Information Notice 2004-04, Fuel Damage During Cleaning At a Foreign Pressurized Water Reactor

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Fuel Damage During Cleaning At a Foreign Pressurized Water Reactor
ML040540778
Person / Time
Issue date: 02/24/2004
Revision: 0
From: Beckner W D
NRC/NRR/DIPM/IROB
To:
Dozier J I, NRR/IROB 415-1014
References
IN-04-004
Download: ML040540778 (8)
v • d • e


February 24, 2004

NRC INFORMATION NOTICE 2004-04:FUEL DAMAGE DURING CLEANING AT AFOREIGN PRESSURIZED WATER REACTOR

Addressees

All holders of operating licenses for light-water reactors, except those who have permanentlyceased operations and have certified that fuel has been permanently removed from the reactor.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to informaddressees about a recent fuel damage event that occurred during chemical cleaning of the fuel at a foreign pressurized-water reactor (PWR). The fuel cleaning system involved in the event was not of domestic (U.S.) design or manufacture; however, the fuel and processes used at the affected PWR are similar to those that may be used in domestic light-water reactor This event involved a release of radioactive material to the environment and was publicly reported in the news medi The occupational dose to workers was well within regulatory limits, and the estimated dose to members of the public was a small fraction of regulatory limits and less than 1 day's exposure to natural background radiatio The event was classified as Level 3 on the International Nuclear Event Scale, based on substantial damage to irradiated fuel.The NRC expects recipients to review the information in this notice for applicability to their facilitiesand consider actions, as appropriate, to avoid similar problem However, suggestions contained in this information notice do not constitute NRC requirements and, therefore, do not require any specific action or written response.

Description of Circumstances

The event in question occurred at a foreign PWR that was undergoing chemical cleaningof the fuel because the reactor had experienced corrosion product deposition that affected core thermal performanc This corrosion product deposition was attributable to a variety of factors, including earlier steam generator chemical decontaminatio The plant's management elected to conduct the chemical cleaning, which was originally scheduled to take place during anupcoming refueling outage to improve core thermal performance during the subsequent operating cycle. The facility had received licensing approval for the fuel cleaning system, based in part onprevious successful cleaning of seven-assembly batches of fuel that had decayed for more than a yea The operator installed the fuel cleaning system in the cask transfer area adjacent to the spent fuel poo The fuel cleaning system consisted of a large tank designed to hold 30 fuelassemblies, other tanks to hold and collect the cleaning solution, pumps to circulate the cooling water and cleaning solutions, filters to trap removed corrosion products, and valves and hoses to control and direct the flow of the cleaning solutio The tank containing the fuel assemblies was insulated to facilitate the maintenance of temperatures to support the cleaning proces Openings in the top of the tank consisted only of a small line to vent noncondensible gases and a covered access opening to permit movement of the fuel assemblie (The latter opening was closed during the cleaning process.) The cooling flow entered the bottom of the tank, flowed up through the fuel assemblies, flowed down around the shroud surrounding each assembly, and exited the tank through a plenum at the botto However, bypass flow paths reduced the effectiveness of the available cooling flo The flow during the cleaning process was high, but the standby cooling pump used after completion of the cleaning cycle produced much lower flow.Following reactor shutdown on March 29, 2003, the reactor operator began fuel cleaning operationswith fuel removed from the reactor vesse The operators successfully cleaned three batches of recently irradiated fuel without inciden However, unlike the earlier batches, the operators did not remove the tank access cover shortly after the completion of the cleaning process for the fourth batch on April 10, 2003, because the crane was being used for another tas The 30 fuel assemblies in the tank represented about 10 percent of the core and had an estimated decay heat rate of 240 to 270 k Analyses later demonstrated that the single cooling pump in operation after the completion of the cleaning process provided insufficient flow to effectively cool the fuel assemblies with the access cover in place because bypass flow paths and the development of a negative thermal head precluded upward flow through the fuel assemblies.The decay heat began producing steam within the cleaning tan Because the vent linewas inadequate for the rate of steam generation, the steam displaced the water surrounding the fuel assemblies within several hour In a steam environment, the fuel temperature increased rapidly to an estimated 1,200 Kelvi This temperature increase caused a minor release of noble gases from the fuel assemblies, which was detected by plant instrument In response to this release, plant operators decided to remove the cleaning tank access cove The absence of instrumentation within the cleaning tank precluded the assessment of conditions within the cleaning tank prior to removal of its access cove When the access cover seal was broken early in the morning of April 11, 2003, water entered the tank and contacted the hot fuel assemblie Subsequent video examination of the cleaning tank revealed severe fuel damage that resulted from the water quenching of the hot fuel assemblies and their surrounding shrou The operator estimated that this fuel damage event resulted in the release of a few hundred Tera Becquerels (about 10,000 Curies) of nobel gases, a few tenths of a Tera Becquerel (about 10 Curies)

of radioiodine, and less than one-hundredth of a Tera Becquerel (about a quarter of a Curie)

