Information Notice 2017-03, Anchor/Darling Double Disc Gate Valve Wedge Pin and Stem-Disc Separation Failures: Difference between revisions

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{{#Wiki_filter:ML17153A053 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION OFFICE OF NEW REACTORS WASHINGTON, DC 20555 June 15, 2017 NRC INFORMATION NOTICE 2017-03: ANCHOR/DARLING DOUBLE DISC GATE VALVE WEDGE PIN AND STEM-DISC SEPARATION
{{#Wiki_filter:UNITED STATES
 
NUCLEAR REGULATORY COMMISSION
 
OFFICE OF NUCLEAR REACTOR REGULATION
 
OFFICE OF NEW REACTORS
 
WASHINGTON, DC 20555 June 15, 2017 NRC INFORMATION NOTICE 2017-03:               ANCHOR/DARLING DOUBLE DISC GATE VALVE
 
WEDGE PIN AND STEM-DISC SEPARATION


FAILURES
FAILURES


==ADDRESSEES==
==ADDRESSEES==
All holders of an operating license or construction permit for a nuclear power reactor under Title 10 of the
All holders of an operating license or construction permit for a nuclear power reactor under
 
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of


Code of Federal Regulations (10 CFR) Part 50, "Domestic Licensing of Production and Utilization Facilities," except t
Production and Utilization Facilities, except those that have permanently ceased operations


hose that have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
and have certified that fuel has been permanently removed from the reactor vessel.


All holders of and applicants for a combined license under 10 CFR Part 52, "Licenses, Certifications, and Approvals for Nuclear Power Plants."
All holders of and applicants for a combined license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.


==PURPOSE==
==PURPOSE==
The U.S. Nuclear Regulatory Commission (NRC) is is
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
 
addressees of operating experience regarding Anchor/Darling (a subsidiary of Flowserve)
double disc gate valve (DDGV) failures. This IN provides a discussion of the recent LaSalle


suing this information notice (IN) to inform addressees of operating experience regarding Anchor/Darling (a subsidiary of Flowserve) double disc gate valve (DDGV) failures.  This IN provides a discussion of the recent LaSalle County Station Unit 2 Anchor/Darling DDGV failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that resulted in stem-disc separations. This
County Station Unit 2 Anchor/Darling DDGV failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that resulted in stem-disc separations. This


document contains information available to NRC staff as of May 2017. The NRC expects recipients of this IN to review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.
document contains information available to NRC staff as of May 2017. The NRC expects
 
recipients of this IN to review the information for applicability to their facilities and consider
 
actions, as appropriate, to avoid similar problems. However, suggestions contained in this IN
 
are not NRC requirements; therefore, no specific action or written response is required.


==DESCRIPTION OF CIRCUMSTANCES==
==DESCRIPTION OF CIRCUMSTANCES==
LaSalle County Station, Unit 2 On February 11, 2017, during a refueling outage at LaSalle County Station, Unit 2, the licensee


was attempting to fill and vent the high-pressure core spray (HPCS) system when the Unit 2 HPCS injection isolation valve (an Anchor/Darling 12-inch DDGV) would not open on demand. Initial analysis identified that a stem-disc separation occurred as a result of excessive wear of
===LaSalle County Station, Unit 2===
On February 11, 2017, during a refueling outage at LaSalle County Station, Unit 2, the licensee
 
was attempting to fill and vent the high-pressure core spray (HPCS) system when the Unit 2 HPCS injection isolation valve (an Anchor/Darling 12-inch DDGV) would not open on demand.
 
Initial analysis identified that a stem-disc separation occurred as a result of excessive wear of
 
the valve stem threads and shear failure of the wedge pin. The licensee has not completed
 
their root cause determination. The licensee reported this event in Licensee Event Report
 
(LER) 2017-003-00, dated April 12, 2017 (Agencywide Documents Access and Management
 
System (ADAMS) Accession No. ML17102B424).
 
