ALARA optimization at decommissioning of NPP A1, Slovak Republic, using advancedradiation protection tools

摘要

Decommissioning operations effect changes in the environment and lead to situations whereoccupational doses strongly depend on space distribution of dose rates (DR) and time duration of criticalactivities. In such cases one needs an adequate geometrical and source model that allows the user to calculate theDR dose exposures. In the end a comparison of doses for alternative sets of work trajectories can lead to theselection of the most adequate scenario with minimised dose burden to the workers. The use of laser scanningwith respective as-built 3D modeling software, gamma imagery of the dominant sources and application of 3DALARA planning tool, VISIPLAN, for the above mentioned purposes was the solution advised by EDF, thetechnical advisor within the IAEA TCP SLR/4008 project. The agove-mentioned components were intended tocreate a 3D technological chain ensuring acquisition and evaluation of digitized information leading to ALARAoptimisation of the decommissioning work procedures. In the case of very complex structures to be modelled forALARA purposes, an auxiliary code, VISIMODELLER, allows the direct transfer of already existing 3D objectsto VISIPLAN. This means the saving of a lot of man-power in drawing the geometry. For gamma imaging andpositioning of main sources in the installation the old version gamma camera, ALADIN, owned by NPP A1 wasused. Applications of radiation protection techniques at NPP A1 decommissioning project are presented in thepaper. These range from simple shielding application by the 3D VISIPLAN planning tool, or creating a 3D asbuiltmodel, to ALARA applications for alternative work trajectories in complex geometrical and hostileenvironment with multiple sources. As examples, removal of plastic liner from large underground reservoirs andremoval of contaminated pipes from a long corridor are described in more detail.