Reducing the radioactive doses of liquid samples taken from reprocessing plant vessels by volume reduction

Size reduction is attractive because it should enable a solution to be analysed by much more direct, and therefore faster and simpler, methods. For instance if the traditional 7 ml vials used in reprocessing plants can be replaced by vessels containing less than 1 μl, it should be possible to analyse the non-diluted solutions in gloveboxes. These vessels would be electro-mechanical, so the term MEMS might be appropriate.This paper determines a conservative estimate for the dose reduction that would be obtained if microlitre samples were extracted from an input accountancy tank at a reprocessing plant, in which the spent fuel is dissolved in nitric acid. This estimate has to take into account the self-shielding effect, that varies for different low-energy and high-energy gamma-emitting isotopes. The typical composition of the solution from an input accountancy tank in a reprocessing plant is first derived by means of a burn-up code. Eight different spent fuel cases are considered to cover the range of fission products, that can emit low and high energy gamma's. The neutron and gamma fluxes emitted from the classical 7 ml vial and from a vessel with less than a microlitre solution are calculated by means of Monte Carlo simulations. The resulting doses are calculated and compared in average and in distribution for different cases of spent fuel composition. For a volume size reduction of 6300 an averaged conservative dose reduction of 6000 is obtained.