ML20138B342

Submits Response to Request for Addl Info Re Proposed Amend to Reactor Bldg Structural Integrity Tech Specs.Info Provided in Attachments 2 & 3 Supersedes Revised Pages & Markup Pages in Attachment 1 & 2,respectively

ML20138B342
Person / Time
Site:	Oconee
Issue date:	04/22/1997
From:	Hampton J DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML16141B192	List: ML20138B342
References
NUDOCS 9704290132
Download: ML20138B342 (10)

Text

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J W Xtwm (konce hhwrSar hccl% dst RU SA M19 (M/jiGJ/W D/hre saiaa scha intSG uina DUKEPOWER April 22, 1997 U.

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Nuclear Regulatory Commission ATTENTION:

Document Control Desk Washington, DC 20555

SUBJECT:

Duke Power Company Oconee Nuclear Station, Units 1, 2,

and 3 Docket Nos. 50-269,

-270,

-287 Proposed Amendment to the Reactor Building Structural Integrity Technical Specifications Response to Request for Additional Information In a letter dated October 30, 1996, Duke Power submitted a proposed amendment to the Oconee Technical Specifications which addresses the structural integrity of the reactor buildings.

In a letter dated February 3, 1997, the staff requested additional information regarding this proposed Technical Specification amendment.

Please find attached the following items in response to your request for additional information: :

Responses to the Staff's Questions :

Revised Technical Specification Pages :

Markup of Revised Technical Specification Pages The information provided in Attachments 2 and 3 supersedes the revised pages and markup pages provided in Attachments 1 and 2, respectively, of the October 30, 1996, submittal.

Duke believes the information in Attachments 2 and 3 is responsive to the staff's questions.

The changes proposed in Attachments 2 and 3 of this 1

submittal do not alter the Technical Justification, No g k ),

Significant Hazards Evaluation, and the Environmental g

Impacts Statement provided in the October 30, 1996, submittal.

9704290132 970425 PDR ADOCK 05000269 l.lill ll ll1.1l.l!l.l ll

Duke requests expeditious NRC review and approval of this proposed amendment so ti it can be implemented during the next scheduled post-tensiv...ng inspection.

The next scheduled post-tensioning inspection is scheduled for the Unit 1 End-of-Cycle 17 Refueling Outage currently planned to j

begin on August 9, 1997.

If there are any further questions regarding this matter, please call David Nix at (864) 885-3634.

Very truly yours, f

im Hampton, Site Vice President Oconee Nuclear Station

4 i

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Nuclear Regulatory Commission April 22, 1997 Page 3

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i xc w/att:

L. A.

Reyes Regional Administrator, Region II I

D.

E. Labarge, Project Manager (ONS)

ONRR j

M. A. Scott j

Senior Resident Inspector (ONS) i M. Batavia l

South Carolina Department of Health and Environmental Control I

U.

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Nuclear Regulatory Commission April 22, 1997 Page 4 J. W.-Hampton, being duly sworn, states that he is Site Vice President of Duke Power Company, that he is authorized on the part of said company to sign and file with the Nuclear Regulatory Commission this amendment to the Ocenee Nuclear Station Facility Operating License Nos. DPR-3r, DPR-47, and a

DPR-55; and that all statements and matters set forth herein are true and correct to the best of his knowledge.

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_~ h m Jf WT Ha#mpton,/S'iteficePresident Subscribed and sworn to me M2, /9/7 Date' b.

Ab Notary Public' 8

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My Commission Expires:

c2-M #ddd Date SEAL

4 ATTACHMENT 1 Responses to the Staff's Questions 1.

The discussion on the concept of prestressed concrete containment as contained in Insert B to the BASES section of the revised technical specification is uncalled-for. It contains misleading statements and should be revised so that it will be succinct and to the point.

Response

In accordance with the staff's commento, the summary description has been revised to provide a more concise description of the reactor building post tensioning system. A revised copy of Insert B to the Technical Specification 3.6 BASES is provided in Attachents 2 and 3.

2.

In your procedure for inspection and tendon surveillance of the Reactor Building, you adopt the prescribed lower limit (PLL) required by Regulatory Guide 1.35, Revision 3, as the acceptance criterion for surveillance.

Provide a graph for each group of tendons that shows the PLL, 90 s

l percent PLL, and 95 percent PLL as well as the minimum

(

required tendon force.

In establishing the PLL, refer to Regulatory Guide 1.35 for guidance.

