ML060960563

2006/04/07-Oyster Creek, License Renewal AMP-AMR Audit Questions AMP-141, AMP-356, AMP-210 Set 1 and Cover Email

ML060960563
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Site:	Oyster Creek
Issue date:	04/07/2006
From:	Beck G Exelon Corp
To:	Ashley D, Roy Mathew NRC/NRR/ADRO/DLR/RLRA
Ashley D
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I D. Ashley -FW: Audit Q & A (Question Numbers AMP-141, 210, 356)Page 1r From: <George.BeckO 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 retransmitted without the AMP-210.pdf.

This file will be reconstituted and sent in smaller ".pdf"s; the first 11 pages are attached.George-------Original Message-----

> From: Beck, George> Sent: Wednesday, April 05, 2006 4:39 PM> To: Donnie Ashley (E-mail);

'Roy Mathew (E-mail) '(E-mail)> 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-210 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 reviewed and approved by Technical Lead, Don Warfel.> Regarding AMP-210, please note:> As po nted out in our response to NRC Question AMP-210, (8a)(1), "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 wthin 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 if you have any questions.

> George> >> <<Pages from AMP-210.pdf>>

> > > <<AMP-141.pdf>>

>> <<AMP-356.pdf>>

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Creation Date: From: Created By: FW: Audit Q & A (Question Numbers AMP-141, 210, 356)04/05/2006 5:01:46 PM<George.Beck@exeloncorp.com>

George.Beck@exeloncorp.com Recipients nrc.gov OWGWPOO1.HQGWDOO1 DJA1 (D. Ashley)nrc.gov TWG WPOO1.HQGWDOO1 RKM (Roy Mathew)exeloncorp.com fred polaski CC donald.warfel CC john.hufnagel CC ahmed.ouaou CC Post Office OWGWPOO1.HQGWDOO1 TWGWPOO1.HQGWDOO1 Files MESSAGE TEXT.htm Pages from AMP-210.pdf AMP-] 41.pdf AMP-2.56.pdf Mime.822 Option, Expiration Date: Priority: Reply Requested:

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Securily: Route nrc.gov nrc.gov exeloncorp.com Size 2679 5457 64593 47353 71556 262768 Date & Time 05 April, 2006 5:01:46 PM None Standard No None No 'Standard NRCfInformation Request Form Item No Date Received:

Source AMP-210 1/24/2006 AMP Audit Topic: Status: Open IWE Document

References:

B.1.27 NRCRepresintative 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 measurements (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 circumference?

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 allcw 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, arid 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?

(.7:33 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 fNRCInformation Request FormlCreek sand bed region.Evaluation of UT measurements taken from inside the drywell, in the in the former sand bed region, in 1992, 1994, and 1996 confirmed that corrosion is mitigated.

It is therefore concluded that corrosion in the sand bed region has been arrested and no further loss of material is expected.

Monitoring of the coating in accordance with the Protective Coating Monitoring and Maintenance Program, will continue to ensure that the containment drywell shell maintains its intended function during the period of extended operation.

NUREG-15540, 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 requirementlcommitment documented in NUREG-1540.

(8b)The following statement related to drywell corrosion above the sand bed region needs further explanation and clarification:

Corrective action for these regions involved providing a corrosion allowance by demonstrating, through ana ysis, that the original drywell design pressure was conservative.

Amendment 165 to the Oyster Creek Technical Specifications reduced the drywell design pressure from 62 psig to 44 psig.The new design pressure coupled with measures to prevent water intrusion into the gap between the drywell shell and the concrete will allow the upper portion of the drywell to meet ASME code requirements.

Please describe the measures to prevent water intrusion into the gap between the drywell shell and the concrete that will allow the upper portion of the drywell to meet ASME code requirements".

Are these measures to prevent water intrusion credited for LR? If not, how will ASME code requirements be met during the extended period of operation?

(8c)The following statements related to torus degradation need further explanation and clarification:

Inspection performed in 2002 found the coating to be in good condition in the vapor area of the Torus and vent header, and in fair condition in immersion.

Coating deficiencies in immersion include blistering, random and mechanical damage. Blistering occurs primarily in the shell invert but was also noted on the upper shell near the water line. The fractured blisters were repaired to reestablish the protective coating barrier. This is another example of objective evidence that the Oyster Creek ASME Section Xl, Subsection IWE aging management program can identify degradation and implement corrective actions to prevent the loss of the containment's intended function.While blistering is considered a deficiency, it is significant only when it is fractured and exposes the base metal to corrosion attack. The majority of the blisters remain intact and continues to protect the base metal; consequently the corrosion rates are low. Qualitative assessment of the identified pits indicate that the measured pit depths (50 mils max) are significantly less than the criteria established NRC Information Request Formlin Specification SP-1302-52-120 (141- 261 mils, depending on diameter of the pit and spacing between pits).Please confirm or clarify (1) that only the fractured blisters found in this inspection were repaired; (2)pits were identified where the blisters were fractured; (3) pit depths were measured and found to '50 mils max; (4) the inspection Specification SP-1302-52-120 includes pit-depth acceptance criteria for rapid evaluation of observed pitting; (5) the minimum pit depth of concern is 141 mils (.141) and pits as deep as :261 mils (.261) may be acceptable.

Please also provide the following information:

nominal design, as-built, and minimum measured thickness of the torus; minimum thickness required to meet ASME code acceptance criteria; the technical basis for the pitting acceptance criteria include in Specification SP-1302-52-120 Assigned To: Ouaou, Ahmed Response: (8a) Questicn:

Please explain the underlined statement.

Were water leaks limited to only a porticn of the circumference?

Was wall thinning only in these area?Response: This statement was not meant to indicate that water leaks were limited to only a portion of the circumference.

The statement is meant to reflect the fact that water leakage was observed coming out of certain sand bed region drains and those locations were suspect of wall thinning.No. Wall thinning was not limited to the areas where water leakage from the drains was observed.Wall thinning occurred in all areas of the sand bed region based on UT measurements and visual inspection of the area conducted after the sand was removed in 1992. However the degree of wall thinning variEd from location to location.

