Outlook for Nuclear Power: Presentations at the Technical Session of the Annual Meeting--November 1, 1979, Washington, D.C. (1980)

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Future Nuclear Systems Technology HARVEY BROOKS* The remarks that I have been asked to make pertain to future nuclear systems, and that is a rather large order. In the short time available, what I will try to do is to indicate where I think various directions of advance in nuclear systems are likely to go. I guess I would have to say at the outset that this is all predicated on the assumption that there will be a nuclear industry, something that cannot be entirely taken for granted. I myself subscribe rather strongly to the view of the future that Wolf Hafele presented so eloquently this morning, but there is real doubt as to whether this will survive in the present political debate. It seems to me that one can identify five directions of evolution of nuclear systems, possibly a sixth. These are, first, and perhaps most important, toward a means of extending fissile resources through improve- ment of the efficiency of their use; second, improvements in nuclear safety; third, reduction in the environmental impacts of nuclear elec- tric power generation, particularly water requirements; fourth, improve- ments in proliferation resistance of the nuclear fuel cycle; and, fifth, improvements in economics. And I would add as a sixth, and somewhat more speculative direction, the use of nuclear power for purposes other than the direct generation of electricity. The first and most immediate area of interest is that of the extension of resources. The present light water reactor with a once-through fuel cycle, at least in the present configuration of the reactor, utilizes about 0.6% of the energy potential in natural uranium, about 0.4% of that being due to fissions of U-235 and about 0.2% being due to fissions of plutonium. One can identify a series of technologies for extending resources, which I think are familiar to all of you. They can be classified in the following way: first, ways of extending resources without reprocessing essentially through the once-through cycle; second, ways of extending resources with reprocessing; and finally, ways of extending resources through other than nuclear fission option, namely, the fusion option or possibly combinations of accelerators and reactors. Let me say just a word about each of these. First, in regard to the extension of resources without the reprocessing option, this is something *Harvey Brooks is Benjamin Peirce Professor of Technology and Public Policy, Harvard University. 67

68 that has come into prominence, of course, with the Presidential decision to defer reprocessing and the breeder. One of the main focuses of the INFCE study is to look at ways of extending resources without reprocess- ing. The options are improvements in the design of light water reactors, including increased burnup, changes in enrichment, lower tails assay in enrichment, and tails stripping. Second, under this same rubric, there is possible further extension of resource efficiency through the use of other kinds of reactor designs, spe- cifically advanced converters still using only the once-through fuel cycle. I think one has to state at the outset that the virtue of this direction of evolution is very strongly dependent on what one projects about the future growth of electric power. If you think that the kind of scenario that Wolf Hafele described this morning is almost inevitable, then all of these options really only extend resources something like 2 to l0 years and can be regarded primarily as buying time to offset unforeseen delays in the development of other options. If you assume, as many enthusiasts of conservation do, that, in fact, the demand for electric power—at least in the advanced industrial socie- ties—will saturate and level off after the turn of the century, then the introduction of more advanced reactors, even restricted to no reprocess- ing, could extend resources for periods up to, perhaps, 50 years or more. The figures and tables in this report illustrate this point in a particularly graphic way. They are taken not from the CONAES report (Committee on Nuclear and Alternative Energy Systems, National Research Council), but from the Ph.D. thesis of an MIT student of David Rose's, Richard Lester. Lester considered three different options (Table l) for the extension of resources, sticking with the once-through fuel cycle: first, extending burnup; second, reducing tails assay from the present value of 0.25% to 0.05%, beginning in l988; and, third, replacing the present generation of light water reactors with heavy water reactors, TABLE l Alternative Uranium Conservation Strategies for the Once-Through Fuel Cycle Reference case (0): All-PWR economy 0.2% enrichment tails assay Average discharge burnup= 30,l00 MWD/MT Capacity factor = 75% Reduce Tails Increase Dis- l00% Penetra- Uranium Conservation Strategy Assay to 0.05% in l988 charge Burnup to 50,000 MWD/ MT in l990 tion of l%-U Fueled HWR's by 2000 Capacity Factor (%) A Yes No No 75 B Yes Yes No 75 C Yes Yes Yes 75 In the United States at present, PWR's outweigh BWR's by a ratio of about 2:l. Lifetime natural uranium requirements for the two reactor types differ at most by a few percent, however, and in light of the many other assumptions used here, the error introduced by assuming an all-PWR economy is relatively small.

