Information Notice 1997-49, B&W Once-Through Steam Generator Tube Inspection Findings
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
July 10, 1997
NRC INFORMATION NOTICE 97-49: B&W ONCE-THROUGH STEAM GENERATOR TUBE
INSPECTION FINDINGS
Addressees
All holders of operating licenses or construction permits for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to present
the findings from the examination of tubes in Babcock and Wilcox (B&W\\) once-through steam
generators (OTSGs). 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.
DescriDtion of Circumstances
Licensees using B&W OTSGs have historically observed very little service-induced
degradation in steam generator tubes. During the last few years, however, more degradation
has been observed and this degradation has been seen at a variety of locations, such as
dented (dinged) areas, the expansion transition region, the freespan region, the sludge pile
region, and the sleeve joints. Pertinent inspection findings from steam generator tubes at
several plants with OTSGs are discussed.
Degradation at Dented Locations
Indications of degradation associated with dented (dinged) areas have been found at several
plants-Arkansas Nuclear One, Unit 1 (ANO-1), Oconee Unit 1, and Crystal River Unit 3.
These indications have been axial, circumferential, or volumetric in nature. At ANO-1 (in
1993), two volumetric indications with circumferentially oriented cracklike indications were
found at dents on the secondary face of the upper tubesheet (UTS). These indications were
initially found with a bobbin coil probe and were confirmed to be present with a rotating
pancake coil eddy current inspection probe. At ANO-1 (in 1996), two axially oriented eddy
current indications associated with dented areas in the tube's freespan region were observed.
Similar to the 1993 indications, these indications were also initially found with a bobbin coil
probe. Rotating pancake coil probe inspection of one of these indications confirmed that the
indication initiated from the outside diameter of the tube and that the indication was offset
relative to the tube axis by approximately 35 degrees. At Oconee Unit 1 (in 1995), a
volumetric and a circumferential indication were detected at dents located at the 15th tube
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~IN 97-49 July 10, 1997 support plate. At Crystal River Unit 3 (in 1996), a volumetric eddy current indication was
found at a dented area. This indication was detected with the bobbin coil and confirmed with
a pancake and plus-point coil.
Degradation at the Expansion Transition Region
The expansion transition region of the tubes in B&W OTSGs were heat treated to reduce
residual stresses from tube fabrication and installation, and to increase resistance to primary
water stress corrosion cracking (PWSCC). This heat treatment resulted from a full furnace
stress relief of the entire tube bundle. During the manufacturing process, however, several
tubes were re-rolled into the tubesheet following the full furnace stress relief to temporarily
seal the tube during the shop hydrostatic tests. As a result, a limited population of tubes was
not stress relieved at the expansion transition region (i.e., fewer than 200 tubes are known to
have not been stress relieved). Axial indications associated with the expansion transitions of
both stress-relieved and nonstress-relieved transitions were recently noted in several B&W
units (Davis-Besse, Crystal River 3, ANO-1, and Oconee 3). The inspection findings at these
plants are discussed below.
At Davis-Besse (in the spring of 1996), an axially oriented indication was detected during the
examination of what was believed to be a nonstress-relieved roll transition. This indication
was in the roll transition in the UTS (i.e., the hot leg). Subsequent review of shop records
showed that the expansion transition had not been re-rolled and was, therefore, stress
relieved. The licensee removed the roll transition portion of this tube for destructive
examination. The destructive examination showed that the indication was caused by
PWSCC. To ascertain whether the tube had been stress relieved, the licensee performed
additional analyses and testing. As a result of this testing, the licensee concluded that the
roll transition was not stress relieved (i.e., it had been re-rolled following the full bundle stress
relief process).
At Crystal River 3 (in the spring of 1996), a single axial indication was detected in the roll
transition in a tube that had been re-rolled following the full bundle stress relief (i.e., a
nonstress-relieved transition), and a multiple axial indication was detected in the tube end, above the shop re-roll in the same tube. These indications were located in the roll transition
in the UTS (i.e., the hot leg). The eddy current data clearly indicated that the tube had been
rolled multiple times. The licensee attributed the indication to PWSCC.
