R. H. Iyer

Recovery of fission product palladium from acidic high level waste solutions

Abstract The recovery of palladium from a synthetic pressurized heavy water reactor high level waste (PHWR-HLW) solution has been carried out, and the best reagents to use for the actual HLW solutions are discussed. The extraction of palladium from nitric acid solutions has been carried out using Cyanex-471X (triisobutylphosphine sulfide, TIPS) as the extractant. The metal ion could be quantitatively extracted from solutions with nitric acid concentrations between 2.0 and 6.0 M. The species extracted into the organic phase was found to be Pd(NO3)2 TIPS. Nitric acid in the range of 2. 0 to 5. 0 M had no effect on TIPS for at least 71 hours. A systematic study of gamma irradiation on loading and stripping of palladium from loaded organic phases using several potential extractants, TIPS, alpha benzoin oxime, dioctylsulfide, and dioctylsulfoxide has been made. A flow sheet for the recovery of palladium from actual HLW solutions using TIPS is proposed.

Recovery of neptunium from highly radioactive waste solutions of PUREX origin using CMPO

The partitioning and recovery of237Np from three types of simulated high level waste solutions originating from PUREX processing of spent nuclear fuels such as sulfate bearing high level waste (SB-HLW), HLW from a pressurised heavy water reactor (PHWR-HLW) and from a fast breeder reactor (FBR-HLW) have been carried out using a mixture of 0.2M CMPO and 1.2M TBP in dodecane. Quantitative extraction of neptunium was possible by either oxidizing it to the hexavalent state keeping K2Cr2O7 at 0.01M concentration or by reducing it to tetravalent state keeping Fe2+ at 0.02M concentration. Stripping of neptunium was carried out using different reagents, such as dilute nitric acid, oxalic acid and sodium carbonate. Almost quantitative recovery of neptunium has been achieved during these studies.

Separation of carrier-free 90Y from high level waste by supported liquid membrane using KSM-17

A generator system has been developed for the preparation of carrier-free 90Y from 90Sr present in the high level waste (HLW) of the Purex process by employing a supported liquid membrane (SLM) using 2-ethylhexyl-2-ethylhexyl phosphonic acid (KSM-17 equivalent to PC 88A) supported on a polytetrafluoro ethylene (PTFE) membrane. When uranium depleted Purex HLW at appropriate acidity is passed sequentially through octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) sorbed on chromosorb-102 (abbreviated as CAC) and Zeolite AR1 (synthetic mordenite) columns, all the trivalent, tetravalent and hexavalent metal ions and monovalent 137Cs ions are sorbed. After adjusting to pH 2 with NaOH the resulting effluent is used as feed in a single stage membrane cell partitioned with a PTFE membrane impregnated with KSM-17 and having a feed and receiver compartment with 5.0 ml capacity each. The receiver compartment was filled with a 0.5M HNO3 or 0.5M HCl stripping solution. 90Y alone is preferentially transported across the membrane leaving behind all the impurities viz. 90Sr, 125Sb, 106Ru, 106Rh, etc. in the feed compartment. This technique can yield 90Y in mCi levels in a pure and carrier-free form for medical applications. The feed can be reused repeatedly after allowing for 90Y buildup.

Extraction and extraction chromatographic separation of minor actinides from sulphate bearing high level waste solutions using CMPO

Bench-Scale studies on the partitioning and recovery of minoractinides from the actual and synthetic sulphate-bearing high level waste (SBHLW) solutions have been carried out by giving two contacts with 30% TBP to deplete uranium content followed by four contacts with 0.2M CMPO+1.2M TBP in dodecane. The acidity of the SBHLW solutions was about 0.3M. In the case of actual SBHLW, the final raffinate contained about 0.4% α-activity originally present in the HLW, whereas with synthetic SBHLW the α-activity was reduced to the background level.144Ce is extracted almost quantitative in the CMPO phase,106Ru about 12% and137Cs is practically not extracted at all. The extraction chromatographic column studies with synthetic SBHLW (aftertwo TBP contacts) has shown that large volume of waste solutions could be passed through the column without break-through of actinide metal ions. Using 0.04M HNO3>99% Am(III) and rare earths could be eluted/stripped. Similarly >99% Pu(IV) and U(VI) could be eluted.stripped using 0.01M oxalic acid and 0.25M sodium carbonate, respectively. In the presence of 0.16M SO42− (in the SBHLW) the complex ions AmSO4+, UO2SO4, PuSO42+ and Pu(SO4)2 were formed in the aqueous phase but the species extracted into the organic phase (CMPO+TBP) were only the nitrato complexes Am(NO3)3·3CMPO, UO2(NO3)2·2CMPO and Pu(NO3)4·2CMPO. A scheme for the recovery of minor actinides from SBHLW solution with two contacts of 30% TBP followed by either solvent extraction or extraction chromatographic techniques has been proposed.

