[en] The investigated nuclear piston engines consist of a pulsed, gaseous core reactor enclosed by a moderating-reflecting cylinder and piston assembly and operate on a thermodynamic cycle similar to the internal combustion engine. The primary working fluid is a mixture of uranium hexafluoride, UF₆, and helium, He, gases. Highly enriched UF₆ gas is the reactor fuel. The helium is added to enhance the thermodynamic and heat transfer characteristics of the primary working fluid and also to provide a neutron flux flattening effect in the cylindrical core. Two and four-stroke engines have been studied in which a neutron source is the counterpart of the sparkplug in the internal combustion engine. The piston motions which have been investigated include pure simple harmonic, simple harmonic with dwell periods, and simple harmonic in combination with non-simple harmonic motion. The results of the conducted investigations indicate good performance potential for the nuclear piston engine with overall efficiencies of as high as 50 percent for nuclear piston engine power generating units of from 10 to 50 Mw(e) capacity. Larger plants can be conceptually designed by increasing the number of pistons, with the mechanical complexity and physical size as the probable limiting factors. The primary uses for such power systems would be for small mobile and fixed ground-based power generation (especially for peaking units for electrical utilities) and also for nautical propulsion and ship power

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[en] Molten salt reactors (MSR) are an innovative concept in which the nuclear fuel is dissolved in a molten salt and fission reactions take place in a space where criticality can be reached. This molten salt goes through an exchanger where it gives its heat to a secondary non-radioactive salt that itself goes through steam generators to feed turbines. The MSR concept is not new, the ARE (Aircraft reactor experience in the US) and the MSRE (Molten salt reactor experience at Oak Ridge) were the only 2 molten salt reactors to have worked. The renaissance of the MSR concept is due to its ability to shorten the fuel cycle. In fact, uranium and plutonium are left in the fuel till their disappearing through fission reactions or transmutation, there would be no more need to recover them. The MSR is a breakthrough innovation and 6 issues have been identified to assess its feasibility: 1) selecting materials that resist corrosion, 2) studying neutron transport in MSR, 3) elaborating a preliminary design of the MSR, 4) studying adequate pumps, exchangers,..., 5) optimising salt on line processing, and 6) assessing reactor safety. (A.C.)

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