Since you are not using the relaxed surveillance intervals for a multiple-uni-plant, it appears that either separate graphs for each unit j

or, if justified, combined graphs for the three units may serve the purpose.

Response: On October 11, 1995, Duke submitted Tendon Surveillance Report # 6 for Oconee Unit 3.

The NRC l

requested additional information regarding this report in a letter dated January 19, 1996.

In response to this request for additional information, Duee provided the l

graphs for minimum required tendon force.

These graphs l

were provided in Duke responses dated March 14, 1996, and l

July 30, 1996, for Unit 3 and Units 1/2, respectively.

As stated in our response of March 14, 1996, we have committed to perform a re-analysis of our containment structure to establish more accurate tendon group minimum required values (MRVs), and to evaluate the causes of any

'$-2 loss of prestress in excess of the PLLs computed during original plant design.

Due to observed test results, the existing PLLs have been shown to be inaccurate.

Therefore, as we discussed with your staff in an April 16, 1997, teleconference, we believe that the existing PLLs would not be useful in support of the staff's review and approval of this proposed specification.

It has been j

Duke's intent to focus efforts on the development of new PLLs as part of the containment reanalysis.

3.

Your previous tendon surveillances were based on repeated use of the same presele,ted tendons and the results of the lift-off forces indicated larger prestress losses than predicted.

This can be attributed to the effect of detensioning and retensioning the same tendons through a number of cycles.

Since the forthcoming tendon surveillance for Unit 1 is based on Regulatory Guide 1.35, Rev.

3, which requires the use of randomly selected tendons, indicate how the data of previous surveillances can be used in linear regression analysis to establish the trend of tendon forces.

With only the forthcoming data it may not be possible to perform a trend analysis. This information should be provided in the Bases section.

Response

Seating forces for all tendons were documented at the time of installation, thus providing one data point. A second point will be obtained from data obtained during the initial tendon surveillance for each Unit. The data from the initial surveillance is considered reliable since any error due to tensioning and retensioning had not been introduced. This data will be averaged on a per Unit basis and used in the trend analysis along with new data obtained from the new proposed surveillance program in accordance with Regulatory Guide 1.35 methodology.

This information will j

be included in the Bases Section of Specification 4.4.2.

j i

4.

For Section 4.4.2.1, change " Surveillance Intervals" to

" Inspection Intervals" because " inspection" is more inclusive than " surveillance," which is used here exclusively for inspection of tendons.

Also, change the first sentence to read "The inspection intervals to

demonstrate the structural integrity of the reactor building shall be as follows: "Since this is an amendment, there is no need to mention the required inspection intervals that have passed.

For all the units, the inspection is at 5-year intervals.

For each unit, as a data base, just mention the date of the first inspection performed and the intervals of inspection thereafter and the date of the last inspection conducted. The staff believes that this information is more meaningful than what you have presented.

Further, to be realistic, it would be improbable even though not impossible to perform the inspection exactly at 5-year intervals and therefore some provision should be made for potential deviation in the inspection intervals.

Such deviation is allowed in ASME Section XI, Subsection IWL. This can avoid the future need for requesting relief because of any deviation.

The terms " reactor building," " reactor building structure," and " containment" have been used interchangeably.

To be consistent and to avoid any confusion use " reactor building" throughout since it has been extensively used.

Response

In Section 4.4.2.1,

" Surveillance Intervals" has been changed to " Inspection Intervals".

• The first sentence of Section 4.4.2.1 has been changed to read "The inspection intervals to demonstrate the structural integrity of the reactor building shall be as follows:"

• The description of the periodic inspection requirements of Section 4.4.2.1 have been simplified per the staff's i

comments.

The revisions to 4.4.2.1 now specify the date of the last inspection conducted under the existing technical specification requirements, and denote the periodic inspection requirements as measured from this date.

A description of the original reactor building structural integrity test and the interval of inspections thereafter has not been included in the body of the specification since this information is of large volume.

(This information is provided in the letters dated March 14, 1996 and July 30, 1996, as described in response to Question # 2 above.)

Duke believes this information

~

... - -. ~

should remain appropriately located in the existing 1

licensing correspondence.

A summary description of why the intervals are being measured from the specified date in the specification is now provided in the BASES of proposed specification 4.4.2.

Duke believes this information will meet the intent of the staff's request, while avoiding excessive detail in the specification.

In addition, a provision has been added as 4.4.2.1 (e) to permit relaxation from the five year interval if this relaxation is in accordance with the requirements of ASME Section XI, Subsection IWL.

