by: Michael Hoexter
Nuclear power cannot be classified as renewable, but I wanted to discuss this hot topic within the context of the series on the (renewable) electron economy.
In the course of writing the series, I re-named the central concept “renewable electron economy” from simply the “electron economy” adopted from Ulf Bossel’s work as I have wanted to push to the forefront the importance of renewable over non-renewable energy sources in the increasingly heated debates about clean energy. Still, not to address nuclear power in the discussion surrounding climate change and electricity would be a serious oversight so here goes…
Nuclear power technology
Nuclear power refers to technologies that split or fuse atoms thereby tapping into the energy that holds together the nuclei of atoms. Most observable processes on the surface of the earth, including biological ones, are manifestations of the force of gravity and the electromagnetic force that governs the interactions of the small wave-like particles, electrons and photons, to each other and to the bigger particles called hadrons (protons and neutrons) that make up the nucleus of the atom. The “strong force” that keeps the particles of the nucleus together contains about 137x the energy of the electromagnetic force per unit mass.
Nuclear fission (splitting atoms) works as a net energy positive process with the most massive atoms, usually special isotopes (same element different number of neutrons and therefore different atomic weight) of uranium and thorium, which are two of the heaviest naturally occurring elements. Fuel for nuclear reactions contains a mixture of uranium isotopes but the most common fissionable one is Uranium 235 (atomic weight of 235: altogether 235 protons and neutrons). When uranium 235 is bombarded with neutrons, some atoms become an unstable U-236 and then the nucleus splits into two smaller atoms releasing energy and neutrons. With enough neutron bombardment and fissionable fuel, a chain reaction occurs.
In nature, U-235 is only 0.7% of all uranium and there have been only a few recorded spontaneously occurring chain reactions on earth’s surface in natural uranium deposits as most uranium is the relatively stable U-238. To generate power, there needs to be the right percentage of U-235 in the uranium which means that the uranium blend needs to be enriched to 3-4% U-235 at least. There are also reactors that can use what is called “highly enriched uranium” which means above 20% U-235 and as much as 90% enriched in some specialized reactors that require a compact fuel load. Weapons grade uranium requires a percentage of 20% U-235 or higher to create the uncontrolled chain reaction that leads to a large explosion. Plutonium, a still more fissionable fuel in certain isotopes including P-239, can be created from uranium in reactors and is used mostly in nuclear weapons. The fissionable materials are usually made into pellets and placed in fuel rods to measure and control the chain reaction.
There are many designs of nuclear reactors depending upon the purpose (electric power, propulsion, uranium and plutonium enrichment), fuel used, how they are cooled, how the reaction is controlled and the physical design of the reactor itself. Most existing reactors in the world are pressurized light water reactors that have been pictured in most news accounts of nuclear energy. In a pressurized light water reactor, the heat of the nuclear fission chain reaction in the reactor’s core is transferred by pressurized water coolant at approximately 315 degrees C (600 degrees F) to a secondary circuit of water that drives turbines generating electricity. The typical large cooling towers vent the steam from the secondary circuit that should contain no unusual radioactivity. Not only does the water in the first circuit function as a heat transfer medium but it also moderates the speed of neutrons emerging from the chain reaction, allowing the chain reaction to continue (higher speed neutrons “miss” their nuclear targets thus not participating in the chain reaction). As the water heats up it expands thereby acting as a brake on the chain reaction in the core; boric acid dissolved in the primary water circuit and control rods are also used to control the chain reaction in the core. Refueling the core usually takes a few weeks, so either the power plant must be shut down entirely or one plant would have multiple cores to maintain continuous operation.
Most nuclear submarines and ships use embedded highly enriched uranium in pressurized light water reactors and require no refueling for the lifetime of the ship. Nuclear reactors on ships and submarines can either generate electricity or drive the ships propulsion system directly via a steam turbine. At the end of the lifetime of the ship, the reactor is taken apart and de-fueled. All large naval submarines use nuclear propulsion as do a class of large Russian icebreakers.
Fast Breeder reactors
Fast breeder reactors are an unusual and much more expensive type of reactor that uses fast neutrons rather than the slower thermal neutrons to sustain a chain reaction. Breeder reactors “breed” their own fuel after being initially stoked with plutonium or another highly refined, highly fissionable fuel. Once the chain reaction has started in a breeder reactor, naturally occurring fissionable fuels like natural isotopes of uranium or, theoretically, thorium, can be “bred” via the chain reaction into fissionable fuel via the neutral bombardment from the reactor’s core. Thus a breeder will be converting the much more plentiful U-238 in a fuel along with other uranium isotopes and transuranic (heavier than uranium) elements so this increases the fuel supply for nuclear power.
