Enclosures thickness

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

Protection against contact with live or moving parts inside the enclosure by tools, wires or objects having a thickness greater than 2.5 mm. 

For a near-total shielding of the field produced by the main cotiductors (i.e. for - /. to be very low), it is essential to have the thickness of the enclosure is netir to 5p as possible. But this m iy prove to be a costly proposition. In addition, ti higher induced current in the enclosure will also tnean higher losses. This hits been established by computing the cost of the enclosure and capitalizing the cost of losses for minimum losses in the eticlosure... 

Eoss factor This is a ftmetion of losses (fk ) in the tnain conductor (IV,) and the enclosure (IVi). A curve as illustrated in Figure 31.12 can be established between the losses versus thickness (/) of the enclosure by experiments. 

Optimization factor This is a function of the cost of enclosure for different thickness. /. the cost of the cooling system (if cooling is considered necesstiry) and the capitalized cost of the losses at different thickness /. A curve as shown in Figure 31.13. rather sitnilar to that in Figure 31.12. ciin be established theoretically between the total cost of the IPB system versus /. 

The above two curves will help optitnize the thick-nes.s, /, of the enclosure foi a total minimum cost of the system. Enclosure losses may not be lowest at this thickness as shown in Figure 31.12, but they wotild maintain the tetnperature rise of the enclosure within limits. The magnetic field in the space, being already very low, would require no other measure. Moreover, it small field in the space may ciiusc only a small amount of heat in nearby structures, which may be... 

Thickness of enclosure for minimum cost of IPB system (Figure 31.13)... 

Figure 31.12 Variation in losses with thickness of enclosure...

Figure 31.13 Optimization curve between thickness of enclosure and the total cost of the IPB system...

Current rating varies with the surface area of a conduelor and its thickness (annulus). In our sample calculation, to establish the basic parameters of the conductor and the enclosure, we have considered the current density for both as 400 A/inch. ... 

To apply what we have discussed so far we give below a brief outline of a design for an IPB system. The economics of this design would be a matter of further investigation of its performance versus cost. This will require an optimization on the thickness of the enclosure as discussed earlier. 

Let us assume the thickness of the conductor to be close to but less than say, around 11 mm, to reduce its diameter and hence increase the gap between the enclosure and the conductor. 

If we assume the emissivity factor to be 0.85 the shortfall in the heat dissipation is nearly made up. However, it would be a matter of laboratory testing to establish the suitability of the enclosure section chosen. Otherwise the thickness of the enclosure may be slightly increased and the calculations repeated. 

A vertical CVD reactor (cf. Figure lb) consists of an axlsymmetrlc enclosure with the deposition surface perpendicular to the Incoming gas stream. The reactant gases are typically Introduced at the top and fiow down towards the heated susceptor. Thus, the least dense gas Is closest to the growth Interface which destabilizes the fiow. The result Is recirculation cells which Introduce not only film thickness and composition variations but also broaden Junctions between layers. This Is particularly of... 

Figure 11-17 Establish a Good High-frequency AC Connection to the Enclosure at the Output-end of Power Supply by Means of Thick Braided Wire...

Recommendation 8 (see Figure 11-17) A good high-frequency AC connection between Secondary ground and the enclosure is recommended at the output end. A thick bunch of braided copper helps. 

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 heat transfer into the boundary surface of a compartment occurs by convection and radiation from the enclosure, and then conduction through the walls. For illustration, a solid boundary element will be represented as a uniform material having thickness, 6, thermal conductivity, k, specific heat, c, and density, p. Its back surface will be considered at a fixed temperature, T0. 

If a spare rotor or element is purchased, it shall be prepared for unheated indoor storage of 3 years. Storage preparation shall include treatment with a rust preventive and enclosure in a vapour barrier envelope with slow release vapour phase inhibitor. The rotor or element shall be boxed for the type of shipment specified. A rotor shall have a resilient material (but not lead, TFE or PTFE), at least 3 mm (0,12 in) thick, between the rotor and its support cradle support shall not be at the rotor s Journals. An element shall have its rotor secured to prevent movement within the stator. 

Thicknesses from 1 mm up to at least 50 mm are possible with RTM however, several difficulties can arise for thick parts, such as the problem of race tracking at edges, air enclosures due to uneven mold filling, and problems connected to cure. 

Objects to be flow coated are coated on a conveyor through an enclosure in which streams of coating are squirted on them from all sides. The excess material runs off and is recirculated through the system. There is still some thickness gradation, but much smaller than in dipping. 

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