For example 60% of the measured locations in the sand bed region (bays 1, 3, 5, 7, 9, and 15) indicate that the average measured drywell shell thickness is nearly the same as the design nominal thickness and that these locations experienced negligible wall thinning; whereas bay 19A experienced approximately 30% reduction in wall thickness.

Question:

Please discuss the concrete surface below the sand that is discussed in paragraph above.Response: The concrete surface below the sand was intended to be shaped to promote flow toward each of the five sand bed drains. However once the sand was removed it was discovered that the floor was not properly finished and shaped as required to permit proper drainage.

There were low points, craters, and rough surfaces that could allow moisture to pool instead of flowing smoothly toward the drains.These concrete surfaces were refurbished to fill low areas, smooth rough surfaces, and coat these surfaces with epoxy coating to promote improved drainage.

The drywell shell at juncture of the concrete floc r was sealed with an elastomer to prevent water intrusion into the embedded drywell shell.Question:

Please provide the following information:

JNRCInformation Request 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-1540 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 +/- 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 1Ce92, 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 approximat:ely 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, arid 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 JanLary 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 INRC Information Request Form described in detail in attachment 1 & 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 1II, 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 ergineering 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" Dut thicker than 0.536". Also the actual data for two bays shows that there are more than one 2 Y/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 or 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 Information Request 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 local 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 21Y2 inches ii 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 \JE-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 nargin. 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 RequestFor drywell are substantially larger than the 2 1/2 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 reducei 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.

Therefore, 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 minimu'n thickness of 0.733" is not correct. The correct minimum thickness is 0.736".4. The minimum 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 correspondences 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.

INRC Information Request Form Response: Our review of NUREG-1540, page 2 indicates that the statements appear to be based on 1991, or 1993 GPU commitment to perform periodic UT measurements.

In fact UT thickness measurements were taken n the sand bed region from inside the drywell in 1992, and 1994. The trend of the UT measurements indicates that corrosion has been arrested.

As results GPU informed NRC in a letter dated September 15, 1995 (ref. 2) that UT measurements will be taken one more time, in 1996, and the epoxy coating will be inspected in 1996 and, as a minimum again in 2000. The UT measurements were taken in 1996, per the commitment, and confirmed corrosion rate trend of 1992 and 1994. The results of 1992, 1994, and 1996 UT measurements were provided to the Staff during the AMP/AMIR audits.In response to GPU September 15, 1995 letter, NRC Staff found the proposed changes to sand bed region commitments (i.e. no additional UT measurements after 1996) reasonable and acceptable.

This respon se is documented in November 1, 1995 Safety Evaluation for the Drywell Monitoring Program.For license renewal, Oyster Creek was previously committed to perform One-Time UT inspection of the drywell shell in the sand bed region prior to entering the period of extended operation.

However, in response to NRC Question #AMP-141, Oyster Creek revised the commitment to perform UT inspections Deriodically.

The initial inspection will be conducted prior to entering the period of extended operation and additional inspections will be conducted every 10 years thereafter.

The UT measurements will be taken from inside the drywell at same locations as 1996 UT campaign (8b) Question:

Please describe the measures to prevent water intrusion into the gap between the drywell shell and the concrete that will allow the upper portion of the drywell to meet ASME code requirements.

Are these measures to prevent water intrusion credited for LR? If not, how will ASME code requirements be met during the extended period of operation?

Response: The measures taken to prevent water intrusion into the gap between the drywell shell and the concrete that will allow the upper portion of the drywell to maintain the ASME code requirements are, 1. Cleared the former sand bed region drains to improve the drainage path.2. Replaced reactor cavity steel trough drain gasket, which was found to be leaking.3. Applied stainless steel type tape and strippable coating to the reactor cavity during refueling outages to seal identified cracks in the stainless steel liner.4. Confirmed that the reactor cavity concrete trough drains are not clogged 5. Monitored former sand bed region drains and reactor cavity concrete trough drains for leakage during refueling outages and plant operation.

Oyster Creek is committed to implement these measures during the period of extended operation.

(8c) Please confirm or clarify (1) that only the fractured blisters found in this inspection were repaired;(2) pits were identified where the blisters were fractured; (3) pit depths were measured and found to NRC Information Request Form 50 mils max; (4) the inspection Specification SP-1302-52-120 includes pit-depth acceptance criteria for rapid evaluation of observed pitting; (5) the minimum pit depth of concern is 141 mils (.141) and pits as deep as 261 mils (.261) may be acceptable.

Response: (1) Specification SP-1302-52-120, Specification for Inspection and Localized Repair of the Torus and Vent Systern Coating, specifies repair requirements for coating defects exposing substrate and fractured blisters showing signs of corrosion.

The repairs referred to in the inspection report included fractured blisters, as well as any mechanically damaged areas, which have exposed bare metal showing signs of corrosion.

Therefore, only fractured blisters would be candidates for repair, not those blisters that remain intact. The number and location of repairs are tabulated in the final inspection report prepared by Underwater Construction Corporation.

(2) Coating deficiencies in the immersion region included blistering with minor mechanical damage.Blistering occurred primarily in the shell invert but was also noted on the upper shell near the water line. The majority of the blisters were intact. Intact blisters were examined by removing the blister cap exposing the substrate.

Corrosion attack under non-fractured blisters was minimal and was generally limited to surface discoloration.

Examination of the substrate revealed slight discoloration and pitting with pit depths less than 0.001. Several blistered areas included pitting corrosion where the blisters were fractured.

The substrate beneath fractured blisters generally exhibited a slightly heavier magnetite oxide layer and minor pitting (less than 0.010") of the substrate.

(3) In addition to blistering, random deficiencies that exposed base metal were identified in the torus immersion region coating (e.g., minor mechanical damage) during the 19R (2002) torus coating inspections.

They ranged in size from 1/16" to 1 2" in diameter.

Pitting in these areas was qualitatively evaluated and ranged from less than 10 mils to slightly more than 40 mils in a few isolated cases.Three quantitative pit depth measurements were taken in several locations in the immersion area of Bay 1. Pit depths at these sites ranged from 0.008" to 0.042" and were judged to be representative of typical conditions found on the shell.Prior to 200:2 inspection 4 pits greater than 0.040" were identified.

