Plutonium processing procedures

The wastes from uranium and plutonium processing of the reactor fuel usually contain the neptunium. Precipitation, solvent extraction, ion exchange, and volatihty procedures (see Diffusion separation methods) can be used to isolate and purify the neptunium. 

Disproportionation of Pu(IV). There are several needs associated witn the occurrence, detection, and mitigation of the disproportionation of Pu(IV) in applied plutonium recovery/ purification procedures. First, there is a great need for much more detailed information concerning the effect of typical process conditions [e.g., temperature, concentration of plutonium, hydrogen ion, nitrate ion, nitrite ion, fluoride ion, other metal ions (e.g., A13+, Fe3+, etc.), etc.] on the occurrence and extent of the reaction ... 

Phil Horwitz asked me to comment on what I saw as potential disadvantages of the various plutonium pyrochemical processes extolled by speakers in the Tuesday sessions. I, too, am a fan of pyrochemical techniques. I recognize that pyrochemical processes for Pu processing are just in their infancy - on batch plant-scale. To be truly useful, such processes need to be operated on a continuous basis. Scientists and engineers concerned with such technology need to develop equipment and procedures required to operate pyrochemical processes in a cost-effective, continuous manner."... 

The small number of atoms involved in some radiochemical procedures can alter the expected behavior. Although time-dependent processes obeying first-order kinetics are not changed by changes in concentration, the same is not true of second-order kinetics. For example, at 10-2 M, isotopic exchange between U(IV) and U(VI) has a lifetime of 2h, whereas at 10-10M, the same lifetime is 400 d. Another example is Np(V), which is unstable with respect to disproportionation and yet jjrCi / L solutions of NpOj are stable. The extreme dilution in some solutions can mean that equilibrium is not reached due to kinetic limitations. Fallout plutonium, present in the aqueous environment at concentrations of 10 18-10 17 M, has not reached equilibrium in over 40 y. 

For an experienced analyst who knows the techniques involved, the laboratory time to complete this experiment (excluding time for preparation) is 6-8 hours it will take longer for those new to the procedure. The experiment can be interrupted conveniently before the ion-exchange process (Step 10), after the plutonium is stripped from the column (Step 12), and at the conclusion of the preparation for electrodepositon (Step 14). An alternative procedure is given for a 25-mL sample that skips the concentration Steps 3-8. 

The sampling of nuclear materials and the packaging of samples are very critical steps in the measurement process. Differing conditions at nuclear plants dictate the need for a variety of sample-taking and handling procedures before samples are sent for analysis. SAL has developed a set of procedures that take account of local conditions, and has been instrumental in improving the overall quality of the verification of uranium and plutonium samples. 

Fuel composition may change from uranium to plutonium, and cladding from aluminum to zirconium to stainless steel. In some cases blankets, moderators, and coolants must be processed, and these will introduce thorium, beryllium, NaK, and bismuth to the chemical process. These changes in materials will present new chemical and corrosion problems in waste treatment processes and waste storage procedures. 

The PRF also recovers Am from the raffinate of the TBP-solvent extraction plutonium-purification process. The process employs 30 v/o dibutyl butylphosphonate in CCI4 as the solvent to extract both americium and residual plutonium from the high-nitrate feed solution, adjusted to about pH 1 by the addition of NaOH. Americium is selectively stripped from the solvent and purified by a cation-exchange procedure. 

An EPA-approved procedure for the analysis of plutonium in water is listed in Table 6-2. In addition, the following ASTM standard methods relate to the measurement of plutonium in water D 3648, D 3084, D 3972, and D 1943 (ASTM 1981, 1982a, 1982b, 1987). Recent work has focused on more rapid analytical methods in order to determine monitor plutonium levels in waste process streams at nuclear facilities. For example, Edelson et al. (1986) have investigated the applications of inductively-coupled plasma-atomic emission spectrometry (ICP-EAS) to routinely analyze water samples. 

Chemistry used in the recovery of plutonium from irradiated fuel must provide a separation from all these elements, other fission and activation products, and the actinides (including a large amount of unburned uranium), and still provide a complete recovery of plutonium. The same issues apply to the recovery of uranium from spent thorium fuel. Most of the processes must be performed remotely due to the intense radiation field associated with the spent fuel. As in the enrichment of uranium, the batch size in the later steps of the reprocessing procedure, where the fissile product has become more concentrated, is limited by the constraints of criticality safety. There is a balance between maximizing the yield of the precious fissile product and minimizing the concentrations of contaminant species left in the final product These residual contaminants, which can be detected at very small concentrations using standard radiochemical techniques, provide a fingerprint of the industrial process used to recover the material. 

A scaled down procedure, appKcable to the titration of 4 mg of plutonium, was set up at lAEA/SAL with the assistance of Dounreay (MacDonald and Savage 1987) and of the Nuclear Research Institute in Rez (CSSR) (Kuvik 1991). This made possible to receive and titrate samples of Pu products taken in Japanese fadhties, as only mg amounts of plutonium can be air flown from Japan in Type A packages. The process including the preliminary redox steps, was automatized to achieve coefficients of variation of 0.05% (Kuvik et al. 1992 Ronesch et al. 1992). 23 species do not interfere, but vanadium does quantitatively, and Np partially. The test sample should carry less than mg-amounts of nitrite, fluorosUicate, and iodate. The effect of americium remains to be studied (ISO 2000). 

The reprocessing involves separating the fission products from the actinides, and then separating the plntoninm from the uranium. The best known procedure of this type is the PUREX (Plutonium, URanium Extraction) process that is used for recovery of uranium and plutonium from irradiated fuel (see details in Chapter 2). The separated plutonium can be used for the production of nuclear weapons or converted into the oxide form, mixed with nraninm oxide and can be used as MOX nuclear fuel. 

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