THE ITINERANT EXTRACTION BEHAVIOR OF f-ELEMENTS AND TTRIUM WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYL-ETHYLPHOSPHINE OXIDE

ABSTRACT The extraction behaviour of selected trivalent lanthanides, actinides and yttrium was studied from thiocyanate and nitrate solutions using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide(CMPO) in xylene as an extractant. It was found that these trivalent metal ions were extracted as MX3.3CMPO (where X - SCN - or N03-). The equilibrium constants(K) of the above species were determined by non-linear regression analysis. The K values of trivalent lanthanides in nitrate solutions do not increase monotonically with increasing atomic number(Z), but have a maximum at Eu. On the other hand, in thiocyanate solutions, the K values increase with increasing Z. In the extraction systems containing soft ligands like thiocyanate the distribution ratio (D) of Y is lower than that of La, whereas trivalent actinides Am and Cm have much higher D values than their corresponding counterparts in the lanthanide series. However, in the extraction systems containing a hard ligand such as nitrate, it is interes...

Recovery of Neptunium from Highly Radioactive Waste Solutions of Purex Origin Using Tributyl Phosphate

Abstract The present work deals with the extraction of neptunium into the TBP/dodecane phase under conditions relevant to highly radioactive waste solutions, along with uranium and plutonium, by oxidizing it to the hexavalent state using 0.01 M K2Cr2O7 and subsequently recovering it by selective stripping. Three types of simulated HLW solutions, namely sulfate-bearing (SB, in ∼0.3 M HNO3) and non sulfate wastes originating from the reprocessing of fuels from pressurised heavy water reactors (PHWR) and fast breeder reactors (FBR) (both in 3.0 M HNO3), have been employed in this study. Very high extraction of U(VI), Np(VI), and Pu(VI) was obtained from PHWR and FBR-HLW solutions, whereas extraction was less but reasonably high from the SB-HLW solution. The uptake of cerium at tracer level concentrations in the millimolar range (encountered in HLW solutions) and from the simulated HLW solutions containing 0.01 M K2Cr2O7 by 30% TBP has shown that its extraction takes place only at tracer level concentrations ...

Nuclear track registration from solution media: Alpha track registration in solid state track detectors in solutions of actinides

Abstract The results are reported of a study on various aspects of registration and revelation of alpha tracks in the three most commonly used cellulose nitrate detectors (namely LR 115, Ca 80-15 and Daicel) immersed in solutions of actinide elements. Americium, plutonium and enriched uanium in dilute nitric acid solution were used as alpha sources. Experimentally determined values of Kwet (a measure of the efficiency of track registration from solution) are around 2–5×10−4 cm for the three detectors under various conditions of exposure and etching. These values have been examined in the context of the range of the particle, its energy loss rate in the solution medium and the sensitivity of the detectors. Optimum conditions of track registration and revelation for the analytical applications of the technique have been experimentally established. Linear relationships were obtained between the concentrations of uranium or plutonium in the solution and the number of tracks per cm2 obtained under uniform experimental conditions of exposure and etching.

Application of track registration technique in the estimation of fissile materials: Analysis of uranium in rock samples

Abstract The track registration technique has been employed in the estimation of trace quantities of uranium in rock or ore samples either from their solution or directly from the powdered materials themselves by registering nuclear tracks on dielectric plastic detectors. In the first case, the method of standard addition was adopted to eliminate the matrix effect. By this method, uranium in the ng/ml range could be estimated with a precision of 2%. Based on the experience gained from this work some of the precautions necessary for getting precise data are recommended. Various aspects concerning the estimation of uranium directly by registering spontaneous alpha and induced fission tracks from the powdered matrix itself without taking recourse to the dissolution step are discussed. By a comparative study of fission track registration from a solution of fissile material (uranium) and a powdered rock sample, a factor, K p , which gives a measure of the track registration efficiency in powdered rock was evaluated. For a typical rock powder the value is (6.67±0.46)×10 −4 g/cm 2 for Lexan detector. The applications and significance of this factor are also discussed.

Absolute fission yield measurements by track-etch-cum-γ spectrometry

Abstract As part of a long range program of absolute fission yield measurements in the neutron induced fission of actinide isotopes with emphasis on minimising the various sources of error in the measurements, a fission track-cum-γ-ray spectrometric method has been developed where the total number of fissions occurring in the target is determined directly with an accuracy of 2–3%. The fission product atoms formed are determined by direct γ-ray spectrometry using a Ge(Li) detector coupled to a multichannel analyser. The feasibility of this method has been established by measuring the yield of several fission products in the thermal neutron induced fission of 235 U and 239 Pu, where the data agreed within 1–5% of the best available literature values. The various aspects of the technique are discussed in comparison with other absolute fission yield measurement techniques. The merit, scope and relevance of the method are also discussed.

Application of fission track registration technique in the estimation of fissile materials

Analysis of fissile materials in solution by fission track registration technique has been extended to plutonium in solution of its alloys. In these estimations, the results agreed within 1–4% with the average of those obtained by other chemical and instrumental methods like potentiometry, mass-spectrometry and X-ray fluorescence. Some special practical problems encountered in the analysis of plutonium solutions are noted. Various factors affecting the results have been investigated and the necessary precautions for reducing these errors have been indicated. The advantages of the method over some other conventional methods have also been discussed. It is suggested that a source of about 10 μg of252Cf corresponding to a neutron flux of about 107 n·cm−2·sec−1 is ideal for these experiments.