Section 7.4.4- Pyroprocessing and the Integral Fast Reactor Model (See also 7.4.8- Advanced Liquid Metal Reactor) overview/history/goals

In the 1980s and 1990s, researchers at Argonnes National Labs (ANL) facilities (in Chicago and in Idaho) developed a wide range of new fuel cycle technologies to help America "close the fuel cycle" and solve our spent fuel dilemma. This effort was focused on the development in two areas:1. One focus was on development of a new generation of fast-neutron metal cooled reactors, called the Advanced Liquid Metal Reactor (ALMR). 2. The other focus was a fundamentally different (non-aqueous) method to reprocess spent fuel (i.e. Pyrometallurgical Processing or Pyroprocessing).

Argonne researchers developed an integrated approach with these technologies that they called the Integral Fast Reactor (or IFR). 1

Current Challenges

By the late 1980s, the problems presented by our current "Once Through Fuel Cycle" were apparent to ANL's team:

1. A number of developed nations have a large and rapidly growing volume of spent nuclear fuel, which under present policies will require that we develop several large and expensive national geologic repositories for all of it. This entire volume of spent fuel contains extremely long-lived and powerfully radioactive transuranic isotopes, which require isolation and control for a very long time (10,000 years minimum). The extreme heat produced by these transuranic isotopes also places severe constraints on the storage capacity of any geologic repository we might choose to deploy.

2. Only 10% of the milled uranium is incorporated into fresh nuclear fuel, and only 5% of that fresh fuel is consumed by our Once Through Fuel Cycle. Hence, less than one percent of the milled uranium's fissionable energy content is used to generate power.

3. The world is running out of cheap nuclear fuel. Although we presently are not constrained by this problem, because we are using up sources from recycled weapons, we can expect to run into difficulties based on the expected growth in nuclear power plant construction and ongoing demand. ANL researchers recognized a critical need to be better stewards of this critically important resource.

4. The most widely familiar alternative, the aqueous PUREX reprocessing method, is very expensive and has a limited impact on the most intractable fuel cycle problems. One particularly thorny class of problems relates to the buildup of troublesome gamma-emitting and neutron-absorbing uranium isotopes in PUREX-recycled fuel. (Refer to Section 7.5.5)

Potential of Pyroprocessing

In the course of their basic research, ANL researchers thought they recognized an opportunity (in the composition of spent nuclear fuel) to solve the worst of the problems with the Once Through fuel cycle and other alternatives.

Spent nuclear fuel consists almost entirely of unconsumed U-238 (~ 95% by weight), which is only mildly radioactive. Spent fuel's next largest component consists of Fission Products, which is dominated by Strontium-90 and Cesium-137. The radiation emitted by this component decays by a factor of 1000 within 300 years. The most troublesome component of all is the smallest proportion by weight i.e. the TransUranic elements (or TRUs), which include plutonium, neptunium, americium, and curium. These elements produce the greatest proportion of the emitted heat and radiation, and they represent the greatest long-term threat, owing to their incredibly long half-lives. 1

The ANL team realized that it is practical to reprocess spent nuclear fuel to do the following:- completely separate most of the unburned (U-238) metal- separate the remainder of the U-238 with almost all of the TRU components (including almost all of the plutonium) into a new metal fuel (U-TRU) that is so thermally and radioactively hot as to be completely unsuitable for building nuclear weapons- separate and immobilize the fission products (FP) via ion exchange into zeolite columns that become a stable fused ceramic waste called sodalite1

By doing this kind of separation reprocessing, they realized that it ought to be possible to:- immediately reduce the waste stream mass (by almost 90%) by separating out the U-238 - route the longest-lived and most environmentally noxious portions of the waste stream (U-TRU) back into "new" nuclear fuel without generating pure plutonium and its attendant nuclear weapons proliferation risk- burn the U-TRU fuel very efficiently in fast neutron reactors like the ALMR- ultimately reduce (the overall mass of) the spent nuclear fuel waste stream by >97%, such that it consists almost solely of fission products captured in sodalite with a hazardous lifetime of less than 300 years- (optionally) route the recycled U-238 into fast neutron reactor like the ALMR to breed plutonium, which can be pyroprocessed later into U-TRU and burned in an ALMR 1

Pyroprocessing Flow

The Integral Fast Reactor Model can be implemented with a number of minor and major variations. As envisioned by ANL researchers, the Model is most efficiently and safely implemented with reactors that are metal cooled (typically with liquid sodium) and which use metal fuel (i.e. not UO2 ceramic). The Reduction step described below only applies to processing of oxide (i.e. not metal) fuel.

