Contamination and activation

To reduce the accidental spread of hazardous substances by workers from a contaminated area to a clean area, zones should be delineated on the site where different types of operations will occur, and the flow of personnel among the zones should be controlled. The establishment of work zones will help ensure that personnel are properly protected against the hazards present where they are working, that work activities and contamination are confined to the appropriate areas, and that personnel can be located and evacuated in an emergency. 

Radioactive source materials are removed, but activated and contaminated areas are secured to allow radioactivity to decay over a period to significantly lower levels. Only those structures and equipment necessary to ensure protection of the public from residual radioactivity are maintained, all other structures being removed. During this period of "safe storage" access to the facility remains under the control of a nuclear license. Dismantlement of the storage structures is deferred until radioactivity levels have decayed significantly. Upon completion of dismantlement the property may be released for unrestricted use. 

As with PWRs, several attempts have been made to describe activity and contamination buildup in BWR plants by computerized models. These models are essentially based on materials balances for the iron transport and on materials and activity balances for the cobalt transport. The reaction rates and the reaction orders needed for the calculations in the partly very complex models are in most cases empirical values or even assumptions. The principles of some of the models have been outlined e. g. by Ishigure (1987) and by Alder et al. (1992). 

The problems entailed in reactor operation, viz. activation and contamination by tritium, shielding, remote handling for maintenance, repair and replacement, and the high degree of reliability required characterize the further outlay necessary for development. 

High electrochemical activity and contamination tolerance. An eleetroeatalyst should be of high intrinsic activity, to diminish electrochemical reaction polarization and enhance energy conversion effieiency. More specifieally, the anode catalyst should have the ability to resist detrimental by-products such as CO and other intermediates that poison the active reaction surface the cathode catalyst should have the ability to restrain crossover methanol oxidation when liquid methanol is seleeted as the fuel. 

Recombinant DNA techniques are widely used in the production of therapeutic proteins, and the problems associated with solubility, structural integrity and biological activity, and contamination with host proteins have to be reduced to a minimum. Consequently, the development of fast, reliable analytical assays is essential for monitoring the progress of a purification process and assessing its effectiveness (yield, biological activity, recovery) [4]. 

Nfointenance facilities for NSSS components are provided within the Reactor Building within the transfer corridor and, if necessary, within a specially constructed off-island building. New or replacement reactor components can be delivered to the transfer corridor for movement to the reactor. Transfer of activated and contaminated components from the reactor building or transfer corridor to any off-island facility and vice versa will be within a transit flask, and in conjunction with a special purpose transport system. 

The reactor components located in and around the core become radioactive owing to activation and contamination after the reactor has been operated for some time. These components include structural materials, parts of the core, such as control rods and their associated components, guide tubes, flux and temperature gauges, dummy fuel elements, components of experimental assemblies, reflectors and shielding materials. 

Experimental and mathematical modeling studies were performed to evaluate the potential benefits and limitations associated with the use of nonionic surfactants to enhance the microbial transformation of hexachlorobenzene (HCB) by a dechlorinating mixed culture enriched from a contaminated sediment. In general. Tween series surfactants were shown to have little impact on methanogenesis, whereas, polyoxyethylene (POE) alcohols, Triton X-100 and SDS were found to strongly inhibit methanogenesis and HCB dechlorination. Subsequent experiments conducted with Tween 80 illustrated the ability of this surfactant to enhance the solubility of HCB and to reduce the HCB-soil distribution coefficient. Model simulations demonstrated, however, that the aqueous phase mass fraction of HCB was substantially reduced in micellar solutions, which corresponded with observed reductions in HCB dechlorination. These results indicate that the impacts of surfactants on both biological activity and contaminant phase distributions should be evaluated in order to accurately assess the potential for biotransformation of hydrophobic contaminants in the presence of surfactants. 

Air contaminants are emitted to the indoor air from a wide variety of activities and consumer products, some of which are summarized in Table 11. Most indoor activities produce some types of pollutants. When using volatile products or engaging in the activities Hsted, care should be exercised to minimize exposure through proper use of the product and by providing adequate ventilation. 

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

Product specifications for microbial food enzymes have been estabUshed by JECEA and ECC. They limit or prescribe the absence of certain ubiquitous contaminants such as arsenic, heavy metals, lead, coliforms, E. coli and Salmonella. Furthermore, they prescribe the absence of antibacterial activity and, for fungal enzymes only, mycotoxins. 

Indoor air contaminants can originate within the building or be drawn in from outdoors. If contaminant sources are not controlled, problems can arise, even if the HVAC system is properly designed and well-maintained. Sources can be from outside the building from operating equipment, from human activities, and other or miscellaneous sources. Sources outside a building include contaminated outdoor air, emissions from nearby sources, soil gas, or moisture or standing water. 

Energy generated by physical activity in the room (i.e., movement of people, transport, conveyor, operation of machines) increases turbulent exchange between the upper and the lower zones and may even disrupt temperature and contaminant stratification along the room height. 

The bulk of both monazite and bastnaesite is made up of Ce, La, Nd and Pr (in that order) but, whereas monazite typically contains around 5-10% Th02 and 3% yttrium earths, these and the heavy lanthanides are virtually absent in bastnaesite. Although thorium is only weakly radioactive it is contaminated with daughter elements such as Ra which are more active and therefore require careful handling during the processing of monazite. This is a complication not encountered in the processing of bastnaesite. 

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