ML072770641

Oyster Creek September 2007 Evidentiary Hearing - Applicant Exhibit 14, E-mail from George Beck (Exelon) to Donnie Ashley and Roy Matthew (NRC) Enclosing Amergen'S Response to NRC Audit Question AMP-210, Sub-Question 3, Regarding Drywell.

ML072770641
Person / Time
Site:	Oyster Creek
Issue date:	04/05/2006
From:	Beck G Exelon Corp
To:	Ashley D, Roy Mathew Office of Nuclear Reactor Regulation
SECY RAS
References
50-219-LR, AmerGen-Applicant-14, RAS 14221
Download: ML072770641 (8)

Text

Algal APPLICANT'S EXH. 14 From: <George.Beck@exeloncorp.com>

To: <djal @nrc.gov>, <rkm @nrc.gov>

Date: 04/05/2006 5:02:53 PM

Subject:

FW: Audit 0 & A (Question Numbers AMP-141, 210,356)

Note: As originally transmitted this email was undeliverable to the NRC; it exceeded the size limit. It is; being rotransmitted without the AMP-210.pdf. This file will be reconstituted and sent In smaller ".pdf",;; the first 11 pages are attached.

DOCKETED George USNRC October 1,2007 (10:45am)

> ---. Original Message---

> From: Beck, George OFFICE OF SECRETARY

> Sent: Wednesday, April 05, 2006 4:39 PM RULEMAKINGS AND

> To: Donnie Ashley (E-mail); 'Roy Mathew (E-mail)' (E-mail) ADJUDICATIONS STAFF

> Cc: Ouaou, Ahmed; Hufnagel Jr, John G; Warfel Sr, Donald B; Polaski, Frederick W

>

Subject:

Audit 0 & A (Question Numbers AMP-1 41, 210, 356)

> Donnie/Roy,

> Attached are the responses to AMP-21 0 and AMP-356 in an updated version of the reports from the AMP/AMR Audit database. Also included is a revised version of AMP-141. These answers have been reviewei and approved by Technical Lead, Don Warfel.

" Regarding AMP-210, please note:

" As ponted out.in our response to NRC Question AMP-210, (8a)(1), "The 0.806" minimum average thicknes;s verbally discussed with the Staff during the AMP audit was recorded In location 19A in 1994.

Additional reviews after the audit noted that lower minimum average thickness values were recorded at the same location in 1991 (0.803") and in September 1992 (0.800"). However, the three values are w thin the tolerance of +/-0.010" discussed with the Staff."

> Regarding AMP-141, please note:

> Our response to AMP-141 has been revised to reflect additional information developed during the ongoing preparation of RAI responses.

> Please let John Hufnagel or me know ifyou have any questions.

> George U.S. NUCLEAR REGULATORY COMMISSION

> .A, of In theEI 2 . IIER CO.WLIJ2, Docket NoSD- *9-L- Official Exhibit No. 4-

> >> <<Pages from AMP-210.pdf>> OFFERED by- ensee Intervenor

> > > <<AMP-141.pdf>> NR9Stalf Other IDENTIFIED on */f-*Witness/PaneI 4

> > <<AMP-356.pdf>>

ActionTaken: A( Iy4CTED WITHDRAWN Reporter/Clerk,.12 N This e-mail and any of its attachments may contain Exelon Corporation proprietary information, which is privileged, confidential, or subject to copyright belonging to the Exelon Corporation family of Companies.

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copying, or action taken in relation to the contents of and attachments to this e,-mail is strictly prohibited and may be unlawful. If you have receive J this e-mail in error, please notify the sender immediately and permanently delete the original and any copy of this e-mail and any printout. Thank You.

......... * ............. .. .....*.. .

...

CC: <ahmed.ouaou @exeloncorp.com>. <john.hufnagel@ exeloncorp.com>,

<donalcl.warfel@exeloncorp.com>, <fred.polaski@exeloncorp.com>

Mail Envelope Properties (44343066.C5F : 19: 7263)

Subject:

FW: Audit Q & A (Question Numbers AMP-141, 210, 356)

Creation Date: 04/05/2006 5:01:46 PM From: <George.Beck@exeloncorp.com>

Created By: George.Beck@exeloncorp.com Recipients nrc.gov OWGWPOO1.HQGWDOOI DJA1 (D. Ashley) nrc.gov TWG WPO01.HQGWDO01 RKM (Roy Mathew) exeloncorp.com fred.polaski CC donald.warfel CC john.hufnagel CC ahmed.ouaou CC Post Office Route OWGWPO01.HQGWDO01 nrc.gov TWG\VPOO I.HQGWDOOI nrc.gov exeloncorp.com Files Size Date & Time MESSAGE 2679 05 April, 2006 5:01:46 PM TEXT.htm 5457 Pages from AMP-210.pdf 64593 AMP-141.pdf 47353 AMP-.'-,56.pdf 71556 Mime.822 262768 Option:s Expiration Date: None Priority: Standard Reply Requested: No Return Notification: None Conceaded

Subject:

No '

Security: Standard

INRC Information Request Form]

Item No Date Received: Source AMP-210 1/2412006 AMP Audit Topic: Status: Open IWE Document

References:

B.1.27 NRCRepres.entative Morante, Rich AmerGen (Took Issue): Hufnagel, Joh Question Pages 25 through 31 of the PBD present a discussion of the OCGS operating experience.

