29 research outputs found
Metabolism of phenol and hydroquinone to reactive products by macrophage peroxidase or purified prostaglandin H synthase.
Macrophages, an important cell-type of the bone marrow stroma, are possible targets of benzene toxicity because they contain relatively large amounts of prostaglandin H synthase (PHS), which is capable of metabolizing phenolic compounds to reactive species. PHS also catalyzes the production of prostaglandins, negative regulators of myelopoiesis. Studies indicate that the phenolic metabolites of benzene are oxidized in bone marrow to reactive products via peroxidases. With respect to macrophages, PHS peroxidase is implicated, as in vivo benzene-induced myelotoxicity is prevented by low doses of nonsteroidal anti-inflammatory agents, drugs that inhibit PHS. Incubations of either 14C-phenol or 14C-hydroquinone with a lysate of macrophages collected from mouse peritoneum (greater than 95% macrophages), resulted in an irreversible binding to protein that was dependent upon H2O2, incubation time, and concentration of radiolabel. Production of protein-bound metabolites from phenol or hydroquinone was inhibited by the peroxidase inhibitor aminotriazole. Protein binding from 14C-phenol also was inhibited by 8 microM hydroquinone, whereas binding from 14C-hydroquinone was stimulated by 5 mM phenol. The nucleophile cysteine inhibited protein binding of both phenol and hydroquinone and increased the formation of radiolabeled water-soluble metabolites. Similar to the macrophage lysate, purified PHS also catalyzed the conversion of phenol to metabolites that bound to protein and DNA; this activation was both H2O2- and arachidonic acid-dependent. These results indicate a role for macrophage peroxidase, possibly PHS peroxidase, in the conversion of phenol and hydroquinone to reactive metabolites and suggest that the macrophage should be considered when assessing the hematopoietic toxicity of benzene
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ACCELERATOR TRANSMUTATION OF WASTE TECHNOLOGY AND IMPLEMENTATION SCENARIOS
During 1999, the U.S. Department of Energy, in conjunction with its nuclear laboratories, a national steering committee, and a panel of world experts, developed a roadmap for research, development, demonstration, and deployment of Accelerator-driven Transmutation of Waste (ATW). The ATW concept that was examined in this roadmap study was based on that developed at the Los Alamos National Laboratory (LANL) during the 1990s. The reference deployment scenario in the Roadmap was developed to treat 86,300 tn (metric tonnes initial heavy metal) of spent nuclear fuel that will accumulate through 2035 from existing U.S. nuclear power plants (without license extensions). The disposition of this spent nuclear reactor fuel is an issue of national importance, as is disposition of spent fuel in other nations. The U.S. program for the disposition of this once-through fuel is focused to characterize a candidate site at Yucca Mountain, Nevada for a geological repository for spent fuel and high-level waste. The ATW concept is being examined in the U.S. because removal of plutonium minor actinides, and two very long-lived isotopes from the spent fuel can achieve some important objectives. These objectives include near-elimination of plutonium, reduction of the inventory and mobility of long-lived radionuclides in the repository, and use of the remaining energy content of the spent fuel to produce power. The long-lived radionuclides iodine and technetium have roughly one million year half-lives, and they are candidates for transport into the environment via movement of ground water. The scientists and engineers who contributed to the Roadmap Study determined that the ATW is affordable, doable, and its deployment would support all the objectives. We report the status of the U.S. ATW program describe baseline and alternate technologies, and discuss deployment scenarios to support the existing U.S. nuclear capability and/or future growth with a variety of new fuel cycles
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A roadmap for the development ATW technology: Systems scenarios and integration
As requested by the US Congress, a roadmap has been established for development of ATW Technology. The roadmap defines a reference system along with preferred technologies which require further development to reduce technical risk, associated deployment scenarios, and a detailed plan of necessary R and D to support implementation of this technology. Also, the potential for international collaboration is discussed which has the potential to reduce the cost of the program. In addition, institutional issues are described that must be addressed in order to successfully pursue this technology, and the benefits resulting from full implementation are discussed. This report uses as its reference a fast spectrum liquid metal cooled system. Although Lead-Bismuth Eutectic is the preferred option, sodium coolant is chosen as the reference (backup) technology because it represents the lowest technical risk and an excellent basis for estimating the life cycle cost of the systems exists in the work carried out under DOE's ALMR (PRISM) program. Metal fuel and associated pyrochemical treatment is assumed. Similarly a linear accelerator has been adopted as the reference. A reference ATW plant was established to ensure consistent discussion of technical and life cycle cost issues. Over 60 years of operation, the reference ATW plant would process about 10,000 tn of spent nuclear reactor fuel. This is in comparison to the current inventory of about 40,000 tn of spent fuel and the projected inventory of about 86,000 tn of spent fuel if all currently licensed nuclear power plants run until their license expire. The reference ATW plant was used together with an assumed scenario of no new nuclear plant orders in the US to generate the deployment scenario for ATW. In the R and D roadmap, key technical issues are identified and timescales proposed for the resolution of these issues. For the accelerator the main issue is the achievement of the necessary reliability in operation. To avoid frequent thermal transients and maintain grid stability the accelerator must reach levels of performance never previously required. For the target material the main technical choice is between solid or liquid targets. This issue is interlocked with the choice of coolant. Lead-Bismuth eutectic is potentially a superior choice for both these missions but represents a path with greater technical risk. For the blanket metal fuel has been selected. The reference method of processing of spent fuel from LWRs to provide the input material for ATW is chosen to be aqueous because of the large quantity of uranium that needs to be brought to a state that it can be treated as Class C waste. Again this is the path of least technical risk although the pyrometallurgical option will be pursued as an alternative. Processing of the fuel after irradiation in ATW will be undertaken using pyrometallurgical methods. The transmutation of Tc and I represents a special research issue and various options will be pursued to achieve these goals. Finally the system as a whole will need optimization from a reactivity and power control perspective. Varying accelerator power is feasible but can lead to overdesign of the accelerator; other options are movable control rods, burnable poison rods, and adaptations of the fuel management strategy