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| CENTEMOR
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| ' W ENBRGY ,
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| i Donald C. Sh 300 Madison Avenue _
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| Vice President Nuclear Toledo, OH 436524001
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| - Davis Besse - -(419)2 O 2300 -
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| Docket Number 50-346 License Number NPF-3 Serial Number 1871- l December 3, 1990 >
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| 1 United States Nuclear Regulatory Commission Document Control Desk Vashingt'on, D. C. 20555
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| ==Subject:==
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| High_ Pressure Injection /Hakeup, Nozzle and Thermal Sleeve Program Davis-Besse Nuclear Power Station Unit 1 Gentlemen:
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| By letter dated May 3, 1990 (Berial Number 1802), Toledo Edison summarized ,
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| the actions-taken dur'.ng cycle'6:and the sixth refueling outage (6RFO) resulting from the discovery of the failed HPI/ Makeup-nozzle thermal sleeve
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| -during the fifth refueling outage (5RFO):at~the: Davis-Besse Naclear Power Station (DBNPS) Unit 1. On-May 10, 1990, representatives of Toledo' Edison met with the NRC staff to discuss the actions taken. Toledo Edison's: letter to the NRC dated May 25, 1990 (Serial Number 1808) documents this. meeting.-
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| "i The major actions taken-through the end of the 6RFO vere directed toward the
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| assessment and preservation of the structural integrity of the nozzle which experienced the thermal sleeve failure. At the May'10, 1990 meeting, the NRC staff accepted the conclusion that an intact. thermal sleeve effectively protects the HPI/ Makeup nozzle-from the' effects of, thermal cycling fatigue due to cold makeup or HPI water and hot reactor coolant being' mixed in the-vicinity of the-nozzle. Consequently, assurance of..long term' thermal _ sleeve integrity is.a matter of continuing importance.. The improvements made.in makeup flow control described in Tqledo Edison's lett'ers to the NRC dated September 19, 1908 (Serial Number.1580), May 3, 1990 (Serial Number 1802) and May 25, 1990 (Serial Humber 1808)-provide. assurance,that' thermal sleeve life in makeup service is greater than the-four operating cycles experienced by the original thermal sleeve.1 By letter dated May 3, 1990 (Serial ~
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| Number 1802), Toledo Edison stated its intention to continue to investigate mechanisms which affect-. thermal sleeve life,-and evaluate alternatives which ;
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| might-be pursued to ensure long-term-reliability. The purpose'of.this-letter is to provide details of Toledo Edison's plans and schedule to address thermal sleeve reliability.
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| 9012110157 901203
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| ,PDR ADOCK 05000346 bP PDC g() I Operahn0 Componies: A I
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| Cleveland Electnc illummotng
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| Toledo Edison
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| L Dockst Nu bar 50-346 Licensa Nunb3r NPF-3 Serial Number 1871.
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| -' Page 2 Toledo Edison's plans to address thermal sleeve reliability focus on the conservative assessment of-thermal sleeve life.- A conservative estimate of thermal sleeve life is essential to-development of an effective strategy to manage thermal sleeve reliability. A fracture mechanics approach vill be used to predict thermal sleeve life for various makeup flow: conditions. .
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| Flav initiation and growth studies vill beLperformed for the thermal sleeve to predict thermal sleeve life for various makeup flov: conditions. Fluid temperature distributions for bounding states of each of the defined flow.
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| conditions vill be developed. The fluid temperature distributions vill be used to perform thermal stress analysis of the-thermal 1 sleeve. The stress analysis vill subsequently be used in fracture mechanics evaluations of the thermal ~ sleeve with respect to-both flav initiation and flav growth. Prom-the fracture mechanics analysis, the life of the-thermal sleeve vill be determined for various makeup flow conditions. Multiple makeup flow conditions vill _be investigated to provide insight into the optimization of makeup flow control from_the standpoint of thermal sleeve-life. This-prediction of thermal sleeve liferin combination with a review of operating experience vill provide a conservative estimate-of expected thermal sleeve life.
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| The strategy. developed to assure thermal sleeve reliability during plant operation vill depend on this conservative estimate of thermal sleeve life.