The pits depth are 0.058" (1 pit in 1988), 0.05' (2 pits in 1991), and 0.0685" (1 pit in 1992). The pits were evaluated against the local pit depth acceptance criteria and found to be acceptable.

(4) Specification SP-1302-52-120, Specification for Inspection and Localized Repair of the Torus and Vent System Coating, includes the pit-depth acceptance criteria for rapid evaluation of observed pitting. The acceptance criteria are supported by a calculation C-1302-187-E310-038.

Locations that do not meet the pit-depth acceptance criteria are characterized based on the size of the area, center to center distance between corroded areas, the maximum pit depth and location in the Torus based on major structural features.

These details are sent to Oyster Creek Engineering for evaluation.

(5) The acceptance criteria for pit depth is as follows:-Isolated Pit; of 0.125" in diameter have an allowed maximum depth of 0.261" anywhere in the shell provided the center to center distance between the subject pit and neighboring isolated pits or areas of pitting corrosion is greater than 20.0 inches. This includes old pits or old areas of pitting corrosion that have been filled and/or re-coated.

NRCInformation Request Form-Multiple Piis that can be encompassed by a 2-1/2" diameter circle shall be limited to a maximum pit depth of 0.141" provided the center to center distance between the subject pitted area and neighboring isolated pits or areas of pitting corrosion is greater than 20.0 inches. This includes old pits or old areas of pitting corrosion that have been filled and/or recoated.Question:

Please also provide the following information:

nominal design, as-built, and minimum measured thickness of the torus; minimum thickness required to meet ASME code acceptance criteria; the technical basis for the pitting acceptance criteria include in Specification SP-1302-52-120 Response: Submersed area: (a) The nominal Design thickness is 0.385 inches (b) The as-built thickness is 0.385 inches (c) The minimum uniform measured thickness is, 0.343 inches -general shell 0.345 inches -shell -ring girders 0.345 inches -shell -saddle flange 0.345 inches -shell -torus straps (d) The minimum general thickness required to meet ASME Code Acceptance is 0.337 inches.Technical basis for pitting acceptance criteria included in Specification SP-1302-52-120 is based on engineering calculation C-1302-187-E310-038.

At the time of preparation of calculation C-1302-187-E310-038 in 2002 there were no published methods to calculate acceptance standards for locally thinned areas in ASME Section III or Section VIII Pressure Vessel codes. Therefore, the approach in Code Case N-597 was used as guidance in assessing locally thinned areas in the Torus. This is based on the similarity in approaches between Local Thinning Areas described in N597 and Local Primary Stress areas described in Paragraph NE3213.10 of the ASME B&PV Code Section III, particularly small areas of wall thinning which do not exceed 1.0 x (square root of Rt). In addition, the ASME B&P'/ Code Section III, Subsection NB, Paragraph NB-3630 allows the analysis of pipe systems in accordance with the Vessel Analysis rules described in Paragraph NB-3200 of the same Subsection as an alternate analysis approach.

Therefore, the approach used in N597 for local areas of thinning vias probably developed using the rules for Local Primary Membrane Stress from paragraph NB-3200 in particular Subparagraph 3213.10. The Local Primary Stress Limits in NB-3213.10 are similar to those discussed in Subsection NE, Paragraph NE-3213.10.

Since the Code Case had not yet been invoked in to the Section Xl program, the calculation provided a reconciliation of the results obtained from the code case against the ASME Section III code requirements as discussed above. This reconciliation demonstrated that the approach in N597 used on a pressure vessel such as the Torus would be acceptable since the results are conservative compared tc the previous work performed in MPR-953 and Lm(a) (defined in N597 Table- 3622-1) £(Rmintmin)1

/2.Currently, the maximum pit depth measured in the Torus is a 0.0685" ( measured in 1992 in bay 2). It was evaluated as acceptable using the design calculations existing at that time and was not based on NRC Information Request Form Calculation C-1302-187-E310-038.

This remains the bounding wall thickness in the Torus. The criterion developed in 2002 for local thickness acceptance provides an easier method for evaluating as-found pils. The results were shown to be conservative versus the original ASME Section III and VilI Code requirements for the Torus.The Torus inspection program is being enhanced per IR 373695 to improve the detail of the acceptance criteria and margin management requirements using the ASME Section III criteria.

The approach used in C-1 302-187-E310-038 will be clarified as to how it maintains the code requirements.

If Code Case N-597-1 is required to develop these criteria for future inspections, NRC review and approval will be obtained.

It should also be noted that the program has established corrosion rate criteria and continues to periodically monitor to verify they remain bounded.LRCR #: LRA A.S Commitmtent

1. IR#: Approvals:

Prepared By. Ouaou, Ahmed 4/ 5/2006 Reviewed By: Miller, Mark 4/ 5/2006 ApprovedBy:

Warfel, Don 4/ 5/2006 NRCAcceptance (Date):

INRC Information Request Form Item No Date Received:

Source AMP-356 2/16/2006 AMP Audit Topic: Status: Open IWE Document

References:

NRC Representative Morante, Rich AmerGen (Took Issue): Question IWE AMP Question 4 IWE AMP Revised Feb. 17, 2006 R. Morante (AMP-356)(1) Identify the specific locations around the circumference in the former sandbed region where UT thickness readings have been and will be taken from inside containment.

Confirm that all points previously recorded will be included in future inspections.

(2) DescribE the grid pattern at each location (meridional length, circumferential length, grid point spacing, total number of point readings), and graphically locate each grid pattern within the former sandbed region.(3) For each grid location, submit a graph of remaining thickness versus time, using the UT readings since the initiation of the program (both prior to and following removal of the sand and application of the external coating).(4) Clearly describe the methodology and acceptance criteria that is applied to each grid of point thickness readings, including both global (entire array) evaluation and local (subregion of array)evaluation.

Assigned To: Ouaou, Ahmed Response: Response: 1. The circumference of the drywell is divided into 10 bays, designated as Bays 1, 3, 5,7, 9, 11,13, 15, 17, and 19. UT thickness readings have been taken in each bay at one or more locations.