of other particulate radionuclides (principally Cesium isotopes). Offsite environmental measurements were consistent with these release estimates.The failure of the fuel cladding and surrounding shroud resulted in a redistribution of fuel material,with much of it settling to the bottom of the cleaning tan This distribution of fuel material was outside the configurations analyzed to verify a substantial margin to criticalit To ensurean adequate margin to criticality, the operators substantially increased the dissolved boron concentration in the spent fuel pool and adjacent cask transfer pit.Discussion:Provision of adequate cooling, maintenance of a margin to criticality, and maintenance of fuelintegrity for fission product retention are essential functions for the safe storage of irradiated fue These functions are normally accomplished through passive design features incorporated in the design of the fuel and the storage racks.This event demonstrates the importance of maintaining adequate cooling of fuel after dischargefrom the reactor vesse In this event, the design features that provide adequate natural circulation cooling were not maintained in the design of the cleaning syste Instead, the cleaning system design relied on forced circulation cooling without adequate consideration of the reliability and capability provided for this functio The damage to the integrity of the fuel, which resulted from the inadequate cooling, threatened the maintenance of an adequate margin to criticality and released a substantial quantity of radioactive material to the environment.Related Generic Communications:The following NRC generic communications describe related reactor operating experience:(1)Information Notice 97-85, "Effects of Crud Buildup and Boron Deposition on Power Distributionand Shutdown Margin," December 11, 1997.(2)Information Notice 97-14, "Assessment of Spent Fuel Cooling," March 28, 1997.(3)Generic Letter 88-17, "Loss of Decay Heat Removal 10 CFR 50.54(f)," October 17, 1988.(4)Generic Letter 87-12, "Loss of Residual Heat Removal (RHR) while the Reactor Coolant System(RCS) is Partially Filled," July 9, 1987.This information notice does not require any specific action or written respons If you haveany questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate project manager in the NRC's Office of Nuclear Reactor Regulation./RA/William D. Beckner, Chief Reactors Operations Branch Division of Inspection Program Management Office of Nuclear Reactor RegulationTechnical contacts:S.R. Jones, NRRJerry Dozier, NRR(301) 415-2712(301) 415-1014 Email: srj@nrc.govEmail: jxd@nrc.gov

Attachment:

List of Recently Issued NRC Information Notices was outside the configurations analyzed to verify a substantial margin to criticalit To ensurean adequate margin to criticality, the operators substantially increased the dissolved boron concentration in the spent fuel pool and adjacent cask transfer pit.Discussion:Provision of adequate cooling, maintenance of a margin to criticality, and maintenance of fuelintegrity for fission product retention are essential functions for the safe storage of irradiated fue These functions are normally accomplished through passive design features incorporated in the design of the fuel and the storage racks.This event demonstrates the importance of maintaining adequate cooling of fuel after dischargefrom the reactor vesse In this event, the design features that provide adequate natural circulation cooling were not maintained in the design of the cleaning syste Instead, the cleaning system design relied on forced circulation cooling without adequate consideration of the reliability and capability provided for this functio The damage to the integrity of the fuel, which resulted from the inadequate cooling, threatened the maintenance of an adequate margin to criticality and released a substantial quantity of radioactive material to the environment.Related Generic Communications:The following NRC generic communications describe related reactor operating experience:(1)Information Notice 97-85, "Effects of Crud Buildup and Boron Deposition on Power Distributionand Shutdown Margin," December 11, 1997.(2)Information Notice 97-14, "Assessment of Spent Fuel Cooling," March 28, 1997.(3)Generic Letter 88-17, "Loss of Decay Heat Removal 10 CFR 50.54(f)," October 17, 1988.(4)Generic Letter 87-12, "Loss of Residual Heat Removal (RHR) while the Reactor Coolant System(RCS) is Partially Filled," July 9, 1987.This information notice does not require any specific action or written respons If you haveany questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate project manager in the NRC's Office of Nuclear Reactor Regulation./RA/William D. Beckner, Chief Reactors Operations Branch Division of Inspection Program Management Office of Nuclear Reactor RegulationTechnical contacts:S.R. Jones, NRRJerry Dozier, NRR(301) 415-2712(301) 415-1014 Email: srj@nrc.govEmail: jxd@nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDISTRIBUTION:ADAMSIN FileDOCUMENT NAME: G:\OES\Staff Folder's\Dozier\Paks2INfinal.wpdADAMS ACCESSION NUMBER: ML040540778OFFICERSE:RORP:DRIPTech EditorRSE:SPLB:DSSANAMEIJDozierPAGarrity*SRJonesDATE02/09/200402/09/200402/09/2004OFFICEBC:SPLB:DSSASC:OES:IRIB:DIPMC:IROB:IROB:DIPMNAMEJNHannonTReisWDBecknerDATE02/10/200402/20/200402/24 /2004OFFICIAL RECORD COPY

______________________________________________________________________________________OL = Operating License CP = Construction PermitAttachment 1 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICES_____________________________________________________________________________________InformationDate of Notice N SubjectIssuanceIssued to_____________________________________________________________________________________2004-03Radiation Exposures toMembers of the Public in Excess of Regulatory Limits Caused by Failures to Perform Appropriate Radiation Surveys During Well-logging OperationsPendingAll well-logging licensees.2004-02Strontium-90 Eye ApplicatorsNew Calibration Values and Use02/05/2004All U.S. Nuclear RegulatoryCommission (NRC) medical-use licensees and NRC master materials license medical-use Permittees.2004-01Auxiliary Feedwater PumpRecirculation Line Orifice Fouling - Potential Common Cause Failure01/21/2004All holders of operating licensesor construction permits for nuclear power reactors, except those that have permanently ceased operations and have certified that fuel has been permanently removed from the reactor.2002-26, Sup 2Additional Failure of SteamDryer After A Recent Power Uprate01/09/2004All holders of an operating licenseor a construction permit for nuclear power reactors, except those that have permanently ceased operations and have certified that fuel has been permanently removed from the reactor.Note:NRC generic communications may be received in electronic format shortly after they areissued by subscribing to the NRC listserver as follows:To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the followingcommand in the message portion:subscribe gc-nrr firstname lastname


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