Information Notice 1989-69, Shadow Corrosion Resulting in Fuel Channel Bowing
| ML032380003 | |
| Person / Time | |
|---|---|
| Issue date: | 08/25/2003 |
| From: | Beckner W NRC/NRR/DIPM |
| To: | |
| Dozier J, NRR/IROB 415-1014 | |
| References | |
| IN-89-069, Suppl 1 | |
| Download: ML032380003 (9) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 August 25, 2003 NRC INFORMATION NOTICE 89-69, SUPPLEMENT 1: SHADOW CORROSION RESULTING
IN FUEL CHANNEL BOWING
Addressees
All holders of operating licenses for boiling water reactors (BWRs), except those who have
permanently ceased operations and have certified that fuel has been permanently removed
from the reactor vessel.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform the
addressees of control blade shadow corrosion resulting in fuel channel bowing in BWR plants.
The NRC anticipates that recipients will review the information for applicability to their facilities
and consider taking actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Background
Fuel channel bow is elongation of one fuel channel face relative to the opposite fuel channel
face. Fuel channel bow has been known to occur, and has been modeled in fuel licensing
(thermal limits) analysis, and mitigated in core design. Previous occurrences of fuel channel
bow have been known to arise from three sources: initial manufacturing, residual stress
relaxation under irradiation, and differential irradiation growth caused by fast fluence gradients.
These effects have been explicitly incorporated in fuel licensing (thermal limits) analysis.
Description of Circumstances
Recent experience has shown a new phenomenon called shadow corrosion-induced channel
bow. Shadow corrosion of the channel outer surface can occur when a control blade is inserted
next to the fuel channel. When controlled early in life, the resulting shadow corrosion can result
in increased absorbed hydrogen-induced growth of the channel wall closest to the control
blade, which leads to channel bowing towards the control blade late in fuel bundle life.
IN 89-69, Sup 1 There are two effects from the new phenomenon and direction of the channel bow: (1) the bow
assumed in the thermal limits calculation may not represent the new data, and (2) the bow
towards the control rod blade can lead to control rod-fuel channel interference. The concerns
related to the control blade/channel interference are: (1) that friction causes the fuel bundles to
lift, (2) that the stresses are transferred to the reactor internals and (3) that scrams are slower.
GE Nuclear Energy (GENE) recommends an additional surveillance to detect this control
blade/channel interference. These recommendations provide the methodology for identifying
the most susceptible locations for significant shadow corrosion-induced channel bow and for
measuring the settle time/scram time for control rods in the sampled area. The available
experience and channel dimensional characterization shows the condition to be most significant
where there is a large control blade with a small channel-to-control blade gap. These
conditions contribute both to develop shadow corrosion and shadow corrosion-induced channel
bow, and additionally result in a greater channel-control blade interference for a given channel
bow magnitude.
GENE has completed an evaluation of the impact on thermal limit calculations and identified
the following. An inaccuracy is introduced into the thermal limits calculation if the assumed bow
does not represent the actual channel bow data. The impact on thermal limit calculations can
be greater than 0.01 on minimum critical power ratio (MCPR), which exceeds the threshold for
report ability. Absent a detailed plant-specific calculation, GENE recommends a generic interim
penalty of 0.02 on the operating limit MCPR (OLMCPR) for all affected BWR/6 plants until a
plant-specific calculation can be performed.
GENE has also evaluated the impact on thermal limits calculations for BWR/2-5 plants. The
maximum MCPR impact on any operating cycle has been found to be 0.002. This is within the
uncertainty range for this calculation and is below the threshold for a Reportable Condition.
GENE indicated that long-term actions are to update the channel bow data used in the
approved fuel licensing models and incorporate the effects of shadow corrosion into future
reload licensing analyses.
Discussion
During shutdown for the Cycle 9 refueling outage at Limerick 1, the licensee noticed significant
difficulty with control rod settling in fuel bundles of symmetric control cell locations. Review of
post shutdown scram times revealed longer than expected scram times for these locations.
This prompted the licensee to investigate. The preliminary investigation showed that excessive
channel bowing caused the control blade interference. After reviewing the operating history, the licensee determined that the channels in these control cells had been exposed to fast flux
gradients for two successive cycles that were sufficient to cause significant channel bow toward
the control blade. The investigation also revealed that shadow corrosion was a contributor to
the channel bow. The combined effects led to the interference condition.
A similar event occurred at the Grand Gulf Nuclear Station during their twelfth operating cycle.
While inserting a control blade, the licensee noticed that the insertion was slower than expected
and the blade did not settle appropriately into an even notch position. Settling problems were
also noted at other symmetric control cell locations. During the refueling for Cycle 13, the
licensee discovered that control rod blade position indication was temporarily lost from one of
IN 89-69, Sup 1 these symmetric control cells. The licensee visually examined the bundles and control blades
in these affected cells and discovered contact patterns consistent with excessive channel bow.