At ANO-1 (in the fall of 1996), 24 axially oriented and volumetric indications were detected in
stress-relieved roll transitions in the UTS (i.e., the hot leg). The licensee attributed the axial
indications to inside diameter-initiated stress corrosion cracking (i.e., PWSCC). The
volumetric indications had been initiated on the outside diameter, pointing perhaps to
IN 97-49 July 10, 1997 intergranular attack (IGA) or to closely spaced cracks. To further characterize the nature and
cause for the upper roll transition indications (and other indications), the licensee for ANO-1 removed several tube sections for destructive examination. The destructive examination
findings from the one roll transition indication that was removed confirmed that the indication
was attributable to PWSCC. This transition had been stress relieved.
At Oconee Unit 3 (in the fall of 1996), 19 tubes were identified by eddy current testing as
having PWSCC at the roll transition region in the UTS. Of the 19 indications, 15 were axial
indications in the roll transition region, 3 were axial indications in the rolled area , and 1 was
a volumetric indication at the roll transition region. One tube was removed for laboratory
analysis of the indication at the upper roll transition region. The laboratory destructive
examination findings were not available at the time this notice was prepared.
Degradation at Freespan Locations
Axially oriented degradation in the freespan region has been observed in several B&W
OTSGs (Oconee 1, Oconee 2, Oconee 3, and ANO-1). Freespan degradation is degradation
observed above the sludge pile region and not located at any support structure (e.g., tube
support plates). A freespan axial indication was first identified at Oconee I in May 1994.
This indication was identified with a bobbin coil and confirmed to be present with a rotating
pancake coil probe. This tube along with six others were removed for destructive
examination. The destructive examination confirmed the presence of freespan axially
oriented IGA in all seven tubes. The tube with the indication detected with a bobbin coil was
the most significant with a through-wall depth of 47 percent and a burst pressure of
7400 pounds per square inch (psi), well above the structural criteria specified in Regulatory
Guide 1.121. The IGA in the remaining tubes ranged from 5 percent to 28 percent through- wall.
Subsequent bobbin coil inspections at Oconee Units 1, 2, and 3 identified additional tubes
with freespan axial indications. For example, 9 tubes with indications were detected at
Oconee 2 in October 1994, 22 tubes with indications were detected at Oconee 3 in June
1995, 40 tubes with indications were detected at Oconee 1 in November 1995, and 173 tubes
with indications were detected at Oconee 2 in April 1996. During the Oconee 2 inspection
outage in April 1996, four tubes were removed for destructive examination. The selection
criteria for these, tubes included small and large indications, the number of indications per
tube, and a sampling across the tube bundle. The burst pressures for these tubes ranged
from 5700 psi to 11000 psi. In November 1996, the most recent steam generator inspection
outage at an Oconee unit, 67 tubes with confirmed bobbin coil indications were identified at
Oconee 3. An assessment performed by the licensee, based on previous tube pull analysis, indicated that these tubes had adequate structural integrity. All tubes with axially oriented
freespan IGA, which were confirmed to be present with a rotating pancake coil probe, were
removed from service upon detection. During the Oconee 3 outage in November 1996, three
tubes with IGA were removed for destructive examination. The laboratory destructive
examination findings were not available at the time this notice was prepared.
IN 97-49 July 10, 1997 The root cause analysis from the Oconee I tube pull analysis did not identify any unique
feature to this degradation mechanism that would indicate that the problem was limited to the
Oconee Units. That is, the base material properties met specific values, no high residual
stresses were measured, and no detrimental environmental or chemical species were
identified. These results indicate that all B&W OTSGs are potentially susceptible to this
mechanism. In September/October 1996, the licensee for ANO-1 detected freespan axial
indications similar to those observed at the three Oconee units. Approximately 13 tubes with
freespan axial indications were identified and plugged at ANO-1 during this outage. These
indications were initially detected with a bobbin coil probe. In-situ pressure testing of two of
the more severe indications (as identified by nondestructive examination) indicated burst
pressures for these freespan axial indications in excess of 4550 and 5750 psi. No leakage
was observed from either of these two indications during the in-situ test. Ea:ch Vf the Oconee
units and ANO-1 inspected 100 percent of the inservice tubes with a bobbin coil during their
last inspection outage.
