Information Notice 2013-10, Programs for Monitoring Boiling-Water Reactor Steam Dryer Integrity: Difference between revisions

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| issue date = 06/14/2013
| issue date = 06/14/2013
| title = Programs for Monitoring Boiling-Water Reactor Steam Dryer Integrity
| title = Programs for Monitoring Boiling-Water Reactor Steam Dryer Integrity
| author name = Dudes L A, Kokajko L E
| author name = Dudes L, Kokajko L
| author affiliation = NRC/NRO/DCIP, NRC/NRR/DPR
| author affiliation = NRC/NRO/DCIP, NRC/NRR/DPR
| addressee name =  
| addressee name =  
Line 15: Line 15:
| page count = 5
| page count = 5
}}
}}
{{#Wiki_filter:ML13003A049 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION OFFICE OF NEW REACTORS WASHINGTON, DC  20555-0001 June 14, 2013
{{#Wiki_filter:UNITED STATES


NRC INFORMATION NOTICE 2013-10: PROGRAMS FOR MONITORING   BOILING-WATER REACTOR
NUCLEAR REGULATORY COMMISSION
 
OFFICE OF NUCLEAR REACTOR REGULATION
 
OFFICE OF NEW REACTORS
 
WASHINGTON, DC 20555-0001 June 14, 2013 NRC INFORMATION NOTICE 2013-10:                 PROGRAMS FOR MONITORING
 
BOILING-WATER REACTOR


STEAM DRYER INTEGRITY
STEAM DRYER INTEGRITY


==ADDRESSEES==
==ADDRESSEES==
All holders of operating licenses for boiling-water reactors (BWRs) under Title 10 of the
All holders of operating licenses for boiling-water reactors (BWRs) under Title 10 of the Code of
 
Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization


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


has been permanently removed from the reactor vessel.
has been permanently removed from the reactor vessel.
Line 30: Line 40:
All holders of and applicants for a BWR early site permit, combined license, standard design
All holders of and applicants for a BWR early site permit, combined license, standard design


certification, standard design approval, or manufacturing license under 10 CFR Part 52,  
certification, standard design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.
"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 about the importance of establishing programs to monitor the structural integrity of
 
steam dryers in BWR nuclear power plants, as evidenced by the examples provided in this IN,
and to raise industry awareness regarding the possibility of cracking in new and existing steam


suing this information notice (IN) to inform addressees about the importance of establishing programs to monitor the structural integrity of
dryers. The NRC expects that recipients will review the information contained in this IN for


steam dryers in BWR nuclear power plants, as evidenced by the examples provided in this IN, and to raise industry awareness regarding the possibility of cracking in new and existing steam dryers.  The NRC expects that recipients will revi
applicability to their facilities and consider actions, as appropriate, to avoid similar issues at their


ew the information contained in this IN for applicability to their facilities and consider actions, as appropriate, to avoid similar issues at their facilities. However, suggestions contained in this IN are not NRC requirements; therefore, no
facilities. However, suggestions contained in this IN are not NRC requirements; therefore, no


specific action or written response is required.
specific action or written response is required.
Line 47: Line 61:


===New Steam Dryers===
===New Steam Dryers===
The licensee for the Susquehanna Steam Electric Station (SSES) replaced the steam dryers in
SSES Units 1 and 2 as part of its license amendment request to allow operation of the SSES
units at extended power uprate (EPU) conditions. The replaced steam dryers have a curved
hood design developed by General Electric Hitachi. The licensee installed the new steam
dryers at SSES Units 1 and 2 in 2008 and 2009, respectively. The EPU license amendment
specifies periodic inspection of the steam dryers in SSES Units 1 and 2 during refueling outages
to confirm their continued structural integrity. After one cycle of EPU operation for each SSES


The licensee for the Susquehanna Steam Electric Station (SSES) replaced the steam dryers in
unit, the licensee identified intergranular stress corrosion cracking (IGSCC) in both of the