The licensee had been using industry guidance to perform visual evaluations and diagnostic


the valve stem threads and shear failure of the wedge pin. The licensee has not completed
testing on the valve. The guidance was based on earlier operating experience from an event on


their root cause determination. The licensee reported this event in Licensee Event Report
October 20, 2012, at Browns Ferry Nuclear Plant, Unit 1. This event resulted in two reports


(LER) 2017-003-00, dated April 12, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No.
ML17153A053 under 10 CFR Part 21, Reporting of Defects and Noncompliance. The first Part 21 report was


ML17102B424
issued by the Tennessee Valley Authority (TVA), Anti-Rotation Pin Failure in Anchor Darling
).    The licensee had been using industry guidance to perform visual evaluations and diagnostic testing on the valve.  The guidance was based on earlier operating experience from an event on


October 20, 2012, at Browns Ferry Nuclear Plant, Unit 1.  This event resulted in two reports under 10 CFR Part 21, "Reporting of Defects and Noncompliance."  The first Part 21 report was issued by the Tennessee Valley Authority (TVA), "Anti-Rotation Pin Failure in Anchor Darling
(Flowserve) Double Disc Gate Valve, dated January 4, 2013 (ADAMS Accession


(Flowserve) Double Disc Gate Valve," dated January 4, 2013 (ADAMS Accession
No. ML13008A321) and the second by Flowserve, Wedge Pin Failure in Anchor/Darling


No. ML13008A321) and the second by Flowserve, "Wedge Pin Failure in Anchor/Darling Double-Disc Gate Valve at Browns Ferry Nuclear Plant Unit 1," dated February 25, 2013 (ADAMS Accession No. ML13064A012
Double-Disc Gate Valve at Browns Ferry Nuclear Plant Unit 1, dated February 25, 2013 (ADAMS Accession No. ML13064A012).
). Browns Ferry Nuclear Plant, Units 1 and 2 


===Browns Ferry Nuclear Plant, Units 1 and 2===
On October 20, 2012, a Browns Ferry Nuclear Plant, Unit 1, high-pressure coolant injection
On October 20, 2012, a Browns Ferry Nuclear Plant, Unit 1, high-pressure coolant injection


(HPCI) steam isolation valve, which also serves as a containment inboard isolation valve, failed its local leak rate test. Investigation revealed that, although the event was not a stem-disc separation, the wedge pin failed and one of the two disc retainers (see Figure 1) fell from the
(HPCI) steam isolation valve, which also serves as a containment inboard isolation valve, failed
 
its local leak rate test. Investigation revealed that, although the event was not a stem-disc
 
separation, the wedge pin failed and one of the two disc retainers (see Figure 1) fell from the


stem-to-upper wedge connection into a space between the valve discs, causing one of the two
stem-to-upper wedge connection into a space between the valve discs, causing one of the two


discs not to properly seat. The valve was a 10-inch Anchor/Darling DDGV. It was installed in
discs not to properly seat. The valve was a 10-inch Anchor/Darling DDGV. It was installed in
 
2007 and had not been disassembled since installation. The licensee, TVA, submitted a
 
10 CFR Part 21 report, dated January 4, 2013 (ADAMS Accession No. ML13008A321), for this


2007 and had not been disassembled since installation. The licensee, TVA, submitted a 10 CFR Part 21 report, dated January 4, 2013 (ADAMS Accession No.
failure. In the report, TVA determined that the wedge pin failed because the vendor had not


ML13008A321
properly torqued the stem-to-upper wedge connection during manufacture.
), for this failure.  In the report, TVA determined that the wedge pin failed because the vendor had not properly torqued the stem-to-upper wedge connection during manufacture.


Before the 2012 failure, Browns Ferry Nuclear Plant experienced two other wedge pin failures in
Before the 2012 failure, Browns Ferry Nuclear Plant experienced two other wedge pin failures in


10-inch Anchor/Darling DDGVs. The first wedge pin failure involved a Unit 2 HPCI outboard steam isolation valve installed in 2001 that failed during testing that same year. The vendor determined that the stem-to-upper wedge connection was not properly torqued. The second
10-inch Anchor/Darling DDGVs. The first wedge pin failure involved a Unit 2 HPCI outboard
 
steam isolation valve installed in 2001 that failed during testing that same year. The vendor
 
determined that the stem-to-upper wedge connection was not properly torqued. The second


wedge pin failure occurred in 2008 and involved a Unit 1 HPCI outboard steam isolation valve
wedge pin failure occurred in 2008 and involved a Unit 1 HPCI outboard steam isolation valve


installed in 2006 that failed during local leak rate testing. Internal inspection of the valve
installed in 2006 that failed during local leak rate testing. Internal inspection of the valve
 
revealed that the stem-to-upper wedge connection was not properly torqued. Figure 1 Typical Anchor/Darling DDGV (ADAMS Accession No. ML13064A012)
 
