Contamination of occupational radiation exposure in nuclear power plants with pressurized water reactors

In the precursor project of this study a simulation procedure was developed, consisting of a 3D-CAD model, a mathematical method for coordinate transformation, the software MicroShield and an empiric job model, to calculate the occupational exposure for definable jobs at the primary circuit. It was validated for inspection and maintenance jobs at PWRs of the second and third KWU/Siemens generation. With that the aptitude of this tool for prognosis of radiation exposure was demonstrated. Adhering contaminations within the primary circuit are considered as relevant sources, whereas activated core-near components are neglected. In this study, the model was extended by PWR of the so-called Convoy generation, which differ from older plants in the material composition and consequently in the relevant nuclide vectors. With information from a visit at a nuclear power plant and conversation with the staff, the model could be adjusted appropriately. The radionuclide Cobalt-60 is indeed less important compared to older plant-types, but it is still the dominant nuclide in facilities of the fourth KWU/Siemens generation, so that it is used as reference nuclide. Due to the contemporary planned final shut-down of the three Convoy plants (besides other), dismantling work was set into focus of simulation. Simulation was conducted and results compared for Convoy plants and for plants of the older generations two and three. Furthermore, by comparative simulations the question was answered if full system decontamination in Convoy plants before dismantling lead to benefits that justify this measure. The determined dose saving during unmounting works at the steam generators caused by the decontamination is remarkable. An abdication of decontamination at this location would lead to doses much higher than the occupational job dose during steam generator dismantling in a decontaminated generation 2 facility.