Patent Number: 051981823
Section: summary

BACKGROUND OF THE INVENTION This invention relates to neutron-absorbing or neutron-shielding material, and in particular to a novel process of forming such material into a tube, and the resulting tube. In U.S. Pat. No. 4,027,377, which is assigned to the assignee of the present application and the disclosure of which is incorporated herein by reference, disclosed is the production of neutron-absorbing or shielding material comprised of a thin, rigid sheet having a neutron-absorbing material, preferably boron carbide, surrounded by aluminum plate. In forming the sheet, an ingot is first formed with a hollow interior, and a mixture of neutron-absorbing material, such as boron carbide powder, and a finely divided metal powder, such as atomized aluminum, is installed in the hollow interior of the ingot. Thereafter, the ingot is sealed, heated to a temperature below the melting point of the metal powder, and is then hot rolled to reduce its thickness a desired amount. The hot rolling causes the particles of metal powder and boron carbide to become metallurgically bonded together so that in subsequent use the material retains its neutron-absorbing properties. A problem with the material of U.S. Pat. No. 4,027,377 is its inability to be bent and retain its neutron-absorbing capacity at the area of the bend. Consequently, the process of U.S. Pat. No. 4,751,021 was developed to provide a sheet that can be bent. However, the bend cannot be abrupt, and therefore a relatively gentle bend is the result, with the neutron-absorbing boron carbide core being offset to one side of the sheet. That patent requires precision in manufacture, and although a quite satisfactory neutron-absorbing sheet is produced, the process is expensive. SUMMARY OF THE INVENTION The present invention relates to a method of making sections of a neutron-absorbing tube, or a tube itself, through a series of steps. First, an elongate, generally rectangular metal ingot is formed having a hollow interior. At least one elongate metal divider is installed in the hollow interior to form at least two chambers in the interior of the ingot. The chambers are then filled with a substantially uniformly dispersed mixture of a finely divided neutron-absorbing boron compound and a finely divided metal powder. Thereafter, the ingot is soaked to bring it to an elevated temperature below the melting temperature of the metal powder. With the temperature of the ingot thus-elevated, the ingot is hot rolled to reduce its thickness to form a thin, rigid neutron-absorbing sheet having opposite metal edge portions and an elongated metal spacer portion at the location of each metal divider. Finally, the sheet is longitudinally bent at each spacer portion. In accordance with the preferred form of the invention, only one metal divider is installed in the ingot, and the bending step includes longitudinally bending the sheet to an L-shaped cross section. A tube is formed by making a second, substantially identical section and joining the two sections at their metal edge portions to form the tube. Preferably, one of the metal edge portions of each of the sheets is also bent to an L-shaped cross section before the sheets are joined and welded along their side edges to form a tube. In accordance with the preferred form of the invention, when the sheet is formed and before bending of the sheet, one of the metal edge portions of the sheet is formed with a greater width than the other edge portion. That greater-width edge portion is the edge portion which is then bent to an L-shaped cross section. In accordance with a second form of the invention, a neutron-absorbing tube is formed by forming an elongate, generally rectangular metal ingot having a hollow interior, and a series of elongate metal dividers are installed in the interior of the ingot to form at least four chambers in the interior. Those chambers are then filled with the uniformly dispersed mixture of the finely divided neutron-absorbing boron compound and metal powder, the ingot is soaked to bring it to an elevated temperature, and the ingot is then hot rolled to reduce its thickness to form a thin, rigid neutron-absorbing sheet having opposite metal edge portions and an elongated metal spacer portion at the location of each of the metal dividers. The sheet is then longitudinally bent at each of the spacer portions, and the metal edge portions are joined to form a tube. In this form of the invention, also, it is preferred that the formation of the metal edge portions of the sheet is such that one of the metal edge portions has a greater width than the other edge portion so that the one metal edge portion can be bent to an L-shaped cross section before the two edge portions are joined.