Yukiko Hanzawa

Determination of 79Se and 135Cs in Spent Nuclear Fuel for Inventory Estimation of High-Level Radioactive Wastes

79Se and 135Cs are long-lived fission products and are found in high-level radioactive waste (HLW). The estimation of their inventories in HLW is essential for the safety assessment of geological disposal, owing to their mobility in the strata. In this study, the amounts of 79Se and 135Cs in a spent nuclear fuel solution were measured. About 5 g of irradiated UO2 fuel discharged from a commercial Japanese pressurized water reactor (PWR) with a burn-up of 44.9 GWd/t was sampled and dissolved with 50mL of 4M nitric acid in a hot cell for 2 h. After Se and Cs were chemically separated, the amounts of 79Se and 135Cs in the spent nuclear fuel solution were measured by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The amounts of 79Se and 135Cs were 5:2 ± 1:5 and 447 ± 40 g/MTU, respectively. The results presented in this study, which are the first postirradiation experimental data in Japan, showed good agreement with those obtained by the ORIGEN2 code using the data library of JENDL-3.3.

Preparation of Microvolume Anion-Exchange Cartridge for Inductively Coupled Plasma Mass Spectrometry-Based Determination of 237Np Content in Spent Nuclear Fuel

Microvolume anion-exchange porous polymer disk-packed cartridges were prepared for Am/Np separation, which is required prior to the measurement of Neptunium-237 ((237)Np) with inductively coupled plasma mass spectrometry (ICPMS). Disks with a volume of 0.08 cm(3) were cut out from porous sheets having anion-exchange-group-containing polymer chains densely attached on the pore surface. Four different amine-based groups, N,N-dimethylaminoethyl methacrylate, trimethylammonium, diethylamine, and triethylenediamine (TEDA), were selected as the anion-exchange groups to be introduced into the porous sheets. The separation performances of Am/Np were evaluated using a standard solution of (243)Am, which had the same activity as its daughter nuclide (239)Np in secular equilibrium. (239)Np recovery of close to 100% with practically no contamination of (243)Am was achieved using the TEDA-introduced disk-packed cartridge. The time to elute (239)Np from the cartridge was approximately 40 s. The TEDA-introduced disk-packed cartridge was applied to the separation of Np from a spent nuclear fuel sample to confirm its separation performance. A known amount of (243)Am ((239)Np) was added to the spent nuclear fuel sample solution to monitor the chemical yield of Np. The chemical yield of Np calculated from a measured concentration of (239)Np was 90.4%. Am leakage in the Np-eluted solution was less than 1 ppt, corresponding to 0.001% of the original Am concentration in the sample. This indicates that no additional (239)Np was produced by the decay of the (243)Am remaining in the Np-eluted solution, thus providing a reliable chemical yield. U, which can cause a serious spectral interference involving the peak tail from the mass spectrum of (238)U, was thoroughly removed with the TEDA cartridge, providing interference-free measurement of (237)Np. The concentration of (237)Np obtained by ICPMS was 718 ± 12 ng/mg-U, which agrees well with the theoretically calculated value. Compared with the conventional separation technique using commercially available anion-exchange resin columns, the time required to adsorb, wash, and elute Np using the TEDA- introduced disk-packed cartridge was reduced by 75%.

Temporal variations in metal enrichment in suspended particulate matter during rainfall events in a rural stream

We studied enrichment of heavy metals (V, Zn, Cr, Ni, Cu, Pb, As, Sb, and Cd) in a rural stream of the Kuji River basin in central Japan in suspended particulate matter, and associated transport flux during two rainfall events (in November 2003 and in April 2008). The concentration of heavy metals in suspended particulate matter (SPM) exhibited a distinctive temporal variation, wherein the concentrations decreased with increasing water discharge and then increased as the discharge decreased. Concentration of dissolved metal forms showed a slight increase with scatters around the flow rate peak. Enrichment factors for those metals in the SPM decreased sharply as the flow rate increased, making an obvious concave shaped curve (the November 2003 rainfall event). The metal enrichment factors under low flow conditions had a similarity to those found in atmospheric deposits at a foot of the Kuji River basin, suggesting atmospheric source would contribute to enriching the SPM with those metals in part. Mineralogical analyses and carbon content analysis (the April 2008 rainfall event) of the SPM suggests the SPM matrix became more lithological as the flow rate increased. The changes observed in the matrix are thought to be directly related to progressive changes in metal enrichment within the SPM. Concerning the transport phase of several heavy metals, a dynamic change in transport phase partitioning within a rainfall event was suggested. The present enrichment factor study and the SPM matrix characterization implied the partitioning change is due to an increase in lithologic solids during high flow conditions.

