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- Author or Editor: C. Miro x
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Abstract
We describe the procedure developed for the electrolytic concentration of3H in water, together with systematically applied checks to guarantee the reproducibility of the process and to minimize the variability between water samples concentrated simultaneously in the different electrolytic cells. Starting from initial volume of 250 ml water, we obtained enrichment parameters normally greater than 70%, with a dispersion always less than 5%. Measuring the concentrated and the unelectrolyzed samples under the same conditions, we found that the lowest detectable activities had been improved from around 1.5 to 0.3 Bq/l. This allowed us to quantify the3H activity levels of 100% of the rainwater samples collected in Cáceres from 1994 to 1996. The resulting average value for this period was (0.79±0.38) Bq/l.
Abstract
From 1994 to 1996 we have studied a number of radioactive (total b and residual b-activity levels and 3H activity) and physico-chemical (pH, conductivity, and natural potassium content) parameters in the water of two Alcántara and Guadiloba reservoirs, which are artificially connected by interbasin transfers. The analysis of the results showed the existence of major correlations between the two systems for tritium activity, conductivity, and stable potassium content. A model based on the water balance in the Guadiloba reservoir was also elaborated which allowed us to forecast its effective surface area monthly, which varied extraordinarily between 0.405 and 135 km2.
Abstract
With the object of quantifying the radiological impact that the Almaraz Nuclear Power Station, situated beside the Tajo river in Spain, induces on its ecosystem, since 1986 we have been carrying out multiple gamma-spectrometric studies and determinations of90Sr concentrations on the receptor media: surface waters, sediments, fishes, aerosols, and soils, in the two likeliest critical transmission pathways of transmission of the radioactive contamination. The principal results are summarized in the present work, and they allow the impact to be quantified, as well as the most probable source to be assigned for each of the levels detected.
Abstract
An analysis has been made of the surface distribution of137Cs and90Sr in soils of the province of Cáceres (Spain), of some 20.000 km2 area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding137Cs/90Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.
Abstract
The radioactive concentrations of226Ra,232Th,235U and40K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationA e =(P 1/R)+P 2 describes the dependence of the specific activityA e on radiusR, P 1 andP 2 being parameters that are related to the surface area and volume activities of the grains. The isotopes226Ra,232Th and235U accumulate with greater intensity on the surface of the grains than40K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.
Abstract
We have quantified the evolution during 1994 of the impact on the Tagus river of liquid releases of3H (51.3 TBq in the cited year), originating from the functioning of the Almaraz Nuclear Power Plant, and conditioned by the management of the cooling reservoir water. Taking into account, on the one hand, that tritiated water is hydrodynamically indistinguishable from untritiated water when both form part of the same mass of liquid, and, on the other, the practically null stratification and forced circulation of the water in the cited cooling reservoir, together with the hydrological fluxes interchanged between the said reservoir and the Tagus river (which is entirely regulated in the section under study and, because of prolonged drought, had a relatively small flow during the study period), we were able to model satisfactorily the temporal evolution of the3H activity in the cooling reservoir.
Abstract
The mean weekly levels of7Be in the atmosphere of Cáceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of7Be into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of7Be out of the atmosphere by rain. From the quantification of these two effects, the residence time of7Be was determined in the atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of7Be, we were able to justify the diversity of values obtained for the deposition of137Cs in different soils of the province of Cáceres due to the fallout from atmospheric nuclear blasts.