The specific locations around the circumference in the former sand bed region where UT thickness reading have been taken from inside containment are Bay 1D, 3D, 5D, 7D, 9A, 9D, 11A, IC, 13A, 13C, 13D, 15A, 15D, 17A, 17D,17/19 Frame, 19A, 19B, and 19C. For each location, UT measurements were taken centered at elevation 11 '-3". These represent the locations where UT measurements were taken in 1992, 1994, and 1996.

INRC Information RequestFor In addition UT measurements were taken one time inside 2 trenches excavated in drywell floor concrete.

The purpose of these UT measurements is to determine the extent of corrosion in the lower portions of the sand bed region prior to removing the sand and making accessible for visual inspection.

Future UT thickness measurements will be taken at the same locations as those inspected in 1996 in accordance with Oyster Creek commitment documented in NRC Question #AMP-209.2. For locations where the initial investigations found significant wall thinning (9D, 1 1A, 1 1C, 13A, 13D, 15D, 17A, 17D, 17/19 Frame, 19A, 19B, and 19C) the grid pattern consists of 7 x 7 grid centered at elevation 11 '-3 (meridian) and centered at the centerline of the tested location within each bay, which consists of 6"x 6" square template.

The grid spacing is 1" on center. There are 49 point readings.

For graphical location of the grid, refer to attachment 1.For locations where the initial investigations found no significant wall thinning (1 D, 3D, 5D, 7D, 9A, 13C, and 1A) the grid pattern consists of 1 x 7 grid centered at elevation 11 '-3" (meridian) on 1" centers. There are 7 point readings.

For graphical location of the grid, refer to attachment 1.3. A graph representing the remaining thickness versus time using UT reading since the initiation of the program (both prior to and following removal of the sand and application of the external coating)for location 9D,11A,11C,13A,13D,15D,17A,17D,17/19,19A,19B, and 19C is included in the attached graph. Other locations (i.e.1 D, 3D, 5D, 7D, 9A, 13C, and 15A) are not included because wall thinning is not significant and the trend line will be essentially a straight line.4. The methodology and acceptance criteria that is applied to each grid of point thickness readings, including both global (entire array) evaluation and local (subregion of array) is described in engineering specification IS-328227-004 and in calculation No. C-1 302-187-5300-011.

These documents were submitted to the NRC in a letter dated November 26, 1990 and provided to the Staff during the AMP/AMR audit. A brief summary of the methodology and acceptance criteria is described below.The initial locations where corrosion loss was most severe in 1986 and 1987 were selected for repeat inspection ovier time to measure corrosion rate. For location where the initial investigations found significant wall thinning UT inspection consists of 49 individual UT data points equally spaced over a 6"x 6" area. Each new set of 49 values was then tested for normal distribution.

The mean values of each grid were then compared to the required minimum uniform thickness criteria of 0.736. In addition each individual reading is compared to the local minimum required criteria of 0.49. The basis for the required minimum uniform thickness criteria and the local minimum required criteria is provided in response to NRC Question #AMP-210.A decrease in the mean value over time is representative of corrosion.

If corrosion does not exist, the mean value will not vary with time except for random variations in the UT measurements.

fNRCInformation Request Form If corrosion is continuing, the mean thickness will decrease linearly with time. Therefore the curve fit of the data is tested to determine if linear regression is appropriate, in which case the corrosion rate is equal to the slope of the line. If a slope exists, then upper and lower 95% confidence intervals of the curve fit are calculated.

The lower 95% confidence interval is then projected into the future arid compared to the required minimum uniform thickness criteria of 0.736.A similar process is applied to the thinnest individual reading in each grid. The curve fit of the data is tested to determine if linear regression is appropriate.

If a slope exists, then the lower 95%confidence nterval is then projected into the future and compared to the required minimum local thickness criteria of .49.LRCR #: LRA A.5 Commitment

1. IR#: Approvals:

Prepared By.- Ouaou, Ahmed 4/4/2006 ReviewedBy:

Getz, Stu 4/ 5/2006 ApprovedBy:

Warfel, Don 4/ 5/2006 NRCAcceptance (Date):