Degradation in the Sludge Pile Region
At ANO-1 (in the fall of 1996), nine axially oriented indications were observed above the
lower tubesheet. These indications were in the sludge pile region, approximately 0.25-inch
above the lower secondary face of the tubesheet The indications were found with a bobbin
coil and were confirmed with a motorized rotating pancake coil inspection. Two tubes were
removed for laboratory examination. The laboratory destructive examination pointed to these
indications being initiated from the outside diameter of the tube and were a result of axially
oriented IGSCC. The licensee also observed areas of shallow intergranular corrosion
initiating from the outside diameter of the tube near the fracture faces. This corrosion was
three-dimensional in nature, similar to IGA regions; however, many of the affected grains
were no longer present, resulting in the removal of tube material and appearance of shallow
wastage. These "IGA wastage" regions were relatively shallow (less than 24-percent
through-wall) and in the form of meandering grooves or gullies. The metallurgical results
suggested to the licensee that the axial cracks originated at the bottom of these IGA wastage
zones. On the basis of nondestructive examination, these meandering grooves appeared to
be located at or near sharp edges of surface deposits.
Degradation at Sleeved Locations
B&W mechanical sleeves have been installed in all operating B&W OTSG plants in order to
mitigate tube leaks caused by high-cycle fatigue and to repair tubes with other indications of
degradation. The number of sleeves in service at these plants varies from a few hundred to
approximately one thousand. These sleeves, fabricated from either alloy 600 or alloy 690,
have three roller-expanded joints to seal them into the parent tube (one at the top of the
sleeve and two at the bottom of the sleeve). These joints have not undergone any type of
process to relieve stress.
IN 97-49 July 10, 1997 Axial, circumferential, and volumetric indications were detected in the joints of B&W
mechanical sleeves at ANO-1 (in 1996) although no tubes were removed to learn the nature
of the degradation. The indications were found at the joints of both alloy 600 and alloy 690
sleeves with a plus-point coil. The licensee believes that 9 of the 10 indications detected are
associated with the parent tube rather than with the sleeve itself. The degradation has been
observed at both the upper joint (located within the UTS) and the lower joints (in the tube
freespan region); 8 of the 10 indications were observed at the upper joint. One
circumferential indication was detected at an alloy 600 sleeve joint at Oconee Unit 3 (in 1996)
with a plus-point coil. This indication was associated with the upper of the two lower joints
(i.e., the upper lower joint). The licensee for Oconee Unit 3 believes that the indication could
be the result of a scratch made during the rolling process; however, this cannot be confirmed, since current technology does not permit the sleeve to be removed from the steam generator
for destructive examination because of its location.
Discussion
The inspection findings from B&W OTSGs indicate that a number of locations are susceptible
to degradation. In addition, studies of removed tubes have confirmed in several instances
that the eddy current indications are attributable to such degradation mechanisms as IGA and
stress corrosion cracking. Frequently these indications can only be reliably detected with
specialized probes such as rotating probes (e.g., roll transition indications, indications in
sleeve joints). In addition, the depth of many of these types of indications cannot be reliably
determined.
To effectively manage the degradation mechanisms being observed, a variety of actions have
been taken by licensees. These actions include inspecting locations potentially susceptible to
degradation with techniques capable of reliably detecting these forms of degradation (or
using the best available technique) and ensuring that the frequency and scope of inspection
are sufficient at identifying and removing degradation from service to prevent the degradation
from progressing to the point at which tube integrity is impaired. For example, the sleeve
joints at ANO-1 and Oconee 3 were examined with a plus-point coil, and 100 percent of the
tubes were examined with a bobbin coil at ANO-1 and Oconee Units 1, 2, and 3 during their
last outage. Other actions taken by licensees include removing tubes from service based
upon detection when the degradation cannot be reliably depth-sized (unless an alternative
tube repair criterion has been approved by the NRC), and assessing significant indications in
steam generator tubes to determine whether adequate structural and leakage integrity was
maintained during the previous cycle. Specific actions taken by licensees to assess the
structural and leakage integrity of tubes include removing tubes for destructive examination
as was done at ANO-1, Davis-Besse, and Oconee 1, 2, and 3, and performing in situ
pressure testing.
