The feasibility study on plutonium concentration monitoring

A feasibility study was performed on the determination of plutonium concentration of uranium-plutonium nitrate solution in a container like pulsed column or mixer-settlers by neutron measurement. The neutron emission rate is not only in proportion to the concentration of plutonium but also dependent on its isotopic composition. Therefore, the neutron emission rate was evaluated for the various condition of BWR and PWR spent fuels. Under the assumption of reprocessing of the conventional and near future spent fuels, the neutron counting rate vs. plutonium concentration was analyzed in the geometry of pulsed column and mixer-settlers with uranium-plutonium organic and nitrate aqueous phases. Some parametric surveys for the practical neutron measurement give the results like followings. The concentration of curium should be restricted under some value and the concentration of uranium is limited because of the increase of counting rate due to the effect of neutron multiplication in aqueous solution. The appropriate allocation have to be considered for neutron detectors to detect neutron enough to count with favourable S/N ratio, since the neutron counting rate becomes smaller at the case of some partial accumulation of plutonium in the aqueous solution within mixer-settlers. (author)