Oyster Ceek Drywell Vessel Corrosion Rate Trending Program Average Measured Thicknesses.t 1. O..46 F.b" Ap,41 M.y-S Aug4 S p4 JuI41 0Ot1.0 Junn49 S.p. _ Fb-90t Apr.9 M1r.9 May-91 Nov.9 Ma .9 S 9: S. S 9 ID 1.115 IM. L.IM 3D 1.17 = _ I. 1 173 71) 1.13 1.13 1 13A_1.15 -1 157 1.155 9D 1.07 1.021 1.054 1.020 1.026 1.022 0.993 1.008 0.992 1.0fc I. 0.9 I.00 IIA 0.919 0.905 0.92 0.905 0.913 0.898 0.81 0.892 09881 0.87C 0.845 0.944 0.833 0.642 0.s2 021 0o 31 llC 9oto _ 09917 0.994 0.916 0.909 0.891 0.977 0.991 _ 0.970 -0.90 0.85 0.63 0.856 0982 ON" 09 s1 09 3 To 1.046 1.10 1.075 1.045 1.005 1.016 1.00 0.952 9.97 0.982 1.01 0.964 1.01 097C 0.94 1.042 13A 0.919 S 0.90 0.683 0.9: 0.62 0.85: 0.85 0.85 0.849 0.86 005. 997 0994 13C $01__O1 0.90 0.901 0.90O 0.9 *1 .9 0995 00)p _0_1_rr_ 1.072 1.04 1.0G4 1.0 I M 1.w037 LOSI 13D 0.962 ______ _____ 0.932 O.1 .0- 0.ISA ____11 114 1.12 iI)13 1.w 11.0222 I. t= IG512200 1.051lG OlO~ LG.2 it.065j I.,994 .1.17A S 0996 05 7 096 095! 0954 0.981 0.935 084 0.933 0.948 09411 093J 0099 Tp 0.99 1.13 1.13 1.131 1.128 1.121 1.131 1.12 1.12 1.12 1.125 1.12 9I4 171 0.92 0.89 0.891 089 0.878 0.662 0.857 0.847 0.836 0.82 0.825 0.82 0.0823 OA.17 0Al9 945 17/19 9oton. 1.00 0.89 0.955 1.010 1.00 0.9871 0.99 0.97 0.990 0.19 4.975 o.v7 Tp_ 0.982 1.019 1.131 0.990 0.9861 0.9751 0.965 0.0972 n .97 1 9.9h- ...1 19A 0.884 09873 0.85. 0.8S8 0.84. 0.83 0.82 0.82. 0. 0.83 0 817 0. 0.080 0.809 O.90 9 so Oi15 09B 0.098 0092 0.99$ 0.0 0057 0.026 064 M01 0.93 0.531 0.4 0.84 0.047 .S3 0924 0 037 19C 0.901 0.880 0.08 0.873 0.05 0.U45 0 845 0.83i 0.82 0.6431 0.82 0.82 0.832 0.91 9O72 0049 Sandbed Bay 9 Location D 1.10 1.05 n s 1.00 0.95 0.90 ,%t, 4e e e e e e f G'eCf TIME Based on Calculation C-1302-187-5300-021 Slope Best Est Date-0.0125 0.9932 05/01/92 Average Since 1992 1.00012 Original Nominal Thickness Minimum n Unform Required Thickness 1.154" 0.736" Dates 9D Dec-86 Feb-87 May-87 Aug-87 Sep-07 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 1.0214 1.0540 1.0200 1.0260 1.0217 0.9926 1.0075 0.9924 1.0000 1.0036 0.9920 1.0080 1.0715 Sandbed Bay 11 Location A 0.94 0.92 0.89.~0.881 1.S 0.86 W 0.84 0.82 0.8_ lll 1 ll,l TIME Based on Calculation C-1302-187-5300-021 Slope Best Est. Date Average Since 1992 Original Nominal Thickness Minimum Unform Required Thickness-0.0171 0.83311 05101/92 0.8251 1.154" 0.736" Dates Dec-86 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 IIA 0.9187 0.90464 0.92209 0.9052 0.913 0.8882 0.881 0.8916 0.8808 0.8704 0.8446 0.844 0.8326 0.842 0.8252 0.82 0.83 Sandbed Bay 11 Location C u,.C 1.1 -1.05-1-0.95 -0.9-0.85 -0.8 in ,4 0 ,9 4QG TIME S4K 4QO Based on Calculation C-1302-187-5300-021 Best Best Average Average Slope Slope Est. Est. Date Since Since Original Nominal Thickness Minimum Unform Required Thickness Low High 1992 1992-0.0143 -0.0171 0.8498 0.9642 05101/92 0.8641 0.9984 1.154" 0.736 Dates Dec-86 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 lic Bottom 0.91679 0.95364 0.91571 0.9061 0.8907 0.8768 0.8907 0.8703 0.865 0.8575 0.8626 0.8563 0.882 0.8591 0.8503 0.883 tIC Top 1.046 1.1086 1.0791 1.0454 1.0089 1.0158 1.005 0.9522 0.977 0.9817 1.018 0.9643 1.01 0.9697 0.9836 1.0418 Sandbed Bay 13 Location A CO 0 C)0.94 0.92 0.9 0.88 0.86 0.84 0.82 0.8 co 0 oo o) N 't c.0 co cC N t C90 a CO0 CN 0 CO C 0 CD C CD CC C) C) 0) ) 0) 0) 0 0 0 0 C) U) U) U) U) U) l) U) U) U) a o 0 0 0 0 0 0 0 0 C , TIME Based on Calculation C-1302-187-53004021 Slope Best Est.-0.012 0.8442 Date 05/01192 Average Since 1992 0.8386 Original Nominal Thickness 1.154" Minimum Unfeorm Required Thickness 0.736" Dates Dec486 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr.90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 0.91908 0.9053 0.8828 0.883 0.8615 0.8531 0.8545 0.8529 0.8486 0.8645 0.8576 0.8275 0.843 Sandbed Bay 13 Location C 1.15 Sand Removal 1.1 1.05 1*~0.95 0.9 0.85 0.8 co 1r- Co 0 C '- N ') U CO N- COC 0 On 0 ' N C') 14 LO) CD I- OC CO CO co CO 0) 0) 0) CD 0m 0) a) 0) 0) 0) 0 0 0 0 0 0 0 0 C U) a) a) U) a) a) a) a) a) C) CD a) U) U) a) U) U) a) U) a) a) a) a TIME Based on Calculation C.1302-187-5300421 Slope Slope Best Est. Low Best Est. Hig Date Average Since 1992 Average Since 1992 Original Nominal Thickness Minimum Unform Required Thickness 4.013 4.0146 0.9073 1.06 05/01/92 1.0505 0.9114 1.154" 0.736" Dates Dec-86 Feb-87 Apr.87 May487 Aug47 Sep47 Jul48 Oct48 Jun49 Sep-89 Feb.90 Apr-90 Mar-91 May-91 Nov-91 May492 Sep-92 Sep-94 Sep-96 13C Bottom 0.9094 0.9013 0.8996 0.9305 0.906 0.8953 0.933 13C Top 1.0722 1.0488 1.0479 1.0882 1.0546 1.037 1.0593 Sandbed Bay 15 Location D 1.15 -1.1 -1.05 -0 Un s r_1 -0.95 r r I I r I I I I I I I CDs0 )ON M qt U-) (O P- CO C5 0 Mo n t 0 (O r a U) U) U) U) ) U) U) U) U) U) ) U) U) ) U U) U) U) ) U) ) U) a Q Q C1 Q CQ CQ Q Qc TIME Based on Calculation C-1302-187-5300-021 Slope Best Est.Date Average Since 1992 Original Nominal Thickness Minimum Unform Required Thickness 4.001 1.055 05/01/92 1.0588 1.154" 0.736" Dates Dec-86 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 1.089 1.056 1.06 1.0609 1.0586 1.0565 1.0598 1.0502 1.0417 1.0652 1.0577 1.053 1.066 Sandbed Bay 17 Location A Sand Removal (a 4)U C 1.2 1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 -cxs C.0 00 U)Q CO N o 00 0 oo '0t (. oc 00 O') ) 0 M C) 0 0 0 0 C U) ) a) a) a) U) U) a) U) a) a Q 0 0 0 0 0 0 0 0 0 C TIME Booed on Celouletlon C-1 302-187-5300-021 Slope Slop. BoSt Et Low BoSt Est. High D.t. Averoge Slom 1992 Avr 9 g. Slno 1992 OrlgoIe No.ntol Thioko...