(8a)The following statements related to drywell corrosion in the sand bed region need further explanation and clarification:

As a result of the presence of water in the sand bed region, extensive UT thickness measuremenis (about 1000) of the drywell shell were taken to determine if degradation was occurring. These measurements corresponded to known water leaks and indicated that wall thinning had occurred in this region.

Please explain the underlined statement. Were water leaks limited to only a portion of the circumferenie? Was wall thinning found only in these areas?

After sand removal, the concrete surface below the sand was found to be unfinished with improper provisions for water drainage. Corrective actions taken in this region during 1992 included; (1) cleaning of loose rust from the drywell shell, followed by application of epoxy coating and (2) removing the loose debris from the concrete floor followed by rebuilding and reshaping the floor with epoxy to allow drainage of any water that may leak into the region. UT measurements taken from the outside after cleaning verified loss of material projections that had been made based on measurements taken from the inside of the drywell. There were, however, some areas thinner than projected; but in all cases engineering analysis determined that the drywell shell thickness satisfied ASME code requirements.

Please describe the concrete surface below the sand that is discussed in paragraph above.

Please provide the following information:

(1) Identify the minimum recorded thickness in the sand bed region from the outside inspection, and the minimum recorded thickness in the sand bed region from the inside inspections. Is this consistent with previous; information provided verbally? (.806 minimum)

(2) What was the projected thickness based on measurements taken from the inside?

(3) Describe the engineering analysis that determined satisfaction of ASME code requirements and identify the minimum required thickness value. Is this consistent with previous information provided verbally? (.733 minimum)

(4) Is the minimum required thickness based on stress or buckling criteria?

(5) Reconcile and compare the thickness measurements provided in (1) and (3) above with the .736 minimum corroded thickness that was used in the NUREG-1540 analysis of the degraded Oyster

INRC InformationRequest Form (1) Identify the minimum recorded thickness in the sand bed region from the outside inspection, and the minimum recorded thickness in the sand bed region from the inside inspections. Is this consistent with previous information provided verbally? (.806 minimum)

(2) What was the projected thickness based on measurements taken from the inside?

(3) Describe the engineering analysis that determined satisfaction of ASME code requirements and identify the minimum required thickness value. Is this consistent with previous information provided verbally? (.733 minimum)

(4) Is the minimum required thickness based on stress or buckling criteria?

(5) Reconcile and compare the thickness measurements provided in (1) and (3) above with the .736 minimum corroded thickness that was used in the NUREG-1 540 analysis of the degraded Oyster Creek sand bed region.

Response

1. The minimum recorded thickness in the sand bed region from outside inspection is 0.618 inches.

The minimum recorded thickness in the sand bed region from inside inspections is 0.603. These minimum recorded thicknesses are isolated local measurement and represent a single point UT measurement. The 0.806 inches thickness provided to the Staff verbally is an average minimum general thickness calculated based on 49 UT measurements taken in an area that is approximately 6"x 6". Thus the two local isolated minimum recorded thicknesses cannot be compared directly to the general thickness of 0.806".

The 0.806" minimum average thickness verbally discussed with the Staff during the AMP audit was recorded in location 19A in 1994. Additional reviews after the audit noted that lower minimum average thickness values were recorded at the same location in 1991 (0.803") and in September 1992 (0.800"). However, the three values are within the tolerance of +1-0.010" discussed with the Staff.

2. The minimum projected thickness depends on whether the trended data is before or after 1992 as demonstrated by corrosion trends provided in response to NRC Question #AMP-356. For license renewal, using corrosion rate trends after 1992 is appropriate because of corrosion mitigating measures such as removal of the sand and coating of the shell. Then, using corrosion rate trends based on 1S,92, 1994, and 1996 UT data; and the minimum average thickness measured In 1992 (0.800"), the minimum projected average thickness through 2009 and beyond remains approximately 0.800 inches;. The projected minimum thickness during and through the period of extended operation will be reevaluated after UT inspections that will be conducted prior to entering the period of extended operation, and after the periodic UT inspection every 10 years thereafter.