Pyroprocessing includes the following steps

F. Fuel decladding and voloxidation

Fuel cladding is removed, and volatile fission product gases are captured and decayed off in isolation.

R. Reduction of UO2 (in spent fuel) to metallic uranium (only required for spent UO2 fuel)

Figure 14

ER. This step represents the critical breakthrough in pyroprocessing.

The chopped fuel (either metal fuel or reduced oxide fuel) is dissolved in an anode basket in molten salt (typically LiCl-KCl) at 500 degrees celsius. A very strong current is passed through the mixture and the desired nuclides plate out on the cathode. Two cathodes are generally used, a solid cathode (to extract pure uranium) and a submerged crucible cathode--filled with liquid cadmium (to extract U-TRU).

CP. Cathode Processing

The liquid cadmium cathode is processed at this step to remove the residual salts and cadmium from the U-TRU mixture. The U-238 on the solid cathode is scraped and either stored or incorporated into U-TRU fuel as desired.

RERF

IC. Injection Casting

The U-TRU from the liquid cadmium cathode is injection casted (with or without U-238 from the solid cathode) to create new metal fuel rods for use in the ALMR.

Figure 2 (below) depicts a "bigger picture" of the overall pyroprocessing cycle (without the oxide fuel reduction steps).

Figure 2

Note about Step ER: The fission products and a very small remnant of the TRUs remain in the molten salt electrolyte bath. When the salt becomes saturated with fission products, it is run through a zeolite column to capture and immobilize the fission products, and the salt is recycled back into the electrorefining process. The zeolite column is vitrified to permanently capture the fission products, where they will decay to near background levels in about 300 years.

Global Outlook for Pyroprocessing

ANL researchers concluded that pyroprocessing technology, in tandem with the use of fast spectrum nuclear reactors had the potential to achieve all of the following objectives:- provide a permanent long-term solution to our spent fuel problem- avoid potential nuclear weapons proliferation risk associated with methods that extract pure plutonium from waste (like the PUREX method)- transform our nuclear waste stockpile into a new source of carbon-free electrical power (comparable in scale to all fossil energy sources combined)2

ANL's work on these technologies inspired new research by scientists all over the world, especially in Russia, Japan, and more recently in Korea. The Korean Atomic Energy Research Institute (KAERI) has undertaken a very ambitious research effort to develop commercial scale pyroprocessing technologies (see Section 7.7.1).

Section 7.4.8- Advanced Liquid Metal Reactor and the IFR Model

Fast Reactors are TRU Burners

As early as the 1950s, ANL researchers have explored the potential for the use of fast neutron flux reactors (i.e. fast reactors) to pursue applications (like the IFR) which are not possible with thermal neutron flux reactors. Particularly noteworthy was the construction and operation of ANL's Experimental Breeder Reactor II (or EBR II) in Idaho, which operated safely and successfully for decades.

Fast reactors can extract more energy from nuclear fuel than thermal reactors because their high energy neutrons cause fissions more efficiently than thermal neutrons. This is due to the fact that a large portion of thermal neutrons are absorbed in non-fission reactions. Fast neutrons are much more likely to induce the fuel's plentiful U-238 atoms (as well as an substantial fraction of the TransUranic elements) to fission. One important consequence of this is the large difference in waste output between comparable thermal and fast reactors. A 1000 MWe thermal reactor plant produces 100 tons of spent fuel a year, while the annual waste output from a fast reactor (with the same capacity) is little more than a single ton of fission products, plus trace amounts of TRUs1.

Burning recycled uranium in conventional Light Water Reactors has long been a daunting challenge, owing to the buildup of neutron-absorbing "poison" isotopes in recycled uranium. These isotopes make PUREX-processed uranium more difficult to handle than fresh fuel and necessitates the re-enrichment of such uranium to a U-235 fraction that is higher than that required with fresh fuel (see section 7.5.5).

ANL researchers knew that thermal neutron reactors would be far more effective than fast neutron units for realizing the waste-consuming potential of the closed fuel cycle of the IFR Model.

