Patent Number: 042886988
Section: description

SPECIFIC DESCRIPTION FIGS. 1 and 2 show a transport and/or storage vessel for radioactive materials, e.g. wastes of a nuclear power plant. Basically the vessel comprises a body 1 formed with upright walls 1a, a bottom 1b and a cover 2 fitted into a recess 1c formed in the top of this vessel. While the vessel is shown as generally cylindrical in FIGS. 1 and 2, it can also have a generally rectangular plan configuration with rounded vertical edges as shown in some of the aforementioned copending applications. The vessel defines an inner compartment 1d which is designed to receive the radioactive waste and is composed of a cast material such as cast iron or spherolitic cast iron, suitable as a gamma-radiation shield. The cover 2 has a plug portion 2a which fits tightly into the recess 1c and a flange 2b which overlies an upper face of the vessel and is bolted thereto, e.g. by the bolts 2c. The walls 1a are formed with vertically extending spaced apart circular cross-sectional passages 3 which receive the moderator material 4, e.g. water. The outer surface of the vessel is formed with unitarily cast cooling ribs 5 which, while playing a role in the gamma-shielding, can otherwise be disregarded for the purpose of determining the volume of the passages 3 and hence of the moderator material actually used. Reference may now be made to FIG. 3 which shows an imaginary vessel 1' whose wall thickness T can correspond in gamma-shielding effectiveness to the wall thickness of the vessel 1 of FIGS. 1 and 2 and whose perimeter P corresponds to the perimeter of the vessel 1. For any given radioactive material having a neutron emission, one can imagine a layer 6 of a moderating material which will achieve a given attenuation of the neutron flux. In FIG. 3 which also represents a horizontal section in the plane II--II, this layer has a thickness t and the layer has a volume v. We found that, when the total volume of the bores 3 is equal to or greater than v and the spacing 7 between the bores is at least twice the D thereof, the vessel 1' will have the same radiation-shielding effectiveness as the vessel 1 notwithstanding the large spacing between the passages. Preferably the distance 7 ranges between 2D and 4D. The volume v can thus be equal to or less than (n.times.L.times..pi.D.sup.2 /4) where n is the number of bores 3 filled with the same moderator material as that of the imaginary layer 6, L is the height of each bore and D has been defined above as the diameter. This means that in a horizontal cross section through the vertical axis of the vessel, the total cross-sectional area of the bores 3 (FIG. 2) is at least equal to the cross-sectional area of the layer 6 for the same moderating material. The wall structure of the vessel is thus highly compartmented and mechanically stable. In addition, the cover 2 and at least a central portion 8 of the bottom 1b below the chamber 1d can be formed with bores, channels or chambers 8 containing the moderating material, each of these chambers having a semicylindrical bottom 9a and an outwardly extending portion defined between parallel flanks 9b. The channels open at the surface of the cover and the bottom respectively and are there closed by cover plates 10 and 11 set into recesses 12 and 13 of the body 1 and bolted at 14, 15 in place. As can be seen from FIG. 4, which represents a modification of FIG. 2, the passages can extend in two or more rows around the periphery of the vessel with the passages of each row lying in the gaps between the passages of the other row.