ML12065A201

Requests for Additional Information for the Review of the South Texas Project, Units 1 and 2, License Renewal Application - Aging Management, Set 15 (TAC ME4936 and ME4937) STP-RAIs-Set 15-letter

ML12065A201
Person / Time
Site:	South Texas
Issue date:	03/21/2012
From:	Daily J License Renewal Projects Branch 1
To:	Rencurrel D South Texas
Daily J
References
TAC ME4936, TAC ME4937
Download: ML12065A201 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 March 21,2012 Mr. D. W. Rencurrel Sr. Vice President, Technical Support and Oversight STP Nuclear Operating Company P.O. Box 289 Wadsworth,TX 77483

SUBJECT:

REQUESTS FOR ADDITIONAL INFORMATION FOR THE REVIEW OF THE SOUTH TEXAS PROJECT, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION -AGING MANAGEMENT, SET 15 (TAC NOS. ME4936 AND ME4937)

Dear Mr. Rencurrel:

By letter dated October 25, 2010, STP Nuclear Operating Company (STPNOC or the applicant) submitted an application pursuant to Title 10 of the Code ofFederal Regulations, Part 54, to renew operating licenses NPF-76 and NPF-80 for South Texas Project, Units 1 and 2, for review by the U.S. Nuclear Regulatory Commission (NRC or the staff). The staff is reviewing the information contained in the license renewal application and has identified, in the enclosure, areas where additional information is needed to complete the review.

These requests for additional information were discussed with Arden Aldridge, and a mutually agreeable date for the response is within 30 days from the date of this letter. If you have any questions, please contact me at 301-415-3873 or bye-mail at john.daily@nrc.gov.

Sincerely, John W. Daily, Senior Project Ma ager Projects Branch 1 Division of License Renewal Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

As stated cc w/encl: Listserv

SOUTH TEXAS PROJECT, UNITS 1 AND 2, REQUEST FOR ADDITIONAL INFORMATION AGING MANAGEMENT, SET 15 (TAC NOS. ME4936 AND ME4937)

RAI B2.1.3-2b

Background

By letter dated December 15, 2011, the applicant responded to RAI B2.1.3-2a that addresses the inspections for stud insert #30 (also called stud hole insert #30) of Unit 2, the lugs of which were partially rolled. The applicant's response indicates that procedures will be enhanced to perform a remote VT-1 of stud insert #30 concurrent with the volumetric examination once every 10 years. The applicant also indicated that this enhancement will be implemented prior to the period of extended operation (PEO).

By letter dated January 18, 2012, the applicant responded to Request 4 of RAI 82.1.3 2a that addresses the stress analysis requirements of American Society of Mechanical Engineers (ASME) Code Section III for stud insert #30. The applicant's response indicates that the Rotolok Mechanism is designed under all conditions to meet the requirements ofthe applicable sections of ASME Code,Section III, 1971 edition with addenda through the summer of 1973. However, the applicant did not address the stress analysis results for the emergency conditions. The applicant also stated that due to the nature of the bearing deformation damage, the original stress analysis results were not considered to have changed as the critical cuts and loading did not change.

The applicant further indicated that the bearing stress on the non-deformed surfaces of the insert lugs was determined to be limiting consideration.

In response to RAI4.3-8 dated November 21,2011, the applicant stated the damage to the stud hole insert is along about 17 percent of the length of the lug and that the damage is radially inward from the location of the maximum usage factor (at the intersection of the lug and the vertical cylinder surface of the insert) such that the bending moment loading on the lugs is not as great at maximum usage factor location as at the damaged location. Therefore, the increase in stress at the maximum usage factor location would be less than 17 percent.

The applicant's responses indicate that an additional visual inspection has not been performed on stud insert #30 to confirm no additional reduction in the load bearing surfaces after the damaged stud insert was placed in service in 2007. The applicant's proposed visual inspection schedule for stud insert #30 may delay the successive visual inspections as late as 10 years after entering the PEO; therefore, the absence of additional bearing surface reduction and degradation in the stud insert cannot be confirmed prior to entering the PEO.

ENCLOSURE

- 2 The staff also needs baseline information regarding the depth of the damaged areas of the stud insert lugs and clarification as to why the applicant's response dated January 18, 2012, refers to the Unit 1 Stress Report dated October 1977, rather than Unit 2 Stress Reports, in its discussion on the stress analysis for the faulted condition.

The staff further needs to confirm whether the damaged stud insert complies with the stress limits of ASME Code Section III for the emergency conditions. In addition, the applicant's responses do not provide sufficient information to justify why the partially rolled lugs of stud insert #30 do not change the original stress analysis results that were based on the undamaged stud insert lugs.

It is not clear how the applicant determined that the increase in the stress at the maximum usage factor location would be less than 17 percent and how the applicant can determine the increase in stress at the location of maximum usage factor would not result in exceeding the ASME Code design limit of 1.0.

Request

1. The applicant's proposed schedule for successive visual inspections of stud insert

1. 30, which is once every 10 years during the PEO, appears to delay the successive visual inspections as late as 10 years after entering the PEO. Justify the adequacy of the proposed inspection schedule.

2. Describe the depth of the partially rolled areas of the stud insert lugs as the baseline information for the load bearing surface damage (5.14 in2, which is 17 percent of the total load bearing surfaces of the stud insert lugs). In addition, describe the characteristics of the transition regions of the partial rolling, which are adjacent to the undamaged surfaces of the lugs, in order to assess the degree of stress concentration due to the damage.

3. Since the damaged stud insert (#30) is in Unit 2, provide the correct Unit 2 references, instead of the Unit 1 references cited in the January 18, 2012, RAI response.

4. Justify why the continued use of the damaged stud insert ensures that the stresses on the component for emergency conditions are bounded by the stress limits of ASME Code Section III such that no additional age-related concerns are present for the period of extended operation.

5. Provide additional information to justify why the partially rolled lugs of stud insert #30 do not invalidate the original stress analysis results and original calculated maximum cumulative usage factor for the stud hole insert for the period of extended operation.

As part of the response, provide the maximum acceptable reduction in load bearing surfaces of the stud insert lugs, which complies with the stress limits in ASME Code

-3 ASME Code Section III, assuming the same type of lug damage observed in April 2007. In addition, compare the observed 17 percent reduction in the load bearing surfaces with the maximum acceptable reduction in the load bearing surfaces of the lugs.

6. Justify how it was determined that the increase in the stress at the maximum usage factor location would be less than 17 percent. Provided that this justification is acceptable, justify that the increase in stress at the location of maximum usage factor would not exceed the Code design limit of 1.0 through the period of extended operation.

Letter to D. W. Rencurrel from John W. Daily dated March 21, 2012

SUBJECT:

REQUESTS FOR ADDITIONAL INFORMATION FOR THE REVIEW OF THE SOUTH TEXAS PROJECT, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION -AGING MANAGEMENT, SET 15 (TAC NOS. ME4936 AND ME4937)

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