Mo.n... tUfon. Rqtr4 Tbkk.eo.-0.0058 -0.0017 0.9352 11278 0501192 1.1326 0.9573 1.154 0.736'DMte. D.-06 Fob-B7 Apr.87 Mey.87 Aog-7 Sep.87 Ju148 odt-88 Jun49 S.p-89 Fb.90 Apr-90 M-r-91 Mey.91 Nov-91 Mey-92 Sep-92 Sep-94 Sep-96 17A heot. 0.999 0.9574 0.9645 0.95S2 0.9536 0.9590 0.9347 0.9424 0.932a 0.9481 0.9413 0.9338 0.9969 17ATop 0.999 1.1331 1.13 1.1308 1.128 1.1283 1.1309 1.1293 1.1226 1.1254 1.1248 1.1289 1.1441 Sandbed Bay 17 Location D Co a)0.95 0.93 0.91 0.89 0.87 0.85 0.83 0.81 0.79 0.77 0.75 Cf is ,<: ,& ,oo ,9O 9Oo ,o ,C ,> , geS<Dp g2s <)Q As Aid &>Q (eS 0e S§f 4'0 TIME Based on Calculation C-1302-187-5300-021 Slope Best Est..0.018 0.8057 Date 05101/92 Average Since 1992 0.8239 Original Nominal Thickness 1.154" Minimum Unform Required Thickness 0.736" Dates 17D Dec46 Feb-87 0.92217 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 0.89507 0.89069 0.89528 0.8779 0.8622 0.8568 0.8471 0.8358 0.829 0.8253 0.8291 0.8222 0.823 0.8172 0.81 0.845 Sandbed Bay 17-19 1.1 1.05 s5 0.95 0.9 0.8 0.8 TIME Based on Calculation C-1302-187-5300-021 Slope Slope Best Est. Low Best Est. High Date Average Since 1992 Average Since 1992 Original Nominal Thickness Minimum Unform Required Thickness-0.0087 -0.0107 0.9621 0.9761 05/01/92 0.9871 0.9689 1.154" 0.736" Dates Dec-86 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 17/19 Top 0.9817 1.0191 1.1308 0.9898 0.986 0.9746 0.9693 0.9542 0.9722 0.976 0.963 0.9674 17/19 10038 0.9988 0.9552 1.01 1.0057 0.987 0.9824 0.9711 0.99 0.9887 0.9748 0.9914 Bottom 103 .98 095 .1105 .8 .84091 .9 098 .78 091 Based on Calculation C-1302-187-5300-021 Slope Best Est.-0.015 0.7911 Date 05/01/92 Average Since 1992 0.8071 Original Nominal Thickness 1.154" Minimum Unform Required Thickness 0.736" Dates Dec46 Feb-87 19A 0.88364 Apr-87 May47 Aug47 Sep47 Jul48 Oct48 Jun49 Sep49 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 0.87293 0.8586 0.85829 0.8486 0.8369 0.8288 0.8254 0.8399 0.8076 0.8167 0.8028 0.8032 0.8091 0.8002 0.806 0.815 I Sandbed Bay 19 Location B 0.95'A 0 U 0.9 0.85 0.8 0.75'A eo TI M5 EZ TIME Based on Calculation C-1302-187-5300-021 Slope Best Est. Date-0.0099 0.8330 05/01/92 Average Since 1992 0.8337 Original Nominal Thickness 1.154" Minimum Unform Required Thickness 0.736" Dates Dec-86 Feb-87 Apr-87 May-87 Aug-87 Sep-87 Jul-88 Oct-88 Jun-89 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 19B 0.89763 0.89221 0.8876 0.864 0.8565 0.8256 0.84549 0.812 0.8369 0.8525 0.8444 0.8463 0.8472 0.8396 0.824 0.837 Sandbed Bay 19 Location C 0.95 0.93 an 0.91 0.89 0.87 0.85.S 0.83 0.81 0.79 0.77 0.75 0 (Ril C zi (Z\ Q 59 59 9 $,9,@ ,\,>& ,o Q5 Q1&, TIME Based on Calculation C-1302-187-5300-021 Slope Best Est. Date Average Since 1992 Original Nominal Thickness Minimum Unform Required Thickness 4.015 0.8117 05/01/92 0.829 1.154" 0.736" Dates Dec46 Feb47 Apr-87 May47 Aug47 Sep47 Jul48 Oct48 Jun49 Sep-89 Feb-90 Apr-90 Mar-91 May-91 Nov-91 May-92 Sep-92 Sep-94 Sep-96 19C 0.90051 0.88816 0.88831 0.8735 0.8563 0.845 0.8447 0.8305 0.8251 0.8428 0.8232 0.8223 0.8319 0.8192 0.82 0.848 fNRCInformation Request Form Item No Date Received:

Source AMP-141 10/ 6/2005 AMP Audit Topic: Status: Open IWE Document

References:

B.1.27 NRCRepres.?ntative Morante, Rich AmerGen (Took Issue): Hufnagel, Joh Question AMP B.1.27 IWE a. Visual inspection of the coatings in the former sandbed region of the drywell is currently conducted under the applicant's protective coatings monitoring and maintenance program; only this AMP is credited for managing loss of material due to corrosion for license renewal. Visual inspection of the containment shell conducted in accordance with the requirements of IWE is typically credited to manage loss of material due to corrosion.

The applicant is requested to provide its technical basis for not also crediting its IWE program for managing Icss of material due to corrosion in the former sandbed region of the drywell.B. During discussions with the applicant's staff on 10/04/05 about augmented inspection conducted under IWE, the applicant presented tabulated inspection results obtained from the mid 1980s to the present, to monitor the remaining drywell wall thickness in the cylindrical and spherical regions where significant corrosion of the outside surface was previously detected.The applicant is requested to provide (1) a copy of these tabulated inspection results, (2) a list of the nominal design thicknesses in each region of the drywell, (3) a list of the minimum required thicknesses in each region of the drywell, and (4) a list of the projected remaining wall thicknesses in each region of the drywell in the year 2029.AMP B.1.27 IWE Question on Remaining Wall Thickness in the Former Sandbed Region of the Drywell c. During discussions with the applicant's staff on 10/05/05, the applicant described the history and resolution of corrosion in the sandbed region. After discovery, thickness measurements were taken from 1986 through 1992, to monitor the progression of vwall loss. Remedial actions were completed in early 1993. At that time, the remaining wall thickness exceeded the minimum required thickness.

