Wyniki wyszukiwania - BazTech

1

Assessment of radionuclide migration and radiological human exposure at the closed near-surface radioactive waste repository

Gudelis A., Nedveckaite T., Prokopčiuk N., Filistovič V., Remeikis V., Motiejunas S.

Nukleonika

|

2010

|

Vol. 55, No. 2

251-259

EN

The near-surface “RADON” type radioactive waste repository, installed in 1963 and designed to store radioactive waste formed in industry, medicine and scientific investigations, was closed in 1989 because it did not meet the requirements imposed on the radioactive waste disposal. A comparatively small amount of radioactive waste is stored in this repository, but the inventory comprises various kinds of waste: short-lived low-level radioactive waste, short-lived low and intermediate radioactive waste, long-lived intermediate and high-level radioactive waste. The possible site-specific radionuclide migration through the groundwater pathway as well as the human exposure are considered by the computer program RESRAD-OFFSITE in this paper. The analysis of the obtained data shows that out of all stored radionuclides only H-3, C-14 and Cl-36 exceeding the dose constraint of 0.2 mSv can be considered as dangerous. The monitoring carried out in the repository environment has shown the contamination of groundwater with radioactive tritium and a significant reduction of contamination after construction of additional protective engineering barriers. For the assessment of the contribution of separate site-specific parameters of the model taking into account uncertainties of the model and parameters to the annual effective dose, the computer code RESRAD-OFFSITE provides the possibility of applying the regression analysis. It has been determined that the aquifer lateral dispersion as well as the hydraulic gradient, the radionuclide activity concentration in the repository together with the rate of penetration into the environment and the precipitation amount have the largest influence on the assessment accuracy of annual effective doses.

2

Pu(IV) and Fe(III) accumulation ability of heavy metal-tolerant soil fungi

Levinskaite L., Smirnov A., Lukšiene B., Druteikiene R., Remeikis V., Baltrunas D.

Nukleonika

|

2009

|

Vol. 54, No. 4

285-290

EN

The work was aimed at studying abilities of soil microorganisms to participate in metal/radionuclide mobility processes by accumulating them. Soil microorganisms were treated with a mixture of heavy metals (Cr(III), Ni, Fe(III), Mn(II), Cd) in order to isolate the most tolerant ones. Among more metal-tolerant microorganisms microscopic fungi dominated. Tests of fungal tolerance towards each metal showed that the most tolerant fungi to almost all metals were Aspergillus niger, Penicillium oxalicum and Paecilomyces lilacinus. Accumulation ability of metal-tolerant fungi was tested using Pu(IV) and Fe(III). Investigation of Pu accumulation by fungal biomass showed that all the fungi accumulated Pu, and among the most effective radionuclide accumulators Eupenicillium sp., Penicillium oxalicum and Aspergillus niger could be mentioned. All the fungi showed high Fe-accumulation capacity. While growing in the medium with 1 mM iron, most fungi accumulated over 90% of Fe in their biomass. Very good accumulation and growth abilities in Fe-supplemented medium were demonstrated by Paecilomyces lilacinus.

3

Plutonium and americium in sediments of Lithuanian lakes

Remeikis V., Gvozdaite R., Druteikiene R., Plukis A., Tarasiuk N., Špirkauskaite N.

Nukleonika

|

2005

|

Vol. 50, nr 2

61-66

EN

The assessment of contribution of the global and the Chernobyl NPP (Nuclear Power Plant) accident plutonium and americium to plutonium pollution in sediments of Lithuanian lakes is presented. Theoretical evaluation of activity ratios of 238Pu/239+240Pu and 241Pu/239+240Pu in the reactor of unit 4 of the Chernobyl NPP before the accident was performed by means of the ORIGEN-ARP code from the SCALE 4.4A program package. Non-uniform distribution of radionuclides in depositions on the Lithuanian territory after nuclear weapon tests and the Chernobyl NPP accident is experimentally observed by measuring the lake sediment pollution with actinides. The activity concentration of sediments polluted with plutonium ranges from 2.0 š 0.5 Bq/kg d.w. (dry weight) in Lake Asave . lis to 14 š 2 Bq/kg d.w. in Lake Juodis. The ratio of activity concentrations of plutonium isotopes 238Pu/239+240Pu measured by á-spectrometry in the 10-cm-thick upper layer of bottom sediment varies from 0.03 in Lake Juodis to 0.3 in Lake Žuvintas. The analysis of the ratio values shows that the deposition of the Chernobyl origin plutonium is prevailing in southern and south-western regions of Lithuania. Plutonium of nuclear weapon tests origin in sediments of lakes is observed on the whole territory of Lithuania, and it is especially distinct in central Lithuania. The americium activity due to 241Pu decay after the Chernobyl NPP accident and global depositions in bottom sediments of Lithuanian lakes has been evaluated to be from 0.9 to 5.7 Bq/kg.

4

Evaluation of the activity of irradiated graphite in the Ignalina Nuclear Power Plant RBMK-1500 reactor

Ancius D., Ridikas D., Remeikis V., Plukis A., Plukiene R., Cometto M.

Nukleonika

|

2005

|

Vol. 50, nr 3

113-120

EN

Ignalina NPP Unit 1 with the RBMK-1500 type reactor enters the preparatory stage for its decommissioning. A big volume of graphite has to be dismantled and managed. This paper evaluates the composition of radionuclides in irradiated graphite on the basis of the calculation scheme with computer codes MCNPX and CINDER'90. Full scale calculations take into account the whole energy spectrum of neutrons, the spatial neutron flux in different reactor structures and the impurities of RBMK-1500 graphite measured by two independent methods. Principal contributors to the total activity as well as other radionuclides important from the radiological point of view are identified. The uncertainties of such calculations are discussed.