Japan’s Nuclear Crisis

The 8.9 earthquake, and subsequent tsunami, that rocked Japan on March 11, 2011 have lead to severe damage at Tokyo Electric Power Co.’s Fukushima Daiichi<!–[if supportFields]> XE “Fukushima Daiichi” <![endif]–><!–[if supportFields]><![endif]–> nuclear power plant. The problems at Fukushima Daiichi arose due to the failure of the cooling system and the significant loss of water from the cooling pools.  As authorities continue to work to reestablish the cooling system, Japanese citizens wait anxiously.  Twenty-five years after the meltdown of Chernobyl-4, it seemed that the world was beginning to accept the importance of nuclear power for providing a clean and reliable source of energy in the future.  However, the situation in Japan has awakened our fear of all things nuclear.  Critics argue that the same thing that is happening at Fukushima Daiichi could happen in the U.S. and that the country would be wise to halt all nuclear energy production.  Other, conversely, argue that the Fukushima accident could create a chance for the nuclear industry to “reboot” and look for innovative technologies that may decrease the risk associated with traditional solid-fuel uranium reactors.—Carolyn Campbell

          The core of a traditional nuclear reactor, such as the Fukushima Daiichi<!–[if supportFields]> XE “Fukushima Daiichi” <![endif]–><!–[if supportFields]><![endif]–> reactor, contains both water and fuel rods made of zirconium and pellets of nuclear fuel, usually uranium, which set off a controlled nuclear reaction.  This reaction heats the water, creating high temperature steam, which powers a turbine<!–[if supportFields]> XE “turbine” <![endif]–><!–[if supportFields]><![endif]–> and generates electricity.  A meltdown occurs when the core gets too hot, causing the fuel rods to crack and release radioactive gases.  In the worse case scenario, the fuel pellets melt and fall onto the reactor floor, where they can eat through the protective barriers and eventually reach the surrounding environment.  In Japan, the reactors are designed to turn off automatically in case of a disaster, with the aim of preventing a meltdown.  However, even with the plant shut off, nuclear fuel rods continue to generate a huge amount of heat.  In order to cool the fuel, backup generators are meant to pump water into the plant.  These generators failed at Fukushima Daiichi, leading the fuel rods to boil off remaining water and become partially exposed.  If left exposed for long enough, the fuel rods could melt and leak radiation.  In order to avoid this, authorities are pumping seawater into the reactor to cool the fuel rods.  However, salt buildup on the fuel rods can allow them to heat up more by blocking water circulation between the fuel rods, and, in the worst case, can eventually lead to a meltdown.  Additionally, workers have released built-up gases containing some radioactive material into the atmosphere in order to ease pressure inside the plant. 
          The problems at Fukushima Daiichi<!–[if supportFields]> XE “Fukushima Daiichi” <![endif]–><!–[if supportFields]><![endif]–> have aroused concerns of similar disaster occurring in the United States.  While some critics argue that the US should halt all nuclear power generation others suggest that the accident in Japan lends a chance to recreate the nuclear industry.  It has been suggested in recent years that the solid-fuel nuclear reactors, like the ones in Japan, are an outdated technology and should be replaced by a safer and cheaper kind of nuclear energy. According to Matt Ridley of the Wall Street Journal, thorium has many advantages as a nuclear fuel.  There is four times as much thorium in the world as there is uranium; it is easier to handle and to process; it “breeds” its own fuel by continuously creating uranium 233; it can produce 90 times as much energy from the same quantity of fuel; no plutonium is produced by its reactions; and it generates much less waste, with a much shorter half life.  Neutrons are needed for a thorium reactor to run and can be supplied with a particle accelerator or uranium 235.  Both options are highly controlled and are relatively safe.  Additionally, the fuel in a thorium reactor cannot melt down because it is already molten, and reactions slow as it cools.  Whether it leads to new innovations or a general shift away from nuclear power, the disaster at the Fukushima Daiichi plant will undoubtedly alter the future of nuclear energy generation.  

