ML20212G985

Provides Proposed Response to OI 4.1.3-1 for B Elliott to Consider

ML20212G985
Person / Time
Site:	Calvert Cliffs
Issue date:	04/26/1999
From:	Shaw D BALTIMORE GAS & ELECTRIC CO.
To:	Dave Solorio NRC
Shared Package
ML20212G964	List: ML20212G960 ML20212G975 ML20212G985 ML20212G989 ML20212H018 ML20212H024
References
NUDOCS 9909300177
Download: ML20212G985 (5)

Text

n - usvwesse,suuswans carwswr vaere -

. April 26,1999

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To: Dave Solorio Phone: 301-415-1973 Fax: 301-415-2279 Frotn: Don Shaw Phone: 410-495-4028 Fax 410-495-6946 Pages: 1 (just this cover page)  ;

Conunents: ,

J Dave, Below is a proposed' response to OI 4.1.3-1 for Barry Elliott to consider. Please .

provide feedback.

' Thanks, l

/ Don

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Onen heen 4.1.1-1 .

The list of TLAAs provided pursuant to 10 CFR 54.21(cXI) does not include the upper-shelf energy of the reactor vessel materials, including the most limiting material based en fluence and chemistry of the vessel material. The applicant stated during the on-site meeting held between February 16-18,1999, that

' irradiation embrittlement as measured by the drop in Charpy upper shelf energy (USE) is not a t! e-limited aging analysis (ILAA) since it does not satisfy the TLAA definition in 10 CFR 54.3. The h e C staff, however, has concluded that this is a TTAA. The applicant should include upper shelf energy culuation in their list of TLAAs. This Open Ite c should be resolved in conjunction with Confirmatory item 3.2.3.2.12.

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Analyses applicable to neutroe irradiation of the reactor vessels had been extended from 40 years to 60 years prior to BGE implementing its TLAA identification and evaluation process.

Therefore, the analyses did not meet 10 CFR 54.3(a)(3). Had this not been the case, these analyses would have been identified as TLAAs and the activities that extended them to 60 years would have subsequently caused them to*be dispositioned as "The analyses have been projected to the sad of the period of extended operadon" in accordance with 10CFR54.2)(c)(1)(i).

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CoaGreatoryIten 3.23.2.14

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To manage aging effects associated with SCC cf the control element assembly (CEA) shroud bolts, the applicant, in Section 4.3.2 of Appendix A to the LRA, described a progra:n that would

.I perform an analysis to determine if the applied stresses on these bolts is above or below the

{ " critical stress" for SCC. As discussed during a meeting on Febmary 16,1999 (NRC meeting summary dated March 19,1999), for NRC Question No. 4.3.15, the applicant indicated that after further review, the function of the CEA shroud bolts is not safety related and, therefore, this stress

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analysis program would not be implemented. This is a confirmatory item pending review of an  !

applicant submittal documenting this finding. l In addition, an ARDI program is planned to manage the effects of SCC of the CEA shroud bolts.

However, as discussed in 3.2.3.2.1C(8) of this SER, the applicant indicated that the CEA shroud bolts do r,ot perform a safety function in accordance with the requirernents of 10 CFR 54.4. The applicant was asked to document the resolution of the issue with a description of the function of the CEA shroud bolts that included an explanation of why they do not meet the criteria contained in 10 CFR 54.4. l 1

i BGE Response  !

l Re fhnetion of the CEA Shroud Bolts is to provide lateral support and alignment for the CEAs and to maintain CEA spacing. His is a safety related function and meets the criteria of 10 CFR 54.4. l Additionally, SCC is now considered not plausible for the CEA Shroud Bolts. As explained below, based on the low probability of any degradation resulting from SCC, and taking into consideration the inherent redundancy of the CEA l Shroud Bolts, this ARDM will not prevent the CEA Shroud Bolts from performing their I intended function.

Details: -

There have been no indications of any A286 threaded structural fastener failures to date on any CE reactor vessel internals. Plants which have undergone 10 year inservice inspections'have detected no loose parts or gross indications of structural fastener failures.

Industry experience with failures of A286 vessel internals threaded structural fasteners has been limited to applications in B&W plants. CE has evaluated the st/ esses for the )

CEA Shroud Bolts relative to the stresses experienced by the failed B&W fasteners. CE  !

conservatively projected that the potential for a "small percentage" of failures existed. i l

( CEfasteners didinnot all CEexplicitly applications have quantify been torquod this projec2d to produce operatingfailure stress levelspercentage.

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under 32,000 psi average stress. The failure rate at 36,000 psi in the B&W applications was less than 4%. At 35,000 ps!, no failures were Mantified. It may be implied from

' these results, and considering operating experience to date, that the expected failure rate of the CE fasteners may well be 0%, and should certainly be less than 4%.

