FAST EVALUATION OF 235U/238U RATIO IN NUCLEAR SPENT FUEL

摘要

A direct simple and fast method was established, to overcome the influence of low and high level impuritieson the measurement of 235U/238U isotopic ratio in nuclear spent fuel. The addition of refractory metal oxides formingsolution (RMOFS), in certain proportions alongside the spent fuel solution on the sample filaments were found to beuseful during the analysis of uranium isotopic ratio by thermal ionization mass spectrometry (TIMS). RMOFS (withoxide melting point exceeding 2000°C), and particularly that of magnesium, were found to be very effective inimproving the quality of the ion signal of 235U and 238U, when added without the need for prior purification.Solutions of chromium, cerium, thorium, and magnesium were investigated, to select the more convenient one, and itwas found that magnesium was very useful to start with. The method was very simple, it improves both the accuracyand precision of the collected data, reduces the time required to achieve steady uranium pilot signal, and hence theoverall time of the analysis, regardless of the level of impurities present.