The applicant concluded that it had completely corrected the conditions which led to the corrosion, and terminated its program to monitor the remaining wall thickness.

At that time, the remaining years of operation wets expected to be no more than 16 years (end of the current license term).

INRC Information Request orm The applicant's aging management commitment for license renewals is limited to periodic inspection of the coating that was applied to the exterior surface of the drywell as part of the remedial actions.The applicant has not made a license renewal commitment to measure wall thickness in the sancdbed region in order to confirm the effectiveness of the remedial actions taken.Assigned To: Ouaou, Ahmed Response: a) Visual inspection of the containment drywell shell, conducted in accordance with ASME Section Xl, Subsection IWE, is credited for aging management of accessible areas of the containment drywell shell. Typic:ally this inspection is for internal surfaces of the drywell. The exterior surfaces of the drywell shell in the sand bed region for Mark I containment is considered inaccessible by ASME Section Xl, Subsection IWE, thus visual inspection is not possible for a typical Mark I containment including Oyster Creek before the sand was removed from the sand bed region in 1992. After removal of the sand, an epoxy coating was applied to the exterior surfaces of the drywell shell in the sand bed region. The region was made accessible during refueling outages for periodic inspection of the coating. Subsequently Oyster Creek performed periodic visual inspection of the coating in accordance with an NRC current licensing basis commitment.

This commitment was implemented prior to implementation of ASME Section Xl, Subsection IWE. As a result inspection of the coating was conducted in accordance with the Protective Coating Monitoring and Maintenance Program. Our evaluation of this aging management program concluded the program is adequate to manage aging of the drywell shell in the sand bed region during the period of extended operation consistent with the current licensing basis commitment, and that inclusion of the coating inspection under IWE is not required.

However we are amending this position and will commit to monitor the protective coating in the exterior surfaces of the drywell in the sand bed region in accordance with the requirements of ASME Section Xl, Subsection IWE during the period of extended operation.

For details related to implementation of this commitment, refer to the response to NRC AMP Question #188.b) A tabulation of ultrasonic testing (UT) thickness measurement results in monitored areas of the drywell spherical region above the sand bed region and in the cylindrical region is included in ASNME Section Xl, subsection IWE Program Basis Document (PBD-AMP-B.1.27)

Notebook.

The tabulation contains information requested by the Staff and is available for review during AMP audit. The tabulation is also provided in Table -1, and Table-2 below.c) In December 1992, with approval from the NRC a protective epoxy coating was applied to the outside surface of the drywell shell in the sand bed region to prevent additional corrosion in that area. UT thickness measurements taken in 1992, and in 1994, in the sand bed region from inside the drywell confirmed that the corrosion in the sand bed region has been arrested.

Periodic inspection of the coating indicates that the coating in that region is performing satisfactorily with no signs of deterioration such as blisters, flakes, or discoloration, etc. Additional UT measurements, taken in 1996 from inside the drywell in the sand bed region showed no ongoing corrosion and provided objective evidence that corrosion has been arrested.

fNRCInformation Request Form As a result of these UT measurements and the observed condition of the coating, we concluded that corrosion has been arrested and monitoring of the protective coating alone, without additional UT measurements, will adequately manage loss of material in the drywell shell in the sand bed region.However to provide additional assurance that the protective coating is providing adequate protection to ensure drywell integrity, Oyster Creek will perform periodic confirmatory UT inspections of the drywell shell in the sand bed region. The initial UT measurements will be taken prior to entering the period of extended operation and then every 10 years thereafter.

The UT measurements will be taken from inside the drywell at the same locations where the UT measurements were taken in 1S96.This revises the license renewal commitment communicated to the NRC in a letter from C. N.Swenson Site Vice President, Oyster Creek Generating Station to U. S. Nuclear Regulatory Commission, "Additional Commitments Associated with Application for renewed Operating License -Oyster Creek Generating Station", dated 12/9/2005.

This letter commits to one-time inspection to be conducted prior to entering the period of extended operation.

The revised commitment will be to conduct UT measurements on a frequency of 10 years, with the first inspection to occur prior to entering the period of extended operation.

This response was revised to incorporate additional commitments on UT examinations for the sand bed region discussed with NRC Audit team on 1/26/2006.

This response was revised to reference response to NRC Question #AMP-188 and RAI 4.7.2-1 (d).AMO 4/1/2006.The response was revised to add Table-1, and Table-2, and delete reference to RAI 4.7.2-1 (d) AMAO 4/5/2006.LRCR #: 229 LRA A.S Commitment

1. 27 IR#: Approvals:

Prepared Byu Ouaou, Ahmed 4/ 5/2006 RevieivedBy.

Getz, Stu 4/ 5/2006 ApprovedBjy:

Warfel, Don 4/ 5/2006 NRCAccept!nce (Date):

Table -1. UT Thickness measurements for the Upper Region of the Drywell Shell Average Measured Thickness

""I, inches Monitored Location Minimum Projected Lower Elevation Required 95% Confidence Thickness, 1987 1988 1989 1990 1991 1992 1993 1994 1996 2000 2004 Thickness in 2029 inches 5 Elevation 0.541" 50' 2" Bay 5- 0.743 0.742 0.747 0.741 0.748 0.741 0.743 No Ongoing D12 0.745 0.745 0.747 Corrosion 0.746 0.748 Bay 5- 5H 0.761 0.755 0.758 0.754 0.757 0.754 0.756 0.7384 0.761 0.758 0.758 0.760 Bay 5- 5L 0.706 0.703 0.703 0.702 0.705 0.706 0.701 No Ongoing 0.703 0.705 0.707 Corrosion 0.706 Bay 13- 0.762 0.760 0.765 0.759 0.766 0.762 0.758 No Ongoing 311 0.779 0.758 0.763 Corrosion 0.765 Bay 13- 0.687 0.689 0.685 0.683 0.690 0.682 0.693 No Ongoing 311L 0.684 0.678 0.688 Corrosion 0.688 Bay 15- 0.758 0.762 0.767 0.758 0.760 0.758 0.757 0.738 23H 0.764 0.762 0.763 0.765 Bay 15- 0.726 0.726 0.726 0.728 0.724 0.729 0.727 No Ongoing 23 L 0.728 0.729 0.724 Corrosion 0.725 Elevation 0.54 1" 51' 10" I I Table-I. UT Thickness measurements for the Upper Region of the Drywell Shell Average Measured Thickness

