Page 175 - Dynamics and Control of Nuclear Reactors

172 CHAPTER 13 Boiling water reactors

13.3.2 Recirculation flow and jet pumps
The core flow in a BWR-6 is controlled by two recirculation pumps that distribute the
water to a set of jet pumps surrounding the core. Each recirculation pump distributes
water to one of two manifolds. Each manifold supplies water via pipes to jet pumps.
A pair of jet pumps receives water from a single pipe. There is a total of 20 jet pumps,
with a typical jet pump overall length of 19ft. Mechanical pumps (recirculation
pumps) withdraw water from the downcomer and pump it at elevated pressure into
the jet pumps. The jet pumps have no moving parts, making them maintenance-free
reactor components. Fig. 13.4 illustrates the principle of operation of a jet pump [2].
The recirculation flow enters the jet pump nozzle at a high pressure and increases
to a high velocity as it flows through the narrow throat, and results in a pressure drop.
The suction flow in the downcomer region enters the inlet nozzle at a low pressure.
The pressure decreases as the suction flow passes through the converging section of
this nozzle. The driving flow and the suction flow mix in the throat region (mixing

FIG. 13.4
Operation of a jet pump.
Courtesy of GE Hitachi Nuclear Energy Americas LLC (GE Nuclear Energy, BWR-6: General Description
of a Boiling Water Reactor).