RADIATION SHIELDING AND DOSE ASSESSMENT OF THE CYCLOTRON FACILITY AT INRNE-BAS

The Institute for Nuclear Research and Nuclear Energy at the Bulgarian Academy of Sciences is working on the construction of a cyclotron centre. The facility is on a design level. At this stage of the project, an important task is the radiation shielding assessment of the facility. Nowadays, the Monte Carlo transport codes have become the tool of choice for solving this type of problem. In the current paper, the transport code FLUKA is used for the calculations. It is widely applied for shielding design and analysis of accelerators and their components. The distributions of the radiation fields inside and outside the cyclotron bunker are presented in this paper. Both different irradiation scenarios and bunker configurations are considered in the conducted Monte Carlo simulations. These results will be used as a guidance in site planning.</jats:p

Current status and research activity at the INRNE cyclotron laboratory

A review and update on the status of the Cyclotron Physics Laboratory at the Institute for Nuclear Research and Nuclear Energy as well as related research activity is presented. The main part of the research activities at the Cyclotron Physics Laboratory is directed to simulations for design considerations, for the cyclotron vault for some of the target radioisotopes. In this paper, a review on the simulations, conducted at the laboratory, related to 18F production is included. A model for studying the effect of attenuation and absorption of neutron radiation, emitted by a point source with fixed energy of 14.1 MeV is developed. Preliminary results from this study are shown

Activation cross-sections for short-lived reaction products on hafnium isotopes induced by 1 – 20 MeV neutrons

Results of new activation cross-section measurements for production of 178m1Hf (T1/2 = 4.0 s) and 179m1Hf (T1/2 = 18.67 s) are presented for the following reactions: 178Hf(n,n´)178m1Hf, 179Hf(n,2n)178m1Hf, 180Hf(n,3n)178m1Hf, 179Hf(n,n´)179m1Hf, and 180Hf(n,2n)179m1Hf. The irradiations were carried out at the 7-MV Van de Graaff accelerator at EC-JRC, Geel. Neutrons in the 1-3 MeV energy range were produced via the 3H(p,n)3He reaction. Deuteron beam and a deuterium gas target were used to produce 5 and 6 MeV neutrons. For the production of quasi-monoenergetic neutrons between 16 and 19.5 MeV the 3H(d,n)4He reactions was employed. Both samples with natural composition and isotopic enrichment were employed to differentiate reactions leading to the same product. An automated pneumatic system was used for the sample irradiation, transport and radioactivity measurements. The radioactivity of the samples was determined by standard gamma-spectrometry using HPGe detector. The results obtained in the present work are compared with the data from other authors and TENDL-2017 evaluation

DISTRIBUTION OF TRITIUM IN SURFACE WATER AND PRECIPITATION IN RILA MOUNTAIN, BULGARIA

A study of the tritium content of surface water from three Rila lakes – Moussala lake, Aleko lake and Ice lake, and precipitation at Moussala mount has been performed by means of high precision nuclear and radiochemical methods. The measurements are part of a long-term environmental monitoring program developed and maintained by the Institute for Nuclear Research and Nuclear Energy, Bulgaria Academy of Science. The results for lake water and precipitation samples collected at Moussala part of Rila over the period 2012–2017 were found to range from ˂ 1.20 to 2.77 Bq.L-1 and from 2.14 to 4.12 Bq.L-1 respectively. The content of 3H in all samples is below the recommended level of 100 Bq.L-1. The obtained new results are used to assess the radiation status of the investigated water sources and can be used for evaluation of possible future changes and trends.</jats:p

URANIUM AND 210PO RADIONUCLIDES IN DRINKING WATER IN SOUTHERN BULGARIA AND EXPECTED RADIATION DOSES

Abstract The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have been determined for the first time in drinking water from certain sources in Southern Bulgaria using nuclear and radiochemical methods. The results obtained for the water samples vary in the intervals 0.6–678 mBq l−1 for 238U, 1.4–1484 mBq l−1 for 234U, &amp;lt;0.3–13.6 mBq l−1 for 210Po and 1.04–10.6 for the 234U/238U ratio. The annual effective dose from 238U, 234U and 210Po ranges from 1.09 to 44.1 μSv y−1, 0.78 to 46.8 μSv y−1 and 0.77 to 62.8 μSv y−1 for infants, children and adults, respectively. The annual effective dose due to consumption of drinking water is below the individual dose criterion of 100 μSv y−1 recommended by the World Health Organization. The natural radioactivity of the water sources investigated is below the national and international limits.</jats:p

Efficiency Assessment of Sanitary-Technical Barriers in Nuclear Facilities by Means of Adhesive Decontaminating Foils

The efficiency of sanitary-technical barriers in Kozloduy NPP, Bulgaria, is investigated for the first time with adhesive decontaminating foils. The duration of use and retention coefficient are assessed using gamma-ray spectroscopy. The retained activity increases linearly up to a saturation point at 250 controlled persons. About 6% of the radioactive mechanical fraction is fixed on the adhesive. For three successive sanitary-technical barriers in the controlled zone, the activity is reduced by one to two orders of magnitude on each barrier towards the sanitary complex exit. The total activity released during annual maintenance is estimated to be 105 Bq. The radioactive contamination in the controlled zone is studied and correlations are established between two groups of isotopes, generated by the release of fission products and by neutron activation.Our investigation demonstrates that the sanitary technical barriers prevent efficiently the release of radioactivity from the controlled zone to the environment.</jats:p