Laser Transmutation of Nuclear Waste

The issue of radioactive waste is a major challenge in the widespread acceptance of a nuclear energy industry. The issues of where to store the nuclear waste and the possibility of radioactive materials leaching into the under-ground water supply seriously undermine the potential of nuclear energy.  However, with the ongoing development of ultra-intense laser techniques, researchers are exploring the possibility of laser transmutation of radioactive materials into stable isotopes.  Sadighi-Bonabi et al. (2009) analyzed the opportunity for transmutation of 93Zr, a highly radioactive nuclear waste with a half-life of 1.53 million years.  The authors suggest that through ultra-intense laser transmutation, 93Zr can be converted to 92Zr, its stable isotope.  High-energy electron generation, Bremsstrahlung, and photonuclear reactions were observed and the number of reactions that produced 92Zr calculated.  It was found that the laser intensity, irradiation time, and repetition rate of laser have strong and direct effects on the yield of 92Zr and the number of reactions. —Carolyn Campbell
Sadighi-Bonabi, R., Irani, E., Safaie, B., Imani, Kh., Silatani, M., Zare, S., 2010. Possibility of ultra-intense laser transmutation of 93Zr (γ, n) 92Zr a long-lived nuclear waste into a stable isotope. Energy Conservation and Management 51, 636–639.

          The disposal of long-lived radioactive waste is a significant challenge for the nuclear industry.  Through the development of ultra-intense laser technologies, the possibility of photonuclear transmutation of nuclear waste to more stable isotopes has offered new solutions to solving this problem.  When an ultra-intense laser pulse interacts with the radioactive waste, gamma radiations induce nuclear reactions for transmutation of the waste into a stable isotope.  Sadighi-Bonabi et al. focused their study on Zirconium, particularly 93Zr, a fission product in nuclear reactors with a half-life of 1.53 million years.
          In order to assess the number of reactions and laser-induced photonuclear activation of 93Zr, the authors analyzed available experimental data from focusing intensities onto a solid target.  For this study, the laser intensity was assumed to be 1020W/cm2 with a repetition rate of 10 Hz.  Calculations were also extended to higher intensities of 5 x 1020 W/cm2, 1021 W/cm2, 5 x 1021 W/cm2, and 1022 W/cm2.  The number of reactions was calculated by evaluating the energy spectrum of the laser and a cross section of the photonuclear reaction between threshold and cut-off energy.  It was found that the Bremsstrahlug spectrum, relating to the deceleration of electrons, depended on the intensity of the laser, with higher intensities increasing the number of reactions.  Additionally, irradiation time and repetition rate were found to have substantial effects on the yield of 93Zr (γ, n) 92Zr and the number of reactions.  If the target is irradiated for an hour by a laser light of 1020 W/cm2 at a repetition rate of 10 Hz, approximately 2.7 x 107 reactions will occur.  By increasing the repetition rate, yield would also increase.  However, achieving higher rates also means using more power, and more advanced lasers.  Additionally, although increased intensity of the laser would lead to a higher number of reactions and activity, there is an optimum intensity at which a maximum number of reactions is reached and, beyond that point, the overlap between reaction cross-section and the number of photons disappears.  For 93Zr (γ, n) 92Zr, this optimum intensity was calculated at 3 x 1021 W/cm2
          Through this study, it was found that laser intensity, irradiation time, and repetition rate of the laser have a significant, direct effect on the yield of 92Zr and the number of reactions.  Maximizing the efficiency of laser technology for the transmutation of radioactive isotopes will prove valuable in future efforts to solve the problem of long-lived nuclear waste. 