===SSES Units 1 and 2 as part of its license am===
replacement steam dryers. In addition to the IGSCC findings, a fatigue crack was identified in
endment request to allow operation of the SSES


units at extended power uprate (EPU) conditions.  The replaced steam dryers have a curved hood design developed by General Electric Hitachi.  The licensee installed the new steam dryers at SSES Units 1 and 2 in 2008 and 2009, respectively.  The EPU license amendment
the steam dryer in SSES Unit 2. These findings were summarized in the licensees letters to the


specifies periodic inspection of the steam dryers in SSES Units 1 and 2 during refueling outages to confirm their continued structural integrity. After one cycle of EPU operation for each SSES
NRC, dated July 15, 2010 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML102230125) and September 29, 2011 (ADAMS Accession


unit, the licensee identified intergranular stress corrosion cracking (IGSCC) in both of the replacement steam dryers.  In addition to the IGSCC findings, a fatigue crack was identified in the steam dryer in SSES Unit 2. These findings we
No. ML112730314).


re summarized in the licensee's letters to the NRC, dated July 15, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML102230125) and September 29, 2011 (ADAMS Accession
ML13003A049 The two major causal factors for the IGSCC findings were identified as inadequate quality


No. ML112730314). The two major causal factors for the IGSCC findings were identified as inadequate quality control and fabrication stresses during welding of the replacement steam dryer assemblies.
control and fabrication stresses during welding of the replacement steam dryer assemblies.


Since the IGSCC was observed after only one operating cycle at both SSES units, the NRC
Since the IGSCC was observed after only one operating cycle at both SSES units, the NRC


staff is alerting all BWR nuclear power plant licensees that the incubation period-the time
staff is alerting all BWR nuclear power plant licensees that the incubation periodthe time


necessary to initiate a crack-for IGSCC could be shorter than previously anticipated. The
necessary to initiate a crackfor IGSCC could be shorter than previously anticipated. The


specific fatigue crack in the steam dryer in SSES Unit 2 was the result of a poorly designed weld joint, as well as fabrication and quality control issues.
specific fatigue crack in the steam dryer in SSES Unit 2 was the result of a poorly designed weld


The licensee implemented corrective actions for both SSES units in response to the identification of the cracking in the replacement steam dryers. These actions included
joint, as well as fabrication and quality control issues.


necessary repairs followed by re-inspections during every refueling outage until the absence of crack growth can be confirmed in the existing cracks and no new cracks are identified.
The licensee implemented corrective actions for both SSES units in response to the
 
identification of the cracking in the replacement steam dryers. These actions included
 
necessary repairs followed by re-inspections during every refueling outage until the absence of
 
crack growth can be confirmed in the existing cracks and no new cracks are identified.


===Existing Steam Dryers===
===Existing Steam Dryers===
Following initial EPU operation several years ago, Quad Cities Nuclear Power Station (Quad
Cities), Units 1 and 2, experienced significant fatigue cracking of their original steam dryers with
the generation of loose parts in the reactor coolant and main steam systems. The steam dryers
were subsequently replaced with an improved design. In addition, modifications to several
branch lines connected to the main steam lines were implemented to reduce acoustic loading
on the steam dryer. NRC issued the following INs discussing steam dryer cracking issues: IN


Following initial EPU operation several years ago, Quad Cities Nuclear Power Station (Quad Cities), Units 1 and 2, experienced significant fatigue cracking of their original steam dryers with the generation of loose parts in the reactor coolant and main steam systems.  The steam dryers were subsequently replaced with an improved design.  In addition, modifications to several
2002-26, dated September 11, 2002, Failure of Steam Dryer Cover Plate after a Recent Power


branch lines connected to the main steam lines were implemented to reduce acoustic loading on the steam dryer.  NRC issued the following INs discussing steam dryer cracking issues: IN
Uprate, IN 2002-26, Supplement 1, dated July 21, 2003, Additional Failure of Steam Dryer


2002-26, dated September 11, 2002, "Failure of Steam Dryer Cover Plate after a Recent Power
after a Recent Power Uprate, and IN 2002-26, Supplement 2, dated January 9, 2004, Additional Flow-Induced Vibration Failures after a Recent Power Uprate.


Uprate," IN 2002-26, Supplement 1, dated July 21, 2003, "Additional Failure of Steam Dryer after a Recent Power Uprate," and IN 2002-26, Supplement 2, dated January 9, 2004,
During its operating life, the existing steam dryer at Vermont Yankee Nuclear Power Station
"Additional Flow-Induced Vibration Failures after a Recent Power Uprate." 


