GB2104435A - Cylindrical vessels - Google Patents

Abstract

A cylindrical vessel, suitable for use as a flask for storing and transporting radioactive material, is formed by overlaying similar curved plates (13) contained within the confines of inner and outer tubes (16, 17) which define the inner and outer walls of the vessel. Ductile material defining voidages, such as by perforations or profiling, may be included between the plates to reduce risk of impact damage and avoid the need for a separate impact limiting device. <IMAGE>

Description

SPECIFICATION Cylindrical vessels This invention relates to cylindrical vessels.

The invention is primarily concerned with the problem of providing massive cylindrical vessels for use as "flasks" for storing and transporting radioactive materials. To give an indication of one typical requirement, a steel flask suitable for a single light water reactor fuel element must have a bore of 45 cms and an outside diameter of about 110 cms, that is a wall thickness of about 32 cms. Such dimensions lead one to consider using constructional techniques already known for the manufacture of naval gun barrels but this poses technical problems and is expensive.

A cylindrical vessel according to the present invention is formed by overlaying similar curved plates each of which extends from the nominal inner wall of the vessel to the nominal outer wall of the vessel.

The plates are preferably of a common uniform thickness and formed by a rolling technique and are located between inner and outer tubes forming the vessel walls. When the vessel is required for storing and transporting radioactive material some impact limiting device will generally be required. To provide any known impact limiting device (which device itself has also to be of large dimensions) has the practical result that the vessel is reduced substantially in size as the overall size of a vessel and impact limiting device has restrictions imposed by rail or road gauge limitations.

Also in accordance with the present invention, ductile material, such as aluminium, or lead, is introduced between at least some of the overlaying curved plates which form the vessel, said material defining voidages into which the material can flow under impact on the vessel The material may be of sheet form with perforations to define voidages. Alternatively it could be of profiled form, such as ribbed.

Typically the material could occupy 30% of the wall volume of the vessel and have 20 to 50% voidage.

The fact that voidage exists and the fact that the ductile material (if taken to be aluminium) has a lower shielding capacity than the construction material of the curved plates (taken to be steel) will result in some increase in size of the vessel but this increase will not be so large as that created if any known impact limiting device were fitted: Where the vessel walls are defined by inner and outer tubes, their construction should be thin so as not to contribute too much stiffness under impact conditions. The voidage in the ductile material need not be uniformly dispersed. For example it is preferred that the voidage decreases as one approaches the inner tube of the vessel. Similarly the inner tube of the vessel should be thicker than the outer tube of the vessel.

Under impact sufficient to deflect any of the overlaying curved plates, ductile material is forced to flow into its voids. As the voilds fill so the resistance to further flow is increased.

The invention will now be described further with reference to the accompanying drawings in which: Figure 1 is- a diagrammatic half elevation illustrating construction; and Figure 2 is a similar elevation but on a much reduced scale to illustrate slopes.

A cylindrical vessel 10- (axis horizontal) having- a bore 11 and an outer surface 12 is formed by overlaying similar curved plates 13 of common uniform thickness. The plates may be tack-welded at 14 and 15so that they are held in their correct location.

The vessel 10 is itself located between inner and outer tubes 16, 17 which are supported by and sealed with end closures.

The drawing shows an idealised vessel with the plates 13 in contact. In practice, and to accommodate energy absorbing ductile material, the plates are spaced apart over most of their area. To illustrate this point, the idealised vessel 10 has thirtyfour plates each of 2.54 cms thickness without spaces between the plates. A practical vessel 10 would typically have thirty-two plates with a minimum gap of about 2 mm between the plates and larger gaps where energy absorbing material is used.

The drawing also illustrates the parameters used in the calculations of the curvatures of the plates 13.

The curve of the plates 13 is an involute- with: R cos A r where A = local angle (measured in radions) between the radius of the vessel and the tangent to the curve at that station.

R = base circle radius r = station radius B A-A, where B = angle between radius, where r = R and station radius.

where p = local radius of curvature of vane at radius r C = Angle between local tangent to vane and radius where r = R Knowing the base radius R and choosing a succession of values for C the curve of the vanes can be plotted from x = R (cosC + C sinC) y = R (sinc - C cosC) The base circle does not have to be the same diameter as the bore of the tube and there are some advantages in having it smaller, because the radius of vane curvature becomes very small as the vane approaches the base circle.

When a vessel as above described is used for radioactive material storage or transport it is seen that the curvature of the plates acts to avoid the presence of straight line paths in a radial sense along which nuclear "shine" can occur. There are straight line paths in the longitudinal sense but any shine along these paths can be dealt with at the end closures.

Assembly of the vessel 10 can take place from the ends of the vessels or by constructing two halves and assembling them together as shown on Figure 2.

The aforementioned construction described provides a degree of mechanical interiock protection for individual plates against impact loads. This is illustrated by consideration of Figure 2 in which the interlocking shape of a half vessel is indicated by hatching lines.

Claims (4)

1. A cylindrical vessel formed by overlaying similar curved plates each of which extends from the nominal inner wall of the vessel to the nominal outer wall of the vessel.

2. A vessel as claimed in claim 1 in which the plates are of a common uniform thickness.

3. A vessel as claimed in claim 1 or 2 in which a ductile material is introduced between at least some of the curved plates, said material defining voidages into which the material can flow under impact on the vessel.

4. A cylindrical vessel substantially as described with reference to the drawings.