Assessment of size-fractionated species of curium-244 via alpha spectrometry in groundwater

Lingering radioactivity at the Bikini and Enewetak Atolls

We made an assessment of the levels of radionuclides in the ocean waters, seafloor and groundwater at Bikini and Enewetak Atolls where the US conducted nuclear weapons tests in the 1940's and 50's. This included the first estimates of submarine groundwater discharge (SGD) derived from radium isotopes that can be used here to calculate radionuclide fluxes in to the lagoon waters. While there is significant variability between sites and sample types, levels of plutonium (^239,240Pu) remain several orders of magnitude higher in lagoon seawater and sediments than what is found in rest of the world's oceans. In contrast, levels of cesium-137 (¹³⁷Cs) while relatively elevated in brackish groundwater are only slightly higher in the lagoon water relative to North Pacific surface waters. Of special interest was the Runit dome, a nuclear waste repository created in the 1970's within the Enewetak Atoll. Low seawater ratios of ²⁴⁰Pu/²³⁹Pu suggest that this area is the source of about half of the Pu in the Enewetak lagoon water column, yet radium isotopes suggest that SGD from below the dome is not a significant Pu source. SGD fluxes of Pu and Cs at Bikini were also relatively low. Thus radioactivity associated with seafloor sediments remains the largest source and long term repository for radioactive contamination. Overall, Bikini and Enewetak Atolls are an ongoing source of Pu and Cs to the North Pacific, but at annual rates that are orders of magnitude smaller than delivered via close-in fallout to the same area.

Chromatographic separation of Am and Cm

This paper describes the development of a radioanalytical procedure to separate Am3+ and Cm3+ that relies on chromatography with the TRU® resin available from Eichrom Technologies, Inc. Although the TRU chromatographic materials are not currently recommended for the separation of the trivalent actinides from each other, our work demonstrates their suitability. We explored parameters such as nitric acid concentration, column length, and flow rate; standard chromatographic parameters such as resolution, theoretical plates, and total separation time are reported for each variable. The advantages of the method described herein include use of a commercially available product and no application of an organic solvent during elution. Optimal resolution between the Am3+ and Cm3+ was achieved with the slowest flow rate.