During its operating life, the existing steam dryer at Vermont Yankee Nuclear Power Station (Vermont Yankee) experienced IGSCC cracking. Pre-emptive modifications on the existing steam dryer were completed during its spring 2004 refueling outage (RFO); and all remaining
(Vermont Yankee) experienced IGSCC cracking. Pre-emptive modifications on the existing
 
steam dryer were completed during its spring 2004 refueling outage (RFO); and all remaining


modifications necessary to implement EPU operations were completed during its fall 2005 RFO.
modifications necessary to implement EPU operations were completed during its fall 2005 RFO.


EPU operations were implemented prior to the spring 2007 RFO. Vermont Yankee submitted a license amendment request on December 22, 2011, to revise a license condition related to the
EPU operations were implemented prior to the spring 2007 RFO. Vermont Yankee submitted a


monitoring, inspection frequency, and performance of its steam dryer, which the NRC approved on December 19, 2012 (ML12338A236).  As indicated in the Vermont Yankee licensee's response to an NRC request for additional information (RAI) concerning this amendment request, there have been no signs of crack growth activity and no cracking in the replaced
license amendment request on December 22, 2011, to revise a license condition related to the


hardware for the steam dryer, post EPU.  Furthermore, the licensee stated that the inspection
monitoring, inspection frequency, and performance of its steam dryer, which the NRC approved


results show that the flaw indications caused by IGSCC have stabilized or arrested with no further or minimal growth expected, and that there is no evidence of crack growth post EPU for all other steam dryer flaws. Vermont Yankee continues to perform inspections to monitor the
on December 19, 2012 (ML12338A236). As indicated in the Vermont Yankee licensees
 
response to an NRC request for additional information (RAI) concerning this amendment
 
request, there have been no signs of crack growth activity and no cracking in the replaced
 
hardware for the steam dryer, post EPU. Furthermore, the licensee stated that the inspection
 
results show that the flaw indications caused by IGSCC have stabilized or arrested with no
 
further or minimal growth expected, and that there is no evidence of crack growth post EPU for
 
all other steam dryer flaws. Vermont Yankee continues to perform inspections to monitor the


aging effects of IGSCC to ensure the functionality and structural integrity of its steam dryer.
aging effects of IGSCC to ensure the functionality and structural integrity of its steam dryer.


Additional information is available in the licensee's response to the NRC RAI, dated October 3, 2012 (ADAMS Accession No. ML12284A478).
Additional information is available in the licensees response to the NRC RAI, dated October 3,
2012 (ADAMS Accession No. ML12284A478).


==DISCUSSION==
==DISCUSSION==
The steam dryer in the reactor vessel of a BWR plant removes excess moisture from the steam generated by the reactor core before the steam is directed through piping to the turbine.
The steam dryer in the reactor vessel of a BWR plant removes excess moisture from the steam


Although the steam dryer performs a non-safety related function, it must maintain its structural integrity to prevent the occurrence of loose parts in the reactor vessel and attached steam lines that could adversely affect plant operation, including causing damage to safety-related
generated by the reactor core before the steam is directed through piping to the turbine.


components.  Historically, BWR steam dryers experienced IGSCC over their operating life.  This IGSCC is caused by a lack of hydrogen water protection in the steam dome region of the reactor vessel.  As a result, insufficient hydrogen is present in the steam to minimize IGSCC.
Although the steam dryer performs a non-safety related function, it must maintain its structural


Steam dryers have also exhibited fatigue cracking due to acoustic and hydrodynamic loading caused by steam flow through and around the steam dryer, as well as through the steam lines.
integrity to prevent the occurrence of loose parts in the reactor vessel and attached steam lines


As discussed above, Quad Cities Units 1 and 2 experienced significant fatigue cracking of their original steam dryers following initial EPU operation several years ago. Subsequent improved steam dryer design and, in some instances, steam line modifications, have resulted in
that could adversely affect plant operation, including causing damage to safety-related
 
components. Historically, BWR steam dryers experienced IGSCC over their operating life. This IGSCC is caused by a lack of hydrogen water protection in the steam dome region of the
 
reactor vessel. As a result, insufficient hydrogen is present in the steam to minimize IGSCC.
 
Steam dryers have also exhibited fatigue cracking due to acoustic and hydrodynamic loading
 
caused by steam flow through and around the steam dryer, as well as through the steam lines.
 
