especially a slow-moving one, it will most likely cleave (fission), releasing substantial amounts of energy and several other neutrons. Some of these emitted neutrons then strike other nearby fissile atoms, causing them to break apart, thus propagating a nuclear chain reaction. The resulting heat is conveyed out of the reactor, where it turns water into steam that is used to run a turbine that drives an electric generator. Uranium 238 is not fissile; it is called "fissionable" because it sometimes splits when hit by a fast neutron. It is also said to be "fertile," because when a uranium 238 atom absorbs a neutron without splitting, it transmutes into plutonium 239, which, like uranium 235, is fissile and can sustain a chain reaction. After about three years of service, when technicians typically remove used fuel from one of today's reactors because of radiation-related degradation and the depletion of the uranium 235, plutonium is contributing more than half the power the plant generates. In a thermal reactor, the neutrons, which are born fast, are slowed (or moderated) by interactions with nearby low-atomic weight atoms, such as the hydrogen in the water that flows through reactor cores. All but two of the 440 or so commercial nuclear reactors operating are thermal, and most of them--including the 103 U.S. power reactors-- employ water both to slow neutrons and to carry fission-created heat to the associated electric generators. Most of these thermal systems are what engineers call light-water reactors. In any nuclear power plant, heavy metal atoms are consumed as the fuel "burns". Even though the plants begin with fuel that has had its uranium 235 content enriched, most of that easily fissioned uranium is gone after about three years. When technicians remove the depleted fuel, only about one twentieth of the potentially fissionable atoms in it (uranium 235, plutonium and uranium 238) have been used up, so the so-called spent fuel still contains about 95 percent of its original energy. In addition, only about one tenth of the mined uranium ore is converted into fuel in the enrichment process (during which the concentration of uranium 235 is increased considerably), so less than a hundredth of the ore's total energy content is used to generate power in today's plants. This fact means that the used fuel from current thermal reactors still has the potential to stoke many a nuclear fire. Because the world's uranium supply is finite and the continued growth in the numbers of thermal reactors could exhaust the available low-cost uranium reserves in a few decades, it makes little sense to discard this spent fuel or the "tailings" left over from the enrichment process. The spent fuel consists of three classes of materials. The fission products, which make up about 5 percent of the used fuel, are the true wastes--the ashes, if you will, of the fission fire. They comprise a mlange of lighter elements created when the heavy atoms split. The mix is highly radioactive for its first several years. After a decade or so, the activity is dominated by two isotopes, cesium 137 and strontium 90. Both are soluble in water, so they must be contained very securely. In around three centuries, those isotopes' radioactivity declines by a factor of 1,000, by which point they have become virtually harmless. Uranium makes up the bulk of the spent nuclear fuel (around 94 percent); this is unfissioned uranium that has lost most of its uranium 235 and resembles natural uranium (which is just 0.71 percent fissile uranium 235). This component is only mildly radioactive and, if separated from the fission products and the rest of the material in the spent fuel, could readily be stored safely for future use in lightly protected facilities. The balance of the material--the truly troubling part--is the transuranic component, elements heavier than uranium. This part of the fuel is mainly a blend of plutonium isotopes, with a significant presence of americium. Although the transuranic elements make up only about 1 percent of the spent fuel, they constitute the main source of today's nuclear waste problem. The halflives (the period in which radioactivity halves) of these atoms range up to tens of thousands of years, a feature that led U.S. government regulators to require that the planned high-level nuclear waste repository at Yucca Mountain in Nevada isolate spent fuel for over 10,000 years. An Alternative Approach When the ban was issued, "reprocessing" was synonymous with the PUREX (for plutonium uranium extraction) method, a technique developed to meet the need for chemically pure plutonium for atomic weapons. Advanced fast-neutron reactor technology, however, permits an alternative recycling strategy that does not involve pure plutonium at any stage. Fast reactors can thus minimize the risk that spent fuel from energy production would be used for weapons production, while providing a unique ability to squeeze the maximum energy out of nuclear fuel. Several such reactors have been built and used for power generation--in France, Japan, Russia, the U.K. and the U.S.--two of which are still operating [see "Next-Generation Nuclear Power," by James A. Lake, Ralph G. Bennett and John F. Kotek; Scientific American, January 2002]. Fast reactors can extract more energy from nuclear fuel than thermal reactors do because their rapidly moving (higherenergy) neutrons cause atomic fissions more efficiently than the slow thermal neutrons do. This effectiveness stems from two phenomena. At slower speeds, many more neutrons are absorbed in nonfission reactions and are lost. Second, the higher energy of a fast neutron makes it much more likely that a fertile heavy metal atom like uranium 238 will fission when struck. Because of this fact, not only are uranium 235 and plutonium 239 likely to fission in a fast reactor, but an appreciable fraction of the heavier transuranic atoms will do so as well. Water cannot be employed in a fast reactor to carry the heat from the core--it would slow the fast neutrons. Hence, engineers typically use a liquid metal such as sodium
as a coolant and heat transporter. Liquid metal has one big advantage over water. Water-cooled systems run at very high pressure, so that a small leak can quickly develop into a large release of steam and perhaps a serious pipe break, with rapid loss of reactor coolant. Liquid-metal systems, however, operate at atmospheric pressure, so they present vastly less potential for a major release. Nevertheless, sodium catches fire if exposed to water, so it must be managed carefully. Considerable industrial experience with handling the substance has been amassed over the years, and management methods are well developed. But sodium fires have occurred, and undoubtedly there will be more. One sodium fire began in 1995 at the Monju fast reactor in Japan. It made a mess in the reactor building but never posed a threat to the integrity of the reactor, and no one was injured or irradiated. Engineers do not consider sodium's flammability to be a major problem. Researchers at Argonne National Laboratory began developing fast-reactor technology in the 1950s. In the 1980s this research was directed toward a fast reactor (dubbed the advanced liquid-metal reactor, or ALMR), with metallic fuel cooled by a liquid metal, that was to be integrated with a high-temperature pyrometallurgical processing unit for recycling and replenishing the fuel. Nuclear engineers have also investigated several other fast-reactor concepts, some burning metallic uranium or plutonium fuels, others using oxide fuels. Coolants of liquid lead or a lead-bismuth solution have been used. Metallic fuel, as used in the ALMR, is preferable to oxide for several reasons: it has some safety advantages, it will permit faster breeding of new fuel, and it can more easily be paired with pyrometallurgical recycling. (Hannum, Marsh, Stanford, 2005) In conclusion, the information provided in this paper shows numerous reasons why nuclear power makes a clean, safe, feasible, energy choice that could be the predominant source of electricity in 2020.
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