===Surry Power Station, Unit 2===
On February 2, 2011, Surry Power Station, Unit 2, tripped as a result of a low-flow condition in
 
the reactor coolant system (RCS) C loop. The low-flow condition was the result of a stem-disc
 
separation of the RCS C loop isolation valve. The valve was an Anchor/Darling 30-inch
 
DDGV. Inspection of the valve internals revealed that the wedge pin failed and the upper
 
wedge threads exhibited excessive wear. The root cause was determined to be flow-induced
 
vibration coupled with inadequate torque of the stem-to-upper wedge connection, documented
 
in LER 2011-001-00, dated April 1, 2011 (ADAMS Accession No. ML11105A032). A similar
 
stem-disc separation occurred in 1999 on the RCS A loop isolation valve (also an
 
Anchor/Darling 30-inch DDGV). In the 1999 event, the wedge pin failed, allowing the stem to


revealed that the stem-to-upper wedge connection was not properly torqued. Figure 1 Typical Anchor/Darling DDGV (ADAMS Accession No. ML13064A012)  
unthread from the upper wedge connection (see LER 1999-003-00, dated July 30, 1999 (ADAMS Legacy No. ML9908120152)).
Surry Power Station, Unit 2


On February 2, 2011, Surry Power Station, Unit 2, tripped as a result of a low-flow condition in the reactor coolant system (RCS) "C" loop.  The low-flow condition was the result of a stem-disc separation of the RCS "C" loop isolation valve.  The valve was an Anchor/Darling 30-inch DDGV.  Inspection of the valve internals revealed that the wedge pin failed and the upper
===River Bend Station, Unit 1===
On May 21, 2007, an unexplained drop in the reactor recirculation system loop A flow occurred


wedge threads exhibited excessive wear. The root cause was determined to be flow-induced vibration coupled with inadequate torque of t
at River Bend Station, Unit 1. Reactor power lowered to approximately 96.5-percent power with


he stem-to-upper wedge connection, documented in LER 2011-001-00, dated April 1, 2011 (ADAMS Accession No. ML11105A032
no operator action. Operators determined that the most probable cause for the condition was
).  A similar stem-disc separation occurred in 1999 on the RCS "A" loop isolation valve (also an Anchor/Darling 30-inch DDGV).  In the 1999 event, the wedge pin failed, allowing the stem to


unthread from the upper wedge connection (see LER 1999-003-00, dated July 30, 1999 (ADAMS Legacy No.
that the loop A discharge isolation valve caused partial flow blockage. The valve was a


===ML9908120152===
20-inch Anchor/Darling DDGV. Further investigation during the plant shutdown revealed a
)).   River Bend Station, Unit 1 On May 21, 2007, an unexplained drop in the reactor recirculation system loop "A" flow occurred


at River Bend Station, Unit 1.  Reactor power lowered to approximately 96.5-percent power with no operator action.  Operators determined that the most probable cause for the condition was that the loop "A" discharge isolation valve caused partial flow blockage.  The valve was a 20-inch Anchor/Darling DDGV.  Further investigation during the plant shutdown revealed a
stem-disc separation and severely worn stem and upper wedge threads. The wedge pin failed, with the two portions extending into the upper wedge still in place while the piece that


stem-disc separation and severely worn stem and upper wedge threads. The wedge pin failed, with the two portions extending into the upper wedge still in place while the piece that
transverses the shaft was missing. The licensee identified several contributing causes for the


transverses the shaft was missing.  The licensee identified several contributing causes for the valve failure, including inadequate torque of the stem-to-upper wedge connection during the previous valve assembly, and flow-induced vibrat
valve failure, including inadequate torque of the stem-to-upper wedge connection during the previous valve assembly, and flow-induced vibration at the disc assembly caused by turbulent


ion at the disc assembly caused by turbulent flow through the valve coupled with partial extension of the disc assembly into the flow stream.
flow through the valve coupled with partial extension of the disc assembly into the flow stream.


==DISCUSSION==
==DISCUSSION==
Wedge pin failures and stem-disc separation events associated with Anchor/Darling DDGVs have occurred at both pressurized-water reactor and boiling-water reactor plants. As previously mentioned, the 2012 event at Browns Ferry Nuclear Plant, Unit 1 resulted in the issuance of
Wedge pin failures and stem-disc separation events associated with Anchor/Darling DDGVs
 
have occurred at both pressurized-water reactor and boiling-water reactor plants. As previously
 
mentioned, the 2012 event at Browns Ferry Nuclear Plant, Unit 1 resulted in the issuance of
 
10 CFR Part 21 reports by both TVA (ADAMS Accession No. ML13008A321) and Flowserve
 
(ADAMS Accession No. ML13064A012).


