S. Fried

The Sorption of Technetium and Iodine Radioisotopes by Various Minerals

Radioisotopes of technetium and iodine, elements that are present in reactor wastes, are strongly sorbed (100 ≲ KD ≲ 2000) from aqueous solutions by several naturally occurring minerals (bournonite, chalcopyrite, pyrite, tennantite, and tetrahedrite). This is in contrast to little or no sorption (KD < 1) in other geologic material (anhydrite, basalt, granite, and tuff). The highly sorptive behavior has been investigated using column flow and batch sorption techniques. The results indicate that oxidation reduction and mineral replacement are the mechanisms for the strong sorption of these radionuclides. Such information will be of use in the evaluation of geologic retention of nuclear wastes at future underground repository sites.

Pulse radiolysis studies of U(VI) complexes in aqueous media

The rate constants for the reaction between the hydrated electron and dioxouranium(VI) complexes with carbonate IMDA, NTA, oxalate and chloride ion range from 2 to 4 × 1010 M−1 sec−1. The insensitivity of the reaction rate to formal charge, potential, and number of water molecules in the equatorial coordination sphere of uranium is interpreted in terms of an electron tunneling mechanism for the reaction. Spectroscopic and structural data are cited to provide evidence consistent with such a mechanism.

Retention of Plutonium and Americium by Rock

The relative migration ratio of plutonium in various rocks is approximately 100 micrometers per meter of waterflow; the corresponding migration ratio for americium is about 500 micrometers per meter of water flow. Under these conditions radioactive decay will have taken place to such an extent that little plutonium and americium can reach the external environment from a well-designed and isolated geological repository site.

Measurement of Radionuclide Diffusion in Ocean Floor Sediment and Clay

The mobility of cationic neptunium, plutonium, americium, and sodium, and of the anionic species pertechnetate, TcO/sup -//sub 4/, has been determined in samples of various sediments from the ocean floor, and in bentonite and hectorite clay. The experiments were conducted at ambient temperatures (298 + or - 5 K), and the periods of observation ranged from several hours to ten months. All tests were carried out under static conditions permitting only molecular diffusion of the ionic species. Results indicate very low mobilities for the transuranium elements plutonium and americium, for which the upper limit of the effective diffusion coefficient is <10/sup -10/ cm/sup 2/xs/sup -1/. Sodium, neptunium, and TcO/sup -//sub 4/ were found to have higher mobilities characterized by values for the effective diffusion coefficient of 3 X 10/sup -6/, 1.8 X 10/sup -8/, and 3.2 X 10/sup -6/ cm/sup 2/xs/sup -1/, respectively. Some implications of the measured results for the assessment of barrier effectiveness are discussed.

Migratory properties of some nuclear waste elements in geologic media

To aid in assessing the suitability of geologic disposal, the authors have examined the interactions of trace quantities of cesium, plutonium,, neptunium, and americium in aqueous solutions with rocks from formations that may be suitable for waste repositories. Results indicate that many geologic formations are barriers to the movement of these elements in flowing water. However, reactions that retard element migration are varied and do not lend themselves to simplified descriptions. In experiments with plutonium and americium, kinetics of reactions were seen to differ for each trace element and rock studied. In rock infiltration experiments with radioactive cesium, plutonium, neptunium, and americium, often most of the activity moved slowly compared to the water stream, but small quantities of the trace elements moved downstream from the main peaks of activity because of the slow reaction rates seen in static experiments, or possibly because of multiple speciation, colloid formation, movement of particles with adsorbed nuclides, or other causes. 2 figures, 7 tables.

The α-half-lives of 244Cm, 245Cm and 246Cm

Abstract The α-half-life of 244 Cm, determined from specific activity measurements, and the α-half-lives of 245 Cm and 246 Cm, determined by mass spectrometric analysis of curium and its plutonium daughters, have been determined to be 17·59 ± 0·06 years, 9320 ± 280 years and 5480 ± 170 years, respectively.

Absorption spectra of NpCl3 and NpBr3

Low temperature absorption spectra are reported for NpCl3 and NpBr3 in the range 3300–40 000 cm−1. Term assignments are made to a number of excited levels not previously identified, and the data are interpreted in terms of a refined free‐ion model. Some of the parameters associated with this model are found to have similar values for both 3+ actinide and lanthanide chlorides. The values determined for other of the parameters are in good agreement with those calculated independently using Hartree‐Fock methods. The similar crystal‐field quantum number ordering of levels in the ground states of actinide trichlorides and analogous lanthanides doped into LaCl3 is noted and discussed.

Absorption spectrum of CfCl3

The absorption spectrum of thin films of CfCl3 was measured at 298, 77, and 4°K in the range 6000–46 000 cm−1. Interpretation of the results was based on systematic variation of energy level parameters over the actinide series. Electrostatic, spin‐orbit, and configuration interaction terms were calculated by diagonalization of the complete interaction matrices and a least squares fitting process involving 27‐level assignments. Compared to the energies of the first f→ d transitions observed in lighter actinide trichlorides, the corresponding band in CfCl3 appears to occur at an anomalously low energy.

Heat capacity of 242PuO2 from 12 to 350°K and of 244PuO2 from 4 to 25°K. Entropy, enthalpy, and Gibbs energy of formation of PuO2 at 298.15°K

Heat capacity measurements have been made on a 22.5 g sample of 242PuO2 from 12 to 350°K and on a 3.6 g sample of 244PuO2 from 4 to 25°K. The heat capacity curve has the normal sigmoid shape. At 298.15°K the heat capacity C°p, entropy S°, enthalpy H°−H°0, and tempered Gibbs energy (G°−H°0)/T are, respectively, (66.25±0.26) J °K−1⋅mole−1, (66.13±0.26)J °K−1⋅mole−1, (10 784±43) J mole−1, and −(29.96±0.12) J °K−1⋅mole−1. This value of the entropy is significantly lower than the one previously derived from heat capacity measurements on 239PuO2. At 298.15°K the standard entropy of formation and the standard Gibbs energy of formation are −(195.2±0.4) J °K−1⋅mole−1 and −(998.0±0.7) kJ mole−1, respectively.

Heat capacity, entropy, and enthalpy of 242PuF3 from 10 to 350 °K

Heat capacity measurements have been made on a 17.5 g sample of 242PuF3 from 10 to 350°K. The measurements from 20 to 350°K were made by the quasiadiabatic method with discontinuous electrical heating. Temperature drifts in the region 18–58°K with no electrical heating were compared with the measured heat capacities to evaluate the radioactive self‐heating rate, (1.206±0.004)×10−4 W/g Pu. Heat capacities from 10 to 20°K were obtained from this radioactive self‐heating rate and observations of the temperature drifts with no electrical heating. A transition was observed between 110 and 122°K, with an associated excess entropy of 0.777±0.027 J °K−1 · mole−1 and an excess enthalpy of 92.2±3.4 J mole−1. Magnetic susceptibility measurements showed that PuF3 undergoes anti‐ferromagnetic ordering at 9.0±0.5°K. At 298.15°K the heat capacity Cp°, entropy S°, enthalpy H° ‐ H0°, and Gibbs energy divided by temperature (G° ‐ H0°)/T are, respectively, 92.64±0.28 J °K−1 · mole−1, 126.11±0.36 J °K−1 · mole−1, 18015±54 J ...