3 The engineering analysis that demonstrated compliance to ASME code requirements was performed in two parts, Stress and Stability Analysis with Sand, and Stress and Stability Analyses without Sand. The analyses are documented in GE Reports Index No. 9-1, 9-2, 9-3, and 9-4, were transmitted to the NRC Staff in December 1990 and in 1991 respectively. Index No. 9-3 and 9-4, were revised later to correct errors identified during an internal audit and were resubmitted to the Staff in JanL'ary 1992 (see attachment 1 &2). The analyses are briefly described below.

The drywell shell thickness in the sand bed region is based on Stability Analysis without Sand. As

INR C Information Request Fo m described in detail in attachment I & 2, the analysis is based on a 36-degree section model that takes advantage of symmetry of the drywell with 10 vents. The model includes the drywell shell from the base of the sand bed region to the top of elliptical head and the vent and vent header. The torus is not included in this model because the bellows provide a very flexible connection, which does not allow significant structural interaction between the drywell and the torus. The analysis conservatively assumed that the shell thickness in the entire sand bed region has been reduced uniformly to a thickness o1:0.736 inches.

As discussed with the Staff during the AMP audit, the basic approach used in the buckling evaluation follows the methodology outlined in ASME Code Case N-284 revision 0 that was reconciled later with revision 1 o" the Code Case. Following the procedure of this Code Case, the allowable compressive stress is evaluated in three steps. In the first step, a theoretical buckling stress is determined, and secondly modified using appropriate capacity and plasticity reduction factors. In the final step, the allowable compressive stress is obtained by dividing the buckling stress calculated in the second step by a safety factor of 2.0 for Design and Level A & B service conditions and 1.67 Level C service conditions.

Using the approach described above, the analysis shows that for the most severe design basis load combinations, the limits of ASME Section Il1,Subsection NE 3213.10 are fully met. For additional details refer to Attachment 1 & 2.

As described above, the buckling analysis was performed assuming a uniform general thickness of the sand bed region of 0.736 inches. However the UT measurements identified isolated, localized areas wherE the drywell shell thickness is less than 0.736 inches. Acceptance for these areas was based on engineering calculation C-1302-187-5320-024.

The calculation uses a Local Wall Acceptance Criteria". This criterion can be applied to small areas (less than 12" by 12"), which are less than 0.736" thick so long as the small 12" by 12" area is at least 0.536" thick. However the calculation does not provide additional criteria as to the acceptable distance between multiple small areas. For example, the minimum required linear distances between a 12" by 12" area thinner than 0.736" but thicker than 0.536" and another 12" by 12" area thinner than 0.736" but thicker than 0.536" were not provided.

The actual data for two bays (13 and 1) shows that there are more than one 12" by 12" areas thinner than 0.736" ýut thicker than 0.536". Also the actual data for two bays shows that there are more than one 2 %'" diameter areas thinner than 0.736" but thicker than 0.490". Acceptance is based on the following evaluation.

The effect of these very local wall thickness areas on the buckling of the shell requires some discussion of the buckling mechanism in a shell of revolution under an applied axial and lateral pressure load.

To begin the discussion we will describe the buckling of a simply supported cylindrical shell under the influence of lateral pressure and axial load. As described in chapter 11 of the Theory of Elastic Stability, Second Edition, by Timoshenko and Gere, thin cylindrical shells buckle in lobes in both the

INRC InformationRequest Form axial and circumferential directions. These lobes are defined as half wave lengths of sinusoidal functions. The functions are governed by the radius, thickness and length of the cylinder. If we look at a specific thin walled cylindrical shell both the length and radius would be essentially constants and if the thickness was changed locally the change would have to be significant and continuous over a majority of the lobe so that the compressive stress in the lobe would exceed the critical buckling stress under the applied loads, thereby causing the shell to buckle locally. This approach can be easily extrapolated to any shell of revolution that would experience both an axial load and lateral pressure as in the case of the drywell. This local lobe buckling is demonstrated in The GE Letter Report "Sandbed Local Thinning and Raising the Fixity Height Analysis" where a 12 x 12 square inch section of the drywell sand bed region is reduced by 200 mils and a local buckle occurred in the finite element eigenvalue extraction analysis of the drywell. Therefore, to influence the buckling of a shell the very Ioc;1 areas of reduced thickness would have to be contiguous and of the same thickness.

This is also consistent with Code Case 284 in Section -1700 which indicates that the average stress values in the shell should be used for calculating the buckling stress. Therefore, an acceptable distance between areas of reduced thickness is not required for an acceptable buckling analysis except that the area of reduced thickness is small enough not to influence a buckling lobe of the shell. The very local areas of thickness are dispersed over a wide area with varying thickness and as such will have a negligible effect on the buckling response of the drywell. In addition, these very local wall areas are centered about the vents, which significantly stiffen the shell. This stiffening effect limits the shell buckling to a point in the shell sand bed region which is located at the midpoint between two vents.