As discussed above, Quad Cities Units 1 and 2 experienced significant fatigue cracking of their
 
original steam dryers following initial EPU operation several years ago. Subsequent improved
 
steam dryer design and, in some instances, steam line modifications, have resulted in


successful steam dryer performance to date at both Quad Cities units and other BWR units
successful steam dryer performance to date at both Quad Cities units and other BWR units


during normal operating and EPU conditions. Th
during normal operating and EPU conditions. The NRC staff issued Regulatory Guide (RG)
1.20, Comprehensive Vibration Assessment Program for Reactor Internals during
 
Preoperational and Initial Startup Testing, which addresses vibration assessment of the reactor


e NRC staff issued Regulatory Guide (RG) 1.20, "Comprehensive Vibration Assessment Program for Reactor Internals during Preoperational and Initial Startup Testing," which addresses vibration assessment of the reactor vessel internal components during preoperational and initial startup testing. In addition, this RG
vessel internal components during preoperational and initial startup testing. In addition, this RG


provides information on methods for evaluating the potential adverse effects from pressure fluctuations and vibration in piping systems for all light water reactor plants.  This RG can be
provides information on methods for evaluating the potential adverse effects from pressure


used for establishing a power ascension testing program for operating plants that are proposing to implement an EPU.
fluctuations and vibration in piping systems for all light water reactor plants. This RG can be


Both IGSCC and fatigue are two active aging degradation mechanisms that could potentially create synergistic effects that might compromise the structural integrity of the steam dryer.
used for establishing a power ascension testing program for operating plants that are proposing
 
to implement an EPU.
 
Both IGSCC and fatigue are two active aging degradation mechanisms that could potentially
 
create synergistic effects that might compromise the structural integrity of the steam dryer.


Therefore, as part of implementing EPU operation, BWR licensees initiate an inspection
Therefore, as part of implementing EPU operation, BWR licensees initiate an inspection


program that is consistent with Boiling-Water Reactor Vessel and Internals Project (BWRVIP)-139-A, "BWR Vessel and Internals Project, Steam Dryer Inspection and Flaw Evaluation Guidelines."  The NRC staff approved the BWRVIP-139-A report on July 30, 2008, and the NRC staff's safety evaluation (SE) is available at ADAMS Accession No. ML082070332.
program that is consistent with Boiling-Water Reactor Vessel and Internals Project
 
(BWRVIP)-139-A, BWR Vessel and Internals Project, Steam Dryer Inspection and Flaw


Topical Report BWRVIP-84, "BWR Vessel and Internals Project, Guidelines for Selection and
Evaluation Guidelines. The NRC staff approved the BWRVIP-139-A report on July 30, 2008, and the NRC staffs safety evaluation (SE) is available at ADAMS Accession No. ML082070332.


Use of Materials for Repairs to BWR Internals," provides, in part, fabrication guidelines for
Topical Report BWRVIP-84, BWR Vessel and Internals Project, Guidelines for Selection and


repaired or replacement BWR vessel internals. The NRC staff approved the BWRVIP-84 report on September 23, 2008, and the NRC staff's SE is available at ADAMS Accession No. ML082321084. BWRVIP-84 identifies that tri-junction welds at seismic support blocks and
Use of Materials for Repairs to BWR Internals, provides, in part, fabrication guidelines for
 
repaired or replacement BWR vessel internals. The NRC staff approved the BWRVIP-84 report
 
on September 23, 2008, and the NRC staffs SE is available at ADAMS Accession
 
No. ML082321084. BWRVIP-84 identifies that tri-junction welds at seismic support blocks and


other locations with high-stress concentrations in steam dryers are susceptible to fatigue
other locations with high-stress concentrations in steam dryers are susceptible to fatigue


cracking. Because the fabrication process can affect the occurrence of IGSCC, implementation
cracking. Because the fabrication process can affect the occurrence of IGSCC, implementation


of the fabrication guidelines in BWRVIP-84, in conjunction with the requirements addressed in
of the fabrication guidelines in BWRVIP-84, in conjunction with the requirements addressed in


the NRC staff's SE, could mitigate IGSCC. In addition, conformance with BWRVIP-139-A inspection criteria, in conjunction with implementing early corrective actions and monitoring and trending age-related degradation, can facilitate an effective aging management program for
the NRC staffs SE, could mitigate IGSCC. In addition, conformance with BWRVIP-139-A
 
