the capital cost per kilowatt of the reactor (including the cost of the salts and fertile material, i.e., of all the necessary working fluids except the cost of the fissionable fuel proper) are the same as those for the TVA reactor in Table 2. Recent preliminary design studies of several reactor types carried out by the manufacturers or other especially qualified organizations indicate that the capital costs drop below $100/kw for plants a few times larger than the TVA unit. Since we wish to look a little into the future, we shall assume that the cost of the molten-salt breeder has also been brought to this value by size scaling, or by the use of cheaper materials than INOR-8, or simply by design improvement and evolution. Then, corresponding to the two nuclear columns of Table 2, we obtain the hypothetical results shown

Most

in Table 3. As shown in Table 3, the projected over-all cost of power from a breeder comes to about 1.2 mills/kwh, assuming TVA financing (5.7% fixed charges), and 1.9 mills/kwh, assuming Oyster Creek financing (10% fixed charges). publicly owned plants would fall between these two extremes, and some privately owned plants might show fixed charges a little higher than Oyster Creek.

The road to a successful molten-salt breeder is not an easy one. The main objection to such a system is that it handles intensely radioactive fuel in a highly

Reckoned at 1.5%/yr of the plant capital cost, as in the TVA plant of Table 2.
† No income from the sale of surplus bred fuel has been assumed in these estimates.

labile form. Perhaps the most serious question is: Can such a reactor be serviced, once it has become radioactive?

To answer such intangible, though real, questions of feasibility, we have constructed and operated at ORNL a small molten-salt reactor experiment (Fig. 5) that embodies some of the principles of a full-scale molten-salt breeder. The reactor uses graphite as moderator; but instead of circulating two fluids, a stream containing fertile Th232 and a stream containing fissile U233, it circulates only a stream containing fissile U235. The reactor is therefore not a breeder, but simply burns U235 at very high temperature.

As of this writing, the reactor has completed 1000 hours of operation at a power of about 7.5 Mw. It has operated to date with surprisingly little trouble, especially considering its novelty. The reactor is now undergoing its second endurance run at high power. If the molten-salt reactor experiment continues to go as well as it has thus far, we hope that by the early 1970's we shall be able to construct a true molten-salt breeder.

The Uses of Cheap Energy-Desalting the Sea.-We have tried to make plausible the proposition that within about 20 years or so we may be able to generate electricity on a big scale at costs of perhaps 1.2 mills/kwh (TVA financing) or 1.9 mills/kwh (private financing). We should like now to examine the question: What can one do with blocks of electricity that are this cheap, and that have the great advantage of not requiring a nearby coal field?

If the cost of electricity is so low, thus implying a low cost for prime steam, the cost of steam which has been partially expanded through a turbine will be lower still. The prime steam needed to produce electricity at 1.2 mills/kwh is worth around 10/106 Btu, assuming a high-temperature reactor. If steam is extracted from a back-pressure turbine at 250°F, its value, as measured by its capability to generate 1.2-mill power, is down to about 3/10 Btu.

We doubt that the chemical industry has ever seriously been confronted with the availability of energy as steam at 34/10 Btu or as electricity at 1.2 mills/kwh. Obviously, with energy at this price, it pays to devise a chemical process to trade

off energy for simplicity of capital equipment, i.e., to use energy more lavishly, if in so doing one can simplify the process and its equipment.

It was this basic notion that underlay R. P. Hammond's approach to the desalting of the sea. Sea water contains 35,000 ppm dissolved solids. To remove the salt from 1000 gallons of sea water, about 3 kwh of mechanical work (requiring, at 41% efficiency of converting heat to work, 2.5 X 10' Btu of heat for its production) is necessary, provided the desalting is done reversibly. At 1.2 mills/kwh this energy would cost less than 0.4¢/1000 gallons.

Simple distillation requires over 300 times as much heat as the ideal process. However, this statement exaggerates the difference since the heat required for power production must be at high temperature, whereas heat needed for distilling can be at relatively low temperature and is therefore inexpensive.

Multiple-effect evaporators reuse the heat many times by putting it, so to speak, through many simple distillation steps in series. Raising the performance ratiothe number of times the heat is used-reduces the amount of heat needed. However, higher performance ratio means more expensive equipment -the evaporator, for example, must have at least one additional effect for each unit of performance ratio. Roughly, the capital cost increases linearly with performance ratio. Thus, for each cost of energy and for each incremental capital cost per unit performance ratio, there is a performance ratio that minimizes the cost of water. Reducing the cost of energy lowers the optimum performance ratio.