To Breed or Not

One of the potential benefits of fast neutron reactors is the ability to breed new fissile nuclear fuel (typically plutonium). This is typically achieved by creating a "blanket" of unenriched (mostly pure U-238) fuel rods into a fast neutron reactor in such a fashion that the neutron flux can be absorbed by the U-238 to produce Pu-239. Used in combination with pyroprocessing, this creates the potential to produce a seemingly inexhaustible source of useful nuclear fuel2.

This ability to breed new plutonium has given rise to legitimate concerns about the potential that breeder reactor technology could lead to nuclear weapons proliferation, or could lead to illicit traffic in plutonium that could empower terrorist organizations to build a nuclear weapon. This is particularly of concern in countries (like South Korea) that don't have nuclear weapons.

The ALMR

During the 1980s, an ANL research team, headed by Charles Till at ANL's Argonne West lab in Idaho, started the process of implementing the vision of the IFR model by converting the EBR II into the nucleus of the IFR system--the Advanced Liquid Metal Reactor.

The ALMR was designed to use liquid sodium as its primary coolant, which provided several important advantages. Sodium has an extremely low neutron absorption cross-section, which ensures that fast free neutrons are available to cause more fission reactions with TRUs and U-238 atoms. Sodium is an extremely efficient heat conductor, which optimizes the reactor's overall thermal efficiency performance and reduces thermal stresses in the core.

The ALMR's design also demonstrated early breakthroughs in reliability and passive safety features, which were developed and demonstrated with its predecessor system (the EBR II) in 19862. Because liquid sodium metal has a very high boiling temperature, the cooling system can operate at atmospheric pressure, which drastically reduces the probability of leaks that can cause loss of reactor coolant. Sodium does not readily corrode the structural materials used in the reactor. The core sits in a large pool of liquid sodium. In the event that forced flow of the sodium coolant is lost, this provides the core with a large convective removal capability, unlike previous (less successful) fast reactor designs. The reactor is designed to work with metal fuel (i.e. not oxide). In all reactors, there is a Doppler reactivity effect, which causes the reactivity to increase as the temperature rises. Because of metal fuel's superior thermal conductivity, there is only a small temperature gradient along the radius of the fuel pin, so there is much less heat stored in the fuel at any one time.

Cutaway view of the ALMR1

The IFR Model

As envisioned by ANL researchers, pyroprocessing facilities (which are much more compact in scale than PUREX facilities of comparable capacity) would be co-located within the same secure facilities as one or more ALMR units. See the PRISM Advanced Recycling Center in Figure 4 below.

The facility would receive spent fuel from existing light water reactors, then pyroprocess it to generate three material streams (pure U-238, U-TRU fast reactor fuel, and fission product waste

immobilized in sodalite columns). The thermally and radioactively "hot" U-TRU fuel would be "burned" in an ALMR unit to generate power. The ALMR could be run with or without a "blanket" of U-238 fuel rods, enabling it to be run either as a breeder reactor or simply as a pure TRU burner.

Figure 4PRISM Advanced Recycling Center Concept

(courtesy of GE-Hitachi3)

The ALMR program was on track to demonstrate the ability to consume Spent Nuclear Fuel to produce electricity (and the ability of pyroprocessing to complete the closed fuel cycle) when it was shut down by the Clinton administration in 1995. One of the primary reasons given for this decision was the potential for promoting weapons proliferation that was presented by the ability of the ALMR to breed plutonium. The chief technical officers in charge of the program and many other informed participants contend that the Administration never understood the inherently proliferation-resistant nature of pyroprocessing technology.

In 2001, as part of the Department of Energy's Generation IV roadmap, the DOE tasked a 242-person team of scientists from DOE, UC Berkeley, MIT, Stanford, ANL, LLNL, Toshiba, Westinghouse, Duke, EPRI, and other institutions to evaluate nineteen of the best reactor designs on 27 different criteria. The IFR ranked #1 in their study (2002)

Earlier this year (2010), Energy Secretary Chu convened the first meeting of a new blue ribbon panel to explore various options for solving the spent fuel problem. He "urged the blue ribbon panel to consider a full array of options, including fuel reprocessing or construction of so-called fast reactors that burn the waste of conventional reactors”10. 

PRISM

As of this writing, GE-Hitachi Nuclear Energy (GEH) is seeking to partner with the DOE to complete the scale-up and commercial scale deployment of pyroprocessing and fast burner reactor technologies as part of its PRISM (Power Reactor Innovative Small Modular) Advanced Recycling Reactor system.

