Optimization Study of Ultra-long Cycle Fast Reactor Core

Since it was reported only neutronics point of view, it is expected to optimize UCFR(Ultra-long Cycle Fast Reactor) to perform a feedback from thermal-hydraulic (TH) analysis and mitigate the power peaking issue. Also, further feasibility study on using spent fuel (SF) for the blanket material was expected, which contributes to nonproliferation issues as well as uranium utilization. In this paper, the optimization of UCFR-1000 has been performed. First, the overall core shape and size have been changed to satisfy the safety limit from the TH feedback of the previous UCFR-1000. Second, PWR SF has been tried as the blanket material as well as NU for the fuel composition optimization, which could be one way of solving the SF storage issue in Korea. Core performance and depletion tendency have been analyzed. Last, a small-size UCFR with a power rating of 100 MWe (UCFR-100) has also been developed regarding the neutron flux and fast neutron fluence. It was analyzed with both NU and PWR SF as it has been performed for UCFR-1000. The calculation and evaluation have been performed by McCARD Monte Carlo code. The optimization of UCFR core design has been performed for the aspects of core geometry, fuel composition, and power rating. The UCFR-1000 has been optimized geometrically in the aspects of core size and core shape with the consideration of TH feedback. Enlarging the core in radial direction is followed by slowed axial movement of the active core, shortening the fuel pin length, decreased axial peak factor, and decreased maximum neutron flux by 1/3. A 60-year full power operation without refueling has been achieved with both NU and PWR SF as blanket materials. The core parameters such as multiplication factors and power peaking factors show that the breed-and-burn concept has been successfully implemented for the UCFR, which causes that the total number of uranium atoms decreases and that of plutonium atoms increases in the core. A small-size UCFR, UCFR-100, has been also optimized in the aspects of maximum neutron flux and high energy neutron