Nuclear Waste Disposal

While there is a growing consensus that increased investment in nuclear energy is necessary to satisfy future energy needs, the United States currently lacks a suitable permanent storage site for radioactive waste.  With more than 103 open-cycle nuclear reactors throughout the country, the issue of nuclear waste storage is a growing concern.  Schaffer (2010) assesses the current state of nuclear waste in the U.S. and proposes solutions to developing a viable nuclear waste disposal program.  First, the U.S. should reopen the licensing process for the Yucca Mountain waste disposal facility.  Additionally, to decrease the amount of waste sent to disposal facilities the U.S. should restart PUREX reprocessing plants.  Upon taking these initial steps, the government must continue to search for additionally permanent storage sites and appropriate funds to educate local communities about nuclear waste storage.  The Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC) should also issue guidelines and promotions to encourage the industry to build new TRISO-fueled reactors.  Finally, further research should focus on innovative technologies that burn nuclear fuel waste. —Carolyn Campbell
Schaffer, M.B., 2011. Toward a viable nuclear waste disposal program. Energy Policy 39, 1382–1388.
Of the 103 operating commercial nuclear power plants in the U.S., all of them are of the open-cycle, batch type.  These plants produce long-lived radioactive waste in the form of ceramic-encased low-enriched uranium oxide pellets packed into zirconium-clad rods.  With the 1982 Nuclear Policy Act, the U.S. recognized the need for a consolidated storage site, and in 1987 named Yucca Mountain, Nevada as the site for deep underground repositories.  However, in response to pressures from Nevada politicians, the DOE has filed a motion to withdraw the license application for Yucca Mountain operations.  Due to this decision, the country’s nuclear waste remains stored in on-site tanks and casks, which Schaffer argues is risky, inefficient, and unsustainable.    Additionally, as more open-cycle nuclear plants come on line, the problem only gets worse.
Schaffer suggests that there are two main components to solving the open-cycle nuclear waste disposal program.  First is the issue of community confidence; in order for a permanent storage site to be developed, community endorsement is required.  Therefore, a confidence-enhancing plan should identifying three or four sites instead of just one, specify storage for a nominal period, provide adequate monetary incentives, and disclose the risks and rewards of a nuclear storage site.  The second component of a long-term solution for nuclear waste involves reducing the amount of high-level nuclear waste sent to a storage facility.  One way to achieve this is through the PUREX (Plutonium and Uranium by Extraction) process in which depleted fuel rods are cut into pieces and dissolved in nitric acid.  Uranium, plutonium, and actinides can then be extracted from the resulting liquid.  The extracted uranium-235 can be burned in heavy-water moderated reactors or fast-neutron reactors for additional energy, the plutonium-239 can be used to make MOX (mixed oxide uranium and plutonium) fuel, and the actinides can be vitrified in a design that is resistant to water leaching. 

Additional technological solutions for decreasing waste are described in the paper.  Closed-cycle fast reactor technology, such as an Advanced Liquid Metal Reactor (ALMR), has been studied for many years.  ALMR uses energetic neutrons to interact with uranium-238 to eventually produce plutonium-239.  Through pyrometallurgical processing, a mix of transnuranic elements from the used fuel can be extracted and the uranium can be reused.  This process has advantages over PUREX reprocessing, in a counter-proliferation sense, because it does not produce pure plutonium.  An alternative to reprocessing or refining is to produce nuclear waste that is self-contained, depleted to the point where it is not a proliferation problem, and can be stored in underground sites without concerns of water leaching or seismic damage.  TRISO (tri-structureal isometric) fuel reactors use fuel pebbles that, after spent, are safe to store without cooling, are resistant to water leaching, and contain highly depleted nuclear materials.  By employing such overlooked strategies for waste reduction and reopening the search for a permanent storage site the U.S. will be able to develop a more viable nuclear waste disposal program.

