CERN have put forward a conceptual design for a fast neutron operated high-power energy amplifier (EA) (Figure 13.4). The principles are described in detail in Carminati et al. (1993), Rubbia et al. (1994) and Andriamonje et al. (1995). More recent optimised realisations are described in Rubbia et al. (1997). The EA can operate for an indefinite period in a closed cycle. The fuel load is discharged, apart from fission fragments, and then re-introduced into the sub-critical unit, but with natural thorium introduced to compensate for burnt fuel. Equilibrium is achieved between burning and incineration after several cycles. This represents an extremely efficient use of fuel.

The EA module includes a 1500 MWt unit with a 1.0 GeV proton accelerator of 12.5 mA. The accelerator is a modular cyclotron; i. e. a plant is made up of a number of modules.

Подпись: Buffer region

image073Figure 13.4. Conceptual design concept of the diffuser driven energy amplifier. Source: Carminati et al. (1993).

A fast neutron EA is envisaged if the EA has power commensurate with the current of large pressurised water reactors. The proton beam is a novel element of the design; the current is lower by one order of magnitude than most LINAC designs. The anticipated efficiency, i. e. the beam power over the mains load, is of the order of 40%. The beam penetrates the EA through an evacuated tube and tungsten window, specially designed to withstand radiation damage and thermal stress. The electrical energy to operate the accelerator is about 5% of the primary energy production.

The coolant is molten natural lead at a temperature of 600-700°C; lead being chosen because of its high boiling point (1743°C), which combined with the negative void coefficient of the EA, enables very high operating temperatures to be reached. Heat can be removed by natural convection.

The EA can operate with various different fuels, for plutonium to be transformed into 233U, the EA would be initially loaded with actinide waste and thorium. Other actinides, e. g. americium, or neptunium could also be added. The EA mixture is sub-critical with keff in the range 0.96-0.98.

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