2003 National Meeting - Alternatives to Direct Spent Nuclear Fuel Disposal: Advanced Nuclear Fuel Cycles

2003 National Academy of Engineering National Meeting Symposium
in honor of Foreign Secretary Harold K. Forsen

Dr. Ralph G. Bennett, Director
Advanced Nuclear Energy
Idaho National Engineering and Environmental Laboratory

My presentation will cover alternatives to spent nuclear fuel disposal in the United States, laying out a number of options and opportunities that have created interest within the programs of the Department of Energy. For the past three years I’ve been associated with the Generation IV Initiative of the Office of Nuclear Energy. More recently, I’ve begun working with the Advanced Fuel Cycle Initiative, which as you know, has evolved from a focus on accelerator-driven systems to a broad objective of working toward an advanced fuel cycle in the United States. I lead the unified systems analysis effort for the two programs.

I want to begin by considering the need for an advanced fuel cycle in the U.S. I’ll next turn to an overview of technology options - and I hope to make the point that there are a myriad of options - with the aim of giving you some idea of how they may be fit together. Finally, I’ll share some perspectives on the two programs.

To set the stage for the need, we will begin with a few perspectives on the overall energy situation in the U.S., and not just on the issues of nuclear waste management. In this slide, we see an extract of the recent 2003 Annual Energy Outlook. The total U.S. energy consumption is plotted as a smooth curve to the year 2025. The expected annual growth rate is 1.5%, which will demand close to 50% more energy by 2025. Much of this growth is projected to come from gas and coal, but very importantly, imports will make up the shortfall. You can see that the imports are expected to rise to over one-third of total energy demand.

You are probably aware that the Energy Outlook is based on an assumption of no growth in nuclear generating capacity - only on the license extensions of today’s plants. Any increase in nuclear capacity would offset greenhouse gas-emitting sources. However, looking ahead in this talk, increased generation will produce more nuclear waste, this in turn will increase the need for more effective means to deal with its disposal.

With regard to nuclear capacity and relicensing, this slide shows the capacity curve with time for two cases: the left curve traces the plant retirements without relicensing and the right curve extends their useful lifetimes out under successful relicensing of about 95% of the plants. Plant uprating gives a modest increase. This slide is important when we look at expanding nuclear energy and the capacity of Yucca Mountain later in this talk.

A second and very important perspective on U.S. energy demand is in the transportation sector. This slide plots the growth in the transportation sector out to 2025. In transportation, the expected growth is 2% annually, which is larger than the other sectors of electricity or heating. The dependence on imported oil is much more striking. Here the imports are expected to reach nearly 80%. In fact, nearly the entire increase in production comes from imports. This dependence on imports will certainly heighten the likelihood of further instability of prices and supply.

This is a compelling reason for the development of hydrogen as a transportation fuel, which the President has taken steps to create in the FreedomFUEL program with significant funding. Hydrogen programs, however, need to address significant issues of production, distribution and end-use. With regard to production of hydrogen, it is imperative that clean and economical sources be developed on a large scale. It would take a 30 million tonne/year hydrogen supply to offset one-quarter of our gasoline usage in 2025. This translates into a need for well over 200 GW of thermal energy for a 50% efficient water-cracking-based supply, which is a large increase in the number of plants. This is what nuclear may be best at, however, and it was one of the strongest conclusions of the Generation IV Technology Roadmap completed last year.

Faced with the need for offsetting the impacts of growing needs and dependence on foreign sources, the National Energy Policy made several relevant recommendations: One was to expand the nuclear electricity sector in the U.S. above its current 20%. A second was to develop next generation technology, including hydrogen. A third was that the U.S. should reconsider means to close the fuel cycle.

While no single program was created to tackle these objectives, the Advanced Fuel Cycle and Generation IV initiatives are aligning to advance toward them. While these programs do not prescribe the level of needed expansion, there are many opinions about what the objectives should be. A study group of six national laboratories is considering this issue for their respective directors, and is posing the scenario in the next slide.