Hydrogen Production using Nuclear Energy

It is often argued that hydrogen is the transportation fuel of the future due to its high efficiency and versatility of use.  One way to obtain hydrogen is nuclear-based production using thermochemical water splitting.  Lubis et al. (2010) conducted a life cycle assessment (LCA) of this process in order to determine its environmental impacts.  The authors studied the impacts of both nuclear and copper-chlorine thermochemical plants using LCA methodology framework from the International Organization for Standardization (ISO) and CML-2001 impact categories.  The four main stages of the LCA include: i) goal definition and scope; ii) inventory analysis; iii) impact assessment; and iv) improvement assessment.  From this study it was found that the most significant environmental impacts come from the construction of the two plants and the operation of the nuclear plant.  In contrast, the operations of the thermochemical plant do not significantly contribute to the overall environmental impact.  In order to decrease the environmental impact of nuclear-based hydrogen production, the authors suggest developing more sustainable processes, particularly in the nuclear plant and construction. —Carolyn Campbell
Lubis, L.L., Dincer, I., Rosen, M.A., 2010. Life cycle assessment of hydrogen production using nuclear energy: an application based on thermochemical water splitting. Journal of Energy Resources Technology 132, 1–6.
          The authors undertook a LCA of hydrogen production using nuclear energy.  In order to minimize emissions, hydrogen is produced via a thermochemical cycle that involves a sequence of chemical reactions yielding a net reaction of splitting water.  This study analyzed the copper-chlorine (Cu-Cl) thermochemical cycle in which nuclear energy from a supercritical water-cooled reactor (SCWR) provides the thermal energy for driving the chemical reactions.  Therefore the emissions from the overall system are the sum of the advanced nuclear power plant and the thermochemical hydrogen production plant.  The nuclear plant is taken to be rated at 2060 MWth and the entire thermal output of the plant goes to producing hydrogen.  The thermochemical plant is assumed to have a hydrogen production capacity of 5200 kg/h of H2and a 30-year operational life.  All calculations are based on 1 h of operation of the entire plant.
          Lubis et al. utilized reported literature in order to estimate the emissions of the nuclear and thermochemical plants.  It was estimated that 4.29 kg/h of uranium is needed to produce a thermal output of 2060 MWth. For the thermochemical plant the environmental impact was estimated based on the use of chemicals in the process and use of raw materials.  In order to produce 5200 kg of H2,514,800 kg of CuCl and 189,600 kg of HCl are required.  To assess the impact of hydrogen production, the environmental impacts of emitted substances were classified into environmental impact categories.  These categories include abiotic resource depletion potential (ADP), global warming potential (GWP), ozone depletion potential (ODP), eutrophication potential (EP), acidification potential (AP), photochemical ozone creation potential (POCP), and radioactive radiation (RAD).  The quantitative environmental impacts were then calculated by multiplying the quantity of emitted substances by the relevant classification factor and the GaBi database was utilized to determine the environmental impact of emissions based on inventory analysis. 
          The LCA produced several findings regarding the environmental impact of nuclear-based hydrogen production using thermochemical water splitting.  For GWP, the system emits 0.0025 g CO2-eq over the life of the plant, with 95% of these emissions attributable to the construction of the nuclear plant and the hydrogen plant.  Additionally, regarding the AP, the emissions of the system are 0.00015 g SO2-eq, with the 99% of emissions coming from construction and the nuclear fuel cycle.  Construction contributes significantly to other impact categories including EP, ODP, and POCP, while the nuclear fuel cycle contributes significantly to ADP and RAD.  In order to decrease the environmental effects of this system the authors suggest developing more sustainable processes in the nuclear plant and the construction of hydrogen production. 

Nuclear Energy Consumption and Eco-nomic Growth

Nuclear energy is an important energy source for both long-term energy and environmental strategies and can address energy needs in areas with scarce resources.  Additionally, nuclear energy has been found to have an impact on economic growth.  Apergis et al. (2010) studied the relationship between nuclear energy consumption and economic growth within a multivariate panel framework for the period 1980–2005.  Using a heterogeneous panel cointegration test, the authors found a long-run equilibrium relationship between real GDP, nuclear energy consumption, real gross fixed capital formation, and the labor force.  Additionally, the panel vector error correction model revealed bidirectional causality between nuclear energy consumption and economic growth in the short-run and unidirectional causality from nuclear energy consumption to economic growth in the long run.  These results support the feedback hypothesis that energy consumption and economic growth are interrelated and thus may serve as complements to each other. —Carolyn Campbell
Apergis, N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>., Payne, J.E., 2010. A panel study of nuclear energy consumption and economic growth. Energy Economics 32, 545–549.
Nuclear energy is an important power source of a growing interest as the world develops long-term energy and environmental policy.  The Energy Information Administration anticipates that electricity generation from nuclear power will increase from approximately 2.7 trillion kilowatt hours in 2006 to 3.8 trillion kilowatt hours in 2030.  This increase can be attributed to concerns regarding greenhouse gas emissions from fossil fuel energy sources, volatility of world oil and gas prices, as well as political issues faced by countries dependent on foreign oil.  In discussing nuclear energy as an option for sustainable development, it is important to address its impact on economic growth.  Four main hypotheses have been linked with the causal relationship between energy consumption and economic growth.  First, the growth hypothesis predicts that energy consumption will both directly and indirectly impact economic growth as a complement to labor and capital in the production process.  This hypothesis is supported by unidirectional causality from energy consumption to economic growth.  Second, the conservation hypothesis presumes that energy conservation policies that reduce energy consumption and waste do not negatively impact economic growth, supported by unidirectional causality from economic growth to energy consumption.  Third, the feedback hypothesis suggests that energy consumption and economic growth are interrelated and serve as complements to each other.  This hypothesis is supported when there is bidirectional causality between energy consumption and economic growth.  Finally, the neutrality hypothesis assumes that energy consumption is a relatively small component of overall output and therefore has little or no impact on economic growth, supported by the absence of any causal relationship.
In order to determine the relationship between nuclear energy consumption and economic growth the authors analyzed annual data from 1980 to 2005 for Argentina<!–[if supportFields]> XE “Argentina” <![endif]–><!–[if supportFields]><![endif]–>, Belgium, Bulgaria, Canada<!–[if supportFields]> XE “Canada” <![endif]–><!–[if supportFields]><![endif]–>, Finland, France, India<!–[if supportFields]> XE “India” <![endif]–><!–[if supportFields]><![endif]–>, Japan, Netherlands, Pakistan, South Korea, Spain, Sweden<!–[if supportFields]> XE “Sweden” <![endif]–><!–[if supportFields]><![endif]–>, Switzerland, U.K., and U.S.  Included in the multivariate framework were real GDP, real gross fixed capital formation, total labor force, and nuclear energy consumption.  First, a heterogeneous panel cointegration test was conducted for both panel data sets, one including France and one excluding France due to its heavy dependence on nuclear energy.  The test revealed a long-run equilibrium relationship between real GDP, nuclear energy consumption, real gross fixed capital formation, and the labor force.  Second, to infer the causal relationship between the variables, a panel of error correction models was estimated.  The authors found short-run bidirectional causality between nuclear energy consumption and economic growth and long-run unidirectional causality from nuclear energy consumption to economic growth.  The short-run bidirectional causality supports the feedback hypothesis and suggests that energy policies designed to increase the production and consumption of nuclear energy will have a positive affect on economic growth.  

