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SSINS No.: 6835 IN 83-20 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 April 13, 1983 Information Notice No. 83-20: ITT GRINNELL FIGURE 306/307 MECHANICAL SNUBBER ATTACHMENT INTERFERENCE Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as a notification of a potentially significant interference problem pertaining to ITT Grinnell Figure 306/307 mechanical snubber assemblies. An assembly consists of ITT Grinnell attachment clamps and a Pacific Scientific mechanical snubber. No specific action is required in response to this information notice, but it is expected that recipients will review the information for applicability to their facilities. Description of Circumstances: On January 19, 1983, Arizona Public Service Company reported (DER 82-82) an attachment interference between the ITT Grinnell attachment clamps and their associated Pacific Scientific mechanical snubbers that preventeo the required lateral pipe movement in either direction. Prevention of binding is obtained by designing the snubber attachments to allow for angular movement at each end of the snubber. Typically, an angular cone of five to six degrees from the axis is called for in the design specifications. The utility considered this condition to be reportable because, if left uncorrected, the piping could be restricted from lateral movement, and the resulting reactive forces could cause binding of the snubber, thereby impairing its safety function. The utility's report, which is based on a November 16, 1982 letter from ITT Grinnell, does not highlight the affect that restricted lateral movement could have on the piping systems. Restricted motion could lead to cyclic loadings that were not part of the original design stress analysis. The magnitude of this loading depends on the amount of binding caused by the lateral loading on the snubber. Should it become great enough, the snubber would be damaged permanently and, quite likely, "freeze" (lock permanently in one position). Depending on the snubber position when it "freezes," the piping system could experience a stress reversal when the thermal loading is removed. (It should be noted that the responses to IE Bulletin 81-01, "Surveillance of Mechanical Snubbers", indicate that the Pacific Scientific mechanical snubbers are vulnerable to "freezing" when subjected to lateral loads. This is particularly true with the smaller size snubbers.) 8303040019 . IN 83-20 April 13, 1983 Page 2 of 2 In their November 16, 1982, letter to the utility, ITT Grinnell stated: "Not all Figyre 306/307 mechanical snubbers are affected. Based on our engineering evaluation, we have determined that: 1. All mechanical snubbers produced and shipped by ITT Grinnell prior to October, 1978 should be reviewed to assure sufficient clearance. 2. All mechanical snubbers produced and shipped by ITT Grinnell after April 1980 are acceptable, based on design changes incorporated at that time. 3. Mechanical snubbers produced and shipped by ITT Grinnell between October 1978 and April 1980 may exhibit a reduction of the included angle cone of action. Particularly: a. All mechanical snubbers that incorporate welded rear brackets; and b. Size 3 and 35 clamps. Both of the conditions identified above can be alleviated by slight grinding. The ends of the clamps may be ground to the ITT Grinnell specified minimum edge distance. The problems with the rear brackets/rear pivot fit can be resolved by grinding the welds, in the area of interference, to the ITT Grinnell cified minimum weld sizes. The only grinding required is that which will avoid interface. Both of these problems can be resolved readily without replacing material." On January 10, 1983, Commonwealth Edison reported (deficiency number 82-09) a similar problem at their Byron Station Units 1 and 2 and Braidwood Station Units 1 and 2. In addition, it is known that modifications have been performed at both the Susquehanna and the McGuire sites. No written response to this notice is required. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: Richard J. Kiessel (301) 492-8119 Attachment: 1. List of Recently Issued IE Information Notices .
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