ML17349A534

Special Rept:On 921106 & 12,20th Yr Tendon Insp Determined That lift-off Value for Hoop Tendon 13H54 & Dome Tendon 1D40 Below Min Design Prestress Force.Tendons Restored to Required Level.Addl Rept to Be Submitted by 930129

ML17349A534
Person / Time
Site:	Turkey Point
Issue date:	12/04/1992
From:	Plunkett T FLORIDA POWER & LIGHT CO.
To:	Ebneter S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
L-92-330, NUDOCS 9212100117
Download: ML17349A534 (18)

Text

~~~~~~i~a j.~u UVCUMENT DISTRIBUTION REGULA'lC INFORMATION DISTRIBUTIO~YSTEM (RIDE)

SYSTEM ACCESSION'BR:9212100117 DOC.DATE 92/12/04 NOTARIZED: NO DOCKET FACIL:50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH. NAME, AUTHOR AFFILIATION PLUNKETT,T.F. Florida Power & Light Co.

RECIP.NAME. RECIPIENT AFFILIATION EBNETER,S.D. Region 2 (Post 820201)

SUBJECT:

Special rept:on 921106 & 12,20th yr tendon insp determined

,that lift-off value for hoop tendon 13H54 & dome tendon lD40 below min design prestress force. Tendons restored to required level.Addi rept to be submitted by .930129.

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0 ~t P.O. Bo 9100, Miami, FL. 33102-9100 FPL OEi; 04 ~>S~

L-92-330 10 CFR 50.36 Stewart D. Ebneter Regional'dministrator U. S. Nuclear Regulatory Commission 101. Marietta Street, N.W., Suite 2900 Atlanta, Georgia 30323

Dear Mr. Ebneter:

Re: Turkey Point Unit 4 Docket No. 50-251 Special Report Twentieth Year Tendon Inspection Low Lift-Off Force In accordance with Florida Power and Light Company, (FPL) Turkey Point Units 3 and 4 Technical Specification 3.6.1.6 a., the enclosed Special Report is provided. This report summarizes the low lift-off force inspection results for hoop tendon 13H54 and dome tendon 1D40.

As discussed with the staff on November 30, 1992, a second hoop tendon 35H38 measured a lift-off value below the minimum design prestress force and in accordance with Technical Specification 3.6.1..6 a.,

tendon 35H38'ill be addressed in a separate Special Report to be submitted to the .NRC by December 1'8, 1992.

An additional report will be transmitted to the NRC by January 29, 1993, summarizing the surveillance testing of all hoop and dome tendons inspected during the Unit 4 twentieth year inspection.

Should there be. any questions, please contact us.

Very truly yours, Qj P/~AN.. ,Gd.

T. F. Plunkett Vice President Turkey Point Nuclear TFP/RJT/rt Enclosure cc: USNRC, Document Control Desk, Washington, D.C.

Senior Resident Inspector, USNRC, Turkey Point Plant 1000OJ 92i2100ii7 921204 PDR ADOCK 0500025i pre f:

S, PDR an FPL Group company

il 0 Enclosure NRC S ecial Re ort Turkey Point Unit 4 Twentieth Year Tendon Inspection Low Lift-Off Force on Hoop Tendons 13H54 and Dome Tendon 1D40

0 L-92-330 Special Report Page .2 of 7 TABLE OF CONTENTS 1.0 PURPOSE/SCOPE 2'. 0 ENGZNEERZNG EVALUATZON.

3.0 CONCLUSZON 4.0 CORRECTZVE ACTZONS

5.0 REFERENCES

'l L-92-330 Special Report Page 3 of 7 1.0 Pu ose Sco e During the performance of the twentieth year tendon surveillance of the Turkey Point Unit 4 containment post-tensioning system, two surveillance tendons, 13H54 (inspected on November 6, 1992) of the hoop tendon group and 1D40 (inspected on November 12, 1992) of the dome tendon group were found to have a measured normalized lift-off force below the predicted lower limit (References 5.4 and 5.5) .

Consequently, in accordance with the requirements of the Turkey Point Plant Technical Specifications 4.6.1.6.1 (a), additional lift-off measurements on the adjacent tendons (13H53 and 13H55, inspected on November 6, 1992 and 1D38 and 1D41 inspected on November 13, 1992) were taken for each of the applicable surveillance tendons. Zn each case, since the measured normalized lift-off force in at least one of these adjacent tendons was between the predicted lower limit and 90%

of the predicted lower limit, Turkey Point Unit 4 entered a 15 day ACTZON statement to the LZMZTZNG CONDZTZON OF OPERATZON (Technical Specification 3 '.1.6) . This ACTZON statement required restoration of the tendon(s) to the required level of integrity within 15 days and performance of an engineering evaluation of the cont'ainment, and the submittal of a Special Report to the NRC within 30 days.

The evaluation of the structural integrity of the containment post-tensioning system is included in this engineering evaluation.