In this figure, we can see the current fleet of 100 power plants running to about 2030 and then retiring. If near-term deployment of nuclear is very successful, the new ALWRs could significantly replace and even expand the fleet. Advances brought out by Generation IV - with sufficient competitiveness - may be deployable in the 2025 time frame and bring another ramp up in capacity. In addition, competitive nuclear hydrogen may be developed. This scenario offers a very optimistic 50% of U.S. energy from nuclear by 2050. Yet, even scenarios with much lower nuclear growth would lead to significant increase in nuclear waste, and we need to be ready with solutions to match.

To set the stage for advanced fuel cycles, we have a figure showing the constituents of spent nuclear fuel. The diagram shows isotopic fractions. Most of spent nuclear fuel - almost 97% - is uranium and plutonium, which can be usefully recycled into new fuel. Other important, but small, fractions are the short-lived fission products that produce most of the heat, as well as the long-lived fission products and minor actinides that contain most of the radiotoxicity. For completeness, the masses of selected species and assumptions are also listed on the right.

The AFCI derives several of its goals from opportunity presented by better managing these fractions separately. The goals are shown here: AFCI wants to recover the energy value and reduce the cost of geologic disposal, reduce civilian plutonium, reduce the radiotoxicity of high-level waste bound for disposal, and make optimal use of the limited repository space available in the future. The AFCI Report to Congress was just issued two weeks ago, and it can be found at the web site shown on the slide.

There are many options for advanced fuel cycles, and the next few slides begins to lay them out. On the left is our once-through fuel cycle with all of the high-level waste constituents directly disposed to the repository. In Europe and Japan, conventional reprocessing is used to recover the large fraction of uranium and plutonium that is refabricated into mixed oxide fuel for their current generation reactors. We will return to this slide with more options in a moment.

First, let’s examine the current situation in the U.S. Yucca Mountain has a legislated capacity of 63,000 metric tonnes of civilian high level waste. At the current rate of production with the existing fleet of reactors, we’ll exceed that capacity around the year 2015. Of course, it’s felt that the technical capacity is about double this amount, which would delay the time at which we reach capacity by a decade or more. The treatment of spent nuclear fuel would reduce the cumulative buildup, and various options for storage, recycling and/or transmutation of the components could greatly reduce the technical need for a second repository. To reverse the accumulation of spent nuclear fuel, one would need the capacity to treat about 2,000 metric tonnes per year—which is somewhat larger than the capacity of the LaHague plant in France.

Here we return to our options slide and show the first of two major technology developments - these are so-called series - in the AFCI. Series One aims at the development of advanced proliferation-resistant separations technology for recycle in the current and near-term fleet of LWRs and ALWRs. While not specified at this point, the recycle stream would likely contain one or more actinides that increase the self-protection of the fuel. The benefit is that less is sent to the repository and more energy is derived from the same fuel.

I should note here that still other options exist for the current fleet. For example, the development of higher burnup fuels, or fuels with a higher conversion ratio may have significant benefits.

Another important constituent to deal with is the set of radionuclides with long half-lives and more mobility, such as I-129, Tc-99 and Np-237. The radiotoxicity of these long-lived fission products and minor actinides have an important bearing on long-term repository performance. In a fast neutron spectrum, these nuclides can be transmuted to reduce their radiotoxicity by two to three orders of magnitude with time. This has the benefit of reducing the long-term repository performance requirements. Again though, the specifics have many options that require development.

Here we return to our options slide to show the second of two major technology developments in the AFCI. Series Two aims at the development of technologies for fast-spectrum transmutation. These include a fast spectrum reactor and possibly and accelerator-driven system. This in turn requires new fuels, separations, and supporting technology. The interrelations of the various parts is too complex to show on this figure. I’ll expand and show the various parts in the next slide.

