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What Is the Right Mix for Long Term Stability? Issue 2.4: Nuclear Power

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What Is the Right Mix for Long Term Stability? Issue 2.4: Nuclear Power Theme for Day 2 | AVAILABILITY - What is the right mix for long term stability? Issue 2.4: Nuclear power renaissance or demise? Title: Extending the World’s Uranium Resources through Advanced CANDU Fuel Cycles Authors: Tony De Vuono; Frank Yee; Val Aleyaseen; Sermet Kuran; Catherine Cottrell Atomic Energy of Canada Limited Sheridan Science and Technology Park 2251 Speakman Drive, Mississauga, Ontario, L5K 1B2 Canada Tel: 905-823-9060 Fax: 905-403-7386 Email: [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Abstract: The growing demand for nuclear power will encourage many countries to undertake initiatives to ensure a self-reliant fuel source supply. Uranium is currently the only fuel utilized in nuclear reactors. There are increasing concerns that primary uranium sources will not be enough to meet future needs. AECL has developed a fuel cycle vision that incorporates other sources of advanced fuels to be adaptable to its CANDU technology. Keywords: CANDU; resource sustainability; advanced fuel cycles CANDU is a registered trade-mark of Atomic Energy of Canada Limited (AECL) © Atomic Energy of Canada Limited, 2010 1. INTRODUCTION In recent years, a growing global need for carbon-dioxide free electricity has resulted in more countries embracing the expansion of nuclear power. According to the results of the Organization for Economic Cooperation and Development (OECD) Ministerial Conference held in Paris in 2005, there is a recognized clear value in the use of nuclear power due to the following advantages [1]: It does not cause air pollution or other harmful greenhouse gas emissions It provides competitively priced electricity and contributes to regional and national economic competitiveness It contributes to the security of supply and stability of energy prices The “Red Book”1, which is a publication that tracks world trends and developments in uranium resources, production, and demand, estimates that in the next thirty years, electricity generated from nuclear power will increase by 40-80% of current installed capacity []. Consequently, the demand for uranium as a fuel source will rapidly grow. The projected uranium consumption rates for proposed new build reactors and the large gap between production and consumption have created significant volatility in uranium prices over the last two years. Therefore, it is becoming crucial to secure sufficient uranium supply and take additional measures to ensure the availability of long-term and stable fuel resources for nuclear power plants. Increasing the exploration of uranium and implementing the use of alternate fuels in nuclear reactors can mitigate the approaching uranium constraint. CANDU nuclear technology, in particular, has great flexibility in using a variety of fuels. In addition to natural uranium (NU), CANDU reactors are efficient at utilizing recycled uranium (RU), Mixed Uranium/Plutonium Oxide (MOX), and thorium fuels. Until recently, an abundance of uranium at a favourable price profile did not offer a strong case for the implementation of alternative fuel cycles. However, increasing investments in nuclear power in major developing nations such as China and India are bringing this option to the forefront. CANDU nuclear reactors are the flagship product of Atomic Energy of Canada Limited (AECL). There are a total of forty-eight CANDU-type reactors worldwide. One of AECL’s main products, the CANDU 6, is a highly proven Generation II+ design. Eleven CANDU 6 units have been built and commissioned, achieving an excellent performance record with an average lifetime capacity factor approaching 90%. They have been delivered on time and on budget using AECL’s world-class project management capabilities. Additionally, three CANDU 6 reactors are among the world’s top ten best performed units. The two CANDU 6 units at Qinshan in China are the latest design in this class. This project is internationally recognized for first class project performance and was completed nearly four months ahead of schedule and below the estimated budget. 1 A joint report published by the OECD Nuclear Energy Agency and the International Atomic Energy Agency (IAEA) CANDU is a registered trade-mark of Atomic Energy of Canada Limited (AECL) © Atomic Energy of Canada Limited, 2010 The design has been continuously improved to meet current codes and standards and current Canadian regulatory requirements for construction and operation, reduce cost, enhance performance, and increase plant life up to 60 years. The continuous improvements have led to the Enhanced CANDU 6 (EC6), which is a 740 MWe Class reactor and represents the next evolutionary step of the CANDU 6 product line. The differentiating technical advantage of CANDU reactors in utilizing advanced fuel cycles is summarized below: CANDU reactors utilize heavy water, the most efficient moderator material in any reactor. The function of the heavy water is to slow neutrons down to allow their capture by 235U atoms. This efficient moderation leads to heavy water moderated