French Politics, Culture, and Nuclear Power

With over 80% of its electricity coming from nuclear power, it has been suggested that France is a model for adopting a nuclear energy industry.  However, Coombs (2010) suggests that France’s successful nuclear industry has been driven by the unique political and cultural climate of the country.  France’s independent executive branch, characterized by a lack of division of power, a weak judiciary, and a reliance on bureaucratic capability, had the ability to efficiently institute a nuclear program without objections from outside interest groups.  Additionally, the French people have been won over by the economic growth created by the nuclear industry.  Finally, the lack of natural resources in the country has contributed to the growth of the nuclear power program.   Coombs suggests that the French government’s firm support of the nuclear industry has overshadowed the negative aspects of nuclear power, especially the problem of nuclear waste disposal.—Carolyn Campbell     
Coombs, C., 2010. French Nuclear Power: A model for the world?. Hinckley Journal of Politics. 11, 7–13.

Coombs studied the costs and benefits of nuclear energy by analyzing France’s nuclear industry.  France began looking into nuclear power during the 1960s in order to decrease its dependence on foreign energy sources and was particularly affected by the quadrupling of oil prices from OPEC countries in 1973. The government began to seriously consider adopting nuclear power and was able to efficiently implement a nuclear program without much objection from outside interest groups.  Coombs notes that the French executive-empowering government structure prevents activists from being involved in a transparent debate or influencing policy.  Additionally, there is a cultural tendency within France to yield decision-making to the large group of trusted scientists and engineers in the country.  Furthermore, French nuclear power has a number of benefits including increased job creation, state revenue, and energy independence.  While nuclear power is championed in France, it is often looked upon warily in the United States.  Coombs argues that this is not because the French people do not have fears about nuclear waste and accidents, but because their cultural views and political situation influence their support for nuclear energy.  Additionally, the French have a lack of choice in the matter, with few alternative natural resources and a government structure that does not support political debate on such matters. 
          Despite the success of nuclear power, the disposal of nuclear waste continues to be an issue in France.  The idea of burying the waste has brought up ideas of the profanation of soil and desecration of the Earth.  Additionally, a rural/urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> divide has been intensified with rural populations protesting against the Parisian’s energy waste ending up in their backyards.  In order to combat these issues the state has proposed “stockpiling” the waste.  This implies reversibility; that the waste will not be buried and forgotten and that future scientists may learn how to reduce or eliminate the toxicity.  However, nuclear waste is a long-term problem that France has yet to develop a permanent disposal facility for.  While France has come up with a way to “reprocess” fuel from spent nuclear rods, much of the revenue from this process comes from outside the country.  This means that other countries, including Japan, Germany, Switzerland, the Netherlands, Belgium, and Italy, are shipping their waste to and from France.  This transit of nuclear waste only increases the likelihood of an accident.  However, Coombs argues that the French public places the economic benefits derived from nuclear power above the possible health risks.
          Coombs concludes that since France’s nuclear program has led to enormous economic benefits, the negative byproducts of nuclear energy have been overlooked.  The French government was able to institute a nuclear program due to an executive-empowering institutional structure and a trusting public.  However, other countries must weigh both the costs and benefits of nuclear power when searching for renewable energy alternatives. 

