Geometric optimization of a novel passive flow limiter for nuclear heating reactors

A novel passive flow limiter was designed for the NHR200-II nuclear heating reactor to reduce the break mass flow rate in loss-of-coolant accidents (LOCAs). The flow limiter is mainly composed of a multisection cylindrical flow passage and an internal movable ball, and the flow passage would be blocked automatically by the movable ball while the flow in the passage was accelerated during a LOCA transient. The dimensionless critical flow rate eta was identified as the key performance parameter of the limiter. Important geometric parameters, such as the axial distance H, the shape of the throat section, the blockage ratio of the ball in the pipe, and the front length L were studied numerically to optimize the structure of the passive flow limiter. The dimensionless critical flow rate eta was found to increase rapidly with the axial distance H. The downstream throat shape of the passive flow limiter also affects the performance. The blockage ratio has a relatively small effect on the dimensionless critical flow rate eta, and the dimensionless critical flow rate decreases with the increasing front length L.