2.0 En ineerin Evaluation The Turkey Point Unit 4 containment is a post-tensioned, reinforced concrete structure comprised of a vertical cylinder with a shallow dome and suppozted on a conventional reinforced concrete foundation base slab. The vertical cylinder wall is provided with a system of vertical and hoop tendons. Vertical tendons are anchored at the top surface of the ring girder and at the bottom of the base slab. Each hoop tendon is anchored at alternate vertical buttresses nominally 120 degrees apart. Tendons in the dome consist of three groups of tendons oriented at 120 degrees with respect to each other and are anchored at the vertical face of the dome zing girder.

The tendon surveillance program for the Turkey Point Nuclear Plant Unit 4 containment structure post-tensioning system has been performed at one, three and five years after the containment Znitial Structural Zntegrity Test (ZSZT), and every five years thereafter. Three dome, five hoop, and four vertical tendons were selected for the twentieth year tendon surveillance on a random basis, excluding those tendons which were previously inspected for earlier surveillances. The Turkey, Point Unit 4 twentieth year tendon surveillance is performed in accordance with the requirements of References 5.6 and 5.9 ~

A wire has been removed foz inspection from dome tendon 1D40. Zn addition, grease samples have been removed for each surveillance tendon inspected to date. The visual inspection of the tendon wire and sheath filler samples have revealed no abnormal wire corrosion or grease discoloration.

't L-92-330 Special Report Page 4 of 7.

Also, the concrete at the tendon anchorage area adjacent to the bearing plates, for all hoop tendons has been inspected. This inspection has revealed that no cracks were found which exceed the acceptance. width of 0.01 inches noted in reference 5.8, Section ZWL-3221 '(d) ~

For tendons 1D40 and 1D41, the bearing plates are located in the vicinity of a horizontal construction joint located at approximately mid-height of the ring girder. Some concrete spalling/cavities were observed at this horizontal construction joint during the Unit 3 third year tendon surveillance. The spalling was inspected and evaluated in reference 5.11, which concluded that the structural integrity of the containment is not affected. While inspecting the concrete surface in the vicinity of the bearing plates for tendons 1D40 and 1D41 during the Unit 4 twentieth year surveillance, a similar spalling/cavity was observed at this joints The subject areas were inspected, and it was concluded that the spalling observed, during the Unit 4 twentieth year

.surveillance is similar,to the condition evaluated in reference 5.11 and there will be no adverse effects on, the containment structural The appropriate corrective actions will be specified in integrity. -final the Unit 4 surveillance report to repair the spalled areas to mitigate any potential corrosion, path to the main reinforcing, steel.

The following are the predicted lower limit (PLL) and the minimum design prestress force at the anchorage for hoop and dome tendons:

Twentieth Year Predicted Lower Limit 6.63 kips/wire for Hoop and Dome Tendons.

(Reference 5.6)

Minimum Design Prestress Force 6.29 kips/wire (Based on Original Anchorage for Hoop Tendons Design)'t (Reference 5.3)

Minimum Design Prestress Force ~ 6.55 kips/wire (Based on Original Design) at Anchorage for Dome Tendons (Reference 5.3)

The lift-off forces which are below the surveillance tendons predicted lower limit occurred (13H54) and its adjacent in one of the hoop tendons (13H53 and 13H55) and in one of the dome surveillance tendons

,(1D40) and one of its adjacent tendons (1D41).

From references 5.4 and 5.5, the results of the surveillance on, hoop and dome tendons are as follows:

Measured Normalized Percentage Tendon Lift-Off Force ki s wire of PLL 13H53 6.27 94.6%

13H54 6.37 96.1%

13H55 6.26 94.4%

Average 6.30 kips/wire 95.0%

L-92-330 Special Report Page 5 of 7 Measured Normalized Percentage Tendon Lift-Off Force ki s wire of PLL 1D38 6.84 103.2%

1D40 6.54 98.6%

1D41 6.29 94.9%

Average 6.56 kips/wire 98.9%

As shown, the average lift-offprestress force for the hoop, tendon group is force (6 29 kips/wire) .

larger than the minimum design Also, the average lift-off force for ~

the dome tendon group is larger force (6.55 kips/wire) than the minimum design prestress . Therefore, it is concluded that the subject tendon groups presently provide adequate prestress force to maintain the containment integrity. This conclusion is consistent with the guidance provided in Section 7.1.5 of Regulatory Guide 1.35 (Reference 5.7) and Section IWL-3221.1 (a) of ASME Code (Reference 5.8).

The magnitude of the Unit 4 low lift-off forces for the subject hoop and dome tendons is similar to the Unit 3 lift-off force measurements and correlates well with the results of the evaluation provided to the NRC by Letter L-92-262, dated September 14, 1992 (Reference 5.10) for the Unit 3 low lift-off values. Therefore, it can be stated that the probable cause of the Unit 4 low lift-offmeasurements is also due to increased. tendon wire steel relaxation losses resulting from the temperatures experienced by the tendons. The lift-off readings for the remaining surveillance tendons will provide additional data to further investigate the extent of this condition. Upon completion os the lift-off testing, an engineering evaluation will be prepared to include the additional data and the results of the investigation relative to this condition. A more detailed report will be submitted to the NRC following completion of the tendon surveillance.

