INTRODUCTION 

We've heard a lot about the greenhouse effect from the media over the past couple of years. Initially these articles focused on the climatic disasters[1] looming on the horizon. Gloom and doom pervaded many of them as the problems posed appeared nearly insurmountable and the questions raised seemed unanswerable.  What if the highly populated "developing" countries suddenly attain success in their efforts to modernize and begin to use energy at the per capita rates we in the "developed" world have become accustomed to? What if coastal regions and the rich deltas are flooded? What if our prairie farm lands are turned into deserts? How could we replace the vast quantities of fossil fuels used to feed our industry and commerce? 

More recently the media has begun to raise doubts about the veracity of scientists and their computer models which predict significant warming of the earth's surface. These authors rudely and rightly point out that no significant rising temperature trend[2] has been measured. The scientists who are studying the issue say its still too early to tell but that we should get on with limiting carbon release to the atmosphere or our actions will be too late to save us. 

We hear about potential alternative energy sources which are alleged to be carbon dioxide free. Water, solar, wind, nuclear fusion and nuclear fission are most often touted. Almost all acknowledge that the world's water power is already highly utilized. Wind and solar power can provide small quantities of energy for special purposes. Modern technology, engineering materials and design can wring a little more energy from the wind and the sun. The quest for nuclear fusion based power has been under way for many years. Scientific feasibility has not yet been demonstrated let alone engineering practicality. Fusion power plants are, at best, many decades away. Climate modellers tell us that the greenhouse warming effect will be clearly identifiable within this decade and alternative energy sources or dramatic reductions in energy use will be needed soon if the warming is to be held off. The only source left for consideration is nuclear fission. 

Nuclear fission has been discarded by some as impractical because of excessive costs[3] and by others because of limited uranium supplies[4] and an inherent inability to develop breeder reactors sufficiently quickly[5] to displace fossil fuels. What do we do in the face of this confusion?  A review of the literature generated by nuclear power visionaries[6],[7] indicates that nuclear fission power can indeed make a significant contribution in a timely response to reduce greenhouse warming.  The world has in hand now a bountiful source of relatively carbon dioxide free energy without the need to rely on dramatic breakthroughs in energy technology.    

THE CONSENSUS GLOBAL GREENHOUSE SCENARIO 

Here is the consensus greenhouse warming situation as summarized by Professor Hare[8], a climatologist from the University of Toronto. 

Global surface atmospheric temperatures will increase between 1.5 and 4.5 degrees C over the next 40 years - based on the equivalent of doubling carbon dioxide in the atmosphere through the introduction of trace gases to the atmosphere. High latitudes will warm the most with warmer winters. Equatorial regions will warm to a lesser degree. Its likely that soil moisture will be less in mid latitudes - which include the chief wheat and corn growing areas. Sea-level may rise between 20 and 140 cm during the warming. 

This picture doesn't seem all that serious to the layman. Nevertheless Professor Hare goes on to state; "I have no doubt that we are discussing the central environmental problem of our times". He and many other climatologists clearly believe this is a very serious problem and that adapting to these changes will pose great hardship. What is really driving their concern? What is all the fuss about? 

THE BASIS FOR THE GREENHOUSE SCENARIO 

Oxygen and nitrogen, the main components of the atmosphere, are transparent to radiation to and from the earth's surface. Water vapor, carbon dioxide and other trace gases in the atmosphere are transparent to energy coming from the sun but absorb reradiated energy from the earth's surface. This heats the atmosphere in a manner somewhat analogous to the heating of your car in the sun - or a greenhouse.

 Figure 1: Greenhouse Gases and Fuel Use 

Carbon dioxide levels in the atmosphere are measurably increasing. Other greenhouse gases are increasing as well and provide a comparable heating effect. Figure 1 shows measurements back to 1870 retrieved from various sources[9],[10].The recent rapid rises correlate with increasing fossil fuel use. Measurements of carbon 14 which is formed in the atmosphere and deposited in tree rings[11] provides definitive evidence that fossil fuels are the major source of atmospheric carbon dioxide. Carbon 14 is not present in fossil fuels which are very old but is present in tree rings which are generally much younger than the 5730 year half life of carbon 14. The tree rings indicate that carbon 14 levels in the atmosphere decreased until 1952 when nuclear bomb tests substantially increased atmospheric levels of carbon 14. The pre bomb dilution of carbon 14 levels establishes little doubt that fossil fuels are the major contributors to atmospheric carbon dioxide.