Isotope dilution inductively coupled plasma mass spectrometry for determination of 126Sn content in spent nuclear fuel sample

The 126Sn content in a spent nuclear fuel solution was determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) for its inventory estimation in high-level radioactive waste. A well-characterized irradiated UO2 fuel sample dissolved in a hot cell was used as a sample to evaluate the reliability of the methodology. Prior to the ICP-MS measurement, Sn was separated from Te (126Te), which causes major isobaric interference in the determination of 126Sn content, along with highly radioactive coexisting elements, such as Sr (90Sr), Y (90Y), Cs (137Cs) and Ba (137m Ba), using an anion-exchange column. The absence of counts attributed to Te at m/z = 125, 128, and 130 in the Sn-containing effluent (Sn fraction) indicates that Te was completely removed from the anion-exchange column. After washing, Sn retained on the column was readily eluted with 1 M HNO3 accompanied with approximately 80% of the Cd and 0.03% of the U in the initial sample. Owing to the presences of Cd and U in Sn fraction, the measurements of 116Sn and 119Sn were affected by the isobaric 116Cd and the doubly charged 238U2+ion, resulting in the positive bias of the determined values. With the exception of the isotopic ratios including 116Sn and 119Sn, 117Sn/126Sn, 118Sn/126Sn, 120Sn/126Sn, 122Sn/126Sn and 124Sn/126Sn were successfully determined and showed good agreement with those obtained through ORIGEN2 calculations. The measured concentration of 126Sn in the spent nuclear fuel sample solution was 0.74 ± 0.14 ng/g, which corresponds to 23.0 ± 4.5 ng per gram of the irradiated UO2 fuel (excluding the presence of 126Sn in the insoluble residue). The results reported in this paper are the first experimental values of 126Sn content and isotope ratios in the spent nuclear fuel solution originating in spent nuclear fuel irradiated at a nuclear power plant in Japan.

Determination of 107Pd in Pd Recovered by Laser-Induced Photoreduction with Inductively Coupled Plasma Mass Spectrometry

Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, 107Pd, which can be found in radioactive wastes, is one of the difficult-to-measure nuclides and results in a deficit in experimentally determined contents. In this study, a precipitation-based separation method has been developed for the determination of 107Pd with inductively coupled plasma mass spectrometry. The photoreduction induced by pulsed laser irradiation at 355 nm provides short-time and one-step recovery of Pd. The proposed method was verified by applying it to a spent nuclear fuel sample. To recover Pd efficiently, a natural Pd standard was employed as the Pd carrier. Taking advantage of the absence of 102Pd in spent nuclear fuel, 102Pd in the Pd carrier was utilized as the internal standard. The chemical yield of Pd was about 90% with virtually no impurities, allowing accurate quantification of 107Pd. The amount of 107Pd in the Pd precipitate was 17.3 ± 0.7 ng, equivalent to 239 ± 9 ng per mg of 238U in the sample.

Studies on treatment methods of the safeguards swipe samples for uranium isotope ratio measurement

In the environmental sampling and analyses for safeguards, precise and accurate isotope ratio determination of uranium at trace levels is required for detection of undeclared nuclear activities. Currently, swipe (smear) samples are being taken by IAEA from the nuclear facilities. The amount of uranium collected on the cotton swipe is expected to be in the wide range including the order of nano-gram or less. In order to measure the isotope ratios by ICP-MS, we have studied sample preparation procedures for the trace amount of uranium. Elements causing spectroscopic and non-spectroscopic interferences in ICP-MS measurement were sufficiently removed by anion-exchange of hydrochloric acid media. The uranium contamination introduced throughout the process of sample preparation was below 10 pg uranium per sample. The applicability of the treatment process for uranium isotope measurement up to 100 pico-grams was proposed.

Effect of alkali metals on the accuracy of isotope ratio measurement of uranium by ICP-MSPresented at the 2002 Winter Conference on Plasma Spectrochemistry, Scottsdale, AZ, USA, January 6???12, 2002.

The effect of alkali metals on the accuracy of uranium isotope ratio measurements by inductively-coupled plasma sector field mass spectrometry (ICP-SFMS) was investigated. The isotope ratio measurements were performed on the isotopic reference materials, NBS SRM U-015 and U-350, in solutions containing various amounts of any one of Na, K and Rb. The mass bias of the instrument was corrected using an isotopic standard solution without alkali metals. The observed 235U/238U isotope ratios for SRM U-015 began to increase at around 1 μg g−1 for K and Rb, and at around 10 μg g−1 for Na. The deviations from the certified value at the concentration of 300 μg g−1 were evaluated to be 0.8%, 1.9% and 2.5% for Na, K and Rb, respectively. For SRM U-350, the 234U/238U, 235U/238U and 236U/238U isotope ratios were measured in various K concentrations. The deviation per unit mass at 300 μg g−1 K was evaluated as 0.56%.

