Global Warming and Real Solutions - The Radkowsky cycle

From contributor David Doty - an analysis of a potential major energy solution using nuclear fission via thorium.

Probably 95% of scientists who have looked into the issue of Global Warming have, for at least the past several years, accepted the major role of fossil CO2. The clincher, for those final doubting die-hards, appeared in the June 3 issue of Science, "Earth's Energy Imbalance: Confirmation and Implications", by James Hansen et al. This paper is scientifically spellbinding. It is remarkably clear and full of hard data backing up detailed models with amazing agreement. 

One of the conclusions, based on solid data, is that the mean rate of melting of grounded ice (Greenland, alpine glaciers, West Antarctica ice sheet, etc.) over the past decade has been about seven times the crude estimates generally accepted about six years ago.

One of their key points is that if we don't start taking action fairly soon, because of the inertia built in to the power generation industry (i.e., 40 year lifetime of coal power plants) and the 60-year time constant associated with the response of the climate system to changes in atmospheric CO2, we could find our planet headed for abrupt climate change within this century and be unable to avoid catastrophic effects.

What viable options are available? Most informed scientists today agree that advanced biofuels (like cellulosic ethanol and advanced biodiesel processes), wind, and solar are viable options that need greatly increased funding, but it will be very hard to sustain our standard of living without something to take the place of coal to power cities not located near adequate wind resources. Even the most ardent supporters of hot fusion don't expect it to amount to anything for at least fifty years, and many engineers who have really looked at the cost challenges see it as having no more practical promise than space solar power stations, which many place just a notch above cold fusion.

Unfortunately, uranium is also a very limited resource. The price of natural uranium has nearly quadrupled over the past five years. The level of planning and construction on new nuclear power plants (especially in China), along with a decline in uranium mining capacity, make it seem likely its price will quadruple again in the next decade. The latest official estimates are that total global uranium reserves of usable quality are between 5 and 6 million tones, which is sufficient to sustain current nuclear power plants, with a 2% annual growth rate, only through 2045 at best.

However, the age of nuclear energy is not coming to a close. Rather, it is entering a transitional period during which there will be increased development of several, new advanced fission power plant and fuel concepts that promise to greatly extend the nuclear era. The most promising near-term option appears to be the Radkowsky thorium/uranium fuel system. Its advantages include: (1) much more energy available; (2) much more proliferation resistant; (3) easily configured to burn up existing plutonium of all grades; (4) much less waste to store; (5) less toxic waste; (6) more compatible with high burn-up of long-lived waste isotopes.

This is not your grandfather's thorium/uranium cycle. It is significantly different from other designs because it utilizes a structured fuel package design that separates the fissile seed from the fertile material. In its first implementations, it will be a once-through design with no reprocessing, so it is not a "breeder" in the normal sense. Even so, it increases the available fission resource by an order of magnitude, partly because thorium is four times more abundant than uranium.

Radkowsky's idea was to construct special fuel assemblies that could be used in typical water-cooled reactors with very little modification. These units are made up of a central seed region containing fuel rods filled with reactor-grade uranium (that is, having no more than 20 percent uranium-235) and waste plutonium. Surrounding the seed is a blanket region with fuel rods containing thorium and natural uranium. Having quite a bit of uranium-238 in the blanket prevents anyone from withdrawing these rods and using only simple, chemical means to separate out the fissionable uranium-233 that is created over time. In fact, it would be much more difficult to make a weapon from this waste than from raw, natural uranium ore.

The fertile blankets will have a residence time of 9-10 years. There will be a reduction in the volume of radioactive waste of a factor of two and a reduction in plutonium of a factor of 5. Moreover, the plutonium generated can easily be reprocessed for subsequent burn up. Even without reprocessing, it may permit nearly a factor of 10 increase in total nuclear energy available from economic resources compared to what would be available with conventional reactors. Ultimately, more advanced reprocessing would be brought on line which would increase the amount of energy available by another order of magnitude --enough to power our world for a millennium. Much more information is available from the technical references listed here: Research and development is currently being supported at a modest level by DOE at MIT and elsewhere.

Quite a bit of investment and time will be needed to get the Radkowsky fuel processing infrastructure in place, but then the cost should be similar to current nuclear power costs. Hence, there is no long term energy problem, but the solution makes it even more imperative that we quit wasting uranium in current once-through power plants, as enriched uranium is an essential component of the fuel in advanced uranium/thorium high-burnup plant designs --at least after we burn up the more than 200 tons of excess weapons-grade plutonium and the many hundreds of tons of lower-grade plutonium scattered around the world today.

The biggest impediment to moving forward in this country with advanced nuclear options is the political difficulty of dealing with the waste issue. While the once-through Radkowsky cycle reduces the amount of nuclear waste, it will remain a huge issue until we accept advanced reprocessing. The enormous advances in robotics over the past decade will make it much easier to implement more effective reprocessing than was previously possible, and there really is no other responsible option. The 54,000 tons of high-level waste currently piling up at 104 nuclear plants around the country will exceed the 70,000 ton capacity of the proposed Yucca Mountain facility within two decades. An advanced reprocessing facility could begin extracting useful fuel from this waste and greatly reducing the amount of waste left for storage in a long-term repository. Perhaps the easiest way to begin the process would be to begin incorporating high-level waste products into the fertile blankets of advanced Radkowsky plants.

The monumental work on climate change by Hansen et al referred to at the opening of this note shows with remarkable clarity that there is no longer any reasonable scientific doubt on the issue of global warming, and the time left to avert catastrophe is getting short. Perhaps the Hansen paper will serve to stimulate strong growth in funding of viable solutions for energy for the coming centuries.

F. David Doty

Created: 2005-07-02 23:59:13 by Arthur Smith