Analysis of the evolution of Xe-135 in a KWU-PWR reactor using coupled codes

Abstract

[EN] The fission product Xe-135 has a tremendous impact on the operation of the nuclear reactor and may interfere with the plant's operational capacity. Therefore, the incorporation of Flexible Operation (non baseload) in nuclear power plants requires studies that assess the effect of Xenon oscillations in power production taking into account the requirements of the electrical network as well as the nuclear safety.

To analyze the evolution of the neutronic poison Xe-135, a 3D thermal-hydraulic-neutronic model of the core of a pressurized water nuclear reactor (PWR), with three cooling loops and German Siemens-KWU technology, was developed with the coupled code RELAP5/PARCSv3.2. The model was carried out from the real information of the core state and taking into account the data referring to the position of the Incore detectors of the studied plant.

After validating the 3D thermal-hydraulic-neutronic RELAP5/PARCSv3.2 model, an operational transient of the PWR-KWU reactor is carried out in non-baseload operation. The results verified that the modeling provides good accuracy in predicting the trend of Xenon oscillation behavior. Furthermore, Xenon oscillations in the reactor core are dampened in the same way although the control bank insertion is executed at different ramp rates. The final goal is to use this model in order to define a strategy to move the control rod banks when there is a requirement to decrease the power in the reactor core.