Purex waste

In an important study of accelerated radiation damage effects in polyphase Synroc samples doped with 244Cm, Mitamura et al. (1992, 1994) studied the behaviour of Mo, Sr, Ca, Cs, Ba, and Cm for up to 56 days in distilled water at 90 C. These ceramics were doped with either Na-free simulated Purex waste (PW-4b) or simulated waste containing 1.65 wt% Na20 (e.g., JW-A type). We should note here that the... 

PAH PAN PBN PCT PES PHREEQC PIC PM PMATCHC PM-10 PM-2.5 PRB PUREX PW PWR PZC Polycyclic aromatic hydrocarbon Peroxyacetylnitrate Peroxybenzoylnitrate Product consistency test Plasma emission spectroscopy pH redox equilibrium calculations (computer program) Product of incomplete combustion Particulate matter Program to manage thermochemical data, written in C++ Particulate matter with an aerodynamic diameter <10 p,m Particulate matter with an aerodynamic diameter <2.5 p,m Powder River Basin Pu-U-recovery-extraction Purex waste Pressurized water reactor Point of zero charge... 

Liljenzin, J. 0. Hagstrom, I. Persson, G. Svantesson, I., "Separation of Actinides from Purex Waste", Proc. ISEC 80,... 

Pilot-plant work has been performed for the Savannah River Laboratory and for Battelle s PNL to develop fluidized-bed process flowsheets for solidifying neutralized AEG waste and for acid Purex waste. A Purex waste, partially neutralized and containing 2M Na (type PW-6), will... 

The off gases from the Thorex waste pass through a caustic scrubber to remove the oxides of nitrogen prior to being combined with the Purex waste off-gases. This step is necessary since ammonia is evolved from the Purex waste and the combination of gaseous ammonia with oxides of nitrogen forms ammonium nitrate which sublimes on the filter media... 

Another phase of the management of HLW at NFS is to ensure that the composition does not exceed specifications. These specifications, shown in Table II along with the actual composition of the Purex wastes as of December 1973, include limits for 10 elements, two ions, excess caustic, heat value, and capacity. The governing specifications for the NFS Purex waste are 8.0M sodium plus potassium and the 600,000-gal operational volume of the storage tank. 

The expansion program for NFS includes plans to store any future Purex waste as an acid solution for five years before solidifying as required by the 1971 changes in federal regulations. Figure 4 shows a... 

Some aluminosilicate minerals appear to meet the above criteria rather well, especially with regard to low leachability and chemical and physical stability 1, 2). A low-temperature process for converting the wastes to aluminosilicates with low leachability has now been found (3). Aqueous waste solutions containing NaOH, NaNOa, NaN02, NaAl02, mixed fission products, and minor amounts of other salts are mixed with powdered clays (kaolin, bentonite, halloysite, or dickite) and allowed to react at 30°-100°C to form small crystals of the mineral cancrinite. The sodium aluminosilicate crystal lattice of cancrinite contains large amounts of trapped salts and radioactive fission products. The process is applicable to caustic radioactive liquids such as neutralized Purex wastes or to salts or oxides produced by evaporation or calcination of these liquid wastes. 

Figure 10.10 Steps in Purex waste processing and acid recovery.

Bray, L. A. Denitration of Purex Waste with Sugar, Report HW-76973 Rev., Apr. 1963. 

Recovery and Purification of Cesium-137 from Purex Waste Using Synthetic Zeolites... 

The high level liquid Purex waste (HLLW) contains typically >99.5% of the FPs, <0.5% of the U and <0.2% of the Pu present in the fuel as — 1 M HNO3 solution, see Table 21.9. It is pumped to storage tanks as discussed further in 21.10. Total actual Pu losses during reprocessing is presently 0.2% of the feed. 

The recovery of actinides from such solutions by acidification with HNO3 followed by solvent extraction is hampered by the accumulation of H2MBP and HDBP in the solvent. This problem may be overcome by extracting the H2MBP and HDBP from the acidified carbonate solutions with 2-ethylhexanol, EHOH, prior to acidification. Laboratory trials indicated that such a process was potentially applicable to Purex waste streams. Problems identified were the formation of precipitates of H MBP or HDBP complexes on neutralization of the carbonate solutions and the transfer of some EHOH through the process into the actinide extractant used. The extraction of oxidation state (IV) and (VI) actinides could be accomplished using TBP while DHDECMP could be used to extract oxidation state (III) actinides and lanthanides also. 

Steps in PUREX waste processing and acid recovery. (From Benedict M., Nuclear Chemical Engineering, Pigford T.H., H.W. Levi, Eds, Second Eds., Chap 10—Fuel Reprocessing. McGraw-Hill, 1981. With permission.)... 

Further development was in fact aimed at a different goal, namely the extraction of Cs+, Sr ", and MA (Am + and Cm +) without the extraction of macroamounts of trivalent lanthanides. This would largely relieve the demands on reagent concentration in the organic phase and maybe it is more in agreement with the contemporary trends in the treatment of PUREX waste with the goal to increase the economy of radioactive waste repository by preliminary separation of MAs. The new processes of this UNEX B variant were proposed by Russian scientists in laboratory experiments—see the following text—and are yet to be tested in their countercurrent mode. 

For any practical applications in treatment technologies of PUREX wastes, the acidic HNO3 solutions must be considered. Several synergists are effective here either for Ln/MA or Cs/Sr/Ln separations. 

The major work in the area was done by scientists from KRI, Russia. In several papers, the extraction of elements present in PUREX waste solutions by diamides of dipicolinic acid (DPA, see Strncture 19.6) was evaluated (Alyapyshev, 2004,2009 Romanovskiy, 2006). Other similar reagents with good extraction properties are diamides of 2,2 -dipyridyl-6,6 -dicarboxylic acid (Dyp, see Structure 19.6). 

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