Distribution of Palladium During Spent Fuel Reprocessing

Abstract

The principal purpose of spent fuel reprocessing consists in the recovery of the uranium and plutonium and the separation of fission products so as to allow re-use of fissile and fertile isotopes and facilitate disposal of waste elements. Amongst the fission products present in spent nuclear fuel of Nuclear Power Plants (NPPs,) there are considerable quantities of platinum group metals (PGMs): ruthenium, rhodium and palladium. Given current predictions for nuclear power generation, it is predicted that the quantities of palladium to be accumulated by the middle of this century will be comparable with those of the natural sources, and the quantities of rhodium in spent nuclear fuel may even exceed those in natural sources. These facts allow one to consider spent nuclear fuel generated by NPPs as a potential source for creation of a strategic stock of platinum group metals. Despite of a rather strong prediction of growth of palladium consumption, demand for “reactor” palladium in industry should not be expected because it contains a long-lived radioactive isotope 107Pd (half-life 6,5·105 years) and will thus be radioactive for a very considerable period, which, naturally, restricts its possible applications. It is presently difficult to predict all the areas for potential use of “reactor” palladium in the future, but one can envisage that the use of palladium in radwaste reprocessing technology (e.g. immobilization of iodine-129 and trans-plutonium elements) and in the hydrogen energy cycle may play a decisive role in developing the demand for this metal. Realization of platinum metals recovery operation before HLW vitrification will also have one further benefit, namely to simplify the vitrification process, because platinum group metals may in certain circumstances have adverse effects on the vitrification process. The paper will report data on platinum metals (PGM) distribution in spent fuel reprocessing products and the different alternatives of palladium separation flowsheets from HLW are presented. It is shown, that spent fuel dissolution conditions can affect the palladium distribution between solution and insoluble precipitates. The most important factors, which determine the composition and the yield of residues resulting from fuel dissolution, are the temperature and acid concentration. Apparently, a careful selection of fuel dissolution process parameters would make it possible to direct the main part of palladium to the 1st cycle raffinate together with the other fission products. In the authors’ opinion, the development of an efficient technology for palladium recovery requires the conception of a suitable flow-sheet and the choice of optimal regimes of “reactor” palladium recovery concurrently with the resolution of the problem of HLW partitioning when using the same facilities.

Determination of 107Pd in Pd Recovered by Laser-Induced Photoreduction with Inductively Coupled Plasma Mass Spectrometry

“…Palladium isotopes are generated during nuclear reactions along with many other fission products. Both radio and stable isotopes can be found in spent nuclear fuel and high-level radioactive waste (HLW). , Among these isotopes, 107 Pd is the only long-lived nuclide (half-life: 6.5 × 10 6 y). Thus, the determination of the 107 Pd content in radioactive waste is considered crucial for safety evaluation in managing such wastes.…”

“…Other than the low specific activity of 107 Pd, the instability of trace Pd ions in an aqueous solution may have some connection to the difficulties in detecting 107 Pd in radioactive wastes. Several reports showed that Pd is likely to form a precipitate that can be incorporated into insoluble residue in an HNO 3 matrix. ,, This makes it difficult to track the migration path of dissolved species in waste processing.…”

“…Several reports showed that Pd is likely to form a precipitate that can be incorporated into insoluble residue in an HNO 3 matrix. 1,4,5 This makes it difficult to track the migration path of dissolved species in waste processing.…”