Uncertainties in Activity Calculations of different Nuclides in Rector Steels by Neutron Radiation

Activation processes in a nuclear power plant are mainly due to neutron reactions. The determination of the neutron fluences in the reactor pressure vessel (RPV) is therefore the main task of the reactor dosimetry and the good experience for the activity evaluation has to be used. From 2005 to 2009 trepans were gained from the RPV of decommissioned nuclear power plant in Greifswald for the embrittlement investigation. For the first time, samples could be taken from the inner part of the RPV and activity measurements were performed. Experimental results were obtained for 93Nb, 63Ni and 99Tc. The calculations of the neutron fluences were carried out with the TRAMO Monte Carlo code. Based on these fluence values, the time-dependent activities of different nuclides were estimated. The calculated/experimental (C/E) activity ratios for the selected samples fluctuate between 0.37 and 0.91 for Niobium, while for 63Ni and 99Tc they are approximately between 0.6 and 0.91. The influence of different parameters on the results, for example the boron acid concentration, the thermal data and the local position, are here investigated and discussed.