inspection criteria, in conjunction with implementing early corrective actions and monitoring and
 
trending age-related degradation, can facilitate an effective aging management program for
 
steam dryers, and help maintain the structural integrity of the steam dryer. By performing visual
 
or other appropriate inspections, licensees will have an opportunity to identify potential issues


steam dryers, and help maintain the structural integrity of the steam dryer.  By performing visual
with the structural integrity of steam dryers to allow corrective action that will prevent the


or other appropriate inspections, licensees will have an opportunity to identify potential issues with the structural integrity of steam dryers to allow corrective action that will prevent the generation of loose parts in the reactor vessel and attached steam lines.
generation of loose parts in the reactor vessel and attached steam lines.


Continued occurrences of steam dryer cracking illustrate that, for BWR units that have
Continued occurrences of steam dryer cracking illustrate that, for BWR units that have


implemented EPU operation or are planning to request a license amendment
implemented EPU operation or are planning to request a license amendment to implement EPU
 
operations, effective implementation of inspection programs to monitor the aging effects of
 
IGSCC and fatigue for steam dryers is important. In addition to current operating BWR plants
 
that have implemented or are considering EPU operation, the development of programs for
 
monitoring the structural integrity of steam dryers is important for new BWR plants. The NRC


to implement EPU operations, effective implementation of inspection programs to monitor the aging effects of IGSCC and fatigue for steam dryers is important.  In addition to current operating BWR plants that have implemented or are considering EPU operation, the development of programs for
staff is reviewing plans for developing steam dryer monitoring programs as part of design


monitoring the structural integrity of steam dryers is important for new BWR plants.  The NRC staff is reviewing plans for developing steam dryer monitoring programs as part of design
certification and combined operating license applications for new BWR plants under


certification and combined operating license applications for new BWR plants under 10 CFR Part 52. The NRC staff's review of the steam dryer monitoring programs for new BWR plants will be discussed in the SEs for the applicable design certification and combined operating license applications.
10 CFR Part 52. The NRC staffs review of the steam dryer monitoring programs for new BWR plants will be discussed in the SEs for the applicable design certification and combined
 
operating license applications.


==CONTACT==
==CONTACT==
S This information notice does not require any specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed
S
 
This information notice does not require any specific action or written response. If you have any
 
questions about the information in this notice, please contact one of the technical contacts listed


below or the appropriate NRC project manager.
below or the appropriate NRC project manager.


/RA/   /RA/  
/RA/                                         /RA/
Lawrence E. Kokajko, Director Laura A. Dudes, Director
Lawrence E. Kokajko, Director                 Laura A. Dudes, Director


Division of Policy and Rulemaking Division of Construction Inspection
Division of Policy and Rulemaking             Division of Construction Inspection


Office of Nuclear Reactor Regulation   and Operational Programs
Office of Nuclear Reactor Regulation           and Operational Programs


Office of New Reactors
Office of New Reactors


Technical Contacts: Chakrapani Basavaraju, NRR/DE/EMCB
Technical Contacts:   Chakrapani Basavaraju, NRR/DE/EMCB


301-415-1221 E-mail: Chakrapani.Basavaraju@nrc.gov
301-415-1221 E-mail: Chakrapani.Basavaraju@nrc.gov


Ganesh Cheruvenki, NRR/DE/EVIB
Ganesh Cheruvenki, NRR/DE/EVIB


301-415-2501  
301-415-2501 E-mail: Ganesh.Cheruvenki@nrc.gov
 
Yuken Wong, NRO/DE/EMB
 
301-415-0500
                      E-mail: Yuken.Wong@nrc.gov
 
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
 
ML13003A049              *via e-mail        TAC MF0327 OFFICE      NRR/DE/EVIB*      NRR/DE/EMCB *    NRO/DE/EMB*        Tech Editor*
  NAME        GCheruvenki        CBasavaraju        YWong              CHsu
 
DATE        05/13/13          05/13/13        05/21/13          02/28/13 NRR/DLR/RARB/B                                                        NRR/DPR/PGCB/P


E-mail:  Ganesh.Cheruvenki@nrc.gov
OFFICE                      NRR/DE/EMCB/BC* NRR/DE/EVIB/BC*        NRR/DE/D*
                  C*                                                                      M


