permit significant g-loading. 4 .0 Mass and Area Results 4.1 Power System Mass Comparison The estimated masses of the 9 reactor power systems we investigated are shown in Figures 4.1 and 4.2 as a function of power level. Figure 4.3 is a plot of specific mass versus power level. It is worth reiterating that the absolute values shown for mass are our best estimates, and we have not yet made a large effort to estimate the error associated with them. However, by looking at the SP-100 thermoelectric system mass at 100 kWe, it can be seen that our estimate is about 10% higher than the estimate currently being made by the SP-100 program (Ref. 7). Our estimates for the 10 kWe innovative SP-100 are 7% lower than the DOE estimate (Ref. 19). Also, although we believe the best use for the mass curves is for relative comparisons, they should not be interpreted too literally. Single curves depicting these results can be misleading unless broader issues are considered. For example, our mass estimates for the STAR-C and SP-100 thermoelectric concepts cross over at 22 kWe. However, from separate sensitivity analyses we know that with the uncertainties in actual performance the masses of the STAR-C and SP-100 thermoelectric systems could cross over anywhere between 15 and 30 kW(e). With these caveats in mind, the significance of the curves is described below. 4.1.1 OTR Power Systems The slope of the STAR-C mass curve is steep throughout the power range of 5 to 50 kWe. The reason for this poor scalability is two-fold. First, the OTR concepts are fundamentally different from all of the other concepts. Above about 8 kWe, the size of the reactor core is set by the core surface area needed for heat transfer. Thus, the core size increases linearly with electrical power. Second, the STAR-C design is not optimized. The optimized OTR curve shows the potential that this design concept has to scale with power. The system optimization is achieved by optimizing the reactor core length to diameter ratio and by maximizing the ratio of the inner to outer fuel radius. Ihe optimized OTR is the least massive system below about 25 kWe and is less massive than the SP-100 thermoelectric and innovative SP-100 at power levels below 50 kWe. A detailed discussion on the scalability of OTR power systems can be found in Reference 3. 4.1.2 The SP-100 Power System Figures 4.1 to 4.3 have two curves representing the mass of the SP-100 power system. The more massive of the concepts is for a scaled version of the system being developed in the SP-100 program. The less massive is the innovative SP-100, which does not have a secondary coolant loop and only applies to power levels below about 30 kWe. The slope of both of the SP-100 systems is much steeper than the slopes of the other liquid metal cooled concepts. In fact, the slope is the same as that of the optimized OTR. The steep slope can be seen best in Figure 4.2. There are two
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