In this work the development results of the TRI-TIUM project is presented. The main objective of the project is the construction of a near real-time monitor for low activity tritium in water, aimed at in-situ surveillance and radiological protection of river water in the vicinity of nuclear power plants. The European Council Directive 2013/51/Euratom requires that the maximum level of tritium in water for human consumption to be lower than 100 Bq/L. Tritium levels in the cooling water of nuclear power plants in normal operation are much higher than the levels caused by the natural and cosmogenic components, and may easily surmount the limit required by the Directive. The current liquid-scintillation measuring systems in environmental radioactivity laboratories are sensitive to such low levels, but they are not suitable for real-time monitoring. Moreover, there is no currently available device with enough sensitivity and monitoring capabilities that could be used for surveillance of the cooling water of nuclear power plants. A detector system based on scintillation fibers read out by photomultiplier tubes (PMTs) or silicon photomultiplier (SiPM) arrays is under development for in-water tritium measurement. This detector will be installed in the vicinity of Almaraz nuclear power plant (Spain) in Spring 2019. An overview of the project development and the results of first prototypes are presented.

Abstract. The study presented here, being its main goal to evaluate the behaviour of natural radionuclides in coal combustion, is part of a wider study carried out by CIEMAT and the University of Extremadura (UEX). The research is addressed to the radiological evaluation of the workers and the public as a result of the operation of the four biggest Spanish Coal-Fired Power Plants (CFPPs). Some generally used effects were confirmed in this study, as the difference in concentration of 210 Po in fly and bottom-ashes. Enrichment factors relative to 40 K as defined by UNSCEAR were found to be a little different than expected. 210 Po enrichment was found in gypsum (material obtained as a by-product in the desulphuration process). In order to confirm the assumption considered to explain difference in 232 Th activity concentration between bottom and fly ashes, carbon content was measured, obtaining that it should be reviewed.

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In situ gamma spectrometry (ISGS) is a technique mainly focused on the determination of man-made radionuclides deposited on soils. It is widely used for the radioactive characterization of soils in which there has been an incorporation of such radionuclides, especially Cs. Its use for the activity determination of naturally occurring radionuclides in soils has been more limited, and the accuracy associated with those measurements has yet to be treated extensively. There are numerous factors affecting the accuracy of the activity determination of naturally occurring radionuclides, such as the assumed soil geometry, the soil's geological and mineral composition, its moisture content, etc. The present work studies the accuracy associated with the ISGS determination of the activity concentrations of natural radionuclides in soils using a portable HPGe detector. ForK and Th activity determinations, the uncertainties associated with ISGS are generally of the order of 15%. However,Ra activity determined from its daughters Pb andBi can be significantly overestimated when there is a major presence of Rn in the air around the detector. Finally, absorbed dose rate in air values were calculated from the naturally occurring radionuclide concentration in soils. The results showed good correspondence between the values obtained from ISGS and those obtained from laboratory determinations with the same soils.