and cooled CANDU reactors being the most neutron efficient thermal reactors. The thermal neutron spectrum is “softer” than that in a Light Water Reactor (LWR), resulting in reduced loss of neutrons through absorption by other uranium isotopes. The CANDU reactor design is composed of multiple pressure tubes rather than a single, large pressure vessel serving as the reactor core pressure boundary. This feature allows for on-power fuelling, which in turn allows the operator to shape the core properties to optimize fuel utilization. The small size and simplicity of the CANDU fuel bundles can be readily adapted to the differing properties of alternative fuels. Over the years, AECL has carried out theoretical and experimental investigations of different fuel sources such as RU, thorium, and MOX. This paper will discuss the strategy for a successful evolution in advanced fuel cycle implementation. 1.1 Recycled Uranium (RU) and Depleted Uranium (DU) Various countries have adopted or are adopting incremental policies to approach closed fuel cycles. An element of such a policy is one that involves recycling the used fuel to recover fissile material for reuse. Not only does this strategy mitigate the fuel supply challenge, it also reduces waste and enhances proliferation resistance. There is considerable industrial-scale experience in the civilian recycling of used fuel in several countries. There is currently a global recycling capacity of 4,210 tonnes/annum of used LWR fuel in countries such as France, United Kingdom, Japan, and Russia. Appropriate measures are used to ensure the safe operation of recycling facilities and plants. Purification and conditioning for storage, re-enrichment, and/or direct utilization are well controlled. The cost of uranium re- enrichment processes has in effect barred the use of RU in LWR plants. Therefore, most of this valuable RU resource has been placed in temporary storage. Enhanced CANDU 6 and EC6 are registered trade-marks of Atomic of Energy Canada Limited (AECL) © Atomic Energy of Canada Limited, 2010 The Energy Information Administration’s study [3] projects that by 2020, there will be a world cumulative used fuel inventory of around 460,000 tonnes of heavy metal. Typically, about 93% of the heavy metal mass consists of uranium []. Therefore, by 2020, there will be an opportunity to utilize 430,000 tonnes of RU, if all the used fuel is processed. This number will continue to grow at an even faster rate with the influx of new nuclear power generation and operation. RU has a nominal 235U concentration in the range of 0.85-0.99 wt. %, at concentrations higher than natural uranium required for use in CANDU reactors. Another under-utilized nuclear fuel resource, Depleted Uranium (DU), is derived as a by-product of enrichment processing and has a 235U concentration of 0.2-0.3 wt. %. World stocks of DU are plentiful and are estimated at 1.2 million tonnes [5], with an expectation to grow further as nuclear power capacity is increased. Historically, DU has been viewed as a waste product. Currently, there is some commercial use for DU as a shielding material, but the vast majority remains in storage. 1.2 Thorium Fuel As early as the 1950s, the use of thorium was identified as a promising fuel cycle in AECL’s CANDU development program. In fact, thorium was considered as a serious competitor of uranium to facilitate the start-up of the commercial nuclear project in Canada. Thorium (232Th) is a fertile material, requiring the use of a fissile “driver” isotope, such as 235U to initiate the fission process. After absorbing a neutron from the driver isotope fission, the 232Th turns into another fissile isotope of uranium (233U). Thorium has the following potential advantages in terms of nuclear energy use: 1. A clear resource advantage. It is estimated that the reserve of thorium resources in the earth’s crust is two to three times higher than that of uranium resources. It is available in large quantities in countries such as China and India, both of which have rapidly expanding economies requiring additional sustainable power sources. Moreover, there is only one form of natural thorium nuclide, 232Th, and most thorium ores are relatively easily exploitable around the world. This is different from uranium mining, which is slightly more complicated due to the presence of additional isotopes. 2. Advantages of nuclear properties. The neutron output of 233U is greater than two in both the fast flux group and the thermal flux group; therefore 232Th has the potential to create more isotopes in the thermal reactor for future use in subsequent cycles. Furthermore, the thermal neutron absorption cross-section of 232Th (7.4 barns) is approximately three times that of 238U (2.7 barns). Therefore, the conversion efficiency of 232Th to 233U is higher than that of 238U to 239Pu, as seen in current conventional reactors. 3. Advantage of environmental protection. The thorium-uranium fuel cycle produces only a small amount of long lived actinide nuclides, and the amount of fission products © Atomic Energy of Canada Limited, 2010 are also one order of magnitude lower than that of uranium fuel, therefore not as persistent in the environment.
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