Monitoring of characteristics of the radiation situation in close surrounding of the decommissioned NPP A1 by an independent organization is described and discussed in the paper. The measurements are carried out in the NPP A1 site close to the VUJE operation building, not far from the places, where the decommissioning activities are concentrated. These activities relate to bringing the NPP A1 to safer conditions, e.g. cleanup of contaminated underground waste water reservoirs, solidification of the removed sludge from these reservoirs by an in situ open air solidification system, cleaning of contaminated concretes and so on. Other activities also relate to radiological impact to the environment, e.g. radioactive waste processing at Bohunice RW -Ttreatment Centre and intensive traffic of sources of ionising radiation to and from this centre located very close to the place mentioned above. Results of the measurements carried out by VUJE accredited laboratory in the frame of Decommissioning project of NPP A1 present an uninterrupted time series of measurements and enable evaluation of development for the last 17 years. The monitoring results demonstrate that the only significant radionuclide indicating radiological impact of the decommissioning is 137Cs. Its activity concentration in atmospheric aerosols at the sampling point has been time to time elevated and in average is by about one order higher in comparison with a 100 km far reference (background) site.
Uncertainty analysis for nondestructive estimation of contamination depth is presented. The contamination depth was determined using the peak-to-peak method as an in-situ measurement in which gamma spectra were measured by an HPGe detector. Since exponential activity distribution is a crucial assumption of this method, the distribution profile was confirmed by laboratory tests of core drill samples. The main parameter influencing uncertainty of contamination depth is uncertainty of relaxation length. The uncertainty is composed for statistical error represented by the ratio of net peak areas and systematic error given detection efficiency of measurement setup. Systematic relative error was evaluated to be 7.45%. Statistical relative error was evaluated to 9.97% for the proposed optimum net peak area. Variability of relaxation length was identified to be very low with mean value 2 mm with standard deviation 0.73 mm. For fixed relaxation length, it should be possible to estimate contamination depth by nonspectrometric devices.
Environmental remediation at NPP A1 site is even presently a continual process of removing the contamination from the ground or auxuliary objects within the NPP A-1 site with accidentally shut down reactor. This paper mainly deal with monitoring, sorting out and disposal of large volumes of removed contaminated soil stored temporarily until now at the site which is necessary for enhancement of environmental radiation situation at the site. It was also one of the topic of the Decommissioning Project of NPP A1, Slovakia, - Phase No I, lasted from 1999 to 2008. Within the project, attention was paid to development of technical tools for handling with and monitoring of large volume of contaminated soil, as well. Besides short description of contaminated lands at the site, sources of their contamination and to date known inventory, details of a pilot contaminated soil sorting facility developed and tested recently within the Decommissioning project will be described and discussed in the papper. The paper topics include description of and uncertainty analysis results for the pilot soil sorting system based on the Canberra-Packard pilot conveyer belt monitor with a pair of 1.5 inch LaBr scintilation detectors and integrated electronic belt scale. In addition experiences learned during the metrological testing and operational trial will be summarised. MDA for Cs-137 of this system is 140 Bq/kg for 30 kg and 50 Bq/kg for 300 kg parts of soil at 500 Bq/kg of 40K and 0.15 mikroGy/h.
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