Figure 2: Global Carbon Cycle Pools and Fluxes

Billions of Tons and Billions of Tons/Year 

A great deal of information on the quantities[12] and flows[13] of carbon from fossil fuels, plants, the atmosphere and the oceans is summarized in Figure 2[14]. Critical points in this article on an alternative to fossil fuels are; a) The atmosphere contains about 700 billion tons of carbon in carbon dioxide. b) About 7 billion tons of carbon as carbon dioxide is released to the atmosphere annually. About 5 billion tons of this is from fossil fuel burning and the remainder is from changing land use (deforestation, farming, etc.). Four billion tons are absorbed by the oceans leaving an additional 3 billion tons to accumulate in the atmosphere each year. c) Recoverable fossil fuels contain 4300 billion + tons of carbon. 

It is apparent from this that fossil fuels are available in sufficient abundance to last about a thousand years at current rates of consumption. The quantity available could well increase atmospheric levels substantially beyond the 25% increase we've observed to date depending on mans rate of use and could increase dramatically if the "developing" majority begins to use fossil energy at the rate of the "developed" minority. 

Predictions of climate change are not as certain as the inexorable rise in carbon dioxide we have observed. Complex computer models are the basis of most predictions. The models include radiative heating effects along with solar heat input variations, atmosphere to ocean energy exchange, atmosphere and ocean circulation, cloud cover effects and other factors. They provide the predictions leading to the summary from Professor Hare.  Stephen Schneider discusses validation of these models in a recent issue of Trends in Computing[15]. He compares model predictions with seasonal variations of climate and with changes occurring following the last ice age.  Schneider goes on to discuss three dimensional models which couple oceanic and atmospheric circulation.  He concludes that they are not only too consumptive of computer time to predict the greenhouse effect of the next century but are also not yet sufficiently trustworthy. Recent modeling efforts with coupled atmosphere - ocean models are tending to predict lower temperature increases than the results which form the consensus[16] presented earlier from Professor Hare. A recent article in Forbes[17] magazine summarizes comments from several authorities on climate who are skeptical that the degree of warming predicted by computer models will actually occur. 

The bottom line is that there is still substantial uncertainty in prediction of climatic warming. Those who believe it will happen think action should be taken now to reduce carbon dioxide emissions. The skeptics believe action should be delayed till we know what will happen or the effect is measured. The believers expect we will feel the greenhouse effect in a decade or two anyway. Certainly a substantial research effort to validate models, refine relevant measurements and identify appropriate action is warranted.  

CAN NUCLEAR ENERGY HELP?  

Predictions of the warming due to the greenhouse effect are fraught with difficulty and uncertainty. The role that nuclear fission can play in reducing carbon dioxide is much easier to define.  

Carbon dioxide from fossil fuel burning contributes about one half of the global warming attributed to mans activities. An additional fraction is due to other gases which are associated with combustion[18] such as nitrous oxides. Nuclear fission can thus directly help reduce warming by serving as a replacement for fossil fuels. This ability could become even more significant if the "developing" countries expand their economic activities in a way which leads to per capita energy consumption approaching that of the "developed" countries. This scenario would lead to vastly increased fossil fuel use and potential for greenhouse warming if alternatives are not adopted. 

The world uses nearly incomprehensible amounts of energy for electricity, heating, transportation and chemical processes. In order to put this into language I can understand I'll talk in terms of numbers of 1000 megawatt nuclear power plants. Data on world generating capacity[19] and the fraction of primary energy used for electricity generation[20] indicates that seventy five hundred 1000 megawatt power plants would be able to replace all this energy. I'm not quibbling over capacity factors or efficiency of various end use applications. This is close to an estimate of 8000 such plants made by others[21] who have based their projection on a population growth projection to 2025 and replacing projected increases in coal use with nuclear power. It is far below an estimate[22] of 100 000 such reactors needed to support 15 billion people at United States energy consumption standards. About 1/3 of world energy consumption is used for electricity production at present. Thus twenty five hundred 1000 megawatt nuclear power plants would replace existing electricity generating capacity. 

We've already built about 600  plants in the short time we've been dabbling in nuclear power. It doesn't take a big stretch of imagination to consider building another 2000 of them to replace current means of electricity production. This would reduce global carbon dioxide emissions about 25% but would not go very far in ameliorating the greenhouse effect on its own.  In fact this would amount to only a 10% to 15% reduction of current greenhouse gas production since it would have little effect on the other greenhouse gases man is responsible for generating. 

Utilizing the energy from another 5000 nuclear plants to displace fossil fuel transportation systems and production processes requires some more effort. Greater use of electricity could help with some transport and production processes.  Hydrogen[23] fuel generation generated by nuclear electricity could be a route to maintaining other aspects of existing systems.  

