Analysis of Minor Actinides in Mixed Oxide Fuel Irradiated in Fast Reactor, (I)

The MOX (mixed oxide) fuels, 29.97 wt% (analytical value is 28.08 wt%) plutonium in 8.3 or 12.1 wt% enriched uranium were irradiated up to 120 GWd/t in the MARK-II core of JOYO. The irradiated MOX fuels were dissolved in 8M nitric acid solution. Anion exchange chromatographic procedures were developed for the isolation of neptunium contained in these MOX solutions. Neptunium-237 was separated from the other actinides by using the developed chromatographic technique and the content of 237Np was determined by α spectrometry. It was found that the content of 237Np slightly increased with increasing burnup. The content did not exceed 0.08 wt% in the 30 wt% MOX fuels irradiated up to about 120 GWd/t. Model calculation by ORIGEN-2 reproduces well the observed content of 237Np.