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Improvement of the Neutronic Performance of the Hybrid Reactor Rejuvenating Spent Fuels Using Various Moderators

Sebahattin Ünalan, S. Orhan Akansu

Fusion Science and Technology / Volume 34 / Number 2 / September 1998 / Pages 109-127

Technical Paper /

Effects on the neutronic performance of the hybrid blanket rejuvenating light water reactor and CANDU spent fuels of moderators (Be, C, and D2O) inserted between the fusion chamber and the fissile zone of deuterium-deuterium and deuterium-tritium-driven hybrid reactor were investigated to obtain the best rejuvenation performance and more energy production. The calculations were carried out for different thicknesses of the moderator zone (DR). In addition, to eliminate local heating, the analysis was also repeated for reduced radius of the spent fuel rods in the first and the second fuel rows of the fissile zone.

It was observed that while Be and D2O improved the rejuvenation performance and energy production, C had a negligible effect. All moderators decreased the tritium breeding capability of the hybrid reactor with increasing DR values. To breed enough tritium (tritium breeding ratio: >1.05), the moderator zone thickness was determined to be smaller than DR = 6 cm as an average value. The rejuvenation performance reached a maximal value of DR = ~4 cm, increased two times in comparison with the blanket without moderator material, although the energy production was almost constant. However, to produce more energy, DR has to be ~20 cm. The energy releasing in the hybrid blanket with DR [approximately equal to] 20 cm is nearly two times that in the hybrid blanket without moderator material. The high energy production caused the fuel rod temperatures in the first fuel row of the fissile zone to reach the melting point. Hence, as a positive result, radiation damage in the first wall did not vary. However, the melting problem was eliminated by reducing the radius of the fuel rods in the first and second fuel rows, and the neutronic performance of the hybrid reactor has not been affected by this radius reduction.

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