Patent Number: 051184680
Section: description

EXAMPLES The following examples illustrate some aspects of the invention. EXAMPLE 1 A stainless steel tube (AISI 316L) is used, thickness 0.8 mm, inside diameter 2.5 mm, length 1000 mm, sealed at the lower end by a welded plug 10 mm high. The tube is kept vertical for filling. 625 g of electrolytic Hf crystals is inserted in three stages, each insertion being followed by pressing by a needle with a flat end 8.2 mm in diameter. The final level of the compressed crystals is about 5.5 mm below the opening at the end of the container. The plug 10 mm high is then put into position without any difficulty, leaving an average clearance of 0.5 mm below it. It is welded on in the usual way with the interior under vacuum, by lateral welding across the end of the tube. In this example the sealed container is 98% full and the apparent density of the layer of compressed Hf crystals is about 85%. EXAMPLE 2 The tube used is identical with than in Example 1 except for its length, which is 1400 mm. 75 pellets, 8.2 mm in diameter and with a unit height of 20 mm, are prepared from equal fractions of a mixture of: electrolytic Hf crystals: 207 g (37.5%) PA0 zircaloy 4 chips: 345 g PA0 first batch: Hf crystals 60 g (32.5%)-zircaloy chips 124 g. PA0 second batch: Hf crystals 69 g (37.5%)-zircaloy chips 115 g. PA0 third batch: Hf crystals 78 g (42.5%)-zircaloy chips 102 g. In the precompressed state the apparent total volume of the pellets is 79.2 cm.sup.3 and their total theoretical volume, derived from the specific weights, is 207/13.29+345/6.5=68.65 cm.sup.3. The apparent density of the compressed crystals and chips is thus 86.7%. 40 pellets are placed in the tube and a first recompression is carried out, reducing their total height by about 10 mm by making them wider and denser. The other 35 pellets are placed in the tube and recompression is continued at a slightly higher pressure, bringing the upper level of the last pellet to about 5.5 mm from the open end of the container. In this state, with the pellets slightly wider and crushed, the apparent density or relative density of the compressed crystals and chips is 88%. The plug is positioned and welded as before. EXAMPLE 3 The tube used is identical with that in Example 2. The same types and quantities of compactable products are used, although they are divided up differently in three batches of the same weight, 184 g: Equal fractions by weight of each of the batches are used to prepare 26 pellets for the first batch, 25 for the second and 24 for the third. The 26 pellets of the first batch are placed in the tube and a first recompression process is carried out. The 25 pellets of the second batch are placed in it and further recompression is effected, then the 24 pellets of the third batch are inserted, and the final recompression and sealing are carried out as in Example 2. The absorbing element obtained has the same weight of Hf as the element in Example 2, but in three portions with different Hf content.