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)

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)

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)

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

are also one order of magnitude lower than that of uranium fuel, therefore not as persistent in the environment. 4. Advantage in material properties. The melting point of thorium dioxide is high enough to permit higher operating temperatures than natural uranium. Thorium dioxide is more chemically stable than uranium dioxide. It cannot be oxidized further; therefore it is suitable for long-term storage. Thorium dioxide possesses high thermal conductivity and low thermal expansion properties. Thus thorium dioxide has the potential of better performance than uranium dioxide and MOX fuel. In addition, the fission gas produced in thorium dioxide fuel has the potential to be contained within the fuel matrix; therefore higher burnup may be achievable as compared to natural uranium.

In the 1960s and 1970s, rapid development of nuclear power attracted Canada, the United States of America, Europe, India, and other countries to conduct extensive research on the use of thorium-based fuel cycles and thorium resources in order to expand the sources of supply of nuclear fuels and the development of thorium-based nuclear energy. However, as the First Nuclear Era waned and new uranium deposits were discovered and developed, the enthusiasm for the use of thorium-based fuel cycles to generate nuclear power gradually declined.

Nevertheless, the potential and advantages of the thorium-based fuel cycle to generate nuclear power still remain as the ultimate pathway to a fully self-sustainable nuclear fuel cycle, especially in light of the rapidly developing nuclear renaissance. Some countries, such as Canada and India, have continued to develop the thorium-based fuel cycle with the goal of supplying a thorium-based commercial nuclear power plant.

2. DESIGN/SETUP

The general strategy for implementation of advanced fuel cycles in CANDU reactors is a systematic, step-by-step approach. AECL’s work showed that the lowest cost path to efficient utilization of alternative fuel sources in the current CANDU reactors, without modifications to the existing licensing basis, is the application of a blended fuel of RU and DU, called Natural Uranium Equivalent (NUE) fuel in a standard 37-element CANDU fuel bundle. The NUE fuel design is described in greater detail in Section 2.1. Successful implementation of NUE fuel in a commercial CANDU 6 reactor will clearly demonstrate the CANDU reactor’s capability in utilizing advanced fuel cycles safely and efficiently, without the requirement to make changes in the reactor. In the near future, varied combinations of RU and DU will be blended to create a higher burnup fuel.

Right on the footsteps of the NUE initiative is the development and reactor implementation of thorium-based fuel in CANDU reactors. The initial fuel bundle for thorium reactors proposed is a bundle of Low Enriched Uranium (LEU) and thorium arranged in a CANFLEX fuel bundle (LEU/Th). This is an immediate step towards introducing thorium fuel into EC6 reactors and would not require many changes to the reactor design itself.

Over the next twenty years, when global recycling capacities have matured, there will be excess plutonium available from used LWR fuel and/or fast breeder fuel. This excess fissile plutonium, which would act as a driver for the fertile thorium, would further reduce the need for uranium and would be a step towards closing the thorium fuel cycle.

Finally, as a long-term strategy, a synergistic relationship between the planned fast breeder reactor technology, recycling facilities, and more advanced CANDU-type plants (using RU and thorium) would be reached to create a sustainable closed or semi-closed fuel cycle that minimizes the waste stream to only fission products. This closed cycle approach will provide enormous future economic and supply chain benefits to nuclear technology.

This section discusses the current product development work that AECL has begun in the pursuit of advanced fuel cycles. In partnership with Third Qinshan Nuclear Power Company (TQNPC), China North Nuclear Fuel Corporation (CNNFC), and Nuclear Power Institute of China (NPIC), AECL is working towards implementing NUE fuel in Qinshan CANDU 6 reactors. AECL and its Chinese partners are also working towards building a Thorium Capable CANDU Reactor (TCR) in China that will have the ability to utilize LEU/Th fuel.

2.1 Natural Uranium Equivalent (NUE) Fuel

NUE fuel is a mixture of RU and DU combined so that the resulting fuel will be neutronically equivalent to NU fuel. RU and DU are blended in such a manner that NUE will have a 235U concentration similar to NU, 0.71 wt. % at almost the same burnup of 7,500 MWd/kg HM. This

 CANFLEX is a registered trade-mark of Atomic Energy of Canada Limited (AECL)

© Atomic Energy of Canada Limited, 2010 blending for CANDU fuel manufacturing can be done in solid, liquid, or gaseous state and is a low cost activity, requiring fewer processes compared to LWR fuel manufacturing requirements.

The application of NUE fuel in CANDU reactors has been shown to be technically feasible. It overcomes the challenge of dealing with used LWR fuel that would otherwise require monitored storage or costly re-enrichment and handling of radioactive fuels for reuse in LWRs. Using RU in existing CANDU nuclear power reactors will improve the utilization rate of NU resources and ultimately improve the sustainability of fuel resources. In addition, NUE reintroduces the fissile content in DU back into the fuel cycle; an effective application of an otherwise limited use by- product from the uranium enrichment process.