• The terminology throughout the proposed technical specification amendments has been revised to consistently indicate " reactor building" in lieu of other similar descriptive terms such as " containment structure",

" containment", and " reactor building structure".

I All of the above revisions are provided in Attachments 2 and 3.

5.

Under a.

in Section 4.4.2.2, the first sentence states to the effect that predicted limits have been established for each tendon.

Since the surveillance is to be based on l

randomly selected tendons, and there are hundreds of

)

tendons, it would be a major task to do so, but realistically this is not necessary.

It should have been remembered that you are using a sample tendon to represent the behavior of a sampled population. Therefore, what is required.:Us the predicted limit for each group of tendons as indicated in item 2 above. Change "each tendon" to "each tendon group."

The predicted limits should be based on initial seating forces of the tendons in the group normalized for the effects of elastic deformation.

Response

Section 4.4.2.2, Item a, has been revised to indicate "each tendon group" in lieu of "each tendon".

Attachments 2 and 3 contain this revision.

6.

Under b, in Section 4.4.2.2, the first sentence mentions g

"a previously stressed tendon."

What this means is not clear, since all the tendons are stressed.

A change of this statement appears to be in order.

i

Response

Duke agrees that the terminology "previously l

stressed" is irrelevant to the requirements of this l

specification.

Accordingly, Section 4.4.2.2 (b) has been revised to indicate "a tendon" instead of "a previously stressed tendon".

Attachments 2 and 3 contain this i

revison.

1 7.

Under c.

in Section 4.4.2.2, in the middle of the paragraph it states "...between zero and the tendon seating force."

In order to establish the useful linear relationship between force and elongation, the following information should be obtained: (a) the pretensioned force (PTF), which is the force necessary to bring the tendon into a slightly stressed condition to remove slack and seat the buttonheads and is the base for elongation measurement, (b) lock off force (LOF) is the force at which the tendon load 4

l transferred to the shim stack from the ram and is j

representative of the force at which the tendon lift occurred during the monitoring of the tendon force, and (c) the overstress force (OSF) is that force at which the maximum elongation is determined.

The three approximately equally spaced levels of force and elongation as required by Regulatory Guide 1.35 are to be between PTF and LOF, i.e.,

two additional readings should be made between PTF and LOF.

In view of the above considerations, a revision of the statement is required. Instead of the statement, the following table may serve the purpose.

4 Actual Observed Force and Elongation Measurement For Retensioned Tendons Force (Kips)

Pressure (psi)

Eloncation (in)

PTF Step 1 Step 2 LOF OSF Total Elongation (actual)

(LOF - PTF) Elongation

=

List the definitions of the terms as indicated above.

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i j

On the basis of the information in the table, a graph to show the force-elongation relationship should be provided in i

the surveillance report for each retensioned tendon. From j

this graph, we can see how well the measurements were made and the tendon surveillance was performed.

i e

Response: A table has been added to 4.4.2.2 (c) as j

recommended by the staff in Question #7 above.

i a.

j Attachments 2 and 3 contain these revisions.

t I

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8.

On the basis of comments 3.

and 4.

above, the statement j

in the BASES should be revised.

For instance, the first j.

sentence mentions " Reactor Building prestressed concrete containment."

This is confusing, because it can be interpreted that within the reactor building there is a prestressed concrete containment.

I

Response

The BASES of proposed Technical Specification i

4.4.2 have been clarified, in accordance with the staff's i

recommendations, to ensure that no implication is made l

that there is a prescressed concrete. containment within l

l the Oconee reactor buildings.

Attachments 2 and 3 contain these revisions.

i 9.

Section 4.4.2.3 indicates that only bottom grease caps i

of vertical tendons are to be inspected.

At Farley, a lower anchor head failure was found as a result of the discovery of grease and deformed the grease cap at the top of the vertical tendon.

The failure of the vertical tendon lower anchor head was attributed to the presence of water in the lower grease cap, leading to the hydrogen stress cracking of the anchor head material.

The large force, thus released, deformed the top grease cap resulting in the leakage of the grease.

In view of this, both top and bottom grease caps of vertical tendons should be visually inspected, unless it can j

be justified.

Response: In accordance with the staff's recommendations, proposed specification Section 4.4.2.3 has been revised to require inspection of both the top and the bottom grease caps of vertical tendons.

Attachments 2 and 3 contain this revision.

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