[en] Thorium fuel cycles for light-water reactors, heavy-water CANDU-type reactors and high-temperature gas-cooled reactors have been studied in this thesis. Fissile makeup consists of enriched ²³⁵U or plutonium from uranium-fueled reactors. Uranium resource requirement for each of the thorium fuel cycles has been calculated and compared with the uranium requirement of the fuel cycles of the corresponding uranium-fueled reference designs. Using thorium in the existing light-water reactors is the easiest way of introducing thorium fuel cycles in this country. The uranium ore requirement over a 30-year reactor lifetime, for the fully-enriched-uranium-thorium fuel cycle is only 17% less than that for the uranium fuel cycle, with uranium and plutonium recycle. Among all the fuel cycles studied in this thesis, the 93.5% ²³⁵U-Th CANDU fuel cycle needs the least uranium resources. Self sustaining thorium breeding is also a possibility, with only small changes to the thorium-fueled CANDU reactor operating conditions. Therefore, this fuel cycle could be a logical choice if there were a serious delay in the commercialization of liquid-metal fast breeder reactor

[en] Actinide material quantities and lifetime uranium ore requirements are calculated for thorium fuel cycles in pressurized-water reactors, high-temperature gas-cooled reactors, and pressure-tube heavy-water reactors, and are compared with similar quantities for reference uranium--plutonium fueling in light-water reactors and in fast breeders. Flowsheets are presented for national--international fuel cycles for safeguard controls, including dispersed national reactors fueled with thorium and denatured uranium. Long-term radioactivity properties of high-level radioactive wastes are compared. Also compared are the production of ¹⁴C, ³H, ²³²U, and other activated radionuclides from these reactors and fuel cycles

[en] It is usually assumed that carcinogens are activated by the monooxygenase or aryl hydrocarbon hydroxylase (AHH) system of the endoplasmic reticulum and then enter into the cell nucleus to react with target molecules. However, the AHH system also exists in the nuclear envelope. It may be proposed that due to its close proximity to the genetic apparatus, the nuclear AHH is the major site of carcinogen activation and the metabolism by the endoplasmic reticulum would result in detoxification. The above two hypotheses were tested in a model system which consists of isolated nuclei and [³H]benzo[a]pyrene (BP). The covalent binding of [³H]BP to nuclear DNA, RNA, histones and nonhistone proteins were analyzed by procedures involving stepwise enzyme digestions and solvent extractions. At the present time, there is no good experimental result for assessing the relative importance of each mechanism. Since the pattern of BP metabolites produced by the nuclei is similar to that produced by microsomes, it appears that the site of carcinogen activation is determined not by the specificity of the enzyme but by the rates of metabolism and transport of the carcinogen and its metabolites in the cell

[en] Fuel cycles are examined that utilize dispersed national reactors fueled with uranium denatured by diluting the fissile uranium with ²³⁸U. Discharged fuel is to be stored or is to be reprocessed in an international center, where the recovered plutonium is to be consumed in a plutonium-burner reactor. Material quantities are calculated for national pressurized water reactors (PWRs) or heavy water reactors (HWRs) exchanging fissile material with international PWRs or liquid-metal fast breeder reactors. The national reactors are fueled with low-enrichment uranium or with denatured uranium and thorium. The plutonium-burner reactors are fueled with plutonium and natural uranium or plutonium and thorium. The greater ratio of power of national reactors to the power of the plutonium-burning reactors occurs for national HWRs fueled with uranium and thorium and for international reactors fueled with plutonium and thorium. The vulnerability of denatured uranium to further enrichment and the complexity of reprocessing, refabrication, and enrichment operations at the international center are analyzed. PWRs and high-temperature gas-cooled reactors fueled with denatured uranium and operating without fuel reprocessing are also considered

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[en] We present the magnetic properties of ultrathin Co films deposited at 120 and 300 K on a Ge(1 0 0) surface. As deposited at 120 K, coercive force increases monotonically from 30 to 70 Oe as the coverage of the cobalt film increases from 8 to 28 monolayers (ML). No Kerr intensity has been observed for samples with Co thickness below 5 ML. However, this nonmagnetic Co layer increases to 12 ML as the substrate temperature increases to 300 K, and the coercive force is roughly 15±5 Oe lower than the sample with the same thickness deposited at 120 K. This could be attributed to the thermal annealing effect. From the linear extrapolation of the Kerr intensity below 28 ML, the nonmagnetic behavior of the initial deposit (∼5 ML) is attributed to the formation of nonmagnetic Co-Ge compound at the interface

[en] In the design of an off-shore tower-like structure, which consists of two pipe sections assembled with universal joints and attached to a buried sinker block on the sea bed, enough buoyancy can be provided to keep the structure vertical. It is desirable to reduce both the structural oscillations due to random wave excitation forces and the reaction forces acting on the sinker block. Assuming that the motion of the structure is two-dimensional in the vertical plane, these design requirements can be effectively satisfied if appropriate restoring and damping coefficients are provided at the joints. In this study, the authors employed the statistical equivalent linearization technique to linearize a nonlinear fluid drag force, and applied a sub-optimal control theory with control sturctural constraints to obtain the optimal stiffness and damping coefficients required at the joints after a trade-off between the rms valves of control moments at the joints. The presented examples showed that the hollowness of the pipe sections and the length ratio of the two pipes are important design considerations

[en] Electrochemical etching of CR-39 polymeric track etch neutron detectors results in proton-recoil tracks can be distinguished from background tracks much better than tracks developed solely by chemical etching. A newly designed and constructed electrochemical etching apparatus allows large numbers of dosimeters to be processed simultaneously with consistent results. Many processing systems have been developed for chemical and electrochemical etching of the track etch dosimeters. Three systems specifically show great promise and are being studied extensively