Yuken Wong, NRO/DE/EMB    301-415-0500    E-mail: 
NAME          BPham            AMcMurtray      SRosenberg          PHiland        ARussell
Yuken.Wong@nrc.gov


Note:  NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
DATE        05/14/13          05/17/13        05/14/13          05/22/13        05/30/13 NRR/DPR/PGCB/L


ML13003A049        *via e-mail              TAC MF0327  OFFICE NRR/DE/EVIB* NRR/DE/EMCB
OFFICE                     NRR/DPR/PGCB/BC      NRO/DCIP/D      NRR/DPR/DD        NRR/DPR/D


* NRO/DE/EMB* Tech Editor* NAME GCheruvenki CBasavaraju YWong CHsu DATE 05/13/13 05/13/13 05/21/13 02/28/13 OFFICE NRR/DLR/RARB/BC* NRR/DE/EMCB/BC*NRR/DE/EVIB/BC*NRR/DE/D* NRR/DPR/PGCB/P
A


M NAME BPham AMcMurtray SRosenberg PHiland ARussell DATE 05/14/13 05/17/13 05/14/13 05/22/13 05/30/13 OFFICE NRR/DPR/PGCB/L
NAME         CHawes          EBowman (A)        LDudes          SBahadur        LKokajko


A NRR/DPR/PGCB/BCNRO/DCIP/D NRR/DPR/DD NRR/DPR/D NAME CHawes EBowman (A) LDudes SBahadur LKokajko DATE 05/30/13 05/30/13 06/03/13 6/ 13 /13 6/ 14 /13}}
DATE         05/30/13           05/30/13         06/03/13         6/ 13 /13       6/ 14 /13}}


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

Latest revision as of 17:54, 11 November 2019

Programs for Monitoring Boiling-Water Reactor Steam Dryer Integrity
ML13003A049
Person / Time
Issue date: 06/14/2013
From: Laura Dudes, Kokajko L
Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking
To:
Russell A
References
TAC MF0327 IN-13-010
Download: ML13003A049 (5)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NEW REACTORS

WASHINGTON, DC 20555-0001 June 14, 2013 NRC INFORMATION NOTICE 2013-10: PROGRAMS FOR MONITORING

BOILING-WATER REACTOR

STEAM DRYER INTEGRITY

ADDRESSEES

All holders of operating licenses for boiling-water reactors (BWRs) under Title 10 of the Code of

Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization

Facilities, except those who have permanently ceased operations and have certified that fuel

has been permanently removed from the reactor vessel.

All holders of and applicants for a BWR early site permit, combined license, standard design

certification, standard design approval, or manufacturing 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 about the importance of establishing programs to monitor the structural integrity of

steam dryers in BWR nuclear power plants, as evidenced by the examples provided in this IN,

and to raise industry awareness regarding the possibility of cracking in new and existing steam

dryers. The NRC expects that recipients will review the information contained in this IN for

applicability to their facilities and consider actions, as appropriate, to avoid similar issues at their

facilities. However, suggestions contained in this IN are not NRC requirements; therefore, no

specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

New Steam Dryers

The licensee for the Susquehanna Steam Electric Station (SSES) replaced the steam dryers in

SSES Units 1 and 2 as part of its license amendment request to allow operation of the SSES

units at extended power uprate (EPU) conditions. The replaced steam dryers have a curved

hood design developed by General Electric Hitachi. The licensee installed the new steam

dryers at SSES Units 1 and 2 in 2008 and 2009, respectively. The EPU license amendment

specifies periodic inspection of the steam dryers in SSES Units 1 and 2 during refueling outages

to confirm their continued structural integrity. After one cycle of EPU operation for each SSES

unit, the licensee identified intergranular stress corrosion cracking (IGSCC) in both of the

replacement steam dryers. In addition to the IGSCC findings, a fatigue crack was identified in

the steam dryer in SSES Unit 2. These findings were summarized in the licensees letters to the

NRC, dated July 15, 2010 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML102230125) and September 29, 2011 (ADAMS Accession

No. ML112730314).

ML13003A049 The two major causal factors for the IGSCC findings were identified as inadequate quality

control and fabrication stresses during welding of the replacement steam dryer assemblies.

