Simulation of Neptunium Extraction in an Advanced PUREX Process—Model Improvement

Abstract

Routing neptunium to a single product in spent nuclear fuel reprocessing is a significant challenge. In this work, we have further improved the simulation of neptunium extraction in an advanced PUREX flowsheet by applying a revised model of the Np(V)-Np(VI) redox reaction kinetics, a new nitric acid radiolysis model, and by evaluating various models for the nitrous acid distribution coefficient. The Np disproportionation reaction is shown to have a negligible effect. The models are validated against published 'cold test' experimental results; the 'hot test' simulation suggests that high neptunium radiolysis could help to achieve high recoveries using this flowsheet.

Homogenous recycling of transuranium elements from irradiated fast reactor fuel by the EURO-GANEX solvent extraction process

“…The Np profile, therefore, reflects the changing Np oxidation state through the contactor bank as well as the differing extractabilities of the oxidation states (IV), (V) and (VI). Models of Np extraction have been developed for the analogous PUREX extract-scrub flowsheet that can be adapted to explain the behaviour of Np in the EURO-GANEX process [41][42]. However, in this test it was proven that Np reached a steady state value, where the feed input of Np to the scrub section balanced the organic output from stage 16, and that >99 % Np was routed with the organic phase in the extract-scrub section which is substantial improvement over the 'cold' test with a surrogate feed where ≈30 % was lost to the HA raffinate [31].…”

New insight on the simultaneous H2and HNO2production in concentrated HNO3aqueous solutions under alpha radiation

“…Moreover, when using internal a particle emitters, radionuclides-specic yields have been recorded due to the progressive disproportionation as a function of the nitric acid concentration induced by the complexing nature of HNO 3 and its chemical involvement in the investigated processes. 46,49,[104][105][106][107][108][109][110][111][112][113] Simultaneously, investigations using radionuclides may pose exposure and contamination risks to the manipulators and require special equipment for safe handling that render them cumbersome. At the same time, questions are imposed about loss of products during handling.…”

Application of SAFT-VRE in the Flowsheet Simulation of an Advanced PUREX Process

“…The neptunium distribution coefficients are calculated following the approach of Chen et al. 21 In which the distribution coefficient of neptunium (V) was set to 0.01 18 and the distribution coefficient of neptunium (VI) was calculated from aqueous concentrations using the model of Kolarik and Petrich. 15 The parameters of this model were fitted to the KfK4660 dataset.…”

“…21,44 The disproportionation of neptunium (V) was neglected. 21 The distribution coefficient of nitrous acid was calculated from the empirical equation published by Tachimori. 18 3 1.…”

“…21 Nevertheless, there are some contradictory results. As captured by the simulation code, the distribution coefficients of Np(VI) and nitrous acid both depend on the aqueous-phase uranium and nitric acid concentrations 21 predicted by the model. Therefore, the difference in the predicted aqueous-phase uranium concentrations in stages 1 to 6 causes the two modelling approaches to predict different neptunium concentrations.…”