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Another odd assumption many fuel cycle analyses make is that building fast reactors is an

“all-or-nothing” proposition. In reality, the nuclear industry will need time to become

comfortable with a completely new technology, and utilities are unlikely to build fast reactors immediately and as fast as possible once they become available. Indeed, there is an advantage to building a small fleet of FRs early: we can observe how well (and at what cost) they operate, and let those data inform our decisions about whether to more extensively deploy FRs later. Adding in the option to build a fraction of the “allowable” FRs (given availability of SNF) paints a different picture again of the desirability of TFRs.

The tree including options for partial build of TFRs is shown inFigure 5-10. Everything is the same as for the two-period tree above, except now there are two more options for fast reactors at the first decision node. Decision makers can choose to build as many TFRs as are allowed by SNF availability, as before, or can choose to build TFRs at a rate that is 25% the allowed amount throughout the first decision period. Similarly, decision makers can choose to build EUFRs at 25% their “allowed” rate, but recall that EUFRs are not restricted by the availability of LWR SNF. The “25% EUFR” decision thus corresponds to building EUFRs at

71 25% of electricity demand, with the remaining demand met by LWRs. Partial build options are similarly available in the second period. In the second period, the decision maker can choose to build 50% of the allowed FR amount, or can build 100% as before.

The decision results for the first period with partial build options are shown in Figure 5-11. Each line represents the demarcation between the spaces where FRs vs. LWRs are more desirable for the first period course of action. The line through the green triangles indicates the same basic result presented in the previous section (compare to Figure 5-6). Waste weights are the same (Table 5-2) as for the previous two sections.

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Figure 5-10: Two-period tree with partial build options

73 Table 5-2: Standard weighting scheme for partial build analysis

Weight Value

Figure 5-11: Desirable first-period decisions when building fractions of FRs is allowed

To the left of the line through the red squares, building TFRs in the first period at 25% of the allowable amount is desirable. Similarly, to the left of the line through the blue diamonds, building TFRs at 10% of the allowable amount is the desirable course of action. Decreasing the amount of FRs built in the first period actually makes the choice to begin builds a better one for a wider range of cost weights.

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As mentioned above, this makes intuitive sense because we would learn about TFRs by building a smaller number of them and would be able to make future decisions based on real deployment data. This effect, however, is not modeled in this tree structure. In fact, re-ordering the tree branches to model a version of path dependency (where we only learn about the cost of fast reactors if we build some first) has virtually no impact on the decision result. Rather, the effects seen in Figure 5-11are due to the waste management benefit that comes from building a few FRs early in the simulation, for relatively less cost than building a large number of FRs.

A comparison between the partial and full build TFR scenarios is presented in Figure 5-12. The figure clearly shows that building 10% or 25% of the allowed TFRs in the first period, then switching to full deployment of as many TFRs as possible (red and green lines), entails a waste management benefit close to that of starting with 100% TFRs immediately in 2040 (solid blue line). The waste penalty for starting with 10% or 25%, vs. starting immediately with 100%

TFRs, is a little less than 20,000 MTHM of SNF. Compare this to a much larger penalty associated with waiting until 2065 to start building TFRs at 100% (dotted blue line: a nearly 60,000 MTHM difference from starting 100% TFRs in 2040 by the end of the century). The cost, moreover, for these small-percent scenarios is significantly less than for building 100% TFRs at 2040. For all three 2040 TFR scenarios, close to the same number of fast reactors is built by the end of the century. Building 100% TFRs early, however, means that more reactors are built sooner, when costs are not as steeply discounted.

75 Figure 5-12: Waste benefit of building a few reactors early

Growth effects are responsible for the difference in slope (seen in Figure 5-11) between the results for 10% vs. the 25% build profile. At low growth, the differences between the two percentage build choices are almost imperceptible (and hence the two demarcation lines between optimal decisions meet on the x-axis). The 25% pathway entails building very slightly more TFRs early on, but because the percentages are taken out of a small growth number, the

difference between 10% and 25% of possible builds are small. Almost exactly the same number of fast reactors is operating at the end of the century in both scenarios if growth is low. If growth is high, however, the 25% TFR scenario is more costly because it does require building more FRs early on. The end-of-century waste benefit, however, is not larger for the 25% scenario, as can be seen in Figure 5-12. Therefore, at high growth, the 25% scenario is less desirable (and the TFR-desirable space is smaller) than the 10% build scenario.

The ultimate conclusion from this study is that even before considering the value of information learned by building a small fleet, building some smaller number of fast reactors early on is desirable. The final decision will depend heavily on the decision makers’ cost weights, and building LWRs is still more robust to a wider range of weightings, but decreasing the amount of FRs built in the first “wave” makes an early FR pathway much more attractive.

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5.3 Key Takeaways from the analysis on Building the FR Fleet Gradually

Building a small number of traditional fast reactors in the first period (starting in 2040) is much more desirable than immediately building as many FRs as possible given the availability of spent nuclear fuel. The additional desirability comes because there is a waste benefit to starting with some fast reactors, but relatively little cost penalty; the gains from the “value of information” in terms of lessons learned from a small fast reactor fleet would be an additional reason to build a few early on.