Neutron activation analysis of metal foils placed inside an ex-core instrumentation channel of a Siemens/KWU PWR

In the framework of German nuclear power plant (NPP) decommissioning studies, a 3D detailed Monte Carlo model of a Siemens/KWU pressurized water reactor (PWR) was developed to evaluate the neutron fluence characteristics within the components of such a nuclear reactor type. To ensure that the model is reliable and suitable for achieving this task, the model was optimized and validated based on metal foil-activation measurements. Several activation monitors composed of thin metal foils of different materials were placed along one of the idle ex-core instrumentation channels of an active Siemens/KWU PWR. The monitors were irradiated in the reactor for half a cycle and for one complete cycle. After the monitors were removed, the activation of the metal foils was measured with a coaxial N-type high-purity germanium (HPGe) detector. The measured values were then compared against the results obtained from the Monte Carlo calculations. The results presented in this paper show that the calculated activation of the metal foils agreed well with the measured values. This indicates that the developed Monte Carlo model is reliable and can be used to calculate the neutron fluence in the reactor components.