Potential Releases of ¹²⁹I, ²³⁶U, and Pu Isotopes from the Fukushima Dai-ichi Nuclear Power Plants to the Ocean from 2013 to 2015

After the Fukushima Dai-ichi nuclear accident, many efforts were put into the determination of the presence of ¹³⁷Cs, ¹³⁴Cs, ¹³¹I, and other gamma-emitting radionuclides in the ocean, but minor work was done regarding the monitoring of less volatile radionuclides, pure beta-ray emitters or simply radionuclides with very long half-lives. In this study we document the temporal evolution of ¹²⁹I, ²³⁶U, and Pu isotopes (²³⁹Pu and ²⁴⁰Pu) in seawater sampled during four different cruises performed 2, 3, and 4 years after the accident, and we compare the results to ¹³⁷Cs collected at the same stations and depths. Our results show that concentrations of ¹²⁹I are systematically above the nuclear weapon test levels at stations located close to the FDNPP, with a maximum value of 790 × 10⁷ at·kg^–1, that exceeds all previously reported ¹²⁹I concentrations in the Pacific Ocean. Yet, the total amount of ¹²⁹I released after the accident in the time 2011–2015 was calculated from the ¹²⁹I/¹³⁷Cs ratio of the ongoing ¹³⁷Cs releases and estimated to be about 100 g (which adds to the 1 kg released during the accident in 2011). No clear evidence of Fukushima-derived ²³⁶U and Pu isotopes has been found in this study, although further monitoring is encouraged to elucidate the origin of the highest ²⁴⁰Pu/²³⁹Pu atom ratio of 0.293 ± 0.028 we found close to FDNPP

Radiochemical Determination of Long-Lived Radionuclides in Proton-Irradiated Heavy-Metal Targets: Part ITantalum

In this study, distillation, precipitation, and ion-exchange methods were chosen for the separation of the long-lived β-emitters ¹²⁹I, ³⁶Cl and the α-emitters ¹⁵⁴Dy, ¹⁴⁸Gd, ¹⁵⁰Gd, and ¹⁴⁶Sm from Ta targets irradiated with protons up to 2.6 GeV to determine their production cross sections. Measurements of ¹²⁹I/¹²⁷I and ³⁶Cl/³⁵Cl ratios were performed with accelerator mass spectrometry. After separation of the lanthanides, the molecular plating technique was applied to prepare thin samples to obtain highly resolved α-spectra. Autoradiography and focused ion beam/scanning electron microscopy techniques were used to characterize the lanthanide deposited layer. Experimental cross-section data are compared with theoretical predictions obtained with INCL++ and ABLA07 code, and a satisfactory agreement is observed