Isotopic Composition Changes in the Fuel Assembly of a Hybrid Reactor with a Neutron Source Based on D-D Reaction in plasma Column (Computer Simulation of a Long Operation Cycle)

To study the neutron-physical characteristics of thorium-plutonium fuel, we have previously proposed to construct a facility consisting a subcritical assembly of a high-temperature nuclear reactor and a source of additional neutrons in the form of a plasma column. Additional neutrons are generated as a result of the D-D synthesis in this column of high-temperature plasma, which is created and confined in a long magnetic trap. The article presents the computer simulation results of the nuclear fuel evolution in the proposed facility. The simulation was carried out for plasma parameters, in which the D-D synthesis reaction gives the total neutron yield of 2 × 10¹⁶ neutrons/s from the plasma column inside the subcritical assembly with a length of 3 m. Two variants of the fuel assembly operation mode, differing in the content of plutonium in the original thorium-plutonium fuel, are considered. In the first one, the initial plutonium fraction is 4 %, which ensures the subcritical state of the fuel assembly with an effective neutron multiplication factor k ef = 0.95. In the second variant, the part of plutonium is increased up to 5 %, which allows the assembly to have k ef = 0.99 at the operation conditions. The choice of such values of plutonium percentage was made according to the results of a detailed computer simulation of the main neutron-physical processes in the reactor core. The evolution of the fuel isotopic composition was calculated for the total time of the assembly operation - 3000 days. In the process of the fuel “burning” at the conditions of unchanged neutron yield from the plasma, a time decrease in the neutron multiplication factor and the power of the nuclear fission process in the reactor core from the beginning of the operating cycle was detected. To compensate this reduction in produced power, the required increase in the neutron yield from a plasma source is calculated. The article presents the simulation results and discusses various aspects of the solutions obtained.

thorium subcritical fuel assembly, source of thermonuclear neutrons, open magnetic trap, evolution of fuel composition

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