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PubMed1984

Sorption of radiocesium by active silica.

Cement and cement components have previously been shown to exhibit negligible sorption for cesium. Pyrogenic silica has been examined as an additive to cement materials for its ability to reduce the leachability of cesium and to provide a host material with permanent sorption sites. The incorporation of silica into cement composites can also improve the physical characteristics and strength of these materials as long ages. At neutral pH values, there is significant sorption of cesium by silica, but in high pH regimes, such as occur in cement environments, initial sorption is enhanced but this high level of sorption is followed by a gradual release of Cs. This apparent desorption is due to the consumption of SiO2 by Ca(OH)2 to form products which have little sorption potential for cesium. If, however, sufficient SiO2 is added to the system initially such that an excess remains after satisfying the demands of the Ca(OH)2 reaction, permanent sorption sites for cesium may be created.

Calcium Hydroxide↗
PubMed1985

Radiocesium levels in Irish Sea fish and the resulting dose to the population of the Irish Republic.

Discharges of radioactive materials from the nuclear fuel reprocessing plant at Sellafield in the United Kingdom give rise to 137Cs and 134Cs in fish caught in the Irish Sea. Measurements made on fish catches landed in the Irish Republic show average activities of 68 and 3 Bq/kg (wet) of 137Cs and 134Cs, respectively. The estimated population dose to the Irish public is approximately 2 man-Sv y-1 and the possible dose to a member of the critical group is 1.4% of the limit recommended by the International Commission on Radiological Protection.

Animals↗
PubMed1985

A field study of Ra accumulation in trout with assessment of radiation dose to man.

The purpose of this study was to determine the concentrations of 226Ra in edible fish from surface ponds near an open pit U mine. Because one reclamation plan for the U mine proposed formation of an artificial lake in the open pit, potential radiation dose to man from ingestion of fish needed to be investigated. Trout were collected from four existing ponds which varied in mean 226Ra concentration from 12-33 pCi/l. and in Ca concentration from 30-330 mg Ca/l. Radium and Ca accumulation in trout flesh, skin, fins and bone were measured. Geometric mean concentrations of 226Ra in trout flesh from four ponds ranged from 6.3-30 pCi/kg wet weight. The distribution of Ra in the trout body was similar to that of Ca. Of the total 226Ra in trout carcasses, 6% was in flesh, 25% was in skin, 28% was in fins, and 41% was in bone. Mean concentration factors for 226Ra in trout flesh from the four ponds ranged from 0.29-2.5. Bone concentration factors were up to 260 times higher than for flesh. Observed ratios (Ra/Ca in fish tissue divided by Ra/Ca in water) were used to normalize the differences in Ca availability among the locations. Observed ratios were higher in all tissues of fish which had been in the ponds for a longer time, indicating that 226Ra concentrations in fish may increase with continued exposure to the nuclide. The calculated dose equivalent commitment to human endosteal tissue ranged from 0.2-2 mrem per fish consumed, depending on the assumed dietary and environmental parameters. Neglecting the consumption of trout skin underestimated the ingestion dose from 226Ra by a factor of 5-10. Estimated annual dose equivalent rates to human endosteal tissue ranged from 1.0-83 mrem/yr for an individual who consumed one fish per week for a 50-yr period. The dose to man from ingestion of 226Ra in fish would not likely preclude the establishment of a recreational lake at this site.

Animals↗
PubMed1985

Efficiency estimation for detecting U alpha particles in solid-state nuclear track detectors.

The detection efficiencies of solid-state nuclear track detectors, made with cellulose nitrate materials (LR-115 II) or allyl diglycol carbonate (CR-39) were investigated. Detection efficiency for a surface alpha source was experimentally obtained by changing the dimensions between the detector and the source, while alpha-particle incident efficiency was calculated. The ratio of the detection efficiency to the incident efficiency was then determined. It was confirmed that the ratio for LR-115 II was dependent on energy, but for CR-39 the ratio showed almost no dependency. Considering the relationship between solid absorber thickness and detection efficiency of the surface alpha source, detection efficiencies of U in various metals were estimated. The efficiency for U contained in Al and Fe was proposed as 16% for LR-115 II and 22% for CR-39. Using these efficiencies, amounts of U in some Al and Fe ingots were determined. These agreed with concentrations obtained by neutron-activation analysis with deviations of less than 15%.

