Primary vacuum pumps for the fusion reactor fuel cycle

Abstract

The primary vacuum system for a tokamak-type controlled thermonuclear reactor with 1-GW thermal output is analyzed. The need for recovery, purification, and recycling of deuterium–tritium (D–T) fuel to the reactor leads to the following basic requirements for vacuum pumps at the reactor exhaust: effective pumping speed ∼250 m3 s−1; inlet pressure ∼0.1 Pa; outlet pressure ≥10 Pa (at full flow rate of ∼25 Pa m3 s−2); compatibility with tritium, nuclear radiation, static and dynamic magnetic fields, mechanical shock, and up-to-air accidents; and no contamination of pumped gases (primarily D–T and 4He) by vacuum pump media such as lubricants, operating fluids (vapors), or gases other than D–T and 4He. Based on present experience, the turbomolecular pump appears suitable. It would, however, require a substantial development effort both in technology and unit size to meet the requirements. There remains some doubt about its compatibility with mechanical shock, radiation, magnetic fields, and sudden up-to-air accidents, etc. Therefore, alternative pumping principles are proposed, all shown to work at least in laboratory size models: thermodynamic pumps for transport pumping to replace turbomolecular pumps and selective storage pumps for effluent processing in situ. The proposed systems require development efforts similar to the turbomolecular pump, but are shown to meet all requirements without the need for large protective valves. Selective pumps, pumping none of the hydrogen isotopes (but helium and impurities such as DTO, CO2, methane) or combinations of thermodynamic transport pumps, and regenerable volume getter pumps are shown to perform the major processing task, i.e., purification and recycling of DT, directly at the reactor exhaust.