With funding support from Congress, GEH proposes to undertake a series of projects to demonstrate the potential for these technologies:- Installation of a full-sized PRISM "R&D Platform" (filled with water to simulate sodium) at a U.S. university to improve component and system technology readiness levels. Anticipated benefits of this include reduced overall project risk and shortened time for licensing activities.- Fabrication of a sodium cooled PRISM unit at a U.S. national laboratory (as a user demonstration facility). Purposes of this project would be to further improve component and systems development, and to provide performance data for U.S. policy makers about the cost and potential benefits of a complete closed fuel cycle solution- Operation of a pyroprocessing demonstration of used nuclear fuel at an American lab that is equipped to deal with these kinds of materials (e.g. Idaho National Labs or PNNL's Fuels Materials Examination Facility)

Section 7.7.1- South Korea's Closed Fuel Cycle Effort

The economy of South Korea or Republic of Korea (ROK) has grown at a rapid rate in this first decade of the 21st century. Unfortunately, its carbon emissions have grown just as quickly. Seoul (its largest city) has the second highest carbon emission growth rate in the world. This situation would have been even worse were it not for the ROK's 20 nuclear reactors, which generated more than one-third of the country's electricity in 2008. South Korea's planners want to increase the nuclear component of their domestic electricity generation to 59 percent by 2030. To achieve this, it will need to build 18 more reactors. The ROK has a serious developing problem with spent fuel storage capacity. At the end of 2008, South Korea had 10,083 tons of spent nuclear fuel, and was adding 700 tons per year to that total. If all of their planned reactors are built, that annual growth rate will increase to 1100 tons per year. The country's spent fuel pools, despite their ongoing efforts to expand their capacity, are expected to reach full capacity by 20167.

Like the USA, the ROK has not yet made a confirmed selection of a high-level waste repository site. At the predicted growth rate, the cumulative amount is expected to require an underground repository (with an exclusion zone around the site) as much as 80-square kilometers, an area larger than Manhattan. Given that South Korea is a country about the size of Virginia with six times as many people, dedicating a site that large for this purpose would be extremely difficult and astronomically expensive. This seems like a near certainty, since the ROK had to pay billions of dollars to obtain a 2-square kilometer site for low-level waste in Gyeongju7.

Clearly a more effective and efficient disposal option is needed that reduces the land area required for spent fuel disposal, and which reduces the radiotoxic lifetime of the spent fuel. In December of 2008, the ROK's Atomic Energy issued a long-term research and development plan for a next-generation domestic nuclear system based on the use of pyroprocessing (for spent fuel waste stream separation) and fast reactors operating in "burner mode" to use recycled spent fuel for power generation. Their scientists expect that this approach can enable them to make a future spent fuel repository up to 100 times smaller than would be otherwise necessary by reducing the heat load and radiotoxicity of the final waste stream. The Commission mandated that a demonstration of the technical and economic viability of both technologies be completed by 20287.

One of the most compelling attributes of the proposed approach is its resistance to proliferation. Pyroprocessing does not produce even a small stream of pure plutonium. Instead, it produces a U-TRU alloy which can be directly refabricated into metallic fast reactor fuel without further processing or purification. This material is far too thermally and radioactively hot to use for a weapon.

Unfortunately for Korean planners, their plan faces geopolitical obstacles. The ROK's ability to conduct spent fuel reprocessing is subject to the US-ROK nuclear cooperation agreement, which is set to expire in 2014. The ROK would like the United States to allow for pyroprocessing of spent fuel in any new agreement. The original agreement requires that spent fuel be reprocessed at a facility agreeable to both partners under IAEA supervision and inspections8.

Ever since India's "peaceful" nuclear test in 1974, the United States has sought to prevent the spread of reprocessing technology to prevent nuclear weapons proliferation8. North Korea has already extracted weapons-grade plutonium from a research reactor, and the United States has

previously denied permission for the ROK to reprocess its spent fuel out of fear for a nuclear arms race on the Korean peninsula9.

Japan has been more successful prevailing upon American planners to accept its own efforts to develop pyroprocessing and other spent fuel reprocessing technologies. In the late 1970's, Japan's prime minister asserted that it "was a matter of life or death" for Japan to reprocess spent nuclear fuel to recycle plutonium and thereby to guarantee its energy security. Japan's Central Research Institute of Electric Power Industry (CRIEPI) has conducted a particularly ambitious program of pyroprocessing technology development, including advanced electrorefining technologies for plutonium recovery and high throughput uranium recovery.

