Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
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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
.
