Solid, Stable Design

The Reuter-Stokes NA-250 LPRM assembly is a "dry sensor" design in which the sensors are not in intimate contact with the reactor coolant. The LPRM assembly contains a dry tube for each of the four sensors in the assembly, plus one additional dry tube for the TIP sensor.

Each of the four sensor and cable subassemblies in the NA-250 LPRM assembly is a pre-determined length to permit neutron flux measurement at four levels in the reactor core. The fifth dry tube in the assembly is used for the moveable TIP sensor positioned adjacent to each sensor for periodic calibration. The stainless steel cover tube is equipped with end fittings that appropriately interface with the support plates and grid of the reactor core. The cover tube is vented to permit the flow of coolant inside the tube immediately adjacent to the dry tubes containing sensors.

Nominal lifetime is 1.75 E22 nvt, but operational experience at some power plants exceeds an average life of 2.4 E22 nvt.