Breeder reactors are also proposed as part of a process of fuel reprocessing which would reduce the amount of waste by 90% and its radioactive half-life. Fuel reprocessing can extract highly radioactive transuranic elements (like plutonium) from the surrounding uranium that should theoretically be used to refuel the breeder reactor. Security issues surrounding these extra heavy elements that can be used for nuclear weapons have slowed the development of breeder reactors and the fuel reprocessing cycle in all but a few locations (France, England, Russia, Japan, India). A 2003 MIT study concludes that the traditional once-through nuclear fuel cycle is preferable to a strategy of breeder reactors and fuel reprocessing due to the unproven designs and nature of breeder reactors as well as the security risks.
Pebble bed reactors
A new type of reactor that is considered the most modern design is the pebble bed reactor that puts uranium dioxide fuel coated in a number of chemical layers into a round graphite (pebble) shell. Pebble bed reactors are supposed not to be able to meltdown because the reaction they start slows when temperature rises in the core. They also use the heat of the reaction more efficiently by using helium gas as both the coolant and the propellant of the generator’s turbines. Helium is supposed to remain relatively inert under neutron bombardment so it is supposed to be less dangerous as a waste or if accidentally emitted to the atmosphere. The construction costs and size of a pebble bed reactor are theoretically less because most of the bulk of water cooled reactors is in the primary cooling system, secondary water circuit and cooling towers as well as the high pressure piping for water. Also pebble bed reactors can be constructed in modules so plant size can be scaled up with demand. China now has one pebble bed reactor in prototype and is planning to put one online in the next decade despite the current higher costs of these still experimental reactors.
Critics of nuclear energy and the pebble bed design point out that the use of graphite represents a fire hazard similar to that experienced at Chernobyl where graphite control rods caught fire. Also pebble bed reactors will produce a higher volume of somewhat less radioactive nuclear waste that is also difficult to reprocess, making it less of a security risk but also more of a liability for waste repositories.
Emissions, radiation, nuclear fuel and nuclear waste
Nuclear power plants do not emit under normal operation any carbon dioxide or the other typical chemical pollutants associated with combustion driven electricity generation (NOx, SOx, particulate matter, dioxin, mercury). As the plants are major construction projects that use a lot of concrete and fuel to produce, they do have a substantial carbon debt but during normal operation do not add to greenhouse gas concentrations in the atmosphere.
Outside of major accidents that expose the core or inner coolant loop, well-designed and well-run nuclear power plants are not supposed to emit radioactivity into the environment. On the other hand, major accidents or potential attacks on nuclear facilities can endanger and make toxic large areas as has been witnessed with the Chernobyl accident. The breaching of the protective barriers around the radioactive parts of modern reactors is difficult but not impossible or unthinkable.
In normal operation and without fuel reprocessing, nuclear fission produces the following radioactive elements that must be stored safely for decades, centuries or millenia: uranium 238 +235 (95%), plutonium 239 + 240, cesium 137, strontium 90, iodine 129, technetium 99 and americium 241 (as well as some other heavier transuranic elements). These elements are all highly toxic to biological systems and in combination radiate alpha, beta, gamma and neutron radiation in higher than background doses. Iodine, cesium and strontium are readily absorbed by biological systems; one danger of over-exposure to the products of fission is thyroid cancer where higher doses of iodine 129 have been absorbed.
If we assume normal operation for the nuclear fuel and power generation cycle, the major environmental and social risks are the disposal of nuclear waste and security of nuclear fuel and waste. To date, no country that uses nuclear power has created a satisfactory system by which to dispose of nuclear waste. Current efforts in the US to restart the nuclear industry have been hampered in the permitting stage by the lack of a clear destination for spent fuel in a deep geological repository where the fuel can over a period of thousands of years return to acceptable levels of radioactivity. Local and national political opposition has repeatedly stalled the creation of the Yucca mountain repository in Nevada. In Germany, the Gorleben repository has for over 20 years been the focus of the anti-nuclear movement there.
Fuel reprocessing extracts many of the radioactive elements (plutonium and other transuranics, Uranium 235) with long half-life (thousands of years) from spent fuel and re-uses them in a fast breeder reactor as fuel, reducing the bulk and amount of nuclear waste by 90%. Other than its high expense, one of the negative aspects of fuel reprocessing is that it purifies weapons grade fuels like plutonium that can be diverted to use as weapons rather than as fuel for the breeder reactor.
Nuclear security risks
Nuclear energy requires a high level of security for both nuclear power plants and the nuclear fuel cycle. Nuclear fuels and wastes can be used with conventional explosives as a “dirty bomb” as these lower level radioactive elements can contaminate an area for years. The uranium enrichment processes for nuclear fuel can be used as well to further enrich uranium and transuranic elements to create weapons grade materials. Many of the international political arguments surrounding nuclear programs in countries like Saddam’s Iraq, Iran and North Korea as well as in other areas of the world have to do with the option that nations have to create weapons with ostensibly “peaceful” nuclear power programs. Fuel reprocessing and breeder reactors, which reduce waste volume and radioactivity, also add substantial security risk as they increase the amount of highly enriched uranium and plutonium available at more locations throughout the world.