We will build up the view of Series One and Two in this slide and the next. First we begin on the left with the flows in Series One. You can see the separation and recycle of uranium and plutonium with one or more other constituents. The separated uranium has been demonstrated recently under the AFCI to be low-level waste, and may allow it to be set aside in engineered storage. The remainder goes to the repository. One disadvantage of this scheme is that the waste stream still contains the full heat load and most of the radiotoxicity as the present day stream. That is the reason for going on to Series Two in the future.

Series Two complements the existing fleet of thermal reactors with a second branch shown on the right that is based on fast-spectrum transmutation in reactors. Note that there is now more being recycled from the first branch, especially the minor actinides and possibly even special targets containing long-lived fission products. The right branch depends on our ability to bring an appropriate fast reactor along in the Generation IV program, and there are several candidates I’ll mention later in the talk. Again, I have quite a few constituents labeled and this raises many options to be evaluated in light of their requirements on fuel fabrication and performance, separations performance, and their overall cost, safety and proliferation resistance. You can see the option for an accelerator-driven system on the lower right. There is also indication on the left branch of complementing the existing LWRs with Generation IV thermal reactors for things like hydrogen production or very economical electricity. Finally, note that the repository might be divided into optional hot and cool zones, with the potential for managing the heat load of the short-lived fission products more effectively.

I’ve mentioned Generation IV several times, and have a few slides to summarize it. The preparation of a technology roadmap for next generation systems took two years and was completed last November. The roadmap develops the research and development necessary for six most promising systems. The six were chosen based on their ability to advance in four major goal areas of sustainability, economics, safety and reliability, and proliferation resistance and physical protection.

The participants in the roadmap came from ten countries known collectively as the Generation IV International Forum. The forum began meeting in January 2000, and is chartered to work collaboratively on R&D for the systems that they are interested in. The representatives are typically heads of their respective government organizations for nuclear energy development. They meet several times a year, and are currently engaged on planning for collaborative research, now that the roadmap is done.

I’ll briefly show three of the six systems which are potentially of most interest for the United States. They include a very-high-temperature reactor shown in this figure. The 1000 ?C helium outlet temperature enables water-splitting with high efficiency. The objective is to provide a system without carbon emission, and which is competitive with other hydrogen sources. Its development challenges include design for passive safety, the intermediate heat exchanger and a cost-effective thermochemical cycle.

The gas-cooled fast reactor is one of three fast-spectrum systems in Generation IV. The others include a sodium-cooled and lead- or lead-alloy-cooled reactors. The GFR’s development challenges include design for passive safety, successful fuel development and recycling process technology.

The lead- or lead-alloy-cooled fast reactor uses the relatively inert and high-boiling point of lead or lead/bismuth eutectic for improved safety. Like the gas fast reactor, the lead fast reactor should offer good capability for actinide management. Its development challenges include corrosion-resistant materials, and materials to meet the higher temperature range, and the development of a supercritical-carbon-dioxide energy conversion cycle.

In summary, I’ve shown several alternatives to direct disposal in the United States. The need for developing an advanced fuel cycle is based on the need to expand the use of nuclear energy in the U.S. in order to reduce our greenhouse gas emissions, and our reliance on foreign oil. The current fleet of nuclear reactors will begin to approach the capacity of Yucca Mountain within a few decades, and any expansion of nuclear energy must address the issue of waste management with technology that better fits the optimal use of limited repository space in the future.

There are two programs of the DOE Office of Nuclear Energy that I’ve focused on: The AFCI addresses transmutation in both thermal and fast-spectrum systems. Generation IV addresses the development of those future systems. While I’ve focused on U.S. perspectives almost exclusively, it’s important to note that international leadership in commercial nuclear fuel cycle technology will be a critical success factor in maintaining the proliferation-resistance and safety of the new technologies. I also want to emphasize that these programs are not intended to replace Yucca Mountain. Rather, they seek to increase its usefulness and delay the need for a second repository.

Finally, I hope that the many options and challenges for advanced fuel cycle technology development have been highlighted in this talk. This will clearly be a long-term effort with many alternatives that need to be explored.