Could the world afford such a commitment to nuclear power? Seventy five hundred 1000 megawatt plants would cost about $7.5x10¹². The world gross domestic product[24] was $13x10¹² in 1985. These plants thus represent about 6 months of all out collective effort. Hardly a high price to keep us in energy at current rates of consumption when spread over the life of the plants. 

Are there sufficient nuclear fuel reserves to support a massive conversion to nuclear power? Quick calculations based on the fissile uranium recovery and consumption[25] of existing CANDU (CANadian Deuterium Uranium) and LWR's (Light Water Reactor) reveals that seventy five hundred 1000 megawatt plants would use up current uranium reserves of 24 million tonnes[26] in one or two decades. That's not encouraging. However existing reactors use uranium terribly inefficiently so there is a potential to extend the use of these reserves by a factor of about 50[27] through various forms of "breeding" additional fissile material. This would extend the energy content of these existing  "reserves" to last about 500 to 1000 years. This is just about the same as we would expect fossil fuels to last as revealed by the information on reserves and use in Figure 2. 

An extension of the human life style as we know it for another millennia may seem too short for some of us. Again the nuclear industry is holding a trump card. Estimates of uranium reserves given above are based on ores which allow profitable recovery at a selling price[28] of $130 per kg. The current price is at an all time low[29] of $20 per kilogram. This price is worthy of some reflection. Existing reactors consume about 20 to 30 mg of natural uranium per kWh of electricity. This works out to a current market value uranium cost of about 1/20th of a cent per kWh. This is a very tiny fraction of the current electricity selling price of 5 to 15 cents per kWh in Canada and the United States. An increase in the price of uranium to $4000 per kgm would increase the uranium share of electricity cost to about 10 cents per kWh effectively doubling its cost. We would complain of course but we could cope with such an increase easily through more efficient use and perhaps giving up just a little bit in our lifestyle. The incentive to producers to exploit lower grade uranium deposits would greatly expand usable reserves. Studies of deposits[30] indicate that the earth’s crust contains several orders of magnitude more uranium than is counted as a reserve or resource at current prices. This suggests uranium could serve as our sole source of energy for thousands of years even if used in the current wasteful fashion. The sea also contains about 4 billion tonnes of uranium[31] although it is quite dilute. Japan has undertaken a pilot project to recover it and has found that it would cost in excess of ten times current prices[32]. Although this is a bit indefinite it is well below the uranium cost of $4000 per kgm which we estimated would double electricity costs and suggests this source may be practical. Recovery of half of this uranium would thus supply all our current energy needs from existing reactor technology for about 2000 years.  

So far I have primarily talked about fission power systems as we know them now. We've demonstrated nuclear fuel supplies are available for several thousand years for "once through" fuel use as CANDU and LWR reactors are currently operated. Nuclear power still has a hand full of aces. All existing reactors create additional fissile material which can be used to operate reactors. Some reactor designs, called breeders, produce more fissile material than they use. All of the uranium in natural uranium (140 times more than the original fissile content) is thus potential reactor fuel. In addition thorium, which is about 4 times as abundant in the earth's crust, can be used to create fissile material. Experience shows that inherent losses in the conversion process reduce the net gain[33] to about a factor of 50. We can thus expect fission power to serve us with abundant energy for many tens or hundreds of thousands of years. Fifty years of research and development has provided access to this bounty. Workable techniques to extract it are in place. 

HOW WILL IT HAPPEN? 

Thirty years ago the nuclear industry expected[34] to take over a very large role in energy production. Although nuclear energy is producing a significant fraction of the world's electricity its utilization is far below those expectations. The real incentive to adopt wholesale use of nuclear energy will come from planned avoidance of the greenhouse effect and/or a rational decision to exploit fission in the face of diminishing fossil fuel reserves. Simple switching to fission when fossil reserves deplete may not be so simple as a large energy investment is needed to make the transition. Current economic conditions do not provide a great incentive to change our fossil fuel habit. We are however rationale animals and have the power to change the economic conditions we have established almost overnight. We saw a substantial reduction of fossil fuel use in the early 1970's when the price of oil was raised. If we decide the greenhouse effect is happening or going to happen and is harmful to our wellbeing we will change the economics through carbon dioxide taxes or other incentives to reduce fossil fuel use. The new economics will favor the development of alternative energy, particularly nuclear power.      