Increase in rare earth element concentrations controlled by dissolved organic matter in river water during rainfall events in a temperate, small forested catchment

The distributions of dissolved rare earth elements (REEs) in river water during rainfall events in a forested catchment were studied to contribute to understandings of TRUs behavior. Variations in the concentrations of dissolved REEs and several elements (As, Sb, and V) apparently correlated well with peak intensities in the optical spectra (ultraviolet absorption and fluorescence emission) of the river water. The optical properties were considered to represent humic substances in dissolved organic matter (DOM). Similar hysteretic loops were found for the REE concentrations and optical intensities as a function of the water discharge. This result indicates that the mobile REEs and DOM likely shared flow paths from the soil to the stream during these events. An ultrafiltration study revealed that colloidal REEs present in a size fraction of 10–30 kilodaltons comprised the major component of the dissolved REEs and increased under high water flow. Considering these observations and model interpretations in the precedent literature, complexation of the dissolved REEs with DOM was suggested to occur during the studied rainfall events. A high correlation between the size-fractionated REE concentrations and specific ultraviolet absorbance was observed, suggesting that the aromaticity of DOM plays a role in its complexation with dissolved REEs.

Comparison of Post-Irradiation Experimental Data and Theoretical Calculations for Inventory Estimation of Long-Lived Fission Products in Spent Nuclear Fuel

The inventory estimation of long-lived fission products (LLFP) is essential for the long-term safety assessment of a geological disposal of high-level radioactive waste (HLW). 79 Se and 135 Cs are a main contributor to the total dose from the geological repository of HLW, owing to their solubility in the strata. In this study, the post-irradiation experimental data of LLFPs, such as 79 Se, 99 Tc, 126 Sn and 135 Cs, were compared with ORIGEN2 calculation using the data library of JENDL-3.3. A fragment of the UO2 fuel pellet irradiated in a commercial Japanese PWR was dissolved with nitric acid in a hot cell. The resultant solution was filtered to remove insoluble residue. After Se, Tc, Sn, and Cs were chemically separated, the concentrations of 79 Se, 99 Tc, 126 Sn and 135 Cs were determined with an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS). The concentration of 79 Se, 99 Tc, 126 Sn and 135 Cs in the sample solution were 0.78 ± 0.22, 101 ± 24, 3.2 ± 0.6, and 68 ± 6.0 ng/g of the sample solution (ng/g-sol.), respectively. The results for 79 Se and 135 Cs obtained in this study showed good agreement with those obtained through ORIGEN2 calculation. This indicates that ORIGEN2 calculation is applicable to the estimation of the amounts of 79 Se and 135 Cs generated during irradiation. In contrast, the experimentally determined concentration of 99 Tc and 126 Sn were equivalent to approximately 70% and 60%, respectively, of those obtained through ORIGEN2 calculation.Copyright

Rapid separation of zirconium using microvolume anion-exchange cartridge for 93 Zr determination with isotope dilution ICP-MS

Estimating the risks associated with radiation from long-lived fission products (LLFP) in radioactive waste is essential to ensure the long-term safety of potential disposal sites. In this study, the amount of 93Zr, a LLFP, was determined by ICP-MS after separating Zr from a spent nuclear fuel solution using a microvolume anion-exchange cartridge (TEDA cartridge). Zirconium in 9.4 M HCl was stably retained on the TEDA cartridge and readily eluted with 0.75 mL of a mixed solution of 9.4 M HCl and 0.01 M HF. The time taken to complete the Zr separation was 1.2 min. Almost all the other elements initially present in the spent nuclear fuel sample were removed, leading to accurate measurement of all six Zr isotopes (90Zr, 91Zr, 92Zr, 93Zr, 94Zr, and 96Zr). This demonstrated that the TEDA cartridge allowed highly selective separation of Zr regardless of its small bed volume of 0.08 cm3. The concentrations of these isotopes were determined by an isotope-dilution method using a natural Zr standard that has a different isotopic composition from that of the spent nuclear fuel sample. The amount of 93Zr in an initial spent nuclear fuel pellet was 1081 ± 79 ng per mg of 238U. The measured concentrations of all Zr isotopes, as well as the isotopic composition, were consistent with values predicted using a burnup calculation code.