Sustainability of Nuclear Fission Energy

While nuclear energy has been cited as a potential solution in achieving carbon-free electricity, there are many problems facing its development.  Nuclear generation is met with public and political opposition due to concerns regarding nuclear accidents and nuclear waste.  Additionally, very high initial investment costs make it difficult to find funding for nuclear energy projects.  Piera (2010) examines the sustainability issues related to nuclear fission energy by reviewing ongoing lines of research and development in the field and potential alternative reactor technologies.  While the analysis points out the major drawbacks of nuclear energy, those related to safety, security, and the environment, Piera highlights that nuclear fission is a sound CO2-free source of energy.  The study argues that nuclear fission has a high maturity in its current state of commercial development and has enormous potential in new phases of industrial development.  Carolyn Campbell
Piera, M., 2010. Sustainability issues in the development of nuclear fission energy. Energy Conservation and Management 51, 938–946.

          Emphasized as an important option for keeping atmospheric CO2 below 550 ppm,  nuclear power plants currently provide 16% of the global electricity generation.  While generation is increasing 1% each year, this rate is incredibly modest when compared to the global yearly increase in primary energy consumption.  Nuclear fission energy is well suited to meet the needs of future energy policies due to the guaranty of supply, environmental quality, and moderate energy costs.  However, nuclear energy development is hindered by public and political opposition as well as financing difficulties. 
          Throughout the paper, Piera assessed the concept of sustainable development as applicable to nuclear energy.  First coined in the Brundtland Report, sustainable development stressed the importance of considering social, economic, and environmental issues to ensure the same development and living conditions for future generations.  In this context, energy is a very critical issue.  While nuclear energy is considered an important energy alternative with very low CO2 emissions, current LWR reactors are inefficient.  Only 0.55% of the potential energy in mined uranium is converted into heat in the reactors, a fact that hampers the future development of nuclear energy.  Therefore, Pierra argues, future research should focus on options for new reactors and fuel cycles that could exploit natural resources up to 70% or more.  Additionally, nuclear natural resources could be more completely exploited through nuclear breeding.  Even-numbered heavy nuclei, U-238 and Th-232, cannot be considered true fuels because they do not undergo fission with thermal neutrons.  Through nuclear breeding these even-numbered nuclei can be converted into odd-numbered nuclei, specifically Pu-239 and U-233. 
          While nuclear breeding may be a solution for more efficient use of nuclear natural resources, it causes concerns related to nuclear proliferation.  Pu-239 seems to be a suitable material for nuclear weapons, a social concern that must be addressed in sustainability assessments.  Additionally, the waste burden of nuclear energy hinders the sustainability of nuclear fission energy.  While deep geological repositories have been suggested as a solution for waste storage, the radiotoxicity of nuclear waste can last for 1000 centuries.  Therefore, to make nuclear energy more sustainable the waste must be reduced as much as possible before its final disposal.  The “open cycle” in use today cannot achieve such a reduction.  By switching to a closed cycle with nuclear fuel recycling, much less fuel would need to be disposed of. 
Another concern with nuclear energy generation is nuclear accidents.  The meltdown of Chernobyl-4 had catastrophic affects on humans and the environment.  However, the reactor was running an experiment when the accidents took place and the six-safety systems had been shut off.  Generation 3 reactors have learned from the Chernobyl accident and in turn have incorporated more advanced safety systems. 

          In conclusion, Peira proposes four main sustainability technical criteria for nuclear energy.  First, nuclear reactors and nuclear fuel facilities must have enhanced safety features.  Second, natural nuclear materials must be more highly exploited.  Third, radioactive inventory of waste must be minimized before disposal.  And finally, proliferation-resistant technologies must be developed.  By achieving these criteria, nuclear fission energy will become a more sustainable and viable option for the future.