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Betting on the wrong horse: Fast reactors and climate change

Nuclear Monitor Issue: 
M.V. Ramana − Program on Science and Global Security at Princeton University

NM815.4516 In the last decade or so, many people who would likely identify themselves as environmentalists have turned to nuclear power as a way to deal with climate change. Among them are James Lovelock, Patrick Moore, James Hansen, and George Monbiot. Of these, Hansen has to be, and in some circles has been, taken most seriously. He is, after all, arguably the scientist who has done the most for raising concerns about climate change. What is also notable about Hansen is that he argues not just for any kind of nuclear power, but one based on a specific kind of a reactor − a fast reactor.

Climate change is such an important threat to our planet that it is quite justified to assess whether nuclear power should be deployed to a much larger extent as a way of reducing carbon dioxide emissions. This article does not − deliberately − address that question in general, but focuses on whether fast reactors could play a significant role in such a strategy. I argue below that because of the multiple problems with such reactors, relying on fast reactors to combat climate change is misguided.

In his book, Storms of my Grandchildren, Hansen explains the details of the reactor and how he came to believe in the potential of this reactor system:

"When asked about nuclear power, I am usually noncommittal, rattling off pros and cons. However, there is an aspect of the nuclear story that deserves much greater public attention. I first learned about it in 2008, when I read an early copy of Prescription for the Planet, by Tom Blees, who had stumbled onto a secret story with enormous ramifications − a story that he delved into by continually badgering some of the top nuclear scientists in the world until he was able to tell it with a clarity that escapes technical experts. I have since dug into the topic a bit more and observed how politicians and others reacted to Blees' information, and the story has begun to make me slightly angry − which is difficult to do, as my basic nature is very placid, even comfortably stolid.

"Today's nuclear power plants are "thermal" reactors, so-called because the neutrons released in the fission of uranium fuel are slowed down by a moderating material. The moderating material used in today's commercial reactors is either normal water ("light water") or "heavy water," which contains a high proportion of deuterium, the isotope of water in which the hydrogen contains an extra neutron. Slow neutrons are better able to split more of the uranium atoms, that is, to keep nuclear reactions going, burning" more of the uranium fuel.

"The nuclear fission releases energy that is used to drive a turbine, creating electricity. It's a nice, simple way to get energy out of uranium. However, there are problems with today's thermal nuclear reactors (most of which are light-water reactors). The main problem is the nuclear waste, which contains both fission fragments and transuranic actinides. The fission fragments, which are chemical elements in the middle of the periodic table, have a half-life of typically thirty years. Transuranic actinides, elements from plutonium to nobelium that are created by absorption of neutrons, pose the main difficulty. These transuranic elements are radioactive materials with a lifetime of about ten thousand years. So we have to babysit the stuff for ten thousand years − what a nuisance that is!

"Along with our having to babysit the nuclear waste, another big problem with thermal reactors is that both light-water and heavy-water reactors extract less than 1 percent of the energy in the original uranium.

"Most of the energy is left in the nuclear waste produced by thermal reactors. (In the case of light-water reactors, most of the energy is left in "depleted-uranium tailings" produced during uranium "enrichment"; heavy-water reactors can burn natural uranium, without enrichment and thus without a pile of depleted-uranium tailings, but they still use less than 1 percent of the uranium's energy.) So nuclear waste is a tremendous waste in more ways than one.

"These nuclear waste problems are the biggest drawback of nuclear power. Unnecessarily so. Nuclear experts at the premier research laboratories have long realized that there is a solution to the waste problems, and the solution can be designed with some very attractive features.

"I am referring to "fast" nuclear reactors. Fast reactors allow the neutrons to move at higher speed. The result in a fast nuclear reactor is that the reactions "burn" not only the uranium fuel but also all of the transuranic actinides − which form the long-lived waste that causes us so much heartburn. Fast reactors can burn about 99 percent of the uranium that is mined, compared with the less than 1 percent extracted by light-water reactors. So fast reactors increase the efficiency of fuel use by a factor of one hundred or more.

"Fast reactors also produce nuclear waste, but in volumes much less than slow (thermal) reactors. More important, the radioactivity becomes inconsequential in a few hundred years, rather than ten thousand years."

All of this description clearly suggests that Hansen thinks of fast reactors as a good, if not perfect, solution. Elsewhere he has expanded on the various other virtues of fast reactors. What Hansen does not talk about, however, are the various problems with fast reactors. And we have about six decades of experience with those problems.

Hansen actually does refer to the long history of fast reactors in his book, saying:

"The concept for fast-reactor technology was defined by Enrico Fermi, one of the greatest physicists of the twentieth century and a principal in the Manhattan Project, and his colleagues at the University of Chicago in the 1940s. By the mid-1960s, the nuclear scientists at Argonne National Laboratory had demonstrated the feasibility of the concept."

The demonstration of the feasibility of fast reactors actually goes back to the early 1950s, with the Experimental Breeder Reactor constructed in Idaho in the United States. The term breeder is significant. It refers to the fact that in some fast reactors, those neutrons that are escaping the core are captured by a blanket made of "fertile materials", which then eventually get transformed into a new element that is itself fissile, i.e. can be used as a fuel in a reactor core. An example of such a fertile material is uranium-238, which gets converted into a fissile isotope of plutonium, plutonium-239. Uranium-238 is the most common isotope of uranium, constituting about 99.3 percent of naturally available uranium. It is this process of conversion of uranium-238 into plutonium-239 that makes a fast reactor utilize uranium much more efficiently.

