中文摘要：

增殖比可调快堆（FFBR）是可实现增殖比灵活调节的钠冷金属燃料快堆。它在不改变堆芯结构的前提下，使用相同的燃料设计和相同的控制棒排布，使得增殖比在1．1-1．4之间可调。相比于传统的快堆，FFBR使快堆能灵活地匹配核工业的发展需求。为应对核能发展形势对增殖快堆的需求变化，增殖比可调快堆需有相应的调节方案。本文选取增殖比为1．1和1．4的两个方案进行转换方案的设计。结果表明，通过换料方案的设计能实现增殖比的相互转换，且过程中的关键物理参数满足设计要求。

英文摘要：

The FFBR （flexible fast breeder reactor） is a sodium-cooled fast reactor with flexible breeding ratio （BR） from 1. I to 1.4. It realizes flexible breeding in one designed fast reactor core without changing the pool structure, fuel design and control system arrangement. Comparing with traditional fast reactor design, this concept ena- bles fast reactor to respond to the industrial needs effectively. The transition scheme is necessary to convert the BR when the breeding requirement changes. The feasibility research of transition scheme was performed to convert the BR from 1. 1 to 1.4 and inverse from 1.4 to 1.1, since these two processes appear to be the most challenging transition situations. All the results show that it is feasible to convert the breeding ratio of FFBR through refueling scheme design.