Since the IGSCC was observed after only one operating cycle at both SSES units, the NRC

staff is alerting all BWR nuclear power plant licensees that the incubation periodthe time

necessary to initiate a crackfor IGSCC could be shorter than previously anticipated. The

specific fatigue crack in the steam dryer in SSES Unit 2 was the result of a poorly designed weld

joint, as well as fabrication and quality control issues.

The licensee implemented corrective actions for both SSES units in response to the

identification of the cracking in the replacement steam dryers. These actions included

necessary repairs followed by re-inspections during every refueling outage until the absence of

crack growth can be confirmed in the existing cracks and no new cracks are identified.

Existing Steam Dryers

Following initial EPU operation several years ago, Quad Cities Nuclear Power Station (Quad

Cities), Units 1 and 2, experienced significant fatigue cracking of their original steam dryers with

the generation of loose parts in the reactor coolant and main steam systems. The steam dryers

were subsequently replaced with an improved design. In addition, modifications to several

branch lines connected to the main steam lines were implemented to reduce acoustic loading

on the steam dryer. NRC issued the following INs discussing steam dryer cracking issues: IN 2002-26, dated September 11, 2002, Failure of Steam Dryer Cover Plate after a Recent Power

Uprate, IN 2002-26, Supplement 1, dated July 21, 2003, Additional Failure of Steam Dryer

after a Recent Power Uprate, and IN 2002-26, Supplement 2, dated January 9, 2004, Additional Flow-Induced Vibration Failures after a Recent Power Uprate.

During its operating life, the existing steam dryer at Vermont Yankee Nuclear Power Station

(Vermont Yankee) experienced IGSCC cracking. Pre-emptive modifications on the existing

steam dryer were completed during its spring 2004 refueling outage (RFO); and all remaining

modifications necessary to implement EPU operations were completed during its fall 2005 RFO.

EPU operations were implemented prior to the spring 2007 RFO. Vermont Yankee submitted a

license amendment request on December 22, 2011, to revise a license condition related to the

monitoring, inspection frequency, and performance of its steam dryer, which the NRC approved

on December 19, 2012 (ML12338A236). As indicated in the Vermont Yankee licensees

response to an NRC request for additional information (RAI) concerning this amendment

request, there have been no signs of crack growth activity and no cracking in the replaced

hardware for the steam dryer, post EPU. Furthermore, the licensee stated that the inspection

results show that the flaw indications caused by IGSCC have stabilized or arrested with no

further or minimal growth expected, and that there is no evidence of crack growth post EPU for

all other steam dryer flaws. Vermont Yankee continues to perform inspections to monitor the

aging effects of IGSCC to ensure the functionality and structural integrity of its steam dryer.

Additional information is available in the licensees response to the NRC RAI, dated October 3,

2012 (ADAMS Accession No. ML12284A478).

DISCUSSION

The steam dryer in the reactor vessel of a BWR plant removes excess moisture from the steam

generated by the reactor core before the steam is directed through piping to the turbine.

Although the steam dryer performs a non-safety related function, it must maintain its structural

integrity to prevent the occurrence of loose parts in the reactor vessel and attached steam lines

that could adversely affect plant operation, including causing damage to safety-related

components. Historically, BWR steam dryers experienced IGSCC over their operating life. This IGSCC is caused by a lack of hydrogen water protection in the steam dome region of the

reactor vessel. As a result, insufficient hydrogen is present in the steam to minimize IGSCC.

Steam dryers have also exhibited fatigue cracking due to acoustic and hydrodynamic loading

caused by steam flow through and around the steam dryer, as well as through the steam lines.

As discussed above, Quad Cities Units 1 and 2 experienced significant fatigue cracking of their

original steam dryers following initial EPU operation several years ago. Subsequent improved

steam dryer design and, in some instances, steam line modifications, have resulted in

successful steam dryer performance to date at both Quad Cities units and other BWR units

during normal operating and EPU conditions. The NRC staff issued Regulatory Guide (RG) 1.20, Comprehensive Vibration Assessment Program for Reactor Internals during

Preoperational and Initial Startup Testing, which addresses vibration assessment of the reactor

vessel internal components during preoperational and initial startup testing. In addition, this RG

provides information on methods for evaluating the potential adverse effects from pressure

fluctuations and vibration in piping systems for all light water reactor plants. This RG can be

used for establishing a power ascension testing program for operating plants that are proposing

to implement an EPU.

