The favored fast reactor system in the United States, Great Britain, the USSR, and France—this reactor is now cooled by sodium although NaK systems have been used. Designs generally use mixed oxide fuels in a pin configuration cooled by upflowing coolant to remove anything between 12 to 16 kW/ft (7).

TABLE 2.1
Fast Reactor Types

Temperatures in the system range from 750°F at inlet to 1000°F at the mixed core outlet, while the coolant is kept at a low pressure of 1 atm or a little above.

The heat transfer systems are usually all three cycle systems with an inter­mediate or secondary system to insulate the radioactive primary sodium from the turbogenerator steam cycle. However, present designers are divided on whether the reactor should be a pool or a loop system. The former im­merses the core, heat exchanger, and primary pumps in a single pool of sodium, while the latter uses pipes to connect its primary components and its secondary components. There are advantages and disadvantages for both systems (see Section 4.1) but for the present discussion a loop system is assumed (Fig. 2.1). Table 2.1 shows the main characteristics of the liquid — metal fast breeder reactor (LMFBR).

Flow

/іб"з

Bypass circulators 51.5% Flow

Mam core circulators