Activity enclosure

Safety-related layout of the plant comprises double-walled pipes in product gas carrying ducts and deployment of isolation valves. Released process gases should be routed immediately into the atmosphere to avoid accumulation inside the reactor building. 

In case of a pressure loss accident, the maximum escape rate of the primary coolant is restricted by flow restrictors. A depressurization will take at least two minutes so that destructive dynamic forces in the primary system can be excluded. All heat exchanging components incl. steam reformer are designed to keep their pressure, if there is a pressure loss in the primary system [10]. 

A safety feature, in particular for a nuclear power plant on an industrial site, is a compact arrangement which allows an underground construction. Such an arrangement as was proposed for the HTGR design PR 500 for process steam production would be safe against gas explosions and air craft crashes. 

---

A characteristic safety feature of the HTR-Module is to be found in the fact that, in all operating and accident situations, the radioactive materials formed during nuclear fission are enclosed in the coated particles in such a way that a significant activity release from the coated particles can be excluded. This safe activity enclosure is guaranteed by the design of the fuel particle coatings and the inherent limitation of the maximum possible accident temperature of the fuel elements to approx. 1600 C. 

Personnel are protected in working with tritium primarily by containment of all active material. Containment devices such as process lines and storage media are normally placed in well-ventilated secondary enclosures (hoods or process rooms). The ventilating air is monitored and released through tall stacks environmental tritium is limited to safe levels by atmospheric dilution of the stack effluent. Tritium can be efficiently removed from air streams by catalytic oxidation followed by water adsorption on a microporous soHd absorbent (80) (see Absorption). 

Cross-sectional area of active aluminium Area of enclosure... 

Approximately 20%, since S < 2b. It is recommended to have the centre spacing S at least 2 x 152.4, i.e. 305 mm. If the width of the enclosure poses a limitation, a more appropriate configuration such as in Figure 28.34 or the technigue of interleaving as in Figure 28.35 may be adopted to achieve better utilization of the active metal. In our calculations we have considered all these alternatives. 

The zone model has the following basic limitations 1) complex enclosure geometries cannot be addres.sed, 2) forced ventilation cannot be realistically modeled using simple unit models, 7 ) burning other combustibles remote from the initiating source are not modeled, and 4) siipprcssion activities are not included. 

Air flow technologies that achieve and maintain a safe, healthy, productive and comfortable indoor environment in premises and occupied enclosures where this need is determined not only by human occupancy, normal human activities, and construction and finishing materials but also, and often primarily, by other factors, for example, production processes... 

A number of steps can be taken to minimize dust generation and dispersion. For the clamshell case, an active containment design was pursued to minimize dispersion. Active containment relies upon an inflow of air into some type of enclosure. 

Dust created by mining and milling activities blown by the wind from ore stockpiles is a potential source of environmental contamination. The watering of stockpiles or erection of enclosures is resorted to when necessary in order to prevent the spread of dust. Where ventilation systems collect significant amounts of uranium dust in mills, scrubbers are used to remove the dust from the air before it is discharged to the environment. 

For the transfer of LN2, a simple thick-walled rubber tube or a low-conductivity metallic tube which can be bent to the required shape may be used. In the latter case, a convenient covering, e.g. a flexible foamed neoprene, is needed. Less frequent is the use of double-walled metallic tubes. In this case, the vacuum enclosure must contain some charcoal active as a cryopump. 

The fully developed fire is affected by (a) the size and shape of the enclosure, (b) the amount, distribution and type of fuel in the enclosure, (c) the amount, distribution and form of ventilation of the enclosure and (d) the form and type of construction materials comprising the roof (or ceiling), walls and floor of the enclosure. The significance of each phase of an enclosure fire depends on the fire safety system component under consideration. For components such as detectors or sprinklers, the fire development phase will have a great influence on the time at which they activate. The fully developed fire and its decay phase are significant for the integrity of the structural elements. 

Pressure detection shall be used for closed enclosure applications. Threshold detectors provide an electric signal when a preset overpressure is exceeded. Dynamic detectors provide an electric signal to the control and indicating equipment (CIE). Typically they have both rate-of-rise and pressure threshold triggering points that can be configured specifically to the application conditions. Although this type of detector minimizes spurious activation of the isolation system (due to pressure fluctuations other than explosion pressure rise), care shall be taken to set up such detectors to meet appropriate detection response criteria for the particular application and protected enclosure geometry. 

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Apple does not use brominated flame retardants in the enclosure plastics of its products and is actively seeking alternatives to brominated flame retardants in circuit boards. 

Urine and feces odors of mink applied to soil and vegetation in outdoor enclosures had no effect on gray-tailed voles, Microtus canicaudus, in Oregon. The voles did not seek taller vegetation for cover, and their reproduction was not affected. Specifically, reproductive rates, time to sexual maturation, juvenile recruitment, and activity did not change after exposure to mink odors (Wolff and Davis-Born, 1997). 

When dealing with small, hermetically sealed parts where the enclosure is leaky, krypton 85, a gaseous, radioactive isotope, can first be forced into the device by applying pressure from the outside. Once an exactly measured holding period has elapsed the pressure will be relieved, the component flushed and the activity of the gas charge will be measured. In the same way it is also possible to use helium as the test gas (see Section 5.7.4, bombing test). 

Preliminary experiments with 6-CF loaded mixed vesicles of dipalmitoylphosphat-idylcholine (DPPC) and diacetylenic lipid (22) exhibit only a very slow release of 6-CF after the addition of phopholipase A2. Reasons for this may be headgroup interactions which decrease the enzymatic activity or the fact that multilamellar vesicles were used for this study. Further experiments will be carried out with giant liposomes (visible under the light microscope) which are unilamellar and provide a higher enclosure percentage and low surface curvature (see 4.3.2). 

---