", inches Monitored Location Minimum Projected Lower Elevation Required _ 95% Confidence Thickness, 1987 1988 1989 1990 1991 1992 1993 1994 1996 2000 2004 Thickness in 2029 inches 5 Bay 13- 0.716 0.715 0.717 0.714 0.715 0.715 0.713 No Ongoing 32H 0.715 0.717 Corrosion 0.719 Bay 13- 0.686 0.683 0.683 0.680 0.684 0.679 0.687 No Ongoing 32L 0.683 0.676 Corrosion 0.682 Elevation 0.518" 60' 10" Bay 1 0.693 0.711 0.692 0.689 0.689 No Ongoing 22 l Corrosion Elevation 0.452" 87' 5" Bay 9-20 0.619 0.622 0.619 0.620 0.614 0.629 0.613 0.613 0.604 0.612 0.604.0.620 _ 0.612 0.614 l l l l Bay 13- 0.643 0.641 0.645 0.643 0.635 0.641 0.640 0.636 0.635 0.640 No Ongoing 28 0.642 l 0.629 0.637 l l l l Corrosion Bay 15- 0.638 0.636 0.638 0.642 0.628 0.631 0.633 0.632 0.628 0.630 0.615 31 1 0.636 1 1 1 0.627 0.630 l 1 l l l Notes: I. The average thickness is based on 49 Ultrasonic Testing (UT) measurements performed at each location 2. Multiple inspections were performed in the years 1988, 1990, 1991, and 1992.3. The 1993 elevation 60' 10" Bay 5-22 inspection was performed on January 6, 1993. All other locations were inspected in December 1992.4. Accuracy of Ultrasonic Testing Equipment is plus or minus 0.010 inches.5. Reference SE-000243-002.

Table -1. UT Thickness measurements for the Upper Region of the Drywell Shell

Conclusion:

Summary of Corrosion Rates of UT measurements taken through year 2004* There is no ongoing corrosion at two elevations (51' 10" and 60' 10")* Based on statistical analysis, one location at elevation 50' 2" is undergoing a minor corrosion rate of 0.0003 inches per year,* Based on statistical analysis, two locations at elevation 87' 5" are undergoing minor corrosion rates of 0.0005 and 0.00075 inches per year Table -2 UT Thickness measurements for the Sand Bed Region of the Drvwell Shell Location Sub Dec Feb Apr May Aug Sep Jul Oct Jun Sep Feb Apr Mar May Nov May ep Sep Sep Bay Location 1986 1987 1987 1987 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1991 1992 1992 1994 1996 ID ________l1.11' 1.101 1.151 D 1.178 1.184 1.181 SD 1.17 1.16 1.17 D _ _ _ ___ _ _ _ _ _ _ _ _ __ _ _ 1.13 5 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1.13 0 1.13~A ___ 1.153 1.157 1.15 D 1.072 1.021 1.054 1.02C 1.02E 1.022 0.99' 1.001 0.992 1.000 1.004 0.99: 1.00E I IA 0.91' 0.905 0.92 0.905 0.913 0.881 0.881 0.892 0.881 0.87t 0.84! 0.84 0.83 0.842 0.825 0.82( 0.83(1 C Bottom 0.91 0.95 0.91 0.90 0.89 1 0.87 0.891 0.87 0.86 0.85 0.86 0.85 0.882 0.85 0.85 0.88 Top 1.046 1.109 1.07' 1.045 1.00! 1.01 1.00! 0.952 0.97 0.982 1.01 0.962 1.01( 0.970 0.98 1.04: 13A 0.91 0.90 0.88 0.88 0.86 0.85 0.85 0.85 0.84 0.86 0.85 0.82 0.84 i3C Bottom 0.909 0.901 0.90( 0.931 0.906 0.895 0.93: T__ op 1.072 1.049 1.04i 1.088 1.05' 1.03 1.05!13D 0.962 0.932 1 1.001 0.95! 0.9 I SA _ 1.12( _ 1.114 1.12 15D 1.089 1.051 1.060 1.061 1.05 1.057 1.06C 1.05C 1.04; 1.065 1.058 1.05 1.06 17A Bottom 0.999 0.95 0.965 0.955 0.95' 0.951 0.93! 0.94 0.93> 0.948 0.941 0.93' 0.997 FOP 0.999 1.13' 1,130 1.131 1.12E 1 .128 1.131 1. 12!, 1.12 1.125 1.125 1.12<. 1.144 17D 0.92_ 0.89 0.891 0.89 0.878 0.86 0.85 0.84 0.83 0.82 0.82 0.82 0.82 0.823l 0.81 0.81 0.84 17/19 Top 0.982 1.01 1.131 0.99( 0.98( 0.975 0.96' 0.954 0.972 0.976 0.96 0.96 Boftom 1.00 0.99 0.95 1.01 1.00 0.98 0.98 0.971 0.99 0.98 0.97 0.991 19A 0.884 0.873 0.859 0.85E 0.84 0.83 0.82 0.82 0.84( 0.80E 0.817 0.80 0.80 0.809 0.80( 0.806 0.81 19B 0.898 0.89 0.88E 0.864 0.857 0.82E 0.84 0.81 0.83 0.85 0.84 0.846 0.847 0.84( 0.824 0.837 19C I 0.901 0.88 0.88E 0.87 0.856 0.84 0.84 0.831 0.825 0.843 0.82 0.82 0.832 0.81 0.82 0.84