KAERI Closed Cycle Research

Like the ANL team that preceded them, researchers at the Korean Atomic Energy Institute (KAERI) are pursuing a dual track effort to develop and implement pyroprocessing and fast reactor technology. Since 2001, KAERI planners have planned and pursued the development of liquid metal reactor technologies, culminating in the development of the KALIMER-600 fast reactor design concept in 2007, as well as the more recent concept design depicted below.

Like their colleagues at ANL, KAERI researchers started with an intrinsically safer sodium metal pool configuration (like the EBR II and the ALMR). Like all sodium metal reactors, their design concept uses two sodium metal cooling loops, a primary cooling loop that cools the core and an Intermediate Heat Transport System that transfers heat from the primary cooling loop to the Steam Generation System. Typical of sodium metal reactors, it boasts a very high thermal efficiency of 39%, (compared to 32% for most thermal reactors).

Figure 5- Kalimer 1200 SFR

KAERI researchers have also pursued significant advances in passive safety and maintainability11.

One research area was the development of an improved safety-grade Primary Decay Heat Removal Circuit (PDRC), which is comprised of two independent intermediate sodium cooling loops. In the event of a design-basis accident scenario (e.g. primary coolant pump shutdown), the PDRC is actuated automatically without operator action or active components. (See Figure 6) below11.

One of the great challenges with sodium cooled reactors is the difficulty involved in inspecting the core and other internal components. Sodium is totally opaque to light and is prone to react vigorously, especially with water. KAERI researchers have investigated the use of ultrasonic waveguides and sensors to perform ultrasonic visualization (See Figure 7) 11.

Figure 6 Figure 7

KAERI is also pursuing an active pyroprocessing development program, based on the same electrorefining approach used by researchers in the U.S. and Japan. Even though their research in this area is a national priority, KAERI researchers must be careful neither to violate the reprocessing restrictions of the ROK's treaties nor to complicate the efforts of the Korean government to negotiate less restrictive terms in future treaties with the United States.

Nevertheless, KAERI researchers have ambitious goals for the future of pyroprocessing. These include the development of highly optimized high capacity batch processing, electrolytic reduction of oxide spent fuel, and state of the art proliferation safeguards technology (in close cooperation with the IAEA). A key milestone in their efforts is KAERI's planned launch of its PyRoprocess Integrated DEmonstration facility (PRIDE) in 2011 (See Figure 8). PRIDE will be an integrated engineering-scale facility for testing the performance of individual unit processes, application of remote control and sensing technologies, and non-proliferation safeguards12.

Figure 8- PRIDE facility planned for launch in 2011

Conclusion

These are exciting and dangerous times in the field of spent nuclear fuel recycling. This technology could contribute either to the survival of this planet (through greenhouse gas reduction) or its destruction (through nuclear weapons proliferation). It remains to be seen whether it will even be deployed at all.

REFERENCES

1. W. Hannum, G. Marsh, G. Stanford, "Smarter Use of Nuclear Waste", Scientific American September 2005, pp 84-91

2. Y. Chang, "Advanced Fast Reactor: A Next-Generation Nuclear Energy Concept", Forum on Physics and Society (American Physical Society), April 2002

3. "GE Hitachi Advanced Recycling Center, Solving the Spent Nuclear Fuel Dilemma"

4. Y. Sakamura, "Development of Pyrochemical Reprocessing for Spent LWR Fuels", CRIEPI, 2007

5. "DOE Comparative Study of 19 Reactor Designs on 27 Criteria", U.S. Department of Energy Roadmap Integration Team Presentation, April 9 2002.

6. K. Uozumi, " High Throughput Electrorefining of Uranium in Pyro-reprocessing", CRIEPI, 2008

7. S. Park, "Why South Korea Needs Pyroprocessing", Bulletin of the Atomic Scientists, October 26, 2009

8. T. Stangerone, "A New Nuclear Issue on the Korean Peninsula: The Rise of Korea's Nuclear Power Industry", www.keia.org, April 1, 2010

9. C. Ferguson, "Controlling Asia's Nuclear Power Tigers", Forbes, 5/4/2010

10. “Temporary Homes for Nuclear Waste Have Lasted Decades”, Wall St. Journal 6/2/10

11. D. Hahn, Y. Kim, C. Lee et al, "Conceptual Design of the Sodium Cooled Fast Reactor KALIMER-600", Nuclear Engineering and Technology, June 2007

12.