Environmental Radiological Studies Downstream from the Rancho Seco Nuclear Power Generating Station, 1985
Environmental Radiological Studies Downstream from the Rancho Seco Nuclear Power Generating Station, 1985

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Published: 1986

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Information compiled in 1985 while assessing the environmental impact of radionuclides previously discharged with aqueous releases from the Rancho Seco Nuclear Power Generating Plant is presented. In October 1984, the quantities of gamma-emitting radionuclides in water discharged to Clay Creek from the plant were reduced below operationally defined detection limits for liquid effluents. However, radionuclides previously discharged persist in the downstream environment and are found in many aquatic dietary components. 134Cs and 137Cs are the primary gamma-emitting radionuclides detected in the edible flesh of different fish, crayfish, and frogs. Coefficients for exponential equations are generated, from a least square analysis, that relate the change in concentration of 137Cs in fish to distance downstream and time between March and October 1985. Concentrations of 137Cs in surface creek sediments also decreased in the downstream direction much in the same manner as concentrations decreased in fish. However, there was no significant difference in the radiocesium concentrations in surface sediements collected from comparable locations during both 1984 and 1985.

Environmental Radiological Studies Downstream from Rancho Seco Nuclear Power Generating Station
Environmental Radiological Studies Downstream from Rancho Seco Nuclear Power Generating Station

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Published: 1985

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This report summarizes the information compiled in 1984 while assessing the environmental impact of radionuclides in aquatic releases from the Rancho Seco Nuclear Power Generating Station. Gamma-emitting radionuclides discharged since 1981 are found in many of the dietary components derived from the creeks receiving the effluent wastewater. Some soils and crops are found to contain radionuclides that originate from the contaminated water that was transferred to land during the irrigation season. 134Cs and 137Cs are the primary gamma-emitting radionuclides detected in the edible flesh of fish from the creeks. Concentrations in the flesh of fish decreased exponentially with distance from the plant. No significant differences in the 137Cs activity were found between male and female fish of equal size, but concentrations may vary in fish of different size, with the season and diet. 21% of the total 137Cs and 134Cs discharged between 1981 and 1984 is associated with the creek sediments to a distance of 27 km from the plant. Fractions of the missing inventory have been transferred to land during the irrigation season or to downstream regions more distant than 27 km from the plant. The radiocesium content of the sediments in 1984 decreased significantly in a downstream direction, much in the same manner as concentrations decreased in fish. Radioactivity originating from the plant was not above detection limits in any terrestrial food item sampled beyond 6.5 km from the plant. Based on the usage factors provided by individuals interviewed in a 1984 survey, the fish and aquatic-organism ingestion pathway contributed the largest radiological dose to humans utilizing products contaminated with the radionuclides in the liquid wastes discharged from the Rancho Seco Nuclear Power Generating Station in 1984.

Environmental Radiological Studies in 1989 Near the Rancho Seco Nuclear Power Generating Station
Environmental Radiological Studies in 1989 Near the Rancho Seco Nuclear Power Generating Station

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Published: 1990

Total Pages: 38

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In December 1988, the Sacramento Municipal Utilities District (SMUD) asked the Lawrence Livermore National Laboratory's (LLNL) Environmental Sciences Division (ENV) to collect sediment, water, and fish samples downstream from the Rancho Seco Nuclear Power Generating Station for analysis of radionuclides to compare with results from earlier surveys in 1984 through 1987 (1--8). ENV was, however, asked to reduce the total number of sample collections to a minimum in this study because of financial constraints. The proposal ENV submitted for the 1989 Environmental Radiological Studies downstream of the Rancho Seco Nuclear Power Generating Station reflected this reduction, but we believe, nevertheless, the 1989 efforts do allow us to make some meaningful comparisons with the previous studies. Cesium-137 is the most significant radionuclide still observed downstream from the Rancho Seco Nuclear Power Plant. Only occasionally is 134Cs or 6°CO observed. In 1989, the concentration of 137Cs in the water and fish decreased with distance from the plant to the same level that is was in 1987, and was lower than it had been from 1984 through 1986. The concentration ratio (CR) for 137Cs in fish is between 1000 and 1500, which is below the NRC default value of 2000. Physical mixing in the creek environment has moved the 137Cs deeper into the sediment column, thereby reducing the concentration in the top 12 cm relative to that in previous years. 8 refs., 18 figs., 9 tabs.

Environmental Radiological Studies Conducted During 1986 in the Vicinity of the Rancho Seco Nuclear Power Generating Station
Environmental Radiological Studies Conducted During 1986 in the Vicinity of the Rancho Seco Nuclear Power Generating Station

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Published: 1987

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This report summarizes the information compiled in 1986 for our assessment of the environmental impact of radionuclides discharged with aqueous releases from the Rancho Seco Nuclear Power Generating Plant. In October 1984, a liquid-effluent control program was initiated that significantly reduced the quantities of radionuclides discharged with liquid waste from the plant. However, results from our sampling program in 1986 indicate that previously discharged radionuclides persist in the downstream environment and are found in many aquatic dietary components although at concentrations much lower than those measured in 1984 and 1985. The greatly reduced activities in the dietary components from the aquatic environment attest to the effectiveness of the liquid-effluent control program. Concentrations in the flesh of fish from the creeks have decreased over time and with distance from the plant outfall. The mean concentration of 137Cs in fish collected from Laguna Creek at locations more than 7.5 km from Rancho Seco is now comparable to the concentration determined in fresh-water fish randomly selected from Chicago, Illinois, markets. By August 1986, the mean concentration of 137Cs in the flesh of bluegill had fallen to 7% of the concentration measured in fish from comparable locations in 1984 and was 30% of the mean concentration measured in these fish during August 1985. Stable potassium in the water plays a major role in the accumulation of 137Cs by fish. Concentrations of 137Cs in the surface sections of creek sediments also declined between the end of 1984 and 1986 with an effective half-life of approximately 2 y. Surface soils collected around a perimeter 11 km from Rancho Seco and from ranchlands closer to the plant showed only concentrations of 137Cs originating from global fallout. Soils previously irrigated with Clay Creek water retain levels of both 134Cs and 137Cs.