CE also evaluated the margin for the normal operating plus upset condition loods for the CEA Shroud Bolts to determine the minimum number of f=*=ars required per Shroud to maintain the joint integrity. %e available margin above the ASME Code stress allowables of 37.5% far exceeds the most conservative projected failure rate of the CEA e Shroud Bolts. Based on the comparison of the available margin with the maximum I r conservative projected failure rate, SCC of the CEA Shroud Bolts will not impact the intended function, and SCC is considered not plausibic. l e .- . sme. . p. g .. ,. . * , w. .,

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AtM O-1999 ~09:19 BALTIMORE GAS 8. ELECTRIC 410 495 6945 P.02/03

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Confirmatory Item 3.2J.2.14 i To manage aging effects associated with SCC of the control element assembly (CEA) shroud bolts, the applicant, in Section 4.3.2 of Appendix A to the LRA, described a program that would perform an analysis to determine if the applied stresses on these bolts is above or below the

" critical stress" for SCC. As discussed during a meeting on February 16,1999 (NRC meeting summary dated March 19,1999), for NRC Question No. 4.3.15, the applicant indicated that after further review, the ihnotion of the CEA shroud bolts is not safety related and, therefore, this stress analysis program would not be implemented. This is a confrmatory item pending review of an applicant submittal documenting this finding.

In addition, an ARDI program is planned to manage the effects of SCC of the CEA shroud bolts.

However, as discussed in 3.2.3.2.lC(8) of this SER, the applicant imbH that the CEA shroud ,

bolts do not perform a safety function in accordance with the requirements of 10 CFR 54.4. The  !

applicant was asked to document the resolution of the issue with a description of the ihnetion of  !

the CEA shroud bolts that included an explanation of why they do not meet the criteria contained in 10 CFR 54.4.

BGE Response

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1 Summary:

The function of the CEA Shroud Bolts is to provide lateral support and alignment for the  !

CEAs and to maintain CEA spacing. This is a safee.9elatedsafety-reinted function and meets the criteria of 10 CFR 54.4. Mf F- '!y, e"^ E rrr ::"M rr' p "!* )

{. ahe-CEA-ShsoudBeks. As explained below, based on the low probability of any degradation resulting from SCC, and taking into consideration the inherent redundancy of the CEA Shroud Bolts, thi4MMSCC will not prevent the CEA Shroud Bolts from performing theis_thJs intended Junesien, function. Therefore, SCC is now considered not plausible for the CEA Shroud Bolts.

Details:

There have been no indications of any A286 threaded structural fastener failures to date on any CE reactor vessel internals. Plants my have undergone .1A. pens 10-year l inservice inspections have detected no loose parts or gross indications of structural fastener failures. ,Calvert Cliffs' most recent refbeling outases included such inspections. l Indusuy experience with failures of A286 vessel internals threaded stmetural fasteners has been limited to applications in B&W plants. CE has evaluated the stresses for the CEA Shroud Bolts relative to the stresses experienced by the failed B&W fasteners. CE conservatively projected that the potential for a "small i ,. sage" of failures existed.

CE did not explicitly quantify this projected failure percentage. The threaded structural fasteners in all CE applications have been torquod to pmduce operating stress levels just under 32,000 psi average stress. The failure rate at 36,000 psi in the B&W applications was less than 4%. At 35,000 psi, no failures were identified. It may be implied from these results, and considering operating experience to date, that the expected failure rate of the CE fasteners may well be 0%, and should certainly be less than 4%.

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1. N t?'DTAaXCLA$U 1@A.Y2FC 419 493 6946 P.03 03 CE also evaluated the margin for the nonnal operating plus upset condition loads for the CEA Shroud Bolts to determine the minimum number of fasteners required per Shroud to

( maintain the joint integrity. There are 20 dual (2 CEAs per Assembly) shrouds and 45 single (1 CEA) shrouds. Dual shrouds have 16 bolts. Single shrouds have 8 bolts. Theg are a total of 680 bolts. A minimum of 5 of 8 bolts (62.5%) are required for single shrouds. A minimum of 10 of 16 bolts ((62.5%) are required for dual shrouds. This available margm above the ASME Code stress allowables of 37.5% far exceeds the most conservative projected failure rate of the CEA Shroud Bolts. Based on th= comparison of the available margin with the maximum conservative projected failure rate, SCC of the CEA Shroud Bolts will not impact the intended ^~"r, 2-> function. For an ARDM to )

be plausible fet License Renewal, it must impact the intended function. Therefore, SCC is considered at plausible.

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