In its first version, this proposal aimed primarily at massive energy production. Later on, applications to incineration and transmutation were carefully con­sidered. The accelerating system involves three cyclotrons working in series and bringing protons to an energy of 1 GeV, with an intensity of about 10 mA. Such a system represents a significant technological jump in compari­son with the cyclotrons of SIN (Villigen-CH). The fast subcritical arrange­ment’s multiplication coefficient is about 0.98. The anticipated gain of 120 would yield a total thermal power of 1500 MW and electric power of 600 MW.

In order not to slow down the neutrons, and to extract a specific power on the order of 0.5 MW/l, cooling is ensured by liquid metal. For safety and neutronic reasons, lead is preferred. While molten lead does not present fire and explosion hazards like sodium, it has some drawbacks: chemical toxicity, corrosion and radionuclide production from neutron irradiation or as a result of the spallation process. Cooling by lead or a lead-bismuth alloy has already been used, in particular in the reactors of Russian nuclear submarines. Corrosion of the steel (of martensitic type) components was

Spent fuel

(every 5 years)

Figure 12.1. View of the system proposed by the CERN group. The molten lead pool is 30 m high and 6 m in diameter. It contains 10 000 tons of molten lead.

tempered by controlled oxidation by oxygen dissolved in the molten coolant. Molten lead would allow us, as in the sodium case, to keep a low pressure in the reactor, and to obtain high thermodynamical efficiency, due to the high operating temperature.

Figure 12.1 shows a schematic view of the proposed system, while figure 12.2 shows a more detailed view of the subcritical assembly. The proposed system is characterized by a high level of safety. No major accident, even intentional, is possible.