10 CFR Part 21 reports by both TVA (ADAMS Accession No.
In its Part 21 report, Flowserve concluded that at Browns Ferry Nuclear Plant, Unit 1:
        failure was due to the shearing of the wedge pin which serves a joint locking


ML13008A321) and Flowserve (ADAMS Accession No. ML13064A012
function at the threaded interface between the valve stem and upper wedge. The
).  In its Part 21 report, Flowserve concluded that at Browns Ferry Nuclear Plant, Unit 1:
-failure was due to the shearing of the wedge pin which serves a joint locking


function at the threaded interface between the valve stem and upper wedge.  The
pin is designed to ensure that the joint does not loosen due to vibration and other


pin is designed to ensure that the joint does not loosen due to vibration and other secondary loads. On some valve designs, the pin also is used to attach the disc retainers to the upper wedge. The pin shearing allowed rotation of the stem
secondary loads. On some valve designs, the pin also is used to attach the disc
 
retainers to the upper wedge. The pin shearing allowed rotation of the stem


during the closing stroke when the valve was seating and ultimately resulted in
during the closing stroke when the valve was seating and ultimately resulted in
Line 117: Line 190:
loss of the stem to upper wedge joint integrity.
loss of the stem to upper wedge joint integrity.


Flowserve has completed an evaluation of the failure and concluded the root cause of the wedge pin failure was excessive load on the pin.  The stem operating torque exceeded the torque to tighten the stem into the upper wedge
Flowserve has completed an evaluation of the failure and concluded the root


before installation of the wedge pin. The additional stem torque produced a load
cause of the wedge pin failure was excessive load on the pin. The stem
 
operating torque exceeded the torque to tighten the stem into the upper wedge
 
before installation of the wedge pin. The additional stem torque produced a load


on the wedge pin creating a stress which exceeded the pin shear strength
on the wedge pin creating a stress which exceeded the pin shear strength


causing the failure. The recommended assembly stem torque did not envelope the operating torque for the TVA application providing the potential for an over load situation and ultimate failure. The operating torque for the TVA valve was
causing the failure. The recommended assembly stem torque did not envelope
 
the operating torque for the TVA application providing the potential for an over
 
load situation and ultimate failure. The operating torque for the TVA valve was


unusually high due to the fast closing time of the actuator and very conservative
unusually high due to the fast closing time of the actuator and very conservative
Line 129: Line 210:
closing thrust margin.
closing thrust margin.


This situation can potentially occur on any Anchor/Darling type double-disc gate valve with a threaded stem to upper wedge connection, typically size 2.5" and larger, operated by an actuator that applies torque on the stem to produce the
This situation can potentially occur on any Anchor/Darling type double-disc gate
 
valve with a threaded stem to upper wedge connection, typically size 2.5" and
 
larger, operated by an actuator that applies torque on the stem to produce the
 
required valve operating thrust. An operating stem torque greater than the


required valve operating thrust.  An operating stem torque greater than the
assembly stem torque can provide the opportunity for excessive pin load and


assembly stem torque can provide the opportunity for excessive pin load and potentially failure.
potentially failure.


The stems on most double-disc (DD) gate valves larger than size 2" are attached
The stems on most double-disc (DD) gate valves larger than size 2" are attached


to the upper wedge using UN [unified constant pitch] threads. A pin is installed
to the upper wedge using UN [unified constant pitch] threads. A pin is installed


through the hub of the upper wedge and stem threaded section to prevent the
through the hub of the upper wedge and stem threaded section to prevent the


stem from loosening and eventually unscrewing from the wedge. In addition, the disc retainers on some DD gate valves are attached using the wedge pin. See Figure 1. The output torque of the actuator is transmitted to the stem/wedge joint through the stem and is resisted by the disc wedge pack, therefore the stem to
stem from loosening and eventually unscrewing from the wedge. In addition, the
 
disc retainers on some DD gate valves are attached using the wedge pin. See
 
Figure 1. The output torque of the actuator is transmitted to the stem/wedge joint
 