69 fueled by l.0% to l.2% enriched uranium, with l00% penetration of the new reactor market after the year 2000. Figure l shows the three cases from Table l, including a base case, which is simply business as usual; that is to say, the present design of a reactor with no change and two different estimates of uranium resources, the lower one essentially that used by the uranium resource group of CONAES and the upper one being the somewhat more optimistic inferences that have been made from recent DOE publications. But you see in all of these cases that if the lower value for the uranium resources is the right one, one begins to be in trouble around the year 2000. This table is based on projections of nuclear power that give you a capacity of the order of 350 GWe around the year 2000. I think the problem is illustrated more graphically, however, in Figure 2, which shows things not in terms of the total resources, but rather based on estimates of the rates of production of uranium; again, taken from the work of the Uranium Resource Group of CONAES, which has e o o '= 4 O* m Base Case (0) Mid Scenario U.S. Uranium Reserves and Potential Resources (DOE, 1978) X$50/lb forward cost) Case A Case B CaseC Total U.S. Uranium Resources CONAES/URG Best Estimate (1977) «$30/lb) I 1980 1990 2000 2010 YEAR 2020 2030 FIGURE l Cumulative U.S. uranium commitments: mid scenario.

70 t_ <u a 200 150 •5 100 •S 50 Case A Case B Mid Scenario Requirements — CONAES/URG Supply Projections l.Present Conditions . Moderately Enhanced 111. Full National Commitment 1980 2000 2020 YEAR FIGURE 2 Annual U.S. uranium requirements: mid scenario. been published. The three curves represent three scenarios of business as usual, moderately enhanced efforts at production, and the full national commitment to all-out uranium production. The dotted curves are annual production curves, and the solid curves represent annual requirements. And I think you can see from this pic- ture that, given the assumptions, only Case C really is compatible with the present projections of the producibility of uranium. The base case, zero, would be compatible with the full national commitment case of uranium production, but that is rather deceiving; because you see the uranium supply rather abruptly disappears soon after the year 2000, be- cause part of that national commitment to uranium production is achieved at the cost of depleting reserves very rapidly. Table 2 is an attempt to tie projections of needed nuclear power capacity to the actual scenarios that were used in the CONAES study, and I don't want to take the time to go into detail in these scenarios, except to say that they all represent cases of 3% assumed average econo- mic growth between l975 and 20l0, and the Roman numerals represent a fourfold increase in real prices between l975 and 20l0, with very strin- gent mandatory conservation measures, in addition. Scenario II repre- sents the same fourfold increase in prices, but with less use of regulation. Scenario III represents a doubling of prices, and Scenario IV essentially represents constant prices between now and 20l0. You can, for the moment, ignore the left-hand columns and look only at the right-hand columns, which give the capacity required in the year 20l0 to meet the estimated electricity demand under these assumptions.