The visual examination of the control blades revealed that their function remained intact. As at
Limerick 1, the Grand Gulf cells experiencing the control blade interference were those
containing third cycle bundles that had experienced significant control blade exposure early in
lifetime. GENE concludes the interference condition was most likely caused by shadow
corrosion-induced bow of these higher exposure channels.
The control blade settling problem was also experienced at Clinton, Perry, River Bend, and
Susquehanna. The root cause investigations all identified excessive channel bow as the likely
major contributor. GENE investigation of the Clinton channels confirmed the presence of
excessive channel bow, and was able to associate it with early-in-life control blade exposure
and differential hydride induced growth of opposite channel faces. Although no specific
inspections were performed, GENE believes shadow corrosion-induced channel bow is likely
involved in the other 2 plants.
On March 3, 2003, GENE issued a Part 21 notification describing the control blade shadow
corrosion-induced channel bow phenomenon. On April 28, 2003, GENE provided NRC and
industry interim surveillance recommendations for monitoring fuel channel bow that are in
addition to the required control rod technical specification surveillances. The interim
surveillance program augments the surveillance requirements in the plant technical
specifications until other appropriate actions to mitigate the channel bow problem can be
identified and implemented. The surveillance program is intended to provide early indication of
potentially degraded control blade performance, and assure that appropriate actions are taken
before the friction between the control blades and the channels becomes excessive. This
program also includes the extent and frequency of the surveillance. On June 6, 2003, GENE
informed the NRC staff, that the impact on thermal limits calculations for BWR/2-5 plants is less
than the reportable threshold. GENE indicated that the long-term actions are to update the
channel bow data used in the approved fuel licensing models and incorporate the effects of this
data into future reload licensing analyses.
The following documents provide additional information regarding fuel channel bowing:
Event Notification 39634, Part 21 Notification- Fuel Channel Bow, dated March 4, 2003 and
updated June 9, 2003 Event Notification 39806, Interim Surveillance Program for Fuel Channel Bow Monitoring
(Part 21, dated April 29, 2003 IN 89-69, Loss of Thermal Margin Caused by Channel Box Bow, dated September 29, 1989 Part 21 Notification, Fuel Channel Bow Reportable Condition & 60-Day Interim Notification, dated March 3, 2003, (Adams ML031420086)
Part 21 Notification, Interim Surveillance Program for Fuel Channel Bow Monitoring, Rev. 0
dated April 28, 2003, (Adams ML031420342) and Rev. 1 dated April 30, 2003 (Adams
IN 89-69, Sup 1 Part 21 Notification, Channel Bow Thermal Limits Impact, GNF-A Thick/Thin Fuel Channels, BWR 2-5 Plants, dated June 6, 2003 (Adams ML031700267)
Letter from Exelon Nuclear to NRC, Limerick Generating Station Unit 1 Cycle 9 Channel Bow
Assessment dated July 25,2002 (Adams ML022120417)
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact the technical contact listed below
or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Branch Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: Shih-Liang Wu, NRR Jerry Dozier, NRR
301-415-3284 301-415-1014 E-mail: slws@nrc.gov E-mail: jxd@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
ML032380003 DOCUMENT NAME: G:\RORP\OES\Staff Folders\Dozier\IN89-69 revised.wpd
OFFICE OES:IROB:DIPM Tech Editor SRXB:DSSA SC:SRXB:DSSA BC:SRXB:DSSA
NAME JDozier PKleene SWu FAkstulewicz JWermeil
DATE 07/28/2003 07/28/2003 07/28/2003 07/30/2003 08/01/2003 OFFICE SC:OES:IROB:DIPM BC:IROB:DIPM
NAME TReis WDBeckner/txr
DATE 08/25/2003 08/25/2003
Attachment
IN 89-69, Sup 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2003-11 Leakage Found on Bottom- 08/13/2003 All holders of operating license or
Mounted Instrumentation construction permits for nuclear
Nozzles power reactors, except those that
have permanently ceased
operations and have certified that
fuel has been permanently
removed from the reactor.
2003-10 Criticality Monitoring System 08/04/2003 All U.S. Nuclear Regulatory
Degradation at BWX Commission (NRC) licensees
Technologies, Inc., Nuclear authorized to possess a critical
Products Division, Lynchburg, mass of special nuclear material.
2002-26, Sup 1 Additional Failure of Steam 07/21/2003 All holders of operating license or
Dryer after a Recent Power construction permits for nuclear
Uprate power reactors, except those that
have permanently ceased
operations and have certified that
fuel has been permanently
removed from the reactor.
2003-09 Source Positioning Errors and 07/16/2003 All medical licensees.
System Malfunctions During
Administration of Intravascular
Brachtherapy
2003-08 Potential Flooding Through 06/25/2003 All holders of operating licenses
Unsealed Concrete Floor or construction permits for
Cracks nuclear power reactors.
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