Nuclear power plants are always targets for hostile attack and must maintain a very high level of security. Containment buildings are supposed to be able to resist conventional missile or airplane attack. Ingress and egress should be highly controlled. Employees and visitors should be subject to security checks.
Nuclear power, the anti-nuclear, and environmental movements
Nuclear power has been controversial throughout its history starting with its genesis in the “Atoms for Peace” program of the 1950’s. It has been difficult to view nuclear power as a source of electric power separately from its potential to create destructive weapons, alter geopolitics and threaten human survival. Both critics of nuclear energy and leaders of the traditional nuclear powers are in agreement that proliferation of nuclear power programs throughout the world is a bad thing. The origin of nuclear power as an assertion of political and military might has never been fully divorced from the proposition that atomic nuclei are one more source of energy for peaceful use. Despite the end of the Cold War, nuclear power and nuclear weapons are still risk factors with any increased conflict or competition between nation states that either have or are developing a nuclear power program. It bears restating that nuclear power and by extension nuclear weapons are technologies that transform states and statecraft for both participating and bystander states.
With the revival of the environmental movement in the developed world starting the late 1960’s, nuclear power’s radioactive waste and the environmental risk of plant failure became an object of criticism. The anti-nuclear power movement in most Western countries with the exception of France, was strengthened by opposition to the Cold War geopolitical competition between nuclear-weapons states as well as the perception that cleaner alternatives (solar and wind) as well as a more balanced and perhaps simpler, less energy-intensive lifestyle (hippie/alternative movements) were possible. The partial meltdown of the core of the Three Mile Island nuclear plant in Pennsylvania in 1979 happened to coincide with the release of the “China Syndrome” a Hollywood thriller starring Jane Fonda about a near nuclear meltdown. No one was harmed in the TMI accident and radiation was not released into the atmosphere. However, the combination of the events in combination with a growing anti-nuclear power movement helped to reinforce the perception of nuclear power as technology run amok. A few years earlier, the unexplained death of nuclear whistleblower Karen Silkwood also played into perceptions that all was not right at nuclear plants.
The strength and durability of the German anti-nuclear power movement fed the growth of green institutions including the Green Party that are forerunners of the current Europe-wide interest in sustainable products and energy solutions. In Germany, the anti-nuclear weapons movement also spurred opposition in the 1970’s and 1980’s to nuclear plants, as Germany was particularly vulnerable to geopolitical shifts between NATO and the Warsaw Pact nations. In addition, nuclear power as an institution went against the older “nature-romantic” movement in Germany as well as newer anti-authoritarian trends in Germany society after 1968.
The Chernobyl disaster in 1986, which killed 56 people directly from radioactivity and led to the resettlement of 336,000 people helped further damage the reputation and viability of nuclear power, confirming perceptions worldwide that nuclear power was an inherently dangerous technology. While nuclear advocates took pains to make distinctions between the quality of the Chernobyl reactors and other designs and operating procedures, the international popularity of nuclear power as a solution to the energy crisis sunk to all time lows.
Nuclear power…climate saver?
Nuclear power plants have continued to operate since Chernobyl but few new plants have been commissioned or brought online in the developed world until recently. The “twist” in the nuclear story comes as concern about climate change from carbon emissions has come to outstrip other environmental issues in the last 10 years. James Lovelock, the progenitor of the Gaia hypothesis, came out in 2004 as an advocate of nuclear energy saying that “nuclear is the only green solution” to the climate crisis. There is an international, France-based group called Environmentalists for Nuclear Energy that Lovelock now supports. Lovelock’s and EFN’s contention is that only nuclear power has the track record and power output sufficient to substitute for fossil fuels. Renewable energy is dismissed in his now famous 2004 article as experimental and inadequate for meeting demand for power.
A serious look at analyses of nuclear power yields a somewhat less optimistic picture of nuclear’s potential contribution to the fight against climate change. Most critical is the projected supply of uranium fuel that under current use levels where nuclear power accounts for around 6.5% of total world energy use will last 70 years if military stocks of uranium are used for fuel. If an aggressive campaign of replacing the much larger portions of fossil energy by building many nuclear power plants, increasing the contribution of nuclear by 6 fold (cutting fossil energy use by one-third) would shorten the lifespan of current supplies considerably even with technological improvements in nuclear technology. Assuming a boost in thermal efficiency of reactors by 15% with new designs such as the pebble bed and bringing in fast breeder reactors that can use a wider variety of fuels and recycle fuel from other reactors, uranium supplies would still last less than 50 years with such an aggressive 6-fold increase in nuclear power generation. The introduction of fast breeder reactors and widespread fuel reprocessing also increases geopolitical risk. Nuclear advocates complain that assessments of uranium stocks are out of date and that increased supplies will be found with higher uranium prices.