The acceptance criteria for the thickness of 0.49 inches confined to an area less than 2Y inches il diameter experiencing primary membrane + bending stresses is based on ASME B&PV Code,Section III, Subsection NE, Class MC Components, Paragraphs NE-3213.2 Gross Structural Discontinuity, NE-3213.10 Local Primary Membrane Stress, NE-3332.1 Openings not Requiring Reinforcement, NE-3332.2 Required Area of Reinforcement and NE-3335.1 Reinforcement of Multiple Openings. The use of Paragraph NE-3332.1 is limited by the requirements of Paragraphs NE-3213.2 and N4E-3213.10. In particular NE-3213.10 limits the meridional distance between openings without reinforcement to 2.5 x (square root of Rt) . Also Paragraph NE-3335.1 only applies to openings in shells that are closer than two times their average diameter.

The implications of these paragraphs are that shell failures at these locations from primary stresses produced by pressure cannot occur provided openings in shells have sufficient reinforcement. The current design pressure of 44 psig for drywell requires a thickness of 0.479 inches in the sand bed region of the. drywell. A review of all the UT data presented in Appendix D of the calculation indicates that all thicknesses in the drywell sand bed region exceed the required pressure thickness by a substantial riargin. Therefore, the requirements for pressure reinforcement specified in the previous paragraph are not required for the very local wall thickness evaluation presented in Revision 0 of Calculation C-1302-187-5320-024.

Reviewing the stability analyses provided in both the GE Report 9-4 and the GE Letter Report Sand bed Local Thinning and Raising the Fixity Height Analysis and recognizing that the plate elements in the sand bed region of the model are 3" x 3" it is clear that the circumferential buckling lobes for the

INRC Information Request Form drywell are substantially larger than the 2 % inch diameter very local wall areas. This combined with the local reinforcement surrounding these local areas indicates that these areas will have no impact on the buckling margins in the shell. It is also clear from the GE Letter Report that a uniform reduction in thickness of 27% to 0.536" over a one square foot area would only create a 9.5% reduction in the load factor and theoretical buckling stress for the whole drywell resulting in the largest reduction possible. In addition, to the reported result for the 27% reduction in wall thickness, a second buckling analysis was performed for a wall thickness reduction of 13.5% over a one square foot area which only reduced the load factor and theoretical buckling stress by 3.5% for the whole drywell resulting in the largest reduction possible. To bring these results into perspective a review of the NDE reports indicate there are 20 UT measured areas in the whole sand bed region that have thicknesses less than the 0.736 inch thickness used in GE Report 9-4 which cover a conservative total area of 0.68 square feet of the drywell surface with an average thickness of 0.703" or a 4.5% reduction in wall thickness. lherefore, to effectively change the buckling margins on the drywell shell in the sand bed region a reduced thickness would have to cover approximately one square foot of shell area at a location in the shell that is most susceptible to buckling with a reduction in thickness greater than 25%. This leads to the conclusion that the buckling of the shell is unaffected by the distance between the very local wall thicknesses, in fact these local areas could be contiguous provided their total area did not exceed one square foot and their average thickness was greater than the thickness analyzed in the GE Letter Report and provided the methodology of Code Case N284 was employed to determine the allowable buckling load for the drywell. Furthermore, all of these very local wall areas are centered about the vents, which significantly stiffen the shell. This stiffing effect limits the shell buckling to a point in the shell sand bed region, which is located at the midpoint between two vents.

The minimun thickness of 0.733" is not correct. The correct minimum thickness is 0.736".

4. The minirmum required thickness for the sand bed region is controlled by buckling.

5. We cannot reconcile the difference between the current (lowest measured) of 0.736" in NUREG-1540 and the minimum measured thickness of 0.806 inches we discussed with the Staff. Perhaps the value in NUREG-1540 should be labeled minimum required by the Code, as documented in several corrn*spondences with the Staff, instead of lowest measured. In a letter dated September 15, 1995, GPU provided the Staff a table that lists sand bed region thicknesses. The table indicates that nominal thickness is 1.154". the minimum measured thickness in 1994 is 0.806", and the minimum thickness required by Code is 0.736". These thicknesses are consistent with those discussed with the Staff during the AMP/AMR audit.

Question: NUREG-1540, published in April 1996, includes the following statements related to corrosion of the Oyster Creek sand bed region: (page vii) However, to assure that these measures are effective, the licensee is required to perform periodic UT measurements. and (page 2) As assurance that the corrosion rate is slower than the rate obtained from previous measurements, GPU is committed to make UT measurements periodically. Please reconcile the aging management commitment (one-time UT inspection and monitoring of the condition of the coating) with the apparent requirement/commitment documented in NUREG-1540.Please reconcile the aging management commitment (one-time UT inspection and monitoring of the condition of the coating) with the apparent requirement/commitment documented in NUREG-1540.