Information Notice 2010-22, Fuel Assemblies Damaged During Refueling Operations Due to Misalignment
| ML102200071 | |
| Person / Time | |
|---|---|
| Issue date: | 10/25/2010 |
| From: | Mcginty T Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-10-022 | |
| Download: ML102200071 (3) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 October 25, 2010
NRC INFORMATION NOTICE 2010-22: FUEL ASSEMBLIES DAMAGED DURING
REFUELING OPERATIONS DUE TO
MISALIGNMENT
ADDRESSEES
All holders of an operating license or construction permit for a pressurized-water nuclear power
reactor issued under Title 10 of the Code of Federal Regulations, 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.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of an event at a domestic pressurized-water reactor plant that resulted in damage to
fuel assemblies during a refueling outage because of inadequate verification of core alignment.
The NRC expects recipients to review the information for applicability to their facilities and
consider actions, as appropriate, to avoid similar problems. The suggestions that appear in this
IN are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On November 2, 2009, the Oconee Nuclear Station, Unit 1 (a Babcock & Wilcox Co.
pressurized-water reactor), was unable to couple a control rod drive mechanism to its
associated control rod assembly during reactor vessel reassembly. The licensee subsequently
disassembled the reactor vessel head and upper internals and discovered that multiple fuel
assemblies were damaged during reactor vessel reassembly and that these damaged fuel
assemblies were interfering with proper control rod coupling. The damage to one fuel assembly
resulted in bowed fuel pins and the detachment of pieces of multiple grid straps. The licensee
had to use a specially constructed tool to remove this fuel assembly from the reactor and place
it in the spent fuel pool. Other assemblies had minor damage mostly limited to the upper end
fittings.
A post event examination of the fuel alignment video revealed that the gap between the inner
wall of the baffle and an adjacent fuel assembly was larger than that allowed by the vendor
specifications. The licensees fuel alignment verification procedure was not in accordance with
current vendor guidance; specifically, it did not include the maximum allowed gap value. The
procedure called solely for a qualitative evaluation to determine the existence of gaps and
provided a maximum number of gaps allowed. In accordance with this procedure, the licensee
determined that it met the acceptance criteria for fuel alignment and continued with vessel
reassembly. Because the licensee proceeded with a larger than allowed gap, the fuel assembly
upper end fitting and reactor vessel plenum grid pads could not properly align. The weight of
the plenum rested on the upper end fitting tabs and deformed the fuel assemblies.
Additional information is available in the NRC inspection report, Oconee Nuclear Station
Integrated Inspection Report 05000269/2009005, 05000270/2009005, 05000287/2009005, dated January 28, 2010 (Agencywide Documents Access and Management System, Accession
No. ML100280909).
DISCUSSION
Deformations in fuel assembly geometry can undermine the integrity of the fuel cladding, which
is one of the primary barriers to fission product release. Also, deformed fuel assemblies could
affect reactivity control if they cause control rods to become stuck during reactor operations.
Furthermore, industry operating experience has shown that deformed fuel assemblies can
become stuck within the reactor upper internals without the licensees knowledge. Unknowingly
lifting fuel assemblies that have become stuck to upper internals or upper guide structures
presents a risk of dropping the fuel assembly and the associated risk of fission product release
should a fuel rod be breached.
The importance of verifying adequate core alignment and avoiding misalignments between fuel
and reactor internals is evident and necessitates special preparation and consideration on
behalf of licensees. Before verifying core alignment, licensees should consider reviewing and
applying related operating experience and verifying that their procedures and methods are in
agreement with the latest fuel vendor guidance.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or to the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: David Garmon-Candelaria, NRR Shih-Liang Wu, NRR
301-415-3512 301-415-3284 E-mail: E-mail: shih-liang.wu@nrc.gov
david.garmon-candelaria@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections. upper end fitting and reactor vessel plenum grid pads could not properly align. The weight of
the plenum rested on the upper end fitting tabs and deformed the fuel assemblies.
Additional information is available in the NRC inspection report, Oconee Nuclear Station
Integrated Inspection Report 05000269/2009005, 05000270/2009005, 05000287/2009005, dated January 28, 2010 (Agencywide Documents Access and Management System, Accession
No. ML100280909).
DISCUSSION
Deformations in fuel assembly geometry can undermine the integrity of the fuel cladding, which
is one of the primary barriers to fission product release. Also, deformed fuel assemblies could
affect reactivity control if they cause control rods to become stuck during reactor operations.
Furthermore, industry operating experience has shown that deformed fuel assemblies can
become stuck within the reactor upper internals without the licensees knowledge. Unknowingly
lifting fuel assemblies that have become stuck to upper internals or upper guide structures
presents a risk of dropping the fuel assembly and the associated risk of fission product release
should a fuel rod be breached.
The importance of verifying adequate core alignment and avoiding misalignments between fuel
and reactor internals is evident and necessitates special preparation and consideration on
behalf of licensees. Before verifying core alignment, licensees should consider reviewing and
applying related operating experience and verifying that their procedures and methods are in
agreement with the latest fuel vendor guidance.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or to the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: David Garmon-Candelaria, NRR Shih-Liang Wu, NRR
301-415-3512 301-415-3284 E-mail: E-mail: shih-liang.wu@nrc.gov
david.garmon-candelaria@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ADAMS Accession Number: ML102200071 TAC ME4182 OFFICE NRR:DIRS:IOEB NRR:DSS:SNPB Tech Editor BC:NRR:DIRS:IOEB BC:NRR:SNPB
NAME DGarmon SWu KAzariah-Kribbs JThorp AMendiola
DATE 10/08/10 10/12/10 09/24/10 e-mail 10/20/10 10/20/10
OFFICE D: NRR:DSS NRR:PGCB NRR:PGCB BC:NRR:PGCB D: NRR:DPR
NAME WRuland CHawes BPurnell SRosenberg TMcGinty
DATE 10/22 /10 10/25/10 10/25/10 10/25/10 10/25/10
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