摘要：Thoron (Rn-220) is a gaseous decay product of Th-232 decay chain which becomes a potential source of internal contamination for individuals who handle significant amounts of ores and raw materials containing thorium. With the objective of establishing an occupational control of such workers, a methodology which permits, by means of in-vivo measurements, the determination of the level of internally deposited Rn-220 daughters (Pb-212, Bi-212, and Tl-208), was developed at the Institute of Radiation Protection and Dosimetry/Brazilian Nuclear Energy Commission (IRD/CNEN) whole body counter. Previous calibration of an 8'' x 4'' NaI(Tl) detector was carried out using the Lawrence Livermore National Laboratory (LLNL) thorax phantom with the lung cavity filled with plastic bags containing Th-228 standard solution. After sealing, the bags are stored until radioactive equilibrium is reached. Patients are measured for 1 h in two steps, at an interval of approximately 20 h, positioning the detector over the thorax. A comparison of the activities determined at each measurement allows the discrimination of the contribution of the internally deposited short- and long-lived radionuclides. This technique was recently applied to a group of workers at a gas mantle industry in Rio de Janeiro. Results of these measurements will be shown.

摘要：The yields and energy spectra of primary neutrons emitted from spent molten-salt fuel have been analyzed as a function of cooling time. It was found that (alpha, n) reactions made a major contribution to neutron production in the Th-based molten-salt fuel, in contrast to the case of U-fuels for LWRs where spontaneous fission was a main contributor. One of the consequences of this was that the neutron yield continued to increase to reach a maximum 8-9 yr after irradiation, reflecting variation of the concentrations of strong alpha-emitters in the Th series. This peculiar characteristic requires that attention should be paid to neutron- as well as gamma-shielding of storage facilities of spent molten-salt fuel.

摘要：GDR gamma-rays emission in competition with fission by hot compound nuclei is used to to determine characteristic time scales for the fission process which are translated into nuclear dissipation coefficients for collective mass flow. Systematic studies in nuclei from Thorium to Rutherfordium were used to extract separately friction coefficients of compound nuclear fission inside the saddle and from the saddle to the scission point. Above a marked excitation energy threshold between 60 and 80 MeV dissipation is large and equal to full one body dissipation on the outside, possibly even larger inside the saddle. Below this energy dissipation appears to be small. The time scale for quasifission is shown to be almost-equal-to 5 x 10(-21) s, about 1/6 of that of CN fission. The time scale for deep inelastic scattering is too fast to see GDR decay from the colliding system. We compare these results with global models for one- and two-body nuclear dissipation.

摘要：Solid State Nuclear Track Detection (SSNTD) is a relatively new nuclear particle detection technique. Since its inception, it has found useful application in almost every branch of science. This paper gives a very brief review of the role it has played in solving some geological/geophysical problems. Since the technique has been found useful in a wide spectrum of geological/geophysical applications, it was simply not possible to discuss all of these in this paper due to severe space restrictions. However, an attempt has been made to discuss the salient features of some of the most prominent applications in the geological and geophysical sciences. The paper has been divided into two parts. Firstly, applications based on radon measurements by SSNTDs have been described. These include: Uranium/thorium and mineral exploration, search for geothermal energy sources, study of volcanic processes, location of geological faults and earthquake prediction, for example. Secondly, applications based on the study of spontaneous fission tracks in geological samples have been described briefly. The second group of applications includes: fission track dating (FTD) of geological samples, FTD in the study of emplacement times, provenance studies, and thermal histories of minerals. Necessary references have been provided for detailed studies of (a) the applications cited in this paper, and (b) other important geological/geophysical applications, which unfortunately could not be covered in the present paper.

摘要：The adsorption of organoactinide complexes on dehydroxylated alumina (DA) yields coordinatively unsaturated, highly active catalysts for several demanding chemical transformations. Thus, in the case of Th(eta3-allyl)4 supported on dehydroxylated gamma-alumina (DA), facile arene hydrogenation and alkane activation processes can be effected in slurry reactions at 90-degrees-C and P(H2) = 30-180 psi. Benzene reduction occurs at a turnover frequency of almost-equal-to 25000 h-1 per active site and cyclohexane C-H exchange with D2 at almost-equal-to 1300 h-1 per active site. Active site characterization using D2O poisoning, hydrogenolysis, and CH3Cl dosing indicates less-than-or-equal-to 8 +/- 1 % of the Th surface sites are catalytically significant. EPR and XPS spectroscopy provide no evidence for Th oxidation states less than +4. The mechanisms for the above processes are discussed in terms of electrophilic ''four-center'' activation processes in which the active sites appear to bear sterically significant, nonhydridic ancillary ligation.