7l TABLE 2 Energy Used to Produce Electricity (in quads) 20l0 CONAES Scenario l975 l977 II. Ill IV, Nuclear 2 2.6 8(l60) l8(360) 30(600) Coal 9 l0.l 23(460) 20(400) 29(380) Other 9 9.0 8(l60) ll(220) 9(l80) Total 20 electricity Total primary 7l energy use 2l.7 39(780) 49(980) 68(l,360) 75 ll5 l40 l88 NOTE: Figures in parentheses are installed generating capacity in gigawatts. An approximate conversion factor of 20 GWe per quad is used for 20l0; this makes allowance for a reserve capacity of about l8%. The l977 figures are from actual data. And you can see, in the case of the stringent Conservation Scenario II3, that you can by no means eliminate nuclear power, at least if you follow the assumption of 3% economic growth. On the other hand, l20 GWe is less than would be projected on the basis of the plants now under construction; 2l0 GWe would be just a little bit more than the plants now under construction. With the lowest growth scenario, and optimistic assumptions about uranium supply, nuclear power might be extended well into the twenty-first century and then be gradually phased out in favor of alternative sources, but this could not be confidently anticipated today. Some critics of the CONAES study believed the predictions of elec- tricity growth were low, given the fact that electricity generation is capital-intensive, so that much of the cost is at the front end, and hence less sensitive to rapidly rising fuel costs on a percentage basis. To test the effect of alternate assumptions, I show in Table 3 two different cases of electricity growth. One arises from the CONAES models; the other, the high-electrification case, assumes that half the use of oil and gas in space- heating in the base model was shifted to electric- ity. That is an arbitrary assumption, but it provides a simple way of getting a somewhat higher electricity growth to test its impact. It is assumed that all the extra electricity is produced by nuclear. You can see that the total nuclear capacity required in 20l0 is nearly doubled in the low-growth cases. You can also go all the way down to the case of constant prices, which, of course, I think all of us would agree now is a rather absurd assumption, but put in merely for exploratory purposes. You can get up to 820 GWe required in 20l0, which, by the way, I am told by the Supply Delivery Panel people of CONAES, is still within the capacity of the nuclear industry. I think the basic conclusion is that, as one looks at all of the

72 TABLE 3 The Sensitivity of Outcomes to Assumptions About Electrification QUADS GWe 20l0 — Total 20l0 — Nuclear 20l0 — Total 20l0 — Nuclear I (base) 23 6 460 l20 (high-elec- 27.5 l0.5 550 2l0 tricity) II (base) 39 8 780 l60 (high-elec- 46 l5 920 300 tricity) III- (base) 48 l6 960 320 3 (high-elec- 56 24 l,l20 480 tricity) IV3 (base) 71 25 l,420 500 (high-elec- 87 4l l,740 820 tricity) possibilities of resource extension by use of various advanced reactor cycles without reprocessing, really important extension into the twenty- first century of the nuclear option is going to require reprocessing. And if electric power growth continues at any significant rate—by sig- nificant, I mean by more than l% a year—after the year 2000, it appears that the breeder option is really the only one that is compatible with the resource estimates that I have indicated. Of course, many people regard the CONAES Uranium Resource Group's projections as unduly conser- vative, but the real issue is, what is a prudent base for planning. So the conclusion is that the breeder option dominates the widest variety of assumptions regarding future demands for electricity. The other alternative is, of course, fusion. Almost everbody would agree with the conclusion that fusion is not an option that can be con- sidered as a serious prospect within the time frame of l980 to 20l0, which we have been talking about. Fusion, if it is developed, is an option that comes well into the twenty-first century. Let me now turn to the next topic, the question of prospects for improvements in the safety, health, and environmental effects of nuclear power. At the present time the LWR is the only reactor technology whose safety has been assessed in any detail, and consequently it is probably misleading to try to compare different reactor types. With the LWR the task ahead is the steady reduction of the uncertainties in the predic- tion of accident probabilities and consequences. Ideally we should be able to reduce the upper limit of conceivable hazard per reactor fast enough to offset the growth in the number of reactors. This will come about both from improvements in design and from reduction in the width of the uncertainty band. The greatest value of the fault tree method- ology developed in the reactor safety study lies in its capacity to identify priorities for improvements in safety through pinpointing the