through the stem and is resisted by the disc wedge pack, therefore the stem to
 
wedge connection is loaded by the stem torque and thrust. The wedge pin is not


wedge connection is loaded by the stem torque and thrust. The wedge pin is not
designed to withstand the full actuator output torque. The actuator torque


designed to withstand the full actuator output torque.  The actuator torque
direction tends to tighten the stem into the wedge during closing and tends to


direction tends to tighten the stem into the wedge during closing and tends to loosen the stem during opening. Flowserve's Part 21 also states:  
loosen the stem during opening. Flowserve's Part 21 also states:
Flowserve recommends that all critical An
          Flowserve recommends that all critical Anchor/Darling Double-Disc Gate valves with


chor/Darling Double-Disc Gate valves with threaded stem to upper wedge connections and actuators that produce a torque on
threaded stem to upper wedge connections and actuators that produce a torque on


the stem be evaluated for potential wedge pin failure.
the stem be evaluated for potential wedge pin failure.


This IN provides a discussion of the recent LaSalle County Station, Unit 2 Anchor/Darling DDGV failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that
This IN provides a discussion of the recent LaSalle County Station, Unit 2 Anchor/Darling DDGV
 
failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that
 
resulted in stem-disc separations. This document contains information available to NRC staff as
 
of May 2017. The licensee for LaSalle County Station, Unit 2 is in the process of completing


resulted in stem-disc separations. This document contains information available to NRC staff as of May 2017.  The licensee for LaSalle County Station, Unit 2 is in the process of completing
their root cause determination. Licensees can use this information in addition to the technical


their root cause determination.  Licensees can use this information in addition to the technical information provided in the 2013 Flowserve Part 21 report to consider actions, as appropriate, to
information provided in the 2013 Flowserve Part 21 report to consider actions, as appropriate, to


avoid similar problems.
avoid similar problems.


==CONTACT==
==CONTACT==
This IN requires no specific action or written response. Please direct any questions about this matter to the technical contacts listed below.
This IN requires no specific action or written response. Please direct any questions about this


/ra/      /ra/
matter to the technical contacts listed below.
  Louise Lund, Director Timothy J. McGinty, Director Division of Policy and Rulemaking Division of Construction Inspection


Office of Nuclear Reactor Regulation   and Operational Programs
/ra/                                                /ra/
Louise Lund, Director                                Timothy J. McGinty, Director
 
Division of Policy and Rulemaking                    Division of Construction Inspection
 
Office of Nuclear Reactor Regulation                   and Operational Programs


Office of New Reactors
Office of New Reactors


Technical Contacts: John W. Thompson, NRR/DIRS Michael Farnan, NRR/DE
Technical Contacts: John W. Thompson, NRR/DIRS               Michael Farnan, NRR/DE
 
301-415-1011                          301-415-1486 E-mail: John.Thompson@nrc.gov          E-mail: Michael.Farnan@nrc.gov
 
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library, Document Collections.
 
ML17153A053; *concurred via email      TAC No. MF9698 OFFICE  NRR/DPR/PGCB/LA    TECH EDITOR          NRR/DIRS/IOEB/TL    NRR/DIRS/IOEB/TL  NRR/DIRS/IOEB/BC
 
NAME    ELee              JDougherty*          JThompson*          EThomas*          HChernoff*
DATE    06/02/17          06/05/17            06/12/17            06/12/17          06/12/17 OFFICE  NRR/DPR/PGCB/LA    RI/DRS/DD            RII/DRS/DD          RII/DRP/D          RIII/DRS/D
 
NAME    ELee              JYerokun*            MMiller*            JMunday*            KOBrien*
DATE    06/12/17          06/13/17            06/13/17            06/13/17          06/07/17 OFFICE  RIV/DRP/D          RIV/DRS/DD          NRR/DSS/D          NRR/DRA/DD        NRR/DE/DD
 
NAME    TPruett*          JClark*              MGavrilas*          SWeerakkody* (A)    KCoyne* (A)
DATE    06/12/17          06/12/17            06/12/17            6/13/17            06/13/17 OFFICE  NRR/DLR/D          NRR/DIRS/D          NRR/DPR/PGCB/PM    NRR/DPR/PGCB/BC NRO/DCIP/D


301-415-1011   301-415-1486  E-mail: 
NAME   GWilson*          CMiller*            NMartinez          AGarmoe (A)        TMcGinty
John.Thompson@nrc.gov E-mail:  Michael.Farnan@nrc.gov


Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under "NRC Library," "Document Collections."
DATE    06/13/17          06/13/17            06/14/17            06/14/17          06/14/17 OFFICE NRR/DPR/D


ML17153A053; *concurred via email                      TAC No. MF9698 OFFICE NRR/DPR/PGCB/LA TECH EDITOR NRR/DIRS/IOEB/TL NRR/DIRS/IOEB/TL NRR/DIRS/IOEB/BC NAME ELee JDougherty* JThompson* EThomas* HChernoff* DATE 06/02/17 06/05/17 06/12/17 06/12/17 06/12/17 OFFICE NRR/DPR/PGCB/LA RI/DRS/DD RII/DRS/DD RII/DRP/D RIII/DRS/D NAME ELee JYerokun* MMiller* JMunday*  KO'Brien* DATE 06/12/17 06/13/17 06/13/17 06/13/17 06/07/17 OFFICE RIV/DRP/D RIV/DRS/DD  NRR/DSS/D NRR/DRA/DD NRR/DE/DD NAME TPruett* JClark* MGavrilas* SWeerakkody* (A)  KCoyne* (A) DATE 06/12/17 06/12/17 06/12/17 6/13/17 06/13/17 OFFICE NRR/DLR/D NRR/DIRS/D NRR/DPR/PGCB/PM NRR/DPR/PGCB/BC NRO/DCIP/D NAME GWilson* CMiller* NMartinez AGarmoe (A)  TMcGinty  DATE 06/13/17 06/13/17 06/14/17 06/14/17 06/14/17 OFFICE NRR/DPR/D    NAME LLund     DATE 06/15/17}}
===NAME   LLund===
DATE   06/15/17}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 02:33, 30 October 2019

Anchor/Darling Double Disc Gate Valve Wedge Pin and Stem-Disc Separation Failures
ML17153A053
Person / Time
Issue date: 06/15/2017
From: Louise Lund, Mcginty T
Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking
To:
Nancy Martinez
References
TAC No. MF9698 IN-17-003
Download: ML17153A053 (6)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NEW REACTORS

WASHINGTON, DC 20555 June 15, 2017 NRC INFORMATION NOTICE 2017-03: ANCHOR/DARLING DOUBLE DISC GATE VALVE

WEDGE PIN AND STEM-DISC SEPARATION

FAILURES

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power reactor under

Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of

Production and Utilization Facilities, except those that have permanently ceased operations

and have certified that fuel has been permanently removed from the reactor vessel.

All holders of and applicants for a combined license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees of operating experience regarding Anchor/Darling (a subsidiary of Flowserve)

double disc gate valve (DDGV) failures. This IN provides a discussion of the recent LaSalle

County Station Unit 2 Anchor/Darling DDGV failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that resulted in stem-disc separations. This

document contains information available to NRC staff as of May 2017. The NRC expects

recipients of this IN to review the information for applicability to their facilities and consider

actions, as appropriate, to avoid similar problems. However, suggestions contained in this IN

are not NRC requirements; therefore, no specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

LaSalle County Station, Unit 2

On February 11, 2017, during a refueling outage at LaSalle County Station, Unit 2, the licensee

was attempting to fill and vent the high-pressure core spray (HPCS) system when the Unit 2 HPCS injection isolation valve (an Anchor/Darling 12-inch DDGV) would not open on demand.

Initial analysis identified that a stem-disc separation occurred as a result of excessive wear of

the valve stem threads and shear failure of the wedge pin. The licensee has not completed

their root cause determination. The licensee reported this event in Licensee Event Report

(LER) 2017-003-00, dated April 12, 2017 (Agencywide Documents Access and Management

System (ADAMS) Accession No. ML17102B424).

The licensee had been using industry guidance to perform visual evaluations and diagnostic

testing on the valve. The guidance was based on earlier operating experience from an event on

October 20, 2012, at Browns Ferry Nuclear Plant, Unit 1. This event resulted in two reports

ML17153A053 under 10 CFR Part 21, Reporting of Defects and Noncompliance. The first Part 21 report was

issued by the Tennessee Valley Authority (TVA), Anti-Rotation Pin Failure in Anchor Darling

(Flowserve) Double Disc Gate Valve, dated January 4, 2013 (ADAMS Accession

No. ML13008A321) and the second by Flowserve, Wedge Pin Failure in Anchor/Darling

Double-Disc Gate Valve at Browns Ferry Nuclear Plant Unit 1, dated February 25, 2013 (ADAMS Accession No. ML13064A012).

