Patent Number: 044473885
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is a bolt with an internal chamber or chambers filled with a tag gas, and sealed such as with a seal-welded plug. The tag gas and pressure are selected relative to the chamber size to provide sufficient tag gas, and/or trigger gas for detection. A tag gas is defined herein as a gas or a blend of gases of a chemical and nuclear species which emits radiation of a known energy and variety. A trigger gas is defined herein as a tag gas which is chosen to activate a system or sequence of events upon detection in a certain location by a monitor. For example, a trigger gas could be chosen to trigger a building isolation and alarm system. The technology of tag gases is discussed in an article entitled "Design and Manufacture of Gas Tags for FFTF Fuel and Control Assemblies":, Nuclear Technology, Vol. 26, August 1975, incorporated herein by reference. Refer to FIG. 1 which illustrates a bolt 1 having a single chamber 2 filled with tag gas. Bolt 1 is shown securing together components 3 and 4. Nut 6 and washer 7 attach to bolt 1 at the lower end. The tag gas is contained within chamber 2 having been introduced there via an entry sealed by welded plug 5. Chamber 2 is located along the center line of bolt 1 to reduce strength reduction. A crank along the section of bolt 1 within components 3 and 4 which crack extends between chamber 2 and volume 8, will allow the tag gas to enter volume 8. Because the nut 6 and washer 7 may at least a partial seal, and bolt head 10 may do the same, a passage 19 may be incorporated in the bolt head 10 to allow unhindered passage of the tag gas to the external volume 11 which is monitored for the presence of the tag gas, such presence there indicative of the crack. Refer to FIG. 2 which illustrates an embodiment wherein a plurality of chambers 2 is provided within a bolt head 10. These chambers 2 need not intercommunicate if it is desired to locate different tag gases within each such that the location of the crack within the bolt is to be detectable. Otherwise all chambers may communicate such that only one plug 5 would be required. Refer to FIG. 3 which illustrates the use of a plurality of blind holes 12 to form chambers 2 within the bolt head 10. This invention could be applied to the rods, studs or other structural members with similar benefits as when applied to bolts. An application of especial interest are the guard vessel hold down bolts of a liquid metal reactor since these bolts are inaccessible. While in the drawings and in the specification, a general device has been disclosed, modifications may be made to this device without departure from the true spirit and scope of the invention. Therefore, this specification should be considered illustrative rather than limiting.