Alpha Particles↗
PubMed1986

Steady-state Rn diffusion through tailings and multiple layers of covering materials.

Uranium tailings piles are generally rehabilitated by covering them with a number of layers of earthen materials. This paper derives exact equations for the Rn concentration profile and flux attenuation through any number of covering layers. The equations take account of the distribution of Rn between interstitial air and water. Numerical examples are given to show that approximate methods give rise to significant errors in some circumstances. The flux attenuation factor depends not only on the diffusion coefficient, porosity, moisture content and thickness of each layer but also upon the order of placement. To achieve maximum flux attenuation, the least permeable material should be uppermost.

Air↗
PubMed1986

Transfer coefficient of 226Ra from vegetation to meadow voles, Microtus pennsylvanicus, on U mill tailings.

The 226Ra level in vegetation growing on U mine tailings in Elliot Lake, Ontario, Canada, was 211 + 22 mBq g-1 (dry weight) compared to less than 7 mBq g-1 (dry weight) in material from a control site. Skeletons of meadow voles (Microtus pennsylvanicus) established on the tailings had concentrations of 226Ra of 6,083 +/- 673 mBq per animal in winter; 7,163 +/- 1,077 mBq per animal in spring; 1,506 +/- 625 mBq per animal in summer; and 703 +/- 59 mBq per animal in fall, compared to less than 7 mBq per animal in controls. The 226Ra transfer coefficient from vegetation to voles (defined as total millibecquerels of 226Ra in adult vole per total millibecquerels of 226Ra consumed by the vole in its lifetime) was calculated as 4.6 +/- 2.9 X 10(-2) in summer and 2.8 +/- 0.6 X 10(-2) in fall.

Animals↗
PubMed1986

Radiation data input for the design of dry or semi-dry U tailings disposal.

Before discussion of design criteria for the handling of dry or semi-dry tailings, it is necessary to obtain an insight into the radiation levels associated with the tailings particles and to study the basic physical properties of dry tailings. This article presents the experimental results of assessing Ra and specific alpha-activity distribution with respect to particle size of the Ranger (RUM) and Nabarlek (QML) uranium mines dry tailings samples. The variation of Rn emanation coefficient versus particle size of dry tailings has also been measured. The nuclear-track detection technique, gamma spectrometry and alpha counting were used for the above measurements. Surface Rn flux from the hypothetical Nabarlek semi-infinite dry tailings pile is 32 Bq m-2 s-1 and the Rn flux for Ranger is 10 Bq m-2 s-1. The theoretical exposure rates for 1 m above these hypothetical tailings piles are 0.95 microC kg-1 h-1 and 0.28 microC kg-1 h-1, respectively. The derived air alpha-contamination limits (DAAC) for the tailings dust were calculated to be 1.2 Bq m-3 for workers and 0.034 Bq m-3 for a member of the public. The limit for workers corresponds to the air tailings dust concentration of 0.79 mg m-3 for QML tailings and 2.2 mg m-3 for RUM tailings. The DAAC limit for the public corresponds to the air tailings dust concentration of 0.022 mg m-3 for QML tailings and 0.064 mg m-3 for RUM tailings.

Air Pollution, Radioactive↗
PubMed1988

Uptake of 226Ra by established vegetation and black cutworm larvae, Agrotis ipsilon (class Insecta: order Lepidoptera), on U mill tailings at Elliot Lake, Canada.

Radium-226 levels in samples from an inactive U tailings site at Elliot Lake, Ontario, Canada, were: 9,140 +/- 500 mBq g-1 dry weight in the substrate; 62 +/- 1 mBq g-1 dry weight in rye, Secale cereale, and less than 3.7 mBq g-1 dry weight in oats, Avena sativa, the dominant species established by revegetation of the tailings; and 117 +/- 7 mBq g-1 dry weight in washed and unwashed black cutworm larvae. Concentration ratios were: vegetation to tailings 0.001-0.007; black cutworms to vegetation 3.6 and black cutworms to tailings 0.01. The values are considered too low to be considered a hazard to herring gulls, Larus argentatus, which occasionally feed on cutworms.

Animals↗