Neptunium streams from

Reduction. To convert plutonium to inextractable Pu(III) and neptunium to still extractable Np(IV), 0.5 M U(IV) reductant is added to the aqueous stream from the HC unit. It is necessary to hold the reacting mixture for half an hour or more to obtain nearly complete reduction of neptunium. This is best done batchwise in a set of reactors, some of which would be reducing while others are receiving feed to be reduced. Reduced fuel is then concentrated to 1.172 Af uranium in a set of batch evaporators. 

Neptunium-237 Np-237 has two production routes. The first is rapid /3 decay of U-237 produced by nuclear reactions in the fuel. The second route is /3 decay of Pu-241 to Am-241, which decays losing an a particle to Np-237. This second route will lead to the in-growth of Np-237 in the waste during storage. Np-237 will only be present in waste contaminated with actinides. This is demonstrated by the waste streams that were found to exceed the GQ level. They were IX resin and sludge from BWA and SPF eontents from HPA. Adequate estimates of Np-237 can be made by ratio to Cs-137 determined by FISPIN in the first instance and then refined by taking account of the accumulation and chemistry of other transuranics already measured. At higher concentrations, it can also be measured by y spectrometry of the short-... 

A laboratory study was undertaken to determine the behaviour of neptunium in the WAK flowsheet, and to devise a procedure for its recovery. Based on static ( ) and counter-current experiments (J5), the conclusion was reached that about half of the Np is co-extracted with the U and Pu in the HA-HS mixer-settlers of WAK while the other half is rejected to the HAW, see Fig.1. It could also be shown that an increase of the aqueous acidity, or the addition of pentavalent vanadium as an oxidant into the lower stages of the HA mixer-settler (6), would increase the Np yield in the organic solvent. In the 1BX-1BS mixer-settlers where the partitioning of U and Pu is carried out by use of uranium (IV)nitrate - hydrazine nitrate, a splitting of the coextracted Np between the two product streams was observed the proportions of the (co-extracted) Np which ended up in the 1CU (uranium product) stream fluctuated from 30 to 93 % while the difference amount (from 7 to 70 %) ended up in the 1 BP (plutonium product) stream. 

No definite reason for these fluctuations could be identified, but it is known that neptunium, due to its complicated redox chemistry, reacts in a very sensitive way to even minor process variations (7,8). Based on these results the proposal was made (J5) to recover the "co-extracted" portion of the neptunium by running the second plutonium and uranium purification cycles under conditions where the Np is directed into the aqueous raffinates (2AW and 2DW streams). In the Pu purification cycle, this can be done by adding sufficient nitrous acid to keep the Np pentavalent, while in the U purification cycle (which is run under slightly reducing conditions) a low acidity and a high loading help to reject Np into the aqueous 2DW stream. The two raffinate streams are combined in WAK in the 3W evaporator, and the Np is thus collected in the concentrate from this unit (3WW stream). Consequently the proposal was made to recover the Np from this 3WW stream by use of the well-known anion exchange process (9,J ). 

Based on these proposals, a neptunium production unit called NEPP was designed and installed in WAK for the anion exchange recovery of Np from the 3WW stream. However, NEPP had not gone into operation when the PACT project was terminated in 1973. 

Savannah River [P7]. At the Savannah River Purex plant, neptunium in irradiated natural uranium was recovered by the alternative method of forcing most of it into the aqueous waste stream HAW from the first extraction cycle and then recovering it from waste directly by anion exchange. Neptunium in the first extraction step was converted mostly to the inextractable pentavalent state by adding sufficient nitrite to the next-to-the-last mixer-settler stage of the HA section to make the solvent 0.007 M in HNOj. 

Chemical separation. Current concepts for high-efficiency separation of actinides call for improved plutonium recovery, coextraction of uranium and neptunium with subsequent partitioning by valence control, and extraction of amercium and curium from the HAW stream. There are a number of major problems to be solved before a technically feasible process will be available. 

Over the past 10 years, modifications to the PUREX process have made it possible to more effectively separate neptunium. To effect the efficient separation of Np within the conventional PUREX process, Np is oxidized to VI state by nitrous add and is extracted in the first cycle along with U and Pu into the organic phase. The extracted Np( VI) follows the uranium stream and is later separated during the second purification cycle of uranium. In the RFC, the neptunium is sent to vitrification and disposed of as HLW but in an AFC option, the neptunium can be blended with MOX fuel or fabricated into special targets for later transmutation. The other minor actinides, ameridum and curium cannot be separated by reasonable modifications to the PUREX process. These elements will require the addition of special processing steps to separate them from the PUREX high-level waste stream. 

Each of these elements may be used for production of nuclear fuel or other purposes. The recovery efficiency for uranium is reported as 99.87% and for plutonium 99.36%-99.51% (NEA 2012). The extended PUREX includes separation of neptunium and technetium as well as recovery of americium and curium that are also separated from each other by additional extraction stages as given in detail in the flowsheet (NEA 2012). The advanced UREX-i-3 process generates six streams after separation uranium for re-enrichment Pu-U-Np for mixed oxide fuel c for managed disposal Am-Cm to be used as burnable poisons and for transmutation high-heat-generating products (Cs and Sr) and a composite vitrified waste with all other fission products. Some fuel types may require preliminary steps like grinding to enable their dissolution. 

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