A proton‐driven, intense, subcritical, fission neutron source for radioisotope production

^99mTc, the most frequently used radioisotope in nuclear medicine, is distributed as ⁹⁹Mo■^99mTc generators. ⁹⁹Mo is a fission product of ²³⁵U. To replace the aging nuclear reactors used today for this production, we propose to use a spallation neutron source, with neutron multiplication by fission. A 150 MeV, H⁻ cyclotron can produce a 225 kW proton beam with 50% total system energy efficiency. The proton beam would hit a molten lead target, surrounded by a water moderator and a graphite reflector, producing around 0.96 primary neutron per proton. The primary spallation neutrons, moderated, would strike secondary targets containing a subcritical amount of ²³⁵U. The assembly would show a k_eff of 0.8, yielding a fivefold neutron multiplication. The thermal neutron flux at the targets location would be 2 10¹⁴ n/cm².s, resulting in a fission power of 500 to 750 kW. One such system could supply the world demand in ⁹⁹Mo, as well as other radioisotopes. Preliminary indications show that the cost would be lower than the cost of a commercial 10 MW isotope production reactor. The cost of operation, of disposal of radiowaste and of decommissioning should be significantly lower as well. Finally, the non‐critical nature of the system would make it more acceptable for the public than a nuclear reactor and should simplify the licensing process.