Until Hammond's views prevailed, no one took very seriously the possibility of using energy as cheap as a few cents per 106 Btu in a distillation plant. Most of the development in evaporator design was directed at increasing the performance ratio to 30 or more and raising the maximum water temperature. Hammond's emphasis on the possibility of cheap energy has focused attention on evaporators, especially in large size, with lower performance ratios. The recently described Metropolitan Water District of Los Angeles plant-which is now going forward to constructionis to produce 150,000,000 gallons per day of water at a performance ratio of 10.4. It uses two large light-water reactors and also produces 1500 Mw of power. The estimated water cost at the plant site is 21/1000 gallons, and the power is valued at 2.7 mills/kwh. These costs reflect the usual very low fixed charges assessed against municipal water projects. A more recent study at ORNL using an organiccooled heavy-water reactor as the energy source and a slightly more advanced evaporator with a performance ratio of 10 has come out, under the same general rules, with 250,000,000 gallons per day at 16¢/103 gallons plus some 600 Mw at 2 mills/kwh.10

It appears fair to say that responsible opinion now views 15e/103 gallons as a reasonable target visible along the lines of currently accessible technology. But the next factor of two in cost reduction below that is going to be much more difficult to accomplish. Is there any chance of reaching agricultural water prices, say, less than 10/1000 gallons? Most writers say absolutely no, that completely unforeseen technical breakthroughs are needed to achieve such costs. We think the situation is not anywhere near that hopeless. For if the above 1.2 mills/kwh figure is accepted, with its exhaust steam cost of 3¢/106 Btu, then at a performance ratio of 12, the heat energy costs 2¢/103 gallons (note that this is only a few times the energy cost of the ideal reversible process).

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Vertical-tube evaporators can be made self-pumping to a considerable degree, to reduce pumping power costs; and it may be possible to eliminate the need for the acid treatment employed at present. Improved heat transfer with fluted tubes or special surfaces to promote boiling and dropwise condensation may substantially reduce the tube surface required, and therefore the plant capital cost. These are possibilities that to us seem to lead to water in the agricultural range of interest. At the very least, we believe the goal of agricultural water is a plausible and important one and that the kind of engineering research that led to very cheap reactors surely should lead to very cheap evaporators.

We are assuredly not able to evaluate these possibilities numerically at this time. Much hard work in engineering and research and development must precede any economic assessment, but to sketch one possibility let us suppose the following. Imagine that a large evaporator costs 25¢/daily gallon. Although this is lower than any published figures, it is not impossibly lower. Take the capital charge to be 5.4 per cent annually, and suppose operation and maintenance and interim replacement11 to add another 1.6 per cent for a total of 7 per cent. At 90 per cent load factor this amounts to 5.3¢/103 gallons. We suppose further that it has been possible to reduce pumping power and chemical costs to 1/103 gallons. We would then have a cost for water at the plant as shown in Table 4. Such a cost would probably be said to be in the useful agricultural range.

The preceding supposes that the turbine power generated in expanding the prime steam down to a temperature suitable for evaporator use can be sold at cost as electricity. If this is not the case, mechanical power would be employed to drive a heat pump "topping cycle" to produce additional fresh water in another evaporator. Vapor compressors for this purpose are being studied. The results are not yet in, but it appears probable that the cost of water from such "water-only" stations may be a cent or two higher than from "dual-purpose" stations such as represented in Table 4.

The Uses of Cheap Power-Hydrogen and Other Chemicals.-Can very cheap and very nearly inexhaustible nuclear electricity be converted into other staple requirements of our human existence, in particular the important raw material hydrogen? We choose hydrogen because in some ways hydrogen is the key heavy chemical: It is needed for manufacturing nitrogenous fertilizer and therefore for providing the world's growing billions with food; it is an all but universal reducing agent and, in the very long run, it may displace carbon as the reductant for winning metals from their oxide ores; it is the key element in converting coal (which is hydrogendeficient) into liquid or gaseous fuels.

We at ORNL have thus far done rather little on these intriguing questions; yet we have encountered enough of interest to warrant a much more thorough examination of these matters.