Browns Ferry Nuclear Plant, Units 1 and 2

On October 20, 2012, a Browns Ferry Nuclear Plant, Unit 1, high-pressure coolant injection

(HPCI) steam isolation valve, which also serves as a containment inboard isolation valve, failed

its local leak rate test. Investigation revealed that, although the event was not a stem-disc

separation, the wedge pin failed and one of the two disc retainers (see Figure 1) fell from the

stem-to-upper wedge connection into a space between the valve discs, causing one of the two

discs not to properly seat. The valve was a 10-inch Anchor/Darling DDGV. It was installed in

2007 and had not been disassembled since installation. The licensee, TVA, submitted a

10 CFR Part 21 report, dated January 4, 2013 (ADAMS Accession No. ML13008A321), for this

failure. In the report, TVA determined that the wedge pin failed because the vendor had not

properly torqued the stem-to-upper wedge connection during manufacture.

Before the 2012 failure, Browns Ferry Nuclear Plant experienced two other wedge pin failures in

10-inch Anchor/Darling DDGVs. The first wedge pin failure involved a Unit 2 HPCI outboard

steam isolation valve installed in 2001 that failed during testing that same year. The vendor

determined that the stem-to-upper wedge connection was not properly torqued. The second

wedge pin failure occurred in 2008 and involved a Unit 1 HPCI outboard steam isolation valve

installed in 2006 that failed during local leak rate testing. Internal inspection of the valve

revealed that the stem-to-upper wedge connection was not properly torqued. Figure 1 Typical Anchor/Darling DDGV (ADAMS Accession No. ML13064A012)

Surry Power Station, Unit 2

On February 2, 2011, Surry Power Station, Unit 2, tripped as a result of a low-flow condition in

the reactor coolant system (RCS) C loop. The low-flow condition was the result of a stem-disc

separation of the RCS C loop isolation valve. The valve was an Anchor/Darling 30-inch

DDGV. Inspection of the valve internals revealed that the wedge pin failed and the upper

wedge threads exhibited excessive wear. The root cause was determined to be flow-induced

vibration coupled with inadequate torque of the stem-to-upper wedge connection, documented

in LER 2011-001-00, dated April 1, 2011 (ADAMS Accession No. ML11105A032). A similar

stem-disc separation occurred in 1999 on the RCS A loop isolation valve (also an

Anchor/Darling 30-inch DDGV). In the 1999 event, the wedge pin failed, allowing the stem to

unthread from the upper wedge connection (see LER 1999-003-00, dated July 30, 1999 (ADAMS Legacy No. ML9908120152)).

River Bend Station, Unit 1

On May 21, 2007, an unexplained drop in the reactor recirculation system loop A flow occurred

at River Bend Station, Unit 1. Reactor power lowered to approximately 96.5-percent power with

no operator action. Operators determined that the most probable cause for the condition was

that the loop A discharge isolation valve caused partial flow blockage. The valve was a

20-inch Anchor/Darling DDGV. Further investigation during the plant shutdown revealed a

stem-disc separation and severely worn stem and upper wedge threads. The wedge pin failed, with the two portions extending into the upper wedge still in place while the piece that

transverses the shaft was missing. The licensee identified several contributing causes for the

valve failure, including inadequate torque of the stem-to-upper wedge connection during the previous valve assembly, and flow-induced vibration at the disc assembly caused by turbulent

flow through the valve coupled with partial extension of the disc assembly into the flow stream.

DISCUSSION

Wedge pin failures and stem-disc separation events associated with Anchor/Darling DDGVs

have occurred at both pressurized-water reactor and boiling-water reactor plants. As previously

mentioned, the 2012 event at Browns Ferry Nuclear Plant, Unit 1 resulted in the issuance of

10 CFR Part 21 reports by both TVA (ADAMS Accession No. ML13008A321) and Flowserve

(ADAMS Accession No. ML13064A012).

In its Part 21 report, Flowserve concluded that at Browns Ferry Nuclear Plant, Unit 1:

failure was due to the shearing of the wedge pin which serves a joint locking

function at the threaded interface between the valve stem and upper wedge. The

pin is designed to ensure that the joint does not loosen due to vibration and other

secondary loads. On some valve designs, the pin also is used to attach the disc

retainers to the upper wedge. The pin shearing allowed rotation of the stem

during the closing stroke when the valve was seating and ultimately resulted in

loss of the stem to upper wedge joint integrity.

