Information Notice 2013-10, 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) | |
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