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characteristics of this direct (Brayton) power conversion system allow electric generation with a high<br />

net thermal efficiency of approximately 47%.<br />

This high power conversion efficiency, the fact that 75% of the transmutation is done in a critical<br />

operating mode, and the fact that the proton accelerator is time-shared by four transmuters, leads to a<br />

favourable revenue-cost balance and the potential to attract investment for the deployment of these<br />

units.<br />

Roughly, the cost of the plant configured as shown in Figure 10 (four 600 MW th<br />

transmuters, and<br />

one 15 MW beam accelerator) would be expected to be in the $1.5B to 2.0B range. This would<br />

translate into an annual cost of $190M assuming interest on and return of capital of 8.8%, plus typical<br />

nuclear plant operations and maintenance (O&M) costs increased by 50% to account for accelerator<br />

O&M. It also includes an allowance for decommissioning the plant, but assumes, however, that the<br />

fuel (to be transmuted) is government-supplied.<br />

Figure 10. Thermal-fast plant representative configuration<br />

Operating Sequence<br />

Ti me Tr ansm itter 1 Transmuter 2 Transm uter 3 Transmuter 4<br />

t o<br />

Crit ical Crit ical Cr itical Su bcritical<br />

t + 1 yr o<br />

Crit ical Crit ical Subcrit ical Crit ical<br />

t + 2 yrs o<br />

Crit ical Subcritical Crit ical Crit ical<br />

t + 3 yrs o<br />

Su bcritical Critical Critical Critical<br />

th erm al re gi o n<br />

fast region<br />

Af te r t he 1 y ea r of subcr itica l oper at ion:<br />

é Fr esh fue l g o es i nt o th er ma l se cto r<br />

é Fu el com p acts i rr ad i ated for 4 year s in<br />

ther mal sector are moved to fast sector<br />

1000 MeV, 15 mA Beam<br />

t o + 3 yr<br />

t o<br />

+ 2 yr<br />

Transmuter 1<br />

Tr ansm uter 2<br />

t o + 1 yr<br />

t o<br />

Transmuter 3<br />

Transmuter 4<br />

The revenues, assuming 4 cents per kWe-hr, 75% plant availability, 47% transmuter thermal<br />

efficiency, and an accelerator efficiency (beam to electric power ratio) of 32% would be<br />

approximately $270M per year.<br />

These estimates suggest that transmutation plants of this type have the potential to be<br />

economically viable and possibly attract investment.<br />

From the safety standpoint, there are two important considerations. Criticality and cooling.<br />

Criticality safety in this respect is ensured by the use of erbium in the thermal assembly. Erbium has a<br />

neutron capture cross-section that increases with temperature, and peaks a higher temperature than the<br />

fission cross-section of 239 Pu. Erbium and plutonium quantities can be selected that provide a strong<br />

negative temperature coefficient of reactivity during the entire fuel cycle.<br />

The other important safety consideration is cooling. In this respect, the geometry of the assembly<br />

(tall and thin, and annular thermal configuration) has been shown to provide for passively safe<br />

conduction cool-down of a 600 MW th<br />

thermal spectrum-only assembly, even in a loss of coolant<br />

604

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