Patent Number: 048658049
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 4 thereof, there is shown the new and improved nuclear reactor fuel rod end plug constructed in accordance with the present invention and generally designated by the reference character 100. It is to be initially noted at this juncture that the new and improved end plug 100 of the present invention is similar to the conventional prior art end plug 10 shown in FIG. 1, except of course for the particularly new improvements thereof which in fact constitute the present invention, and consequently, all component parts or structural features which are similar or common to both the conventional end plug 10 and the new and improved end plug 100 of the present invention have been designated with corresponding reference characters except that all structural components of the new and improved end plug 100 of the present invention have been designated with reference characters within a 100 series. In particular, then, in accordance with the teachings of the present invention, it is seen that in lieu of the sharply defined interior corner characteristic of the conventional nuclear reactor fuel rod end plug 10 as formed by the circumferentially extending, axially oriented, land surface 18 and the annularly extending, radially oriented shoulder portion 20, which surfaces are fabricated in accordance with critically toleranced dimensional values, as are the corresponding mating surfaces of the fuel rod cladding tubing, not shown, in order to eliminate the conventional internal structural defects or deficiencies which had previously manifested themselves in connection with the employment of TIG welding techniques for performance of the end plug-fuel rod cladding tubing girth welds, the new and improved nuclear reactor fuel rod end plug 100 of the present has eliminated such precisely fabricated corner structure and has replaced the same with a machined notch or groove 126 which extends annularly about the end plug 100. It is seen that the notch or groove 126 is formed in part by means of the radially oriented, annularly extending shoulder portion 120 as well as by means of a conical surface 128 which extends radially outwardly from the radially innermost portion of shoulder 120 to circumferentially extending, axially oriented land surface 118, surface 128 being disposed at an angle .beta. of 45.degree. with respect to shoulder portion or surface 120 and extending toward the tapered forward end 116 of the plug 100. As has been noted hereinabove, while the conventional nuclear reactor fuel rod end plug 10, with its particular, critically toleranced interior corner structure as defined by annular shoulder surface 20 and land surface 18, has facilitated the production of girth welds defined at the fuel rod end plug-cladding tubing which have been free of internal defects or deficiencies when the girth welds were formed utilizing TIG welding techniques and apparatus, porosity defects in fact manifested themselves within the girth welds at the fuel rod end plug-cladding tubing juncture when the conventional end plugs 10 were employed, and when laser beam welding techniques and apparatus were being utilized, such defects or deficiencies being shown in FIGS. 2 and 3. However, when the new and improved nuclear reactor fuel rod end plug 100 of the present invention was employed within the end plug-cladding tubing assemblies, and the same were welded together by means of laser beam welding techniques and apparatus, the resulting weldments defined between the end plugs and the cladding tubing were free of the aforenoted porosity defects or deficiencies, as best seen with reference being made to FIGS. 5 and 6A-6B. As may be particularly seen from these photographic figures, desirable fillets have formed between the cladding tube walls and the annular shoulder wall 120 of the end plugs, and the entire weldments disclose as absence of porosity defects. A similar appreciation of the defect-free weldment produced as a result of employment of the end plug 100 of the present invention under laser beam welding conditions may also be attained from reference to the photographic figure of FIG. 7. The aforenoted production of the nuclear reactor fuel rod end plug-cladding tubing assembly was in fact produced, for example, by means of welding operations wherein a RAYTHEON 550 YAG laser was employed. The groove or notch 126 was machined within the sidewall of the end plug 100 to a radially inwardly depth or extent of 0.100 inches as measured from the outer surface of the land area 118, however, it later became apparent after production review of, for example, FIG. 5, that a full penetration weld had in fact been adequately achieved, and that a similarly adequate heat affected zone could have been achieved with an annular groove 126 machined to a depth of, for example, only 0.05-0.07 inches. It is also to be noted at this juncture in connection with the actual production of the satisfactory weldment between the fuel rod end plug of the present invention and the fuel rod cladding tubing, that an additional benefit derived from the usage of the end plug 100 of the present invention resides in the fact that as a result of the provision of the groove or notch 126 within the end plug 100, approximately one-half of the end plug's effective heat sink has been removed. Consequently, it was also observed during production of the end plug-cladding tubing weldment utilizing laser beam technology, that in lieu of normally being required to operate the laser equipment at a power rating of, for example, 400 watts