On the possible effects contributing to neutron noise variations in KWU-PWR reactor: Modelling with S3K

In the last years KWU-PWR plants have shown an increase in the neutron noise normalized root mean square. The frequency region of interest is below 1 Hz, so that thermohydraulic fluctuations seem to be one of the main reasons behind. In order to advance in understanding this phenomenon, the code S3K has been used to simulate temperature, flow and combined fluctuations at the core inlet. The S3K model used corresponds to Trillo Nuclear Power Plant which has a Flow Distribution Device, whose effect on the neutron noise levels has also been investigated. The results are compared with an analytical model and real plant data.