摘要：Pumice produced during the subplinian phase of eruption of a peralkaline trachyte lava on the island of Terceira, Azores, has undergone extensive leaching at ambient conditions by groundwater, while remaining in a glassy state. Over 25% of F, Na, K, Si, Fe, Ti, and Mn originally present has been removed, whereas U, Al, Nb, Ca, Y, and Rb show smaller but significant losses. Thorium, Zr, Hf, Ta, and Lu have remained immobile. Water content (measured as LOI) has increased up to tenfold, whereas the Sr content has risen by up to 80%. The absence of devitrification requires that leached elements escaped by diffusing through the glass; a coefficient of chemical diffusion D(Na) between 1.8 X 10(-19) cm2 s-1 and 6.1 X 10(-19) cm2 s-1 has been calculated, in excellent agreement with previously published experimentally derived values for comparably low temperatures. Water has not replaced the leached cations on a charge-equivalent basis, a finding that requires an explanation other than simple binary interdiffusion. We suggest that a simultaneous influx of molecular water and cation exchange between Na+ in the glass and H+ in the groundwater opens the glass structure and frees cations, which can diffuse outward by hydrolysis of bridging oxygen atoms. Reported mobilities have important implications for such diverse fields as igneous petrology, nuclear waste management, and agriculture.

摘要：B&W is completing a $65 million project encompassing the site characterization, decontamination, and dismantlement of its former nuclear fuel conversion plant in Apollo, Pennsylvania. This 90,000 ft2 facility was used from the late 1950s until the early 1980s for the conversion of uranium hexafluoride to various fuel forms, including uranium dioxide powder and pellets. Both high- and low-enriched uranium as well as thorium were processed in the facility. Upon discontinuing fuel manufacturing operations, the chemical processing equipment was decontaminated, removed, packaged, and shipped to a licensed low-level radioactive waste (LLRW) burial site. As a result of plant operations, uranium contamination existed within the building and in the soils on the plant site. A detailed site characterization program was completed to establish the extent of contamination and to plan the subsequent soil remediation and building deconstruction efforts. In February 1990, B&W made the decision to accelerate the final decommissioning of the Apollo site. The project was initiated with the ultimate goal of free release for unrestricted use, or green-field. Factors that led to this decision also became constraints on the completion of the project. They included: Rapidly escalating waste disposal costs, with LLRW burial site surcharges scheduled to increase from $40 to $120 per cubic foot in January 1992. Increasing regulatory uncertainty on the criteria for allowable residual radioactivity contamination levels for a U.S. Nuclear Regulatory Commission (NRC) licensed site to be released for unlicensed, unrestricted use. The anticipated loss of burial site alternatives in January 1993 due to the provisions of the Low-Level Radioactive Waste Policy Amendments Act of 1985. Delays in the siting and construction of the Appalachian Compact's burial site. This paper overviews the Apollo decontamination and decommissioning (D&D) project with emphasis on the key business and technical issues which established constraints for the project.

摘要：A new physics approach is presented to evaluate the theoretical transmutation potential of different nuclear power systems (standard or advanced fission reactors and hybrid accelerator/subcritical blankets). The nuclei to be transmuted are the transuranium (or transplutonium) isotopes produced in the irradiation of naturally occurring fuels (uranium or thorium) and the fission product isotopes. The analysis is based on an evaluation of neutronic constraints on the transmutation rates integrated over the life of the nuclide families, taking into account the overall neutron balance of the system being considered. This method allows a comparison of the potential of different systems and establishes physics limitations, particularly in the field of fission product transmutation.

摘要：On the basis of the reactivity conception of the Chernobyl NPP Unit 4 Accident developed by the author and internally inherent nuclear safety criteria and also the analysis of the results of expert estimation for light water reactor transfer to thorium fuel cycle improving their safety the conclusion that the programe of the atomic power development proposed by FEI of Minatomenergo of RF and baled on symbiosis of thermal thorium breeders and BN type reactors should be supported is reached.

摘要：Impurities such as Sm, Gd, Eu, and Dy will degrade the neutron economy of a nuclear reactor when present even at sub-parts-per-million levels, as a result of their high neutron absorption cross sections. Conventional determinations of lanthanide impurities in uranium require 0.5-100 g of uranium. A coupled-column chromatographic procedure has been developed which dramatically reduces the quantity of uranium required. The first column, a semipreparative reversed-phase column, removes the uranium matrix, while the second column, an analytical-scale cation exchange column, concentrates and separates the lanthanides prior to their postcolumn reaction detection with arsenazo III. The maximum loading of uranium onto the reversed-phase column is determined by the volume overload of the lanthanides rather than the concentration overload of the uranium. Using 20 mg of uranium, a detection limit of 0.02 mug/g of U is achieved for Sm, Gd, Eu, and Dy with no interference from transition or alkaline earth metals present in the uranium.