One of the distinctions between RU and NU is the presence of additional isotopes that have differing impacts on fuel performance. For instance, RU contains 234U and 236U, which are neutron-absorbing isotopes that would result in the need to slightly over-enrich 235U in NUE to compensate for their presence.

The concentration of the isotopes depends on a number of factors such as the type of reactors the fuel had been used in, the degree of initial 235U enrichment, the level of fuel discharge burnup, and the aging period since the fuel had been used.

Additionally, some non-uranium elements are present in RU that are not found in NU. Even though RU goes through a chemical separation method known as Plutonium Uranium Extraction (PUREX), since the separation efficiency is not 100%, traces of light elements, actinides (other than uranium), and fission products are present in RU.

To understand what the impact of these differing properties of RU would have on reactor design, physics, safety, operation, radiation protection, fuel manufacturing, and used fuel storage, AECL, in partnership with TQNPC, CNNFC, and NPIC, is in the process of performing a two-channel test irradiation of NUE fuel bundles in a Qinshan CANDU 6 reactor. A program has been completed to examine and document the feasibility of using NUE in CANDU reactors. The program culminates in the performance of a test irradiation to confirm the fuel behaviour predicted in the studies and document results.

This test irradiation would provide the confidence to evolve to a full core loaded with NUE fuel. Furthermore, in future years, the proportion of RU and DU will be varied in order to create a higher-burnup NUE fuel.

2.2 Low Enriched Uranium (LEU)/Th Fuel

International programs position current-technology thermal reactors and future fast breeding reactors as the starting points for advanced fuel cycle technologies. As an established thermal reactor, CANDU is seen as a key technology for initial use of advanced fuel cycles.

Thorium in particular is a fundamental part of AECL’s fuel cycle vision for CANDU, as it represents a low uranium consumption fuel cycle option. A thorium-fuelled CANDU reactor is very attractive to countries with vast thorium reserves and little uranium, as it addresses their need for energy self-reliance.

To facilitate a practical way of using thorium in the CANDU 6 reactor fuel cycle, AECL has adopted a first-pass, open cycle option that would generate potential fuel material as a fissile material resource for initiating closed fuel cycles in later years, such as an LEU/Th fuel.

LEU/Th fuel is to be implemented in a TCR as a safe and efficient first step of introducing thorium into the CANDU fuel cycle. The LEU/Th fuel bundle would be composed of a mixed bundle of LEU and thorium in a 43-element CANFLEX bundle designed to achieve a target burnup of 20 MWd/kg HM. AECL and other organizations have conducted numerous conceptual and proof-of-principle experimental studies that will provide support in achieving regulatory acceptance for putting forward this fuel, such as:

 Physics tests performed in the ZED-22 experimental facility using various configurations of thorium fuel bundles (235U/Th, 233U/Th, and Pu/Th).  Irradiation testing of various thorium-based fuelled CANDU fuels in research and power reactors that can be used to validate physics codes.  Significant efforts in code development and qualification using the same advanced toolset and methods for code validation. These methods include extensive use of benchmarking (comparison of the standard toolset against a more rigorous calculation).  Design of a suitable fuel carrier (CANFLEX) that is qualified for NU fuel and low-void reactivity LEU fuel.

To determine if this fuel is technically feasible in a CANDU reactor, a number of assessments have been undertaken, such as:

 Reactor physics assessments to identify changes to the operating parameters of the reactor to ensure that it would still meet safety and performance requirements of the reactor with the use of the new fuel.  Impact of changes to the reactor radiation physics, and reactor systems assessments to confirm what (if any) changes are needed to accommodate an LEU/Th fuel loaded reactor core

The results of these assessments demonstrate the technical feasibility and will advance the thorium fuel cycle to more efficient bundle arrangements. Maximum thorium utilization (and sufficiently reduced reliance on uranium resources) will be achieved through recycling fissile 233U in a closed-fuel cycle. Over time and through evolutionary modifications, the CANDU reactor will be optimized to operate with thorium in a complete recycling mode.

2 The Zero Energy Deuterium (lattice-testing reactor) ZED-2 is a low-power, heavy water-moderated reactor used for reactor physics research at Chalk River, Ontario

3. RESULTS

3.1 Natural Uranium Equivalent (NUE) Fuel

Over the course of a year, AECL and its Chinese partners submitted a number of technical analysis documents to National Nuclear Safety Administration (NNSA 3 ) that described the potential impacts of NUE fuel implementation. The results were positive and showed that little to no changes would be required to incorporate the fuel for a two-channel test irradiation in the Qinshan CANDU 6 reactor.

In December 2009, after extensive review of the technical documentation, NNSA approved the use of NUE fuel for a test irradiation in one of Qinshan’s CANDU reactors. NUE fuel will be inserted into the Qinshan CANDU units during the first quarter of 2010.

The results of the test irradiation will be used as input to implementing a full core NUE fuelled CANDU reactor and use of a higher-burnup RU-based fuel in the CANDU fleet.