IN 97-49 July 10, 1997 This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Kenneth J. Karwoski, NRR
301-415-2754 E-mail: kjkl@nrc.gov
Eric J. Benner, NRR
301-415-1171 E-mail: ejbl nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Attachment
July 10, 1997 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
97-48
97-47 Inadequate or Inappro- priate Interim Fire
Protection Compensatory
Measures
Inadequate Puncture
Tests for Type B
Packages Under 10 CFR
71.73(c)(3)
Unisolable Crack in
High-Pressure
Injection Piping
Failure of Reactor
Trip Breaker from
Cracking of Phenolic
Material in Secondary
Contact Assembly
07/09/97
06/27/97
07/09/97
07/02/97
All holders of OLs or CPs
for nuclear power reactors
All "users and fabricators'
of type B transportation
packages [as defined in
All holders of OLs or CPs
for nuclear power reactors
All holders of OL permits
for nuclear power reactors
97-46
96-44, Supp. 1
97-45
Environmental
Qualification
Deficiency for
Cables and Contain- ment Penetration
Pigtails
07/02/97
All holders of OLs or CPs
for nuclear power reactors
97-44
Failures of Gamma
Metrics Wide-Range
Linear Neutron Flux
Channels
License Condition
Compliance
07/01/97
07/01/97
All holders of OLs or CPs
for test and research
reactors
All holders of OLs or CPs
for nuclear power reactors
97-43 OL = Operating License
CP = Construction Permit
IN 97-49 July 10, 1997 This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
original signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Kenneth J. Karwoski, NRR
301-415-2754 E-mail: klki@nrc.gov
Eric J. Benner, NRR
301-415-1171 E-mail: ejbl nrc.gov
Attachment: List of Recently
A *"MJV'kP F la
Issued NRC Information Notices
agkea
DOCUMENT NAME: 97-49.IN
Tech Editor reviewed and concurred on 5/19/97 *See previous
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g OFFICE Contacts
CDDE
C/PECB:DRPM
DIDRPM
NAME
KKarwoski*
BSheron*
AChaffee*
MSIlsson
EBenner*
_ _ _
__l
DATE
05/27/97
06/19/97
06/23/97
07/2J97
05/22/97
OFFICIAL RECORD COPY
_
K>
IN 97- July , 1997 This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Kenneth J. Karwoski, NRR
301-415-2754 E-mail: kjkl@nrc.gov
Eric J. Benner, NRR
301-415-1171 E-mail: ejbl nrc.gov
Attachment: Ust of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\EJB1\\B&WSG.IN
Tech Editor reviewed and concurred on 5/19/97 *See previous
To receive a copy of this document, Indicate In the box: "C" = Copy without
attachment/enclosure
"E" = Copy with attachmentlenclosure "N" = No copy
OFFICE I
D/DE
C/PECB:DRPM
D/DRPM
NAME
KKarwoski*
BSheron*
AChaffee*
MSlosson
EBenner*
DATE
05/27/97
06/19/97
06/23/97
07/ /97
05/22/97
UNFICIAL RECORD cqJY
1///1 7
,
IN 97-xx
June xx, 1997 specialized probes such as rotating probes (e.g., roll transition indications, indications in
sleeve joints). In addition, the depth of many of these types of indications cannot be reliably
determined.
To effectively manage the degradation mechanisms being observed, a variety of actions have
been taken by licensees. These actions include inspecting locations potentially susceptible to
degradation with techniques capable of reliably detecting these forms of degradation (or
using the best available technique) and ensuring that the frequency and scope of inspection
are sufficient at identifying and removing degradation from service to prevent the degradation
from progressing to the point at which tube integrity is impaired. For example, the sleeve
joints at ANO-1 and Oconee 3 were examined with a plus-point coil, and 100% of the tubes
were examined with a bobbin coil at ANO-1 and Oconee Units 1, 2, and 3 during their last
outage. Other actions taken by licensees include removing tubes from service based upon
detection when the degradation cannot be reliably depth-sized (unless an alternative tube
repair criterion has been approved by the NRC), and assessing significant indications in
steam generator tubes to determine whether adequate structural and leakage integrity was
maintained during the previous cycle. Specific actions taken by licensees to assess the
structural and leakage integrity of tubes include removing tubes for destructive examination
as was done at ANO-1, Davis-Besse, and Oconee 1, 2, and 3, and performing in situ
pressure testing.
