[1] Characteristics of fast reactor core

In the primary cooling system of the LMFBR, the high-temperature and low-pressure sodium heated in the core is cooled by the intermediate heat exchangers and then sent back to the core. In the secondary cooling system, the sodium receives heat from the primary cooling system through the inter­mediate heat exchangers and gives heat to water and steam through the steam generators. The energy of the generated steam is converted to electricity through the steam turbines and generators. The secondary cooling system in the LMFBR is necessary for two reasons: the high radioactivity of the primary coolant; and preventing the core from being directly affected by the accidental sodium-water reaction in the steam generator. Sodium as the primary coolant provides forced cooling of the core by single-phase flow under low pressure. It does not evaporate in the core due to its high boiling point.

Figure 4.3 illustrates the cross section of a fast reactor core. In this example, the core consists of 198 core fuel assemblies, 19 control rod assemblies, surrounding blanket fuel assemblies and neutron shieldings. The shape of the whole core is almost hexagonal. Each core fuel assembly contains 169 fuel elements in a hexagonal wrapper tube.