The implementation of alternative energy will occur with the haste needed as determined by the effectiveness of alternative actions such as more efficient use of energy or some degree of energy deprivation for some of us. It's pretty clear there is room for reduced energy use. We could for example move to substantially more fuel efficient cars and smaller houses with little more consequence than a slight bruising to our egos as we adopt the more fuel efficient and smaller models. Nevertheless these are short term options which will not provide us the energy we need in the long run. Fortunately there are a number of graduated options with nuclear power which can be pursued with the haste warranted by our foresight in energy supply. 

With today's economic conditions nuclear and coal generated power costs are about the same. An increase of fossil fuel costs to account for its expected climatic impact would create a very favorable climate for nuclear power development as fossil fuel costs are already a large part of total electricity cost. As we've already pointed out increasing uranium consumption and price will have little initial effect on energy cost. However low cost supplies are short so the use of fissile material from existing reactors, the implementation of breeders and/or the recovery of low grade ores would need to be implemented fairly soon. Should the greenhouse effect become critical more urgent transition could be required. 

Existing power reactor designs can be used to utilize the energy already available from used fuel stockpiles. (Although there are many designs I will tend to focus my review on the CANDU system. This reactor design occupies a unique niche as its use of heavy water moderator and on-power refueling allows it to extract more energy from nuclear fuel than other reactor designs.) A report published by Atomic Energy of Canada[35] provides considerable insight into economical means of making better use of our uranium resources in a graded manner which could develop with the changing economics we would expect should the greenhouse occur. Detailed studies have shown that CANDU reactors can make use of used fuel from LWR reactors in various ways to extract more energy from existing uranium supplies. The possibilities range from direct use of spent material in CANDU to various schemes involving reprocessing of LWR fuel and mixing of plutonium with the discarded uranium from enrichment plants. These schemes extract half as much again to twice as much energy from a given quantity of uranium as LWR or CANDU reactors operating alone. Recent studies[36] indicate that a rearrangement of the geometry of the fuel and moderator by alternating close and far spaced fuel assemblies in the core has the potential to triple[37] the utilization of natural uranium in CANDU reactors without recycling. The youth of the nuclear power industry suggests fertile ground for considerably more innovations and improvements in reactor development.  

Lecocq and Furukawa[38], in order to avoid the needed large inventory of uranium to operate fast breeder reactors, have pointed out that molten salt reactors based on the breeding of fissile uranium from thorium can generate almost as much fissile material as they use. They propose the development of a fuel cycle based on molten salt reactors to generate energy combined with accelerator breeders to generate the fissile supplies needed for a rapidly growing energy system to combat the greenhouse effect. CANDU reactors are also able to utilize the thorium - uranium[39] recycling mode of operation as "near-breeder" reactors. The CANDU reactor might well be a more practical option as it is in commercial operation now so that development effort could concentrate on the accelerator breeder component of the system. 

A study of an accelerator breeder in conjunction with the CANDU reactor system was completed in 1980[40]. The system works by accelerating and impacting protons into uranium-plutonium or thorium-uranium fuel assemblies. The cost of the device studied was estimated to be about $1.5x10⁹. It was sized to serve as the fissile fuel supplier for 12 000 MWe of CANDU reactors. Again this seems a small price to pay should we need to limit carbon dioxide release to the atmosphere. 

SUMMARY AND CONCLUSIONS 

A review of the case for nuclear power has been undertaken in the light of new evidence and awareness that continued and increasing use of fossil fuel may lead to global warming.  

Nuclear power can provide energy in a manner which contributes very little to the greenhouse warming effect through its proven application to generate electricity which will necessarily play a greater role in our lives in the future. Development and implementation of substantial alternative technological systems will be needed to allow nuclear energy to displace our current dependence on fossil fuels for transportation and production processes. 

The alleged shortage of nuclear fuel supplies has been introduced and the availability of naturally occurring fissile fission fuel supplies has been reviewed. Thanks to the very low cost of fuelling reactors it is shown that very large supplies in low grade ores and seawater can supply energy at an acceptable cost for many centuries. When the economics for reprocessing used fuel become favorable, the production of man made fissile material will allow for the further extension of these supplies to last for many tens of thousands of years at current or even substantially greater rates of global energy consumption. 

The eventual outcome of widespread concerns about future changes in our environment is unknown. We don't really know whether the greenhouse effect will happen as a result of our fossil fuel use. Continued study and observation should soon make the future more apparent. We do know our present reliance on fossil fuels must change quite extensively in the next century as oil stocks are exhausted and in the next millennia as coal is used up. In the meantime its good to know we have a reasonably well tested alternative to fall back on.

REFERENCES