In UREX, the Np and Pu are rejected into the aqueous waste stream by the use of AHA. It is then of interest to extract Np and Pu away from the other fission products and minor actinides, especially if the Pu or Pu + Np will be converted to fresh MOX fuel. To accomplish this, the aqueous raffinate from UREX is thermally treated (evaporated) to destroy AHA and increase the nitric acid concentration. The objective is to retain plutonium and neptu­nium in the extractable (IV) and (VI) oxidation states, respectively, and thereby extract them into the organic solvent of TBP in dodecane. In this process, called NPEX, the Np and Pu will behave much like in the PUREX process described earlier. After extraction, the plutonium and neptunium are removed from the solvent using AHA in a stripping stage to obtain a Np/Pu product stream. This was tested at the same time as the UREX test described above (Vandegrift 2004), see Fig. 6.5, and it was observed that the neptunium was not completely extracted due to difficulties maintaining the Np(VI) oxidation state. However, the goal of not creating a pure plutonium product was still fulfilled and the residual Np remaining in the NPEX raf­finate was recovered in the subsequent TRUEX (TRansUranic Extraction) segment of the UREX+ flowsheet (Vandegrift 2004).