Vessel supports skirts

Vessel support skirt Control rod drives In-core flux monitor... 

Fig. 9.6, Sectional view of the Grand Gulf boiling water reactor (courtesy of General Electric Company and Nuclear Engineering International). A, Vent and head spray B, steam dryer C, steam outlet D, core spray outlet E, steam separators F, feedwater inlet G, feedwater sparger H, L.P. coolant injection inlet J, core spray pipe K, core spray sparger L, top guide M, jet pump N, core shroud O, fuel assemblies P, control blade Q, core plate R, jet pump water inlet S, recirculation water outlet T, vessel support skirt U, control rod drives V, in-core flux monitor.

The effectiveness of dry well flooding could be improved if the reactor vessel support skirt were vented in order to reduce the trapped gas volume and increase the fraction of bottom head surface area contacted by water. Partial venting could be achieved by loosening the cover on the support skirt manhole access hole. This would increase the wetted portion of the bottom head from 55% to 73% of the total outer surface area, which delays the predicted time of bottom head creep rupture by about one hour. The predicted failure times for the basic case without skirt venting and for Ae case of partial venting at the manhole access are indicated in the first two entries of Table 2. 

This case corresponds to the last entry in Table 3. The reader is reminded that it is based upon complete venting of the vessel support Skirt, which is not considered practical for the existing facilities. 

The rest of the rules in Part AD for flat heads, bolted and studded connections, quick-actuating closures, and layered vessels essentially duphcate Division 1. The rules for support skirts are more definitive in Division 2. 

Equipment, vessel, and column supports (skirts, legs, etc.) 1-3 hours... 

For the supports of self-supporting skirted columns, towers, and similar vessels by ... 

When vessels have complicated construction (large, heavy bolted connections, support skirts, etc.), it is preferable to estimate their weight and apply a unit cost in dollars per pound. 

Where the vessel wall will be at a significantly higher temperature than the skirt, discontinuity stresses will be set up due to differences in thermal expansion. The British Standard BS 5500 requires that account should be taken of the thermal discontinuity stresses at the vessel to skirt junction where the product of the skirt diameter (mm), the skirt thickness (mm), and the temperature above ambient at the top of the skirt exceeds 1.6 X 10 (mm °C). Similar criteria are given in the other national codes and standards. Methods for calculating the thermal stresses in skirt supports are given by Weil and Murphy (1960) and Bergman (1963). 

However, the bending stresses from wind and seismic loads increase with X. Therefore, the shell thickness must be increased more frequently or in greater degrees in progressing down the column. For example, the second increase in shell thickness may require 1/8 in. increment and may be satisfactory for two or three more courses down. The calculations are continued in this manner until you reach the junction of the vessel with the supporting skirt. 

Figure 3-38. Typical dimensional data, forces, and loadings on a uniform vessel supported on a skirt (5=deflection).

This procedure is based on the "neutral axis method and should be used for relatively small or simple er-tical vessels supported on skirts. 

For vessels where R/t is large in comparison to the supporting skirt, the P.O.V, calculated by this method may be overly conservative. More accurate methods may be employed (see Figure 4.38b). 

Figure 4-39. Vessel supported on conical skirt (Influence of support positioning).

The Equivalent Area Method is also known as file Shifted Neutral Axis Method . This procedure is in contrast with the Centered Neutral Axis Method which assumes that the neutral axis is on the centerline. The Centered Neutral Axis Method is easier to apply but also results in a conservative anchorage design. The Equivalent Area method is more accurate and will result in reduced anchorage requirements. Both methods are used to determine the anchorage requirements and the base plate details of a vertical vessel supported on a skirt. 

The sub-core flux and reaction rate results were determined for the support members, the debris cone, the pressure vessel divided into several polar re ons, the support skirt and the vault floor concrete divided into several radial and axial subdivisions. Results were also produced for the bio-shield concrete below the core support plate level in the bottom comer of the reactor vault in the same regions as those defined for the side-core model described in section 3.3. Results were calculated in 95 separate regions in the sub-core model. 

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