A new approach to determine 147Pm in irradiated fuel solutions

Developments carried out in the Laboratory of Isotopic, Nuclear and Elementary Analyses in order to quantify (147)Pm in spent nuclear fuels analyzed at the CEA within the framework of the Burn Up Credit research program for neutronic code validation are presented here. This determination is essential for safety-criticality studies. The quantity and the nature of the radionuclides in irradiated fuel solutions force us to separate the elements of interest before measuring their isotopic content by mass spectrometry. The main objective of this study is to modify the separation protocol used in our laboratory in order to recover and to measure the (147)Pm at the same time as the other lanthanides and actinides determined by mass spectrometry. A very complete study on synthetic solution (containing or not (147)Pm) was undertaken in order to determine the yield of the various stages of separation carried out before obtaining the isolated Pm fraction from the whole of the elements present in the spent fuel solutions. With the lack of natural tracer to carry out the measurement with the isotope dilution technique, the great number of isotopes in fuel, the originality of this work rests on the use of another present lanthanide in fuel to define the output of separation. The yields were measured at the conclusion of each stage of separation with two others lanthanides in order to show that one of them could be used as a tracer to correct the measurement of the (147)Pm with the separation yield. The total yield (at the conclusion of the two stages of separation) was measured at the same time by ICP-MS and liquid scintillation. This last determination made it possible to validate the use of the (147)Sm (natural) to measure the (147)Pm in ICP-MS since the outputs determined in liquid scintillation and ICP-MS (starting from the radioactive decrease of the source having been used to make the synthetic solution) were equivalent. It is the first time that such measurement is performed in ICP-MS. The measurement of the (147)Pm was finally taken on fuels UOx and MOx by using the (153)Eu like a tracer of the separation yield. The results obtained are in very good agreement with those obtained from neutronic calculation code.