Both IGSCC and fatigue are two active aging degradation mechanisms that could potentially

create synergistic effects that might compromise the structural integrity of the steam dryer.

Therefore, as part of implementing EPU operation, BWR licensees initiate an inspection

program that is consistent with Boiling-Water Reactor Vessel and Internals Project

(BWRVIP)-139-A, BWR Vessel and Internals Project, Steam Dryer Inspection and Flaw

Evaluation Guidelines. The NRC staff approved the BWRVIP-139-A report on July 30, 2008, and the NRC staffs safety evaluation (SE) is available at ADAMS Accession No. ML082070332.

Topical Report BWRVIP-84, BWR Vessel and Internals Project, Guidelines for Selection and

Use of Materials for Repairs to BWR Internals, provides, in part, fabrication guidelines for

repaired or replacement BWR vessel internals. The NRC staff approved the BWRVIP-84 report

on September 23, 2008, and the NRC staffs SE is available at ADAMS Accession

No. ML082321084. BWRVIP-84 identifies that tri-junction welds at seismic support blocks and

other locations with high-stress concentrations in steam dryers are susceptible to fatigue

cracking. Because the fabrication process can affect the occurrence of IGSCC, implementation

of the fabrication guidelines in BWRVIP-84, in conjunction with the requirements addressed in

the NRC staffs SE, could mitigate IGSCC. In addition, conformance with BWRVIP-139-A

inspection criteria, in conjunction with implementing early corrective actions and monitoring and

trending age-related degradation, can facilitate an effective aging management program for

steam dryers, and help maintain the structural integrity of the steam dryer. By performing visual

or other appropriate inspections, licensees will have an opportunity to identify potential issues

with the structural integrity of steam dryers to allow corrective action that will prevent the

generation of loose parts in the reactor vessel and attached steam lines.

Continued occurrences of steam dryer cracking illustrate that, for BWR units that have

implemented EPU operation or are planning to request a license amendment to implement EPU

operations, effective implementation of inspection programs to monitor the aging effects of

IGSCC and fatigue for steam dryers is important. In addition to current operating BWR plants

that have implemented or are considering EPU operation, the development of programs for

monitoring the structural integrity of steam dryers is important for new BWR plants. The NRC

staff is reviewing plans for developing steam dryer monitoring programs as part of design

certification and combined operating license applications for new BWR plants under

10 CFR Part 52. The NRC staffs review of the steam dryer monitoring programs for new BWR plants will be discussed in the SEs for the applicable design certification and combined

operating license applications.

CONTACT

S

This information notice does not require any specific action or written response. If you have any

questions about the information in this notice, please contact one of the technical contacts listed

below or the appropriate NRC project manager.

/RA/ /RA/

Lawrence E. Kokajko, Director Laura A. Dudes, Director

Division of Policy and Rulemaking Division of Construction Inspection

Office of Nuclear Reactor Regulation and Operational Programs

Office of New Reactors

Technical Contacts: Chakrapani Basavaraju, NRR/DE/EMCB

301-415-1221 E-mail: Chakrapani.Basavaraju@nrc.gov

Ganesh Cheruvenki, NRR/DE/EVIB

301-415-2501 E-mail: Ganesh.Cheruvenki@nrc.gov

Yuken Wong, NRO/DE/EMB

301-415-0500

E-mail: Yuken.Wong@nrc.gov

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

ML13003A049 *via e-mail TAC MF0327 OFFICE NRR/DE/EVIB* NRR/DE/EMCB * NRO/DE/EMB* Tech Editor*

NAME GCheruvenki CBasavaraju YWong CHsu

DATE 05/13/13 05/13/13 05/21/13 02/28/13 NRR/DLR/RARB/B NRR/DPR/PGCB/P

OFFICE NRR/DE/EMCB/BC* NRR/DE/EVIB/BC* NRR/DE/D*

C* M

NAME BPham AMcMurtray SRosenberg PHiland ARussell

DATE 05/14/13 05/17/13 05/14/13 05/22/13 05/30/13 NRR/DPR/PGCB/L

OFFICE NRR/DPR/PGCB/BC NRO/DCIP/D NRR/DPR/DD NRR/DPR/D

A

NAME CHawes EBowman (A) LDudes SBahadur LKokajko

DATE 05/30/13 05/30/13 06/03/13 6/ 13 /13 6/ 14 /13


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