Table 1. Effective annual dose for each analysed workspace Radon Concentration estimation for the working area within the Radioactive Waste Treatment Station from Bucharest, Romania L.C. Tugulan1, A. Chirosca2, D. Vlaicu1, C. Ciobanu1, F. Dragolici1 and G. Chirosca3 1Horia Hulubei National Institute for Physics and Nuclear Engineering, IFIN-HH, POB MG-6, Magurele, Bucharest 077125, Romania 2University of Bucharest, Department of Structure of Matter, Earth and Atmospheric Physics and Astrophysics, 405, Atomistilor str., P.O. MG-11, RO - 077125 Magurele (Ilfov), Romania 3University of Bucharest, Doctoral School for Physics, 405, Atomistilor str., P.O. Box MG-11, RO - 077125 Magurele (Ilfov), Romania Keywords: natural radionuclide, radon concentration, dose estimation. Presenting author email: catalin.ciobanu@nipne.ro Introduction The VVR-S research reactor at Magurele was commissioned in 1957 (Pavelescu and Dragusin, 2012), shortly followed by the Radioactive Waste Treatment Station (STDR) in 1975 (Dragolici et al., 2003) as a necessary step in conditioning the radioactive waste produced in research activities performed at this reactor. In the following years, Romania expanded its activities using radioactive materials in fields such as industry, research or medicine and this led to an increase of the volumes of radioactive waste that STDR needs to condition. Radon is a natural occurring radionuclide present in building materials and in small quantities, in the radioactive waste that are collected, handled and conditioned in order to ensure safe storage (only traces of 226Ra or 238U) and it can provide significant contribution to total deep dose for the personnel. This is important especially in the case of long term exposure within the station and other non-ventilated areas. National regulations, through the National Commission for Nuclear Activity Control (CNCAN) limits the Radon exposure to 55 Bq/m3 for the population and 1110 Bq/m3 for exposed personnel leading to an annual dose of 1 mSv/y (CNCAN, 2002). The main component for human exposure to radiation is the Rn-222 present within all enclosed areas. Due to this, the EU Directive 2013/59/EURATOM recommends to all Member States to establish an accurate assessment for the Radon (Rn-222) concentration within working places. Materials and methods All Radon measurements in air were performed with AlphaGUARD PQ2000 produced by Saphymo GmbH. Data processing was performed using the AlphaView-EXPER software provided with the detector. The analysed workplaces within the STDR, where radon concentrations in air were measured are presented in Figure 1. There are two types of places: working areas and waste treatment and characterization areas. All exposed workers within STDR perform activities in both locations, in the offices but also within the waste treatment and characterization areas. In order to provide accurate results, storage places were included in this study even if they are not ventilated rooms (naturally or artificially). This leads to radon accumulation and thus to a higher risk for the workers performing activities within such areas (exposure may vary from one hour to 8 hours). Figure 1. Measurement points for radon in air According to the specific duties, there is a specific cycle when the STDR personnel performs its tasks. For this particular study we considered a cycle of 1 week. This leads to measurements using the 60 minutes integration time while keeping the detector in diffusion mode for up to one week for each of the points from Figure 1. In order to test the efficiency of the ventilation system, another measurement was performed within the waste characterisation and treatment areas while the ventilation system was on. Such measurements used 10 minutes integration time while keeping the detector in flow mode for 2 hours for each analysed point. According the later UNSCEAR report (UNSCEAR, 2008), the conversion factor from radon concentration to EEC is 0.4 leading to an EEC of EEC = 0.4 • Cexp Where Cexp is the recorded concentration. According to literature (UNSCEAR, 2006 and ICRP, 1993) the conversion factor from EEC to equivalent dose is 8 nSv/(Bq·h·m3). Keeping in mind that in one month there are 170 work hours (UNSCEAR, 2008) and 11 working months a year, any STDR worker is exposed for 1870 hours per year. The results from this computations are presented in Table 1 were also average values are presented. All results from Table 1 show that we can define two distinct groups, the working areas and the waste treatment and characterization areas. The concentration to dose rate conversion coefficients present specific issues related to the average value used for the conversion, as you can see in Figure 2, the concentrations determined with the active detector have specific large amplitude oscillations and an average is hard to assess. The biggest amplitude oscillation is due to the ventilation system, when the concentration drops rapidly from 200 Bq/m3 to less than 30 Bq/m3 within less than two hours after the system is started (in the case of Aqueous Radioactive Treatment Area – Figure 2). In Figure 3 we have the radon concentration evolution for Aqueous Radioactive Treatment Area for 2 hours after the ventilation system started. Figure 2. Radon concentration within the Aqueous Radioactive Treatment Area  Figure 3. Radon contribution evolution for Aqueous Radioactive Treatment Area recorded two hours after the ventilation was started. Results and discussion In order to apply the constraints from 2013/59/EURATOM, the annual effective dose was estimated using the concentration to dose rate conversion coefficients proposed by UNSCEAR, 2008; ICRP, 1993 and L.C. Tugulan et al., 2015. For a correct Radon dose assessment, the Equivalent Equilibrium Concentration (EEC) was computed using UNSCEAR coefficients (UNSCEAR, 2006) ensuring that both radon concentration and its descendants are giving their contribution to the computed dose. Table 1. Effective annual dose for each analysed workspace conclusions The raw results from Table 1 show that for certain workplaces the annual effective dose is above the 1 mSv/year constraint and especially for this type of workplaces the use of the ventilation system and the reduction of the exposure time are highly recommended as they are effective in lowering the exposure of human workers employed in STDR. For workplaces like 0-23. 0-23C, 1-10, 1-13 and 1-14 the authors recommend that the activity should start only after completing a 2 hours ventilation cycle.  References: A. O. Pavelescu and M. Dragusin, 2012. Clean-Up and decontamination of hot-cells from the IFIN-HH VVR-S research reactor, Radioactive Waste, Dr. Rehab Abdel Rahman (Ed), ISBN 978-953-51-0551-0, InTech; F. Dragolici, C.N. Turcanu, Gh. Rotarescu, I Paunica, 2003. Technical aspects regarding the management of radioactive waste from decommissioning of nuclear facilities, Waste Management Conference, February 23-27, Tucson, USA; CNCAN, 2002, Radiological safety rules for operational radiological protection in mining and preparation of uranium and thorium ores (NMR 01), Romanian Official Gazette, part 1. Nr. 677 / 12.09.2002; Directive 2013/59/EURATOM. Laying down basic safety standards for protection against the dangers arising from exposure to ionizing radiation; National Commission for Nuclear Activities Control, 2000. Fundamental Norms for Radiological Safety NSR 01, Official Bulletin, part I, no.404/29.08.2000; L.C. Tugulan et al., 2015. Radiation exposure in underground low activity radioactive waste repository. Rom. Journ. Phys., Vol. 60, Nos. 9-10, P. 1598–1605; United Nations Scientic Committee on the Eects of Atomic Radiation - 2006. UNSCEAR 2006. Report to the General Assembly, with Scientic Annexes. United Nations, NewYork; United Nations Scientific Committee on the Effects of Atomic Radiation, 2010. UNSCEAR 2008. Report to General Assembly with Scientific Annexes. United Nations, New York.