We perform a scoping study of seven classes of microreactor technologies with a diverse set of coolants, that is, heat pipes, sodium, lead-bismuth, helium, FLiBe, organic fluid and light water. A point design is developed for each reactor class under a consistent set of assumptions about road transportability, irradiation cycle length, passive decay heat removal and reactivity control. All reactors have a thermal spectrum and use low-enriched (& LE;5%) uranium dioxide fuel, which is readily available and inexpensive. Mature moderator materials, in-core structural and cladding alloys were selected in this study including graphite, Zircaloy and stainless steel 316H. We compare the economic potential of these point designs according to a set of figures of merit including the cost of fuel, coolant, major equipment, instrumentation and control (I & C) systems as well as the complexity of operations and maintenance (O & M). The results of our analyses confirm that economies of scale work against microreactors competitiveness, i.e., relatively small absolute costs become high costs per unit energy generated because of the low power output. We find that all designs have very high fuel costs because of the relatively low achievable burnup, and high I & C costs (in particular for the reactor protection system), compared to traditional large light water reactors. Coolant costs are also notably high for the lead-bismuth cooled, organic-cooled and especially FLiBe-cooled systems. The constraints adopted in this study limited the heat pipe reactor's operating temperature to 650 degrees C, which resulted in low core power density and low electric power output, thus yielding a poor economic performance. When technology maturity, operating experience, O & M complexity and our estimated costs are holistically taken into account, we judge that the most promising designs examined in this study are (in no particular order) the Na-cooled reactor, the HTGR, the organic-cooled reactor and the water-cooled reactor.
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