referring to fig1 a typical 14 × 14 fuel bundle assembly is indicated generally by the reference numeral 10 . fuel assembly 10 includes an upper tie plate 12 and a lower tie plate 14 , capturing at opposite ends a plurality of ( e . g ., 176 ) fuel rods 13 of tubular shape . a plurality of guide tubes 11 are secured to upper tie plate 12 and to lower tie plate 14 . a plurality of grid spacers 15 ( e . g ., eight several of which are shown ) are disposed along the length of fuel rods 13 at locations between tie plates 12 and 14 and form cells , as is well known , through which fuel rods 13 and guide tubes 11 extend . a lowermost one 15 &# 39 ; of the grid spacers is illustrated as a debris - resistant spacer of the type shown and described in u . s . patent no . 4 , 849 , 161 of brown et al . each of fuel rods 13 encloses a stack of fissionable fuel pellets 16 . pellets 16 in each stack are maintained in close proximity to each other by means of a spring 17 disposed between an upper end of the rod 13 and the uppermost one of pellets 16 . a lower end cap 18 of each fuel rod is in close proximity to but spaced away from the upper portion of lower tie plate 14 to take into account the expected linear growth of rods 13 in the operation of the reactor . the total height from the bottom of lower tie plate 14 to the top of the uppermost pellet 16 ( i . e ., the top of the active fuel ) may , for example , be a few inches less than twelve feet . lower tie plate 14 may be entirely conventional or may comprise a debris resistant design above the lower core support plate 22 . coolant supplied from below the lower tie plate 14 may be expected to carry debris of the type noted above . as the coolant ( water ) flows upwardly , some debris will be intercepted and can drop down below the plate 22 . some amount of debris , however , can impact upon the exterior surface of fuel rods 13 , spacers 15 and , in the case of bwr assemblies , enclosing channel structure , particularly at the lower ends thereof . in the case where a fuel assembly does not include a debris catching device or screen , an even greater amount of debris may be expected to impact upon the exterior surface of fuel rods 13 , spacers 15 and other components in the fuel assembly . fuel rod cladding , spacers or channels may be manufactured in accordance with the present invention to include a method for final hardening treatment of the surface ( s ) of the components which are exposed to coolant water and accompanying debris . a process in accordance with this invention , which is applicable to treating either one or more surfaces of zirconium alloy material , whether it is in strip , sheet or tubular form , will produce components having an extended service life . it is preferable , in order to retain the desired metallurgical condition of the component , that hardening operations be conducted without exceeding a temperature of , for example , 500 °- 700 ° c ., the specific limit temperature being dependent upon the function and / or nature of the component and the environment ( pwr or bwr ) in which the component is to be employed as noted above . in accordance with the one aspect of the present invention , a method of improving fretting resistance of zirconium alloy components used in nuclear reactors comprises placing the alloy component into a closed vessel , introducing a gaseous atmosphere containing acetylene and raising the temperature within the vessel to a temperature in the range of 450 ° c . to 500 ° c ., preferably to 475 ° c . for a period of 8 hours so as to produce a hard , wear resistant carbide layer on the surface of the alloy component . the carbide layer will be of the order of one micron thick ( typically slightly less ), and will exhibit a hardness acceptable for resisting fretting in a nuclear reactor environment . the carbide layer which is produced in this manner is black in color . cladding and flat zircaloy material treated with acetylene as described above to produce a wear resistant layer thereafter was subjected to a standard autoclaving test to determine whether the wear resistant layer was also resistant to waterside corrosion . the results of testing for corrosion resistance alone were that such corrosion resistance was equal to or better than that obtained for components which were the same in all respects except that they were not provided with the wear resistant layer . in accordance with a further aspect of the invention , a method of improving fretting resistance of zirconium alloy components used in nuclear reactors comprises placing at least a portion of an alloy component to be treated in a molten bath containing one or more cyanide salts having an effective melting point less than 500 ° c . for a period of four to twelve hours to produce a wear resistant layer on the alloy component . in one particular arrangement , a mixture of 60 % sodium cyanide and 40 % potassium cyanide ( weight percent ) was used to produce a hard , wear resistant layer two microns thick which was black in color . x - ray fluorescence analysis of the layer so formed indicated the presence of oxide material , although it is normally to be expected that a carbonitride layer is formed by means of a cyanide bath . the resulting surface layer was found to be of increased hardness and wear resistance as compared to the zircaloy itself . in accordance with a further aspect of the invention , a method of improving fretting resistance of zirconium alloy components used in nuclear reactors comprises placing at least a portion of an alloy component to be treated in a molten bath containing one or more carbonate salts having an effective melting point less than 500 ° c . for a period of four to twelve hours to produce a wear resistant oxide layer on the alloy component . in one particular arrangement , a mixture of 50 % lithium carbonate and 50 % potassium carbonate ( weight percent ) was used to produce a hard , wear resistant layer two microns thick which was black in color . x - ray fluorescence analysis of the layer so formed indicated the presence of oxide material . the resulting surface layer was found to be of increased hardness and wear resistance as compared to the zircaloy itself . in accordance with a further aspect of the present invention , a method of improving fretting resistance of zirconium alloy components used in nuclear reactors comprises lacing the zirconium alloy component in a closed furnace , introducing an air or oxygen atmosphere into the furnace , and raising the temperature within the furnace to a temperature level between about 400 ° c . and 500 ° c . ( preferably less than 475 ° c .) for a period of between about forty and about eighty hours to grow a hard , wear resistant oxide layer on the surface of the alloy component . the oxide layer so formed typically will be in the range of between about 0 . 7 microns and 1 . 4 microns thick ( that is , of the order of one micron ) and will e black in color . the grown oxide layer exhibits a desired resistance to corrosion which might occur in a nuclear reactor environment while , at the same tie , providing an increased fretting resistance . in each of the foregoing examples , the wear resistant layer was produced without compromising the corrosion resistance characteristics of the zirconium alloy component . particular attention must be paid to the maximum reaction temperature in each case to avoid undesirably changing the metallurgical structure of the components . to that end , temperatures less than about 500 ° c . were employed in each example for cladding in the stress relieved condition . appropriate reaction temperatures ( e . g ., temperatures in the vicinity of about 600 ° c . to 700 ° c .) for components other than stress relieved cladding , such as recrystallized cladding , channel and spacers , similarly should be observed to avoid undesired secondary effects on metallurgical characteristics such as grain size or structure . as is shown in fig2 typical fuel cladding 13 constructed in accordance with the present invention includes an outer wear resistant layer 30 over at least a portion of the length thereof ( typically at least the lowermost portion ). the thickness of layer 30 is exaggerated in fig2 compared to the dimensions of other elements . the inner surface of cladding 13 may be separated from fuel pellets 16 by a barrier layer 32 ( as is known ). the invention is also useful in connection with non - barrier cladding , spacers and channels as noted above . it should be recognized that various modifications may be made in the apparatus and processes described above without departing from the true scope of the present invention , which is pointed out in the following claims .