Flowserve has completed an evaluation of the failure and concluded the root

cause of the wedge pin failure was excessive load on the pin. The stem

operating torque exceeded the torque to tighten the stem into the upper wedge

before installation of the wedge pin. The additional stem torque produced a load

on the wedge pin creating a stress which exceeded the pin shear strength

causing the failure. The recommended assembly stem torque did not envelope

the operating torque for the TVA application providing the potential for an over

load situation and ultimate failure. The operating torque for the TVA valve was

unusually high due to the fast closing time of the actuator and very conservative

closing thrust margin.

This situation can potentially occur on any Anchor/Darling type double-disc gate

valve with a threaded stem to upper wedge connection, typically size 2.5" and

larger, operated by an actuator that applies torque on the stem to produce the

required valve operating thrust. An operating stem torque greater than the

assembly stem torque can provide the opportunity for excessive pin load and

potentially failure.

The stems on most double-disc (DD) gate valves larger than size 2" are attached

to the upper wedge using UN [unified constant pitch] threads. A pin is installed

through the hub of the upper wedge and stem threaded section to prevent the

stem from loosening and eventually unscrewing from the wedge. In addition, the

disc retainers on some DD gate valves are attached using the wedge pin. See

Figure 1. The output torque of the actuator is transmitted to the stem/wedge joint

through the stem and is resisted by the disc wedge pack, therefore the stem to

wedge connection is loaded by the stem torque and thrust. The wedge pin is not

designed to withstand the full actuator output torque. The actuator torque

direction tends to tighten the stem into the wedge during closing and tends to

loosen the stem during opening. Flowserve's Part 21 also states:

Flowserve recommends that all critical Anchor/Darling Double-Disc Gate valves with

threaded stem to upper wedge connections and actuators that produce a torque on

the stem be evaluated for potential wedge pin failure.

This IN provides a discussion of the recent LaSalle County Station, Unit 2 Anchor/Darling DDGV

failure, events at Browns Ferry that led to Part 21 reporting, and other operating experience that

resulted in stem-disc separations. This document contains information available to NRC staff as

of May 2017. The licensee for LaSalle County Station, Unit 2 is in the process of completing

their root cause determination. Licensees can use this information in addition to the technical

information provided in the 2013 Flowserve Part 21 report to consider actions, as appropriate, to

avoid similar problems.

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contacts listed below.

/ra/ /ra/

Louise Lund, Director Timothy J. McGinty, Director

Division of Policy and Rulemaking Division of Construction Inspection

Office of Nuclear Reactor Regulation and Operational Programs

Office of New Reactors

Technical Contacts: John W. Thompson, NRR/DIRS Michael Farnan, NRR/DE

301-415-1011 301-415-1486 E-mail: John.Thompson@nrc.gov E-mail: Michael.Farnan@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library, Document Collections.

ML17153A053; *concurred via email TAC No. MF9698 OFFICE NRR/DPR/PGCB/LA TECH EDITOR NRR/DIRS/IOEB/TL NRR/DIRS/IOEB/TL NRR/DIRS/IOEB/BC

NAME ELee JDougherty* JThompson* EThomas* HChernoff*

DATE 06/02/17 06/05/17 06/12/17 06/12/17 06/12/17 OFFICE NRR/DPR/PGCB/LA RI/DRS/DD RII/DRS/DD RII/DRP/D RIII/DRS/D

NAME ELee JYerokun* MMiller* JMunday* KOBrien*

DATE 06/12/17 06/13/17 06/13/17 06/13/17 06/07/17 OFFICE RIV/DRP/D RIV/DRS/DD NRR/DSS/D NRR/DRA/DD NRR/DE/DD

NAME TPruett* JClark* MGavrilas* SWeerakkody* (A) KCoyne* (A)

DATE 06/12/17 06/12/17 06/12/17 6/13/17 06/13/17 OFFICE NRR/DLR/D NRR/DIRS/D NRR/DPR/PGCB/PM NRR/DPR/PGCB/BC NRO/DCIP/D

NAME GWilson* CMiller* NMartinez AGarmoe (A) TMcGinty

DATE 06/13/17 06/13/17 06/14/17 06/14/17 06/14/17 OFFICE NRR/DPR/D

NAME LLund

DATE 06/15/17


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