73 most likely accident sequences and concentrating design improvements on them. We should avoid the trap of expending our energies on "proving" the safety of reactors rather than "improving" it. While it is not possible to make careful assessments of other reactor types, there are some trends that can be mentioned. The inherent thermal inertia of the HTGR appears to be a safety advantage in principle; it will be hard to confirm this without both operating experience and de- tailed experience in the safety analysis of commercial designs. Some- what the same considerations apply to the LMFBR, which has the important inherent advantage over LWR's that there is less potential for chemical and mechanical energy release in case of malfunction. The sodium cool- ant is not under pressure, and there is thus not the problem of flashing the coolant into vapor; furthermore, there is nothing analagous to the zirconium-water chemical reaction in case of a temperature excursion. On the other hand, the fast reactor is not in a minimum critical mass configuration, and hence the theoretical possibility of a recriticality accident could be higher than for LWR's. For fusion the possibility of supercriticality excursions is elimi- nated, and it seems highly probable that the radioactive waste problem will be somewhat more managable. However, we cannot be confident until work has progressed to the point of firm engineering designs of proto- type commercial systems. The radioactivity problem is highly dependent on choices of materials and detailed configurations. On the next point, reduction of water requirements, important progress can be made. Probably the largest environmental problem associated with nuclear, and indeed all, electric generation is the large water require- ment and the associated issues of thermal pollution. This is true of coal-generated electricity as well, but in that case is probably dominated by other environmental problems. Shifting to the LMFBR or the HTGR would make water requirements comparable to those for other power plants. Helium-cooled reactors, however, are attractive because of the hope that they could ultimately be operated with dry cooling. The HTGR or the gas-cooled fast reactor could be operated with gas tur- bines and thus bypass large water requirements. Although we probably have enough access to water supplies for electric power growth based on wet cooling for the rest of the twentieth century, dry cooling technol- ogy will become increasingly important for the twenty-first century if we are to continue to rely on dispersed electric power generation. With respect to proliferation-resistant fuel cycles, the main issue is that of reprocessing. The breeder—and most advanced converters— depend on recycling fuel to realize their resource-conserving potential. There is a great deal of disagreement—including that within CONAES—as to how important reprocessing really is in relation to the international proliferation problem. Certainly there are cheaper and easier routes to nuclear weapons than through diversion of fissionable material from civilian nuclear power. On the other hand, civilian power is a very good "cover" for clandestine weapons activities; a political leader with a nuclear power industry, including fuel recycling, could retain the option of developing nuclear weapons without committing himself in advance to dedicated production facilities—at least that is the argu- ment.

74 The big question is whether there is a "technical fix" for the pro- liferation problem. One of the principal arguments for going the advanced converter route in preference to fast breeders is the possibility of using a denatured thorium cycle. No consensus has crystalized on this, and there is a real question as to whether the extra costs of more elab- orate fuel cycles can be justified by the real additional insurance they might provide against proliferation. Unfortunately, this is probably not primarily a technical question, because the key parts of the issue involve beliefs about plausible political scenarios. Nevertheless, I suspect that the development of proliferation-resistant fuel cycles will continue to receive some attention, although I do not believe they will prove to be determining in the choice of reactor systems. On the questions of nuclear economics, the fundamental issue seems to be whether resource considerations or economic considerations will be determining. None of the advanced reactor types now being discussed— even the slightly enriched CANDU with a once-through fuel cycle—are economically competitive at current uranium prices. Much hinges on how fast uranium prices will rise, and whether it is necessary to develop and deploy uneconomic but resource-efficient reactor and fuel cycle sys- tems in anticipation of future fuel scarcities. One argument would be that the lead time for reactor development is so much greater than the lead time for finding and mining uranium that we can afford to let uranium economics dominate the choice of reactor designs. This is in turn bound up with the distribution of uranium ore grades. If there is a continuing increase of total contained uranium with declining ore grade, as some think, then the economic approach seems reasonable. But if there are big gaps in distribution, with small resources in ores of intermediate grade—as the CONAES Uranium Resource Group thinks—then there is a case for developing more resource efficient systems well in advance of their economic competitivesness. On the final issue, that of the use of nuclear energy for nonelectric purposes, I will not say much. However, I do agree with Wolf HSfele that this is being neglected in much current discussion. Future advances in reactor design that lead to greater resource efficiency are going to put a higher and higher premium on using off-peak energy. Or to put it another way, as electricity generation becomes more capital-intensive, off-peak electricity or thermal energy derived from off-peak operation of genrating plants will tend to become more and more of a bargain. This should stimulate a search for effective ways of using this cheap source of energy, essentially by storing it for use at different times or in readily transportable form.