with the attendant standardized parameters in order to achieve a satisfactory weld of this type, in accordance with the welding process employing the end plug 100 of the present invention, the aforenoted satisfactory full penetration weld was in fact able to be accomplished utilizing the laser equipment at a power rating of only 340 watts. This is a significantly positive result achieved in connection with the fabrication of the end plug-cladding tubing assemblies in view of the fact that if the laser equipment need not necessarily be operated at its maximum power rating, extending service life will be able to be achieved. It is lastly to be noted that while the present invention has in fact been developed in order to overcome the various drawbacks of accomplishing nuclear reactor fuel rod end plug-cladding tubing welded assemblies utilizing laser beam welding technology, whereby production defects or structural deficiencies have been able to be eliminated, the particular end plug structure of the present invention is likewise applicable to TIG welding technology. It is to be remembered that TIG welding techniques have been heretofore successfully employed in connection with the weld production of nuclear reactor fuel rod end plug-cladding tubing assemblies only because high quality-control criticalities were enforced in connection with the production of the end plugs and their mating cladding tubes. However, as a result of the present invention, such criticalities or production tolerances are no longer mandatory. Consequently, the machining costs involved in connection with the production of end plugs and cladding tubing for the end plug-cladding tubing assemblies may be significantly reduced. It is to be noted that in view of the higher energy input requirements characteristic of TIG welding operations as compared to those of laser beam welding operations, the groove or notch 126 of the end plug 100 of the present invention may have to be larger both in radial depth and axial extent, and in fact may have to be altered so as to comprise a different geometrical configuration, such as, for example, that of a square viewed in cross-section, as opposed to the triangularly configured groove or notch 126 which has effectively been employed in connection with laser beam welding techniques as illustrated in FIG. 4. Thus, it may be seen that the present invention has significant advantages over known prior art nuclear reactor fuel rod end plugs in that by means of the provision of the notch or groove 126 within the end plugs 100 of the present invention, porosity defects or structural deficiencies within the weldment may in fact be eliminated regardless of whether TIG or laser beam welding technology is being employed. It is to be emphasized that while the present invention was initially developed to especially overcome defects or deficiencies manifesting themselves in connection with laser beam welding operations in connection with the fabrication of nuclear fuel rod end plug-cladding tubing assemblies, it is in fact equally applicable to TIG welding operations as noted hereinabove and for the reasons set forth hereinbefore. It is to be especially emphasized at this point, however, and in light of the development of TIG welding operations in connection with the fabrication of nuclear reactor fuel rod end plug-cladding tubing assemblies, that the present invention must be considered to be, in effect, a dramatic teaching away from the prior art. In particular, porosity defects or deficiencies had in fact manifested themselves in connection with the fabrication of nuclear reactor fuel rod end plug-cladding tubing assemblies employing TIG welding technology, however, such defects or deficiencies were able to be subsequently controlled and effectively eliminated by the adherence to strict quality control manufacturing tolerances. Consequently, when such similar defects or structural deficiencies manifested themselves within the end plug-cladding tubing assemblies fabricated in accordance with laser beam welding technology, it would have followed that continued adherence to such manufacturing tolerances, or adherence to increasingly critical manufacturing tolerances would have rectified the problem of the occurrence of the porosity defects within the laser beam welded regions. However, this proved not to be the case. Subsequently, the present invention was developed wherein it is appreciated that the present invention has developed the technology in an effectively diametrically opposite mode or teaching away from such prior art or known processes. In lieu of increasing manufacturing tolerance criticalities, and the requirement of strictly adhering thereto, the present invention has in fact effectively relaxed such requirements. As can be appreciated by those skilled in the art, references in the specification and claims to particular angles and dimensions in describing the end plug of the present invention are to be construed as indicating preferable and general such angles and dimensions. Also, as is known to those skilled in the art and shown in FIG. 8, a typical nuclear reactor fuel rod 200 (which contains fuel pellets 204) employing the present invention would include one end plug 100 as shown in FIG. 4 welded to one end of the cladding tube 202 and a second end plug 100' as shown in FIG. 4 but without the bore 122 and without the bore 124 (i.e. a solid such end plug) welded to the other end of the cladding tube 202. Additionally, the bore 122 is closed by a seal weld at its outside opening 206. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.