Detection model of accidental control rod drop in PWR reactors with in-core and ex-core nuclear instrumentation using Delaunay triangulation

The accidental drop of a control rod may cause the reactor to operate unsafely. In this type of event there is a distortion in the power distribution in the core which may exceed safe operating limits of the reactor. This work aims to develop an alternative model capable of detecting an inadvertent drop event of a control rod and then identifying it using the in-core and ex-core nuclear instrumentation. The proposed model has two stages: The first aims to detect in an online form the inadvertent drop of a control rod at the core through the readings of the ex-core detectors and the second is to identify the dropped control rod through the in-core detectors readings, using a Delaunay triangulation method. The results showed that it is possible to detect the event of a control rod drop using an established limit on the asymmetry of the radial power distribution measured by ex-core detectors and the identification method of dropped control rod depends exclusively of the in-core nuclear instrumentation readings, because it is based on a physical premise that higher power variations occur in the position where the control rod is inserted and its surroundings.