Upward movement of plutonium to surface sediments during an 11-year field study.

An 11-year lysimeter study was established to monitor the movement of Pu through vadose zone sediments. Sediment Pu concentrations as a function of depth indicated that some Pu moved upward from the buried source material. Subsequent numerical modeling suggested that the upward movement was largely the result of invading grasses taking up the Pu and translocating it upward. The objective of this study was to determine if the Pu of surface sediments originated from atmosphere fallout or from the buried lysimeter source material (weapons-grade Pu), providing additional evidence that plants were involved in the upward migration of Pu. The (240)Pu/(239)Pu and (242)Pu/(239)Pu atomic fraction ratios of the lysimeter surface sediments, as determined by Thermal Ionization Mass Spectroscopy (TIMS), were 0.063 and 0.00045, respectively; consistent with the signatures of the weapons-grade Pu. Our numerical simulations indicate that because plants create a large water flux, small concentrations over multiple years may result in a measurable accumulation of Pu on the ground surface. These results may have implications on the conceptual model for calculating risk associated with long-term stewardship and monitored natural attenuation management of Pu contaminated subsurface and surface sediments.

Tritium and plutonium in waters from the Bering and Chukchi seas.

During the summer of 1993, seawater in the Bering and Chukchi Seas was sampled on a joint Russian-American cruise [BERPAC] of the RV Okean to determine concentrations of tritium, 239Pu and 240Pu. Concentrations of tritium were determined by electrolytic enrichment and liquid scintillation counting. Tritium levels ranged up to 420 mBq L(-1) and showed no evidence of inputs other than those attributed to atmospheric nuclear weapons testing. Plutonium was recovered from water samples by ferric hydroxide precipitation, and concentrations were determined by thermal ionization mass spectrometry. 239+240Pu concentrations ranged from < 1 to 5.5 microBq L(-1). These concentrations are lower than those measured in water samples from other parts of the ocean during the mid-1960's to the late 1980's. The 240Pu:239Pu ratios, although associated with large uncertainties, suggest that most of the plutonium is derived from world-wide fallout. As points of comparison, the highest concentrations of tritium and plutonium observed here were about five orders of magnitude lower than the maximum permissible concentrations allowed in water released to the off-site environs from licensed nuclear facilities in the United States. This study and others sponsored by the International Atomic Energy Agency and the Office of Naval Research's Arctic Nuclear Waste Assessment Program are providing data for the assessment of potential radiological impacts in the Arctic regions associated with nuclear waste disposal by the former Soviet Union.

Technetium-99, iodine-129 and tritium in the waters of the Savannah River Site.

Surface water samples were collected from streams on and around the Savannah River Site (SRS) to assess current 3H, 99Tc, and 129I concentrations in the water. The SRS is a nuclear facility operated by Westinghouse Savannah River Company for the US Department of Energy. Water quality parameters were measured at the time of collection using field portable instrumentation. The tritium activity was determined by liquid scintillation spectrometry. The isotopes, 99Tc and 129I, were determined by isotope dilution/inductively coupled plasma-mass spectrometry (D.M. Beals, Determination of technetium-99 in aqueous samples by isotope dilution inductively coupled plasma-mass spectrometry. Presented at the 3rd International Conference on Nuclear and Radiochemistry, Vienna, September 1992, unpublished data; D.M. Beals, P. Chastagner and P.K. Turner, Analysis of iodine-129 in aqueous samples by inductively coupled plasma-mass spectrometry. Presented at the 38th Annual Conference on Bioassay, Analytical and Environmental Radiochemistry, Santa Fe, NM, November 1992). Elevated activities of 3H, 99Tc, and 129I were found in some surface streams of the SRS, principally due to migration of ground water from beneath old seepage basins, however the levels in the waters leaving the SRS are well below any regulatory guidelines.

Environmental monitoring and dose assessment following the December 1991 K-reactor aqueous tritium release.

Between 22 December and 25 December 1991, approximately 570 L of tritiated water was released from the K Reactor at the Savannah River Site. Analyses of river flow rates and measured tritium concentrations showed that approximately 210 TBq of tritium had been released from the reactor and was being transported down the Savannah River. Elevated tritium concentrations in the Savannah River were first detected on 26 December 1991. The maximum measured tritium concentration at Highway 301 (a major sampling point 37 km downstream of the Savannah River Site) was 2.5 Bq mL-1. A hypothetical maximum individual located at Highway 301 would have received a drinking water dose of approximately 0.35 microSv, less than 1% of the Environmental Protection Agency's 40 microSv y-1 drinking water standard. Concentrations at the intake canals to two water treatment facilities, approximately 160 km downstream, began to rise above normal on 28 December. The population dose to users of the downstream domestic water supplies and consumers of Savannah River biota was estimated to be 4.7 x 10(-3) person-Sv.