Information Notice 2009-04, Age-Related Constant Support Degradation
| ML090340754 | |
| Person / Time | |
|---|---|
| Issue date: | 02/18/2009 |
| From: | Mcginty T Division of Policy and Rulemaking |
| To: | |
| Beaulieu, D P, NRR/DPR, 415-3243 | |
| References | |
| IN 2009-04 | |
| Download: ML090340754 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 February 18, 2009 NRC INFORMATION NOTICE 2009-04: AGE-RELATED CONSTANT SUPPORT
DEGRADATION
ADDRESSEES
All holders of operating licenses or construction permits for nuclear power reactors, except
those who have permanently ceased operations and have certified that fuel has been
permanently removed from the reactor vessel.
PURPOSE
The Nuclear Regulatory Commission (NRC) is issuing this information notice to alert
addressees to a possible age-related degradation of mechanical constant supports that may
adversely impact design stresses on piping systems. It is expected that recipients will review
the information for applicability to their facilities and consider actions, as appropriate, to avoid
similar problems. However, suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
During the fourteenth refueling outage at the Palo Verde Nuclear Generating Station, Unit 2, Arizona Public Service (the licensee) tested four safety-related constant supports as part of an
investigation for failures on these components and associated beam attachments for these
supports. The testing performed by the licensee measured deviations in the supporting force of
between 8.7 and 13.3 percent. The allowable deviation of the supporting force, including
friction, specified in American Society of Mechanical Engineers (ASME)Section III, Division I,
Subsection NF, is 6 percent. The licensee and the vendor preliminarily concluded that
deviations in the supporting force resulted from wear on the linkages and increased friction
between the various moving parts and joints within the constant support. The wear on the
linkages may have been caused by cyclic loading or vibration, from the main steam lines. The
measured vibrations on the main steam lines were below the analyzed values of displacement
and velocity but were above the ASME OM-3 value of 0.5 inches per second.
The licensee conducted physical inspections and engineering evaluations to determine whether
any structural damage to the main steam piping had occurred. It did not identify any main
steam line piping operability concerns, although analyzed margins to ASME code allowable
stresses were reduced. The licensee subsequently restored these constant supports and
evaluated the effect on the steam generator nozzles with the measured deviations of supporting
force to ensure that ASME code limits were not exceeded.
BACKGROUND
Constant support hangers are designed to provide a substantially uniform supporting force for a
piping system throughout its full range of pipe movement. This is accomplished through the use
of a spring operating in conjunction with a lever, in such a way that the spring force times the
distance to the main lever pivot is always equal to and opposite of the pipe load times its
distance from the main pivot point (see illustration below). These constant support hangers
have been used to limit nozzle loads on pipes that experience large thermal variations from cold
conditions to normal operating conditions.
DISCUSSION
The licensee for Palo Verde does not routinely test these mechanical constant supports, and
these supports are not part of any routine preventive maintenance program. The vendor, ITT-
Grinnell (now Anvil), did not require any routine maintenance on these supports. The physical
condition of the constant supports is visually examined as required by the ASME Section XI,
Subsection IWF, which calls for inspecting a certain number of supports every outage. This
required visual inspection does not determine whether these supports exceed ASME code
allowable load deviation of 6 percent. Although there is no regulatory requirement to do so, licensees may wish to consider testing the constant supports (e.g., displacement testing while
measuring load) to identify constant supports that exceed the ASME code allowable load
deviation of 6 percent.
The licensee and the vendor have preliminarily determined that deviations in the supporting
force resulted from wear on the linkages and increased friction between the various moving
parts and joints within the constant support. This age-related degradation mechanism may
affect the supporting force provided by constant supports and can adversely affect the analyzed
stresses of connected piping systems.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Jim Melfi, Region IV Gerond George, Region IV
623-386-3638 817-276-6562 E-mail: Jim.Melfi@nrc.gov E-mail: Gerond.George@nrc.gov
301-415-2258 E-mail: Alexander.Tsirigotis@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
CONTACT
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Jim Melfi, Region IV Gerond George, Region IV
623-386-3638 817-276-6562 E-mail: Jim.Melfi@nrc.gov E-mail: Gerond.George@nrc.gov
301-415-2258 E-mail: Alexander.Tsirigotis@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
Distribution: IN Reading File Albert Wong
ADAMS Accession Number: ML090340754 OFFICE RIV:DRP TECH EDITOR EMCB:DE BC:EMCB:DE D:DE
NAME JMelfi KAzariah-Kribbs ATsirigotis KManoly PHiland
DATE 02/03/2009 email 02/11/2009 email 02/06/2009 02/12/2009 02/12/2009 OFFICE BC:RER2 PGCB:DPR PGCB:DPR BC:PGCB D:DPR
NAME RAuluck DBeaulieu CHawes MMurphy TMcGinty
DATE 02/17/2009 02/17/2009 02/18/2009 02/18/2009 02/18/2009 OFFICIAL RECORD COPY