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| Potential strategies which may be. considered. include periodic thermal sleeve inspection / replacement at a frequency dependent on the estimated life. It is.also conceivable that the estimated thermal sleeve life could' exceed-the licensed' life of-the plant under current or future makeup flov scenarios, obviating the need for periodic 11nspection/ replacement.
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| In addition to the estimation of thermal sleeve-life, the-impact of premature thermal sleeve failure on HPI/Hakeup nozzle-structural integrity will be assessed. This assessment, consistent with the-experience following the failure of the makeup thermal sleeve lat. Davis-Besse reported ,
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| in 1988, is expected'to demonstrate that plant operation for the remainder
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| ,- of a fuel cycle would be acceptable in the event of a premature thermal sleeve failure, and that on-line monitoring forLthermal sleeve integrity vould be unnecessary. A fracture mechanics approach vill.be used to assess the impact of_ premature thermal sleeve failure on=the HPI/ Makeup, nozzle structural integrity assuming occurrence of the failure at the beginning of .
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| a fuel cycle. . Existing finite element models of the HPI/Hakeup nozzle.will' be used to analyze stresses in nozzle induced by makeup.flov: cycling-for various makeup flov scenarios. The expected period of time to flav initiation'and rate of propagation vill be determined. This evaluation vill" establish the margin of safety which exists for. continued plant operation _vith a failed thermal sleeve for the remainder'of a fuel cycle without incurring significant' nozzle damage.
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| "S'$ ' Dock 3t Nurbar 50-346
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| # Lic:nsa Nuabar NPF-3 ,
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| Serial Number 1871: ,
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| * Page 3- j Although the above evaluations vill likely demonstrate that on-line monitoring for: thermal sleeve-integrity is unnecessary; as a contingency,'
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| Toledo Edison is conducting preliminary investigations:of the feasibility-of thermal and acoustic monitoring concepts.= The feasibility of thermal-monitoring depends on the ability to' discriminate between nozzle temperature _ distributions with and without an intact thermal sleeve.-
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| Three-dimensional thermal conduction analyses vill be performed for various makeup flow conditions, with and vithout an. intact, thermal sleeve; Temperature contours through the' thickness and around the circumference of -
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| the nozzle vill be determined for these cases. Based on sensitivity-studies of the results of these' analyses,-.the feasibility of strategically.=
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| locating thermocouples to accurat.ely discriminate between cases with intact -
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| and failed-thermal sleeves vill be assessed. -Acoustic-monitoring-involves i discriminating between acoustic signatures an? intact sleeve ~and aLfailed, thermal sleeve. A literature review of acoustic emission technology and a~ l survey of acoustic emissions-experts: vill'be carried out to ascertain whether this concept merits further consideration.
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| Toledo Edison plans to complete and inform the NRC of the results of the above described evaluations by August 1, 1991.
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| .During the Hay 10, 1990 meeting with the"NRC staff, Toledo Edison was requested to add'ess the need for future inspection of..the currently used
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| .HPI/Hakeup nozzle (A2) in conjunction vith activities related to thermal-sleeve reliability. Toledo Edison believes that consideration of further inspection of this nozzle'is not warranted pending completion of the above evaluations. This conclusion is based on the1 fact that this nozzle and-thermal sleeve had not been used for makeup service prior-to Cycle 7, the baseline enhanced-UT of nozzle A2 indicatedsno flaws of' concern,'the thermal 3
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| sleeve life.is reasonably assured to be greater than four operating cycles, and that an intact thermal sleeve _ effectively protects the nozzle-from the thermal fatigue driving force of the cold makeup water / hot reactor coolant 7 interface.
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| Should you have any questions regarding Toledo Edison's plans to address thermal sleeve reliability, please contact Mr. R.-V. Schrauder, Manager --
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| Nuclear Licensing,'at (419) 249-2366.
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| Very t y yours,-
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| PVS/mmb cc: P. H.: Byron, DB-1 NRC Senior Resident Inspector
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| " A. B. Davis, Regional Administrator, NRC Region III H. D. Lynch, DB-1 NRC Senior Project Manager Utility Radiological Safety _ Board l'
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