If the fast reactor is designed suitably, it could produce more fissile material in its blankets than is consumed in its core. It is then said to "breed" plutonium and these reactors are called breeder reactors. The long-standing attraction of breeder reactors for nuclear power proponents is that when nuclear power was first developed, uranium was thought to be scarce and there was widespread concern that global resources would be insufficient to support the anticipated large expansion of nuclear power. This is why the United States started constructing the EBR-I so early into its nuclear power program.

Nuclear meltdowns

Indeed, on December 20, 1951, EBR-I became the world's first electricity-generating nuclear power plant when it produced sufficient electricity to illuminate four 200-watt light bulbs. On June 4, 1953, the U.S. Atomic Energy Commission announced that EBR-I had become the world's first reactor to demonstrate the breeding of plutonium from uranium. About two years later, on November 29, 1955, the reactor had a partial core meltdown, not something that Hansen appears to talk about in any detail.

A decade later, in October 1966, it was the turn of Fermi-1 (yes, named after the famous physicist), a demonstration fast breeder reactor located in Lagoona Beach, Michigan, which suffered a partial core meltdown. What is more interesting is the cause of the accident. Pieces of zirconium from the "core catcher", a safety system that is supposed to prevent molten fuel from liquid sodium into a part of the core, leading to those fuel elements melting down because they could not be cooled. The implication; additional safety features, could, under some circumstances, end up causing accidents in unexpected ways.

These meltdowns also have a different cause that has to do with operating a nuclear reactor using fast neutrons. In fast reactors, when fuel starts melting locally and coming closer together, it increases the rate at which the chain reaction occurs. If this process were not stopped extremely fast − for example, by the insertion of control rods that absorb neutrons − the runaway reaction would cause the pressure inside the core to rise fast enough to lead to an explosion. Again, it was an illustrious physicist, Hans Bethe, who pointed out this possibility back in 1956. Such an explosion could fracture the protective barriers around the core, including the containment building, and release large fractions of the radioactive material in the reactor into the surroundings. This so-called "core disassembly accident" has therefore been a longstanding safety concern with fast reactors.

A second difference between breeder reactors and the more common thermal reactors is their choice of coolant. Because breeder reactors do not have any moderator to slow down neutrons, their cores, where most of the fissions, and thus energy production, occur are smaller in size as compared to thermal reactors. Thus, their power density will be much higher. Efficient transfer of this heat requires the use of liquid metals rather than the more commonly utilized water. The coolant that has been used in all demonstration breeder reactors to date is a liquid metal that melts at relatively low temperatures − sodium.

Though sodium has some safety advantages, it reacts violently with water and burns if exposed to air. This makes fast reactors susceptible to serious fires. Almost all fast reactors constructed around the world have experienced one or more sodium leaks, likely because of chemical interactions between sodium and the stainless steel used in various components of the reactor. Finally, since sodium is opaque, fast reactors are notoriously difficult to maintain and susceptible to long shutdowns.

The question of costs

Having to deal with all these properties and safety concerns naturally drives up the construction costs of fast reactors, to the point that they are significantly more expensive than the more common thermal reactors that Hansen talks about. In addition, they also operate with less reliability. Economically, therefore, fast reactors have proved to be uncompetitive with current generation thermal reactors.

This is the main reason that decades after breeder reactors were piloted, no country has successfully built a commercial breeder reactor. France, the country that is most reliant on nuclear power in the world, did try. The Superphenix started operating in 1986, experienced a series of accidents, and was shut down in 1997. During this period, it generated less then 7% of the electricity of what it could have done at full capacity. Currently, only a few demonstration reactors are being built or operated, the Prototype Fast Breeder Reactor that is being constructed in Kalpakkam in Tamil Nadu being one such reactor. This result is not for want of trying; just the OECD countries, between themselves, have spent about US$50 billion (in 2007 dollars) on breeder reactor research and development and on demonstration breeder reactor projects.

In today's electricity markets, with nuclear power rapidly losing ground to cheaper
renewables, the idea that fast reactors would establish an economically viable path forward for nuclear power is far-fetched, to say the least. Hansen's advocacy of fast reactors therefore seems a little at odds with current economic realities.

What of nuclear waste?

What of the other argument Hansen makes; about the ability of fast reactors to deal with the nuclear waste problem. Here again, what is not mentioned is as important, if not more important, than what is said. First, actinides are not the only long-lived radioactive materials produced in a nuclear reactor. There is also what is called fission products, some of which have a very long radioactive half-life; Technetium-99, for example, has a half-life of 200,000 years.

Second, there are so many actinides and they have a variety of nuclear reactions that are trying to "transmute" (i.e., convert) them into elements that have shorter lifetimes, or even radioactively stable elements, requires an elaborate strategy involving the reprocessing of spent fuel, multiple rounds of special fuel fabrication, and irradiation in fast reactors. In 1996, the U.S. National Academy of Sciences examined the potential benefits of such a scheme and concluded: "none of the dose reductions seems large enough to warrant the expense and additional operational risk of transmutation".

Third, just in the process of doing this transmutation, a large quantity of radioactive materials that are currently held within the spent fuel from nuclear reactors will be released into the biosphere in the form of liquid or gaseous wastes. This is what happens at all reprocessing plants and estimates of the radiation dose to populations around the world from just the gaseous fission products routinely released by reprocessing plants suggest that these exceed the doses from future leakage from geological repositories.

To conclude, James Hansen's advocacy of a nuclear solution to climate change based on fast reactors is misplaced. The six decades of global experience with breeder reactors shows that they are very problematic, much more so than nuclear power in general. So any strategy based on rapid construction of these untested technologies is very likely to suffer from setbacks. There is simply not enough time for us to go down these blind alleys.