An additional strike against an aggressive program of nuclear plant construction are the construction lead times and upfront capital costs associated with new nuclear plants. A 2005 estimate puts the cost of a 1.4 GW plant in the US at $2.6 billion. Nuclear plants take 4 to 6 years to build and with an increasing number of private holding companies responsible for electricity supply distinct from the utility that distributes power to customers, the long lead times yields unacceptable interest expenses accumulated before the plant comes online. Regulatory hurdles can also delay the construction of nuclear plants. Lawmakers in the US have attempted to make the construction of nuclear plants more favorable with production tax credits modeled after the PTC for wind and biomass energy, expedited permitting, as well as government paying for cost overruns due to regulatory delays. In 2006, the US government estimates that lifetime costs for nuclear per megawatt-hour ($59) are higher than wind ($56), natural gas ($52.5) and coal ($53) without a carbon emissions price.
Untested technologies like fast breeders or pebble bed reactors will need longer lead-in times and closer regulatory scrutiny as they present either additional safety concerns and/or security risk. Exporting nuclear technologies outside existing nuclear powers also contains substantial political risk.
With carbon pricing of some sort almost inevitable, the economics of nuclear relative to fossil fuels will improve but will remain the same in relationship to renewables like wind and solar.
Does it make sense to rely on nuclear as one of or even THE solution to the climate crisis? Advocates claim for nuclear the role of a buffer between the era of fossil fuels and the era of renewable energy. Given the above risks, the long wait for electricity production from a new nuclear installation, and the projected short duration (a number of decades) of the new nuclear era, the choice of nuclear would seem to be unnecessarily shortsighted. By contrast, most renewable energy projects with current technologies can be implemented within a year or two; wind and solar thermal can be scaled to large size quite rapidly.
If regulators, energy companies, and managers of electric grids insist upon building new nuclear plants, we should all be realistic about the limits of these efforts as well as the environmental and opportunity costs of focusing on nuclear as a leading response to energy demand and climate change rather than renewable solutions.
Nuclear Power and Technological Optimism
Opponents of nuclear power have employed many arguments against nukes, geopolitical, environmental and philosophical. A pivotal implicit and occasionally explicit argument against nukes that I never found convincing was a technological pessimism, the idea that at some point technology reaches a level of complexity beyond which it is unmanageable or anti-democratic. These arguments have always seemed to me to be poorly constructed, without a clearly demarcated line or evaluation criteria for judging whether a technology will be successful or at least acceptable on operational, economic, ecological or social levels. There are so many different arguments to made against nuclear power (and some for it) that this argument has had the quality of being “heaped on” and has awoken the suspicion that what is being expressed sometimes is simply an aesthetic rejection of the technology or polemical exaggeration.
I don’t think nuclear power breaches some Promethean limit in our ability to construct complex systems nor is it beyond our capacity to substantially improve the current nuclear technology. On the other hand, using nuclear power to generate domestic or industrial electricity is a questionable application of the technology in either its current or some improved form. While estimates vary, the supply of uranium and other fissionable elements is limited; shouldn’t we save this potential energy supply for tasks for which there are no ready alternatives? Think of a future use to power an interplanetary space vehicle or the even the current uses to power icebreakers or submarines; the energy density of nuclear fuel is a necessity in these applications. Should we run through our best supplies of fissionable fuels to power toasters when we already have carbon-free alternatives?
Technological optimists might say that by then we will have learned to control nuclear fusion. To my knowledge, we don’t yet have a believable timeline for the development of controlled fusion and it is therefore foolish to plan on running through a limited resource (uranium etc.) in anticipation of having a future technology to tap into an essentially unlimited one (hydrogen as fuel for nuclear fusion).
The unacceptable degree of complexity and uncertainty in the use of nuclear technology for domestic power comes largely in the form of the political and security issues raised by both ordinary “thermal” and breeder technologies. The introduction of more weapons grade nuclear materials into the world is an unacceptable risk and remains a largely insoluble problem if nuclear power is scaled to a level that will reduce climate risk.
Given the more fitting present and future applications for nuclear technology, there is room for growth in research and development in nuclear, even if mass production of nuclear power is not a sustainable activity. Furthermore, the challenge of developing and refining renewables in ways that satisfy our need for energy is still wide open. A grid that reliably runs on renewables through fluctuations in weather will require a great deal of engineering and scientific talent and will be a technological feat of great complexity. Renewable energy generation technologies, maybe not as interesting to some physicists and nuclear engineers as nuclear fission, will actually be some of the most rewarding engineering and scientific challenges of the next decades. So I believe there is yet room for a focused technological optimism in a resource- and carbon-constrained world.