VIEWPOINT pubs.acs.org/est
Should We Consider Using Liquid Fluoride Thorium Reactors for Power Generation? Nicolas Cooper,†,‡ Daisuke Minakata,†,‡ Miroslav Begovic,§ and John Crittenden*,†,‡ †
Brook Byers Institute for Sustainable Systems, Georgia Institute of Technology, Atlanta, Georgia 30322-0595, United States School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0355, United States § School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0250, United States ‡
’ INTRODUCTION Nuclear power generation is under intense scrutiny due to the recent Japanese disaster. Nuclear programs across the world are re-evaluating regarding their future power source citing valid safety concerns. There is a viable option to replace current nuclear technology: Liquid Fluoride Thorium Reactors (LFTRs).1 LFTRs have distinct safety, environmental, and economic advantages over uranium-based and solid-fuel nuclear power. There are several pathways for using thorium and technical challenges which will not be fully covered here. The precise implementation strategy may change the exact figures cited herein, but the fundamental benefits remain valid. Over the past decade Oak Ridge National Lab’s (ORNL) LFTR research from the 1960s 1970s has been revived in various global programs. A private Japanese company is seeking funding for a LFTR called FUJI.2 Canada is researching a fastbreeder LFTR design in their current CANDU research.3 Thermal LFTRs are part of the Gen IV reactor research in France. China announced a LFTR program in February 2011. At the U.S. federal level, Senators Harry Reid and Orrin Hatch support providing $250 million in federal research funds to revive the ORNL research and draft specific resolutions. Why is there so much interest in nuclear technology that was cast aside 35 years ago? r 2011 American Chemical Society
’ SAFETY ISSUES Solving the real and perceived dangers of nuclear power is critical to future investment. LFTRs show strong potential for significantly improving safety. The greatest advantage of LFTRs is that there is very low chance of a catastrophic, explosive meltdown like Chernobyl, or a partial meltdown like Japan’s Fukushima-Daiichi or Three-mile Island in Pennsylvania. In the event of an earthquake or other disruptive event, a simple freeze drain plug would melt, allowing the fissile material to flow into a containment chamber where the system could be air-cooled. Electricity and active controls are not required for this process.4 LFTRs operate near atmospheric pressure with little possibility of a containment breech or explosion. By using air cooling, not pressurized water, hydrogen gas, which caused the explosions at the Fukushima-Daiichi site, cannot be produced. The liquid fuel allows for online removal of gaseous fission products, such as Xenon, for processing, thereby these decay products would not be spread in a disaster.5 Further, fissile products are chemically bonded to the fluoride-salt, including iodine, cesium, and strontium, capturing the radiation and preventing the spread of radioactive material to the environment.3 There are still risks involved in any nuclear process and extensive safety analysis will be needed. ’ ENVIRONMENTAL ISSUES The entire life-cycle for a thorium reactor shows benefits compared to conventional nuclear and coal, the nation’s largest base-load energy suppliers. Thorium is four times more abundant than uranium and naturally occurs in only one isotope, 232Th, eliminating all enrichment activities inherent in uranium mining and processing. Thorium is a hitchhiker element and almost always found while mining rare earth metals. Rare earth mining operations are beginning again in California at Mountain Pass and possibly in Missouri at Pea Ridge. There is a start-up load of approximately 1.5 tons of fissile material, such as 235U, 238U, or 239Pu, after which the reactor thermally breeds 233U to maintain fission. Conventional nuclear reactors need 5 10 times more initial material to start and continuous feeding of enriched uranium.1 Perpetually needing to transport enriched uranium presents proliferation risks. Thorium by itself does not pose proliferation risks and presents a much smaller radiation risk. Published: July 06, 2011 6237
dx.doi.org/10.1021/es2021318 | Environ. Sci. Technol. 2011, 45, 6237–6238
Environmental Science & Technology
VIEWPOINT
According to the U.S. Geological Survey in 2009, the U.S. proven thorium reserves are approximately 440,000 tons, enough to last for hundreds of years at full-scale LFTR implementation. And it is estimated that the worldwide proven reserves are 1.3 million tons, excluding China. LFTRs use only one ton of thorium per year for a 1000 MW plant and it is the only fuel added during continuous operation.1 The quantity of construction materials is reduced because large cooling towers and containment structures that handle high pressures are not needed.4 LFTRs operate at high temperatures allowing use of higher-efficiency Brayton nitrogen generators rather than steam generators, raising thermal efficiency from ∼35% to ∼50%. At the end-use phase, significantly fewer radioactive materials remain. LFTRs produce one ton of spent radioactive fuel per GW year. The volume of waste products from a LFTR is approximately 300 times less than that of a uranium reactor. The fissile waste is 83% spent within 10 years and below background levels in approximately 300 years.1 Conventional nuclear reactors take thousands of years to decay. LFTRs therefore eliminate the need for a multibillion dollar Yucca Mountain style containment facility.
’ PROLIFERATION ISSUES LFTRs have extraordinary proliferation resistance because thorium cannot be made directly into a weapon.5 The reactor cannot be used to create substantial, pure quantities of plutonium or 238U, which are needed to make bombs. 2 ’ SUMMARY A LFTR program could be achieved through a relatively modest investment of roughly 1 billion dollars over 5 10 years to fund research to fill minor technical gaps, then construction of a reactor prototype, and finally a full-scale reactor.2 Many of the engineering and technological problems of the ORNL program have already been solved through non-nuclear research, including liquid fluorides, resistant metal cladding, and high-temperature turbines. LFTR can mean a 1000+ year solution or a quality low-carbon bridge to truly sustainable energy sources solving a huge portion of mankind’s negative environmental impact. ’ AUTHOR INFORMATION Corresponding Author
*Mail: 800 W. Peachtree, Suite 400 F H, Atlanta, Georgia 303320595, United States; phone: (404)894-5676; e-mail: john.crittenden@ ce.gatech.edu.
’ REFERENCES (1) Engel, J. R.; Grimes, W. R.; Bauman, H. F.; McCoy, H. E.; Dearing, J. F.; Rhoades, W. A. Conceptual Design Characteristics of Denatured MoltenSalt Breeder Reactor with Once-through Fueling; ORNL/TM-7207; Oak Ridge National Laboratory: Oak Ridge, TN, 1980. (2) Furukawa, K.; et al. A road map for the realization of global-scale thorium fuel cycle by single molten-fluoride flow. Energy Convers. Manage. 2008, 49, 1832–1848. (3) Leblanc, D. Molten salt reactors: A new beginning for an old idea. Nucl. Eng. Des. 2010, 240, 1644–1656. (4) Moir, R. W.; Teller, E. Thorium-fueled underground power plant based on molten salt technology. Nucl. Technol. 2005, 151 (Sept.), 334–340. (5) Moir, R. W. Recommendations for a restart of molten salt reactor development. Energy Convers. Manage. 2008, 49, 1849–1858.
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