2.1 Review Of Re ulator Guides and ASME Code Section XI Acce tance Criteria Regulatory Guide 1.35 (reference 5.7), Section 7.0, and ASME Code Section XI (reference 5 '), Section IWL-3221.1, were reviewed relative to the tendon lift-off acceptance criteria to provide additional justification for the adequacy of the containment post-tensioning system. The following summarizes this review:

a) Section 7.1.5 of reference 5.7 and Section IWL-3221.1 (a) of reference 5.8 require that the average of all measured tendon forces be equal to or greater than the minimum required prestress force at the anchorage.

b) Section 7 '.2 of reference 5.7 implies that, lift-off force for a surveillance if the measured tendon lies above 95% of the predicted lower limit, no additional lift-off testing of adjacent tendons is required and the condition should be considered acceptable.

I

il 0 L-92-330 Special Report Page 6 of 7 The measured normalized lift-off forces for surveillance tendons 13H54 and 1D40 were above 95% of the predicted. lower limit. This meets the requirement of reference 5.7 (Criterion (b) above), and no additional testing would have been required if this criterion had been applied.

Finally, as shown in Section 2.0, the average lift-off force for hoop tendons is 1'arger than the minimum design prestzess force (6.29 kips/wire) which satisfies criterion (a) above Also, the average lift-off force for dome tendons is larger than the minimum

~

design prestzess force (6.55 kips/wize). Therefore, based on this

.review, it can also be concluded that the Unit 4 hoop and dome tendon groups have sufficient pzestress force to maintain. the containment integrity, and the intent of the acceptance criteria included in References 5.7 and 5.8 is satisfied.

2.2 Desi' Maz ins Available in the Post-Tensionin S stem Turkey Point UFSAR (reference 5.1), Section 5.1.2 states that any three adjacent tendons in any tendon group can be lost without significantly affecting the strength of the containment structure.

This design feature considers the load redistribution capabilities of the containment shell.

3.0 Conclusion Based on the available margins existing in the design of the Turkey Point post-tensioning system and the level of prestress force available in the subject hoop and dome tendons, it is concluded that the Unit 4 hoop and dome tendon groups have sufficient prestress force to maintain the containment integrity.

As, part of the twentieth year surveillance, lift-off testing will be performed for the remaining hoop and dome surveillance tendons. These lift-off readings will .provide additional data to further investigate the extent of this condition. Upon completion of the lift-off testing, an engineering evaluation will be prepared to include the additional data and the results of the investigation relative to this condition. A more detailed report will be submitted to the NRC following completion of the tendon surveillance.

4.0 Corrective Actions According to the Turkey Point Plant Technical Specifications 3.6.1.6 (a), the lift-off forces in tendons 13H53, 13H54, 13H55, 1D40 and 1D41 have been restored to their required level of integrity by retensioning each tendon to a level equal to or above the twentieth year predicted lower limit. The following summarizes the new lift-off forces for the subject tendons:

Measured Percenta e of Tendon Avera e Lift-Off ki s Predicted Lower Limit 13H53 621.3 104.1%

13H54 619.8 103.9%

13H55 634 ' 106.3%

1D40 622.0 104.2%

1D41 619.0 103.7%

II L-92-330 Special Report Page 7 of 7

'5 ~ 0 References 5.1 Turkey Point Units 3 and 4 Updated Final Safety Analysis Report (UFSAR), Revision 10, dated July 1992, Section 5.0 5.2 Technical Specifications, Amendment 151/146, Sections 4.6.1.6.1(a) and 3.6.1.6, and Amendments 152/147 issued via NRC letter dated August 20, 1992 5.3 'Bechtel Calculation No. C-SJ539-05, "Evaluation of the Fifteenth Year Tendon Surveillance Lift-Off Forces", Revision 0

5. 4 Non-Conf ormance. Report N-92-0292.

5.5 Non-Conformance Report N-92-0301 5.6 Bechtel Technical Requirements Document 21701-561-CP-l, Revision 0 for Unit 4 Twentieth Year Tendon Surveillance 5.7 Regulatory Guide 1.35, "In-service Inspection of Ungrouted Tendons in Prestressed Concrete Containment", Revision 3, dated July 1990 5.8 ASME Code, 1989 Edition,Section XI Division 1, Article IWL-3000, "Acceptance Standards" 5.9 Turkey Point Plant Procedure O-SMM-51.2, "Containment Tendon Inspection", dated June 26, 1992 5.10 FPL Transmittal to the NRC, Turkey Point Unit 3 Twentieth Year Tendon Inspection Report Hoop Tendons Low Lift-Off Force, L-92-262, dated September 14, 1992 5.11 Turkey Point Nuclear Power Plant, Unit 3, "Containment Structure Ring Girder Concrete Inspection", dated February 1975

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