This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Kenneth J. Karwoski, NRR
Eric J. Benner, NRR
(301) 415-2754
(301) 415-1171 E-mail: kjklnrc.gov
E-mail: ejblnrc.gov
Attachment:
List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\EJB1\\B&WSG.IN
Tech Editor reviewed and concurred on 5/19/97 *See previous
To receive a copy of this document, indicate in the box: "C" = Copy without
attachment/enclosure
"E" =,lCr with attachment/enclosure
"N" = No copy
OFFICE Contacs
E
C/PECB:DRPM
NAME
KKarwoski*
BSV
o
AChaffee
IMSlosson
EBenner*
__
__
_
__
__C)
_
_
_
_
_
DATE
05/27/97
(0 l/497
/97 I
/97
05/22/97
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OFFICIAL R6CRD~Y
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IN 97-xx
June xx, 1997 specialized probes such as rotating probes (e.g., roll transition indications, indications in
sleeve joints). In addition, the depth of many of these types of indications cannot be reliably
determined.
To effectively manage the degradation mechanisms being observed, a variety of actions have
been taken by licensees. These actions include inspecting locations potentially susceptible to
degradation with techniques capable of reliably detecting these forms of degradation (or
using the best available technique) and ensuring that the frequency and scope of inspection
are sufficient at identifying and removing degradation from service to prevent the degradation
from progressing to the point at which tube integrity is impaired. For example, the sleeve
joints at ANO-1 and Oconee 3 were examined with a plus-point coil, and 100% of the tubes
were examined with a bobbin coil at ANO-1 and Oconee Units 1, 2, and 3 during their last
outage. Other actions taken by licensees include removing tubes from service based upon
detection when the degradation cannot be reliably depth-sized (unless an alternative tube
repair criterion has been approved by the NRC), and assessing significant indications in
steam generator tubes to determine whether adequate structural and leakage integrity was
maintained during the previous cycle. Specific actions taken by licensees to assess the
structural and leakage integrity of tubes include removing tubes for destructive examination
as was done at ANO-1, Davis-Besse, and Oconee 1, 2, and 3, and performing in situ
pressure testing. The staff believes that an effective tube integrity management program, which includes, in part, the elements discussed above, can provide reasonable assurance of
tube integrity.
This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Kenneth J. Karwoski, NRR
Eric J. Benner, NRR
(301) 415-2754
(301) 415-1171 E-mail: kjkl@nrc.gov
E-mail: ejbl@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\EJB1\\B&WSG.IN
Tech Editor reviewed and concurred on 5/19/97 *See previous
To receive a copy of this document, indicate in the box: "C" = Copy without
attachment/enclosure
"E" = Copy with attachment/enclosure
"N" = No copy
OFFICE Contacts
I_
I
C/PEC B:DRPM I
D/DRPI
NAME
KKarwoski*
BSheron
AChaffee
MSlosson
EBenner*
DATE
05/27/97
/ /97 I /97
/ /97
05/22/97 I
OFFICIAL RECORD COPY
I
IN 97-xx
May xx, 1997 This information notice requires no 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 Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Kenneth J. Karwoski, NRR
(301) 415-2754 E-mail: kjkl@nrc.gov
Eric J. Benner, NRR
(301) 415-1171 E-mail: ejbl@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\EJB1\\B&WSG.IN
Tech Editor reviewed and concurred on 5/19/97 To receive a copy of this document, indicate in the box: "C" = Copy without
attachment/enclosure
"E" = Copy with attachment/enclosure
"N" = No copy
OFFICE Contacts I
DIDE
EC/PECBDRPM l
D/DRPM
NAME
KKarwoski *-S'
BSheron
AChaffee
MSlosson
EBennerf tP6
DATE
5/w$97
//97
//97
/97 OFFICIAL RECORD COPY