3.2 Low Enriched Uranium (LEU)/Th Fuel

AECL and its Chinese partners prepared a detailed Feasibility and Concept Study to determine the commercial viability of the TCR design. Overall, results showed that the technical feasibility of the TCR reactor design is demonstrated by:

 Favourable reactor core physics parameters and design,  Minimal modifications to existing EC6 systems, and  As much as 20% and 50% increased uranium utilization compared to CANDU 6 and LWR respectively.

In November 2009, an expert panel meeting organized by the Department of Nuclear Power of China National Nuclear Corporation (CNNC), which included experts from universities, national energy and safety administrations, engineering companies, and fuel manufacturing companies concluded that the results from the Feasibility and Concept Study show that the proposed LEU/Th bundle is “technically practical and feasible, with enhanced safety and good expected economics”. The experts “unanimously recommended that China consider new build of two more CANDU heavy water reactor units to utilize various advantages of this type of reactor”[6] This result reinforced AECL’s conclusion that thorium can be effectively utilized in CANDU reactors and will help ease the burden of reliance on uranium-based fuels for countries which rely on nuclear technology.

3 NNSA is China’s Nuclear Regulatory Commission

4. CONCLUSION

Global concerns about climate change and energy independence have encouraged many countries to consider nuclear power (or expand their existing nuclear fleet) as a safe, economic, and environmentally sound way to generate electricity. According to the World Nuclear Association, if the social, health, and environmental costs of fossil fuels are also taken into account, the feasibility and economics of nuclear power become even more compelling [7].

The growing demand for nuclear power will cause many countries to consider the challenge of maintaining a self-reliant resource supply to sustain a long-term future. Uranium is currently the only fuel supplied for 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.

The unique capability of CANDU reactors to utilize advanced fuels results from high neutron economy, a versatile fuel channel design, and a simple fuel bundle design. A strategy to capitalize on this unique CANDU feature is in place and will play an important role in ensuring uranium resource sustainability.

This strategy envisages a step-by-step evolutionary approach to the implementation of advanced fuel cycles. AECL has begun this process by proposing the introduction of NUE fuel and LEU/Th fuel into the fuel supply. Both these fuel sources have been deemed technically acceptable by highly regarded institutions and experts.

4.1 Path Forward

It is clear that there is continued global interest in developing and exploring recycling capabilities as a way to manage environmental and resource sustainability concerns. It is imperative that political and economical factors are taken into account in order to realize the full potential of this technology advancement. Public acceptance and understanding will be a critical factor in the implementation of advanced fuel cycles. The nuclear industry will need to collaborate to ensure that supply chain, technological, and economical challenges are properly managed to achieve effective results. Synergies between different technologies are possible, and optimization of these relationships will be essential to meeting the global energy demands.

The successful implementation of NUE and LEU/Th fuel strategy that AECL and its partners have proposed should provide the confidence in the performance and safety of these initial advanced new fuel cycles. These fuel cycles will evolve into more advanced, efficient, and synergistic fuel cycle options that bring even greater resource utilization advantages. The lessons learned from these initial fuel cycle options will be of great value to understanding the technical challenges of more advanced fuel cycle technologies.

5. ACRONYMS

AECL Atomic Energy of Canada Limited CANDU CANada Deuterium Uranium, registered trademark of AECL CANDU 6 CANDU - 600 MWe size CANFLEX CANDU FLEXible fuelling CNNC China National Nuclear Corporation CNNFC China North Nuclear Fuel Corporation DU Depleted Uranium EC6 Enhanced CANDU 6 HM Heavy Metal IAEA International Atomic Energy Agency LWR Light Water Reactor LEU Low Enriched Uranium MOX Mixed Uranium/Plutonium Oxide NNSA National Nuclear Safety Administration NU Natural Uranium NUE Natural Uranium Equivalent NPIC Nuclear Power Institute of China OECD Organization for Economic Cooperation and Development PUREX Plutonium Uranium Extraction RU Recycled Uranium TQNPC Third Qinshan Nuclear Power Company TCR Thorium Capable CANDU Reactor ZED-2 Zero Energy Deuterium

6. REFERENCES [1] http://www.nei.org/resourcesandstats/documentlibrary/protectingtheenvironment/reports /iaeaoecdfinalstatement2005 [2] OECD Nuclear Energy Agency, Uranium 2007: Resources, Production, and Demand (also known as The Red Book), OECD/NEA-IAEA, 2008. [3] http://www.eia.doe.gov/cneaf/nuclear/page/forecast/cumfuel.html [4] Idaho National Laboratory, Advanced Fuel Cycle Cost Basis, INL/EXT-07-12107, 2008. [5] OECD Nuclear Energy Agency, Management of Depleted Uranium: A Joint Report by OECD Nuclear Energy Agency, OECD, 2001. [6] http://www.tqnpc.com.ch [7] http://www.world-nuclear.org/info/inf02.html