ML103280398

RAI, Related to Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures from the Licensing Basis Based Upon Application of LBB Methodology

ML103280398
Person / Time
Site:	Prairie Island
Issue date:	12/14/2010
From:	Thomas Wengert Plant Licensing Branch III
To:	Schimmel M Northern States Power Co
Wengert, Thomas J, NRR/DORL, 415-4037
References
TAC ME2976, TAC ME2977
Download: ML103280398 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 December 14, 2010 Mr. Mark A. Schimmel Site Vice President Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota 1717 Wakonade Drive East Welch, MN 55089-9642 SUB~IECT: PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 REQUEST FOR ADDITIONAL INFORMATION RELATED TO REQUEST TO EXCLUDE THE DYNAMIC EFFECTS ASSOCIATED WITH CERTAIN POSTULATED PIPE RUPTURES FROM THE LICENSING BASIS BASED UPON APPLICATION OF LEAK-BEFORE-BREAK METHODOLOGY (TAC NOS.

ME2976 AND ME2977)

Dear Mr. Schimmel:

By letter to the U.S. Nuclear Regulatory Commission (NRC) dated December 22, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100200129) as supplemented by letters dated July 23,2010 (ADAMS Accession No. ML102040612), August 20, 2010 (ADAMS Accession No. ML102320535) and October 8, 2010 (ADAMS Accession No. ML102810518), Northern States Power Company, a Minnesota corporation (the licensee), doing business as Xcel Energy, submitted a request for approval to exclude certain postulated pipe ruptures from the licensing basis based upon application of the leak-before-break methodology for Prairie Island Nuclear Generating Plant, Units 1 and 2.

The NRC staff is reviewing your submittal and supplements and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with Mr. Sam Chesnutt of your staff on November 19, 2010, it was agreed that you would provide a response to this request by December 22, 2010.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources.

M. Schimmel -2 If circumstances result in the need to revise the requested response date, please contact me at (301) 415-4037.

Sincerely,

~~~r Thomas J. Wengert, Senior Project Manager Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306

Enclosure:

Request for Additional Information cc w/encl: Distribution via ListServ

REQUEST FOR ADDITIONAL INFORMATION PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 DOCKET NOS. 50-282 AND 50-306 In reviewing the Northern States Power Company, a Minnesota corporation (NSPM, the licensee), doing business as Xcel Energy, submittal dated December 22,2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100200129), as supplemented by letters dated July 23,2010 (ADAMS Accession No. ML102040612),

August 20, 2010 (ADAMS Accession No. ML102320535), and October 8, 2010 (ADAMS Accession No. ML102810518), which requested approval to exclude certain postulated pipe ruptures from the licensing basis based upon application of the leak-before-break (LBB) methodology for Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2 (Reference 1),

the U.S. Nuclear Regulatory Commission (NRC) staff has determined that additional information is needed to complete its review.

In its October 8,2010, supplement, the licensee responded to the NRC staff request for additional information (RAI) regarding the reactor coolant system (RCS) leakage detection systems at PINGP. The !\IRC staff has the following clarification questions regarding this RAI response:

1. Regulatory Guide (RG) 1.45 states that ". .. plants should use multiple, diverse and redundant detectors at various locations in the containment, as necessary, to ensure that the transport delay time of the leakage from its source to the detector (instrument location) will yield an acceptable overall response time ... " RG 1.45 suggests that the RCS leakage detection systems should have redundancy, reliability and sensitivity.

In Item 2, Enclosure 2, to the licensee's October 8, 2010, response, the licensee stated that the response time for each of the RCS leakage detection systems in Table 1-1 in the Structural Integrity Associates report in the December 22, 2009, submittal is no longer part of the LBB submittal. The licensee provided additional leakage detection information in its response to NRC question E2-2 in the October 8,2010, letter.

On page 7 of Enclosure 1 to the October 8,2010, letter, in response to NRC RAI E2-2, the licensee stated that the daily RCS inventory balance can detect a leak rate of 0.2 gallons per minute (gpm) in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and that the containment particulate radioactivity monitor (R-11) can detect a leak rate of 0.2 gpm in 53 and 280.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> for Units 1 and 2, respectively. RG 1.45 recommends a detection capability of 1 gpm in one hour. The response time for the R-11 monitor exceeds the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> criterion significantly, which brings into question its usefulness in early detection of a pipe crack. The only credible detection method is the daily RCS inventory balance. If that is the case, there appears to be no diverse detectors that can achieve the capability of 0.2 gpm in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> other than the RCS inventory balance.

a) Justify how the RCS leakage detection systems at PINGP have satisfied the redundancy, reliability and sensitivity recommended in RG 1.45.

b) Provide the number of R-11 monitors in the containment.

Enclosure

-2

2. On page 10 of the October 8, 2010 response, the licensee stated that the RCS leakage detection system is currently under the status of Operable, But Nonconforming (OBN).

The licensee further stated that it is resolving this OBN condition in accordance with the plant corrective action program. The NRC staff has reservations regarding approving an LBB application for a plant with an OBN condition on its RCS leakage detection systems.

Discuss when the OBN will be resolved for the leakage detection systems. After the OBN condition is removed, discuss whether the RCS leakage detection capability will satisfy RG 1.45, Revision 1 and in terms of the LBB analysis assumptions.

3. If the leak rate is as low as 0.2 gpm, the leakage would likely be manifested as either steam or small drops on the floor or on the outside surface of other pipes. Within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the leakage probably will have evaporated. The RCS inventory balance method is based on the measured inventory that remains in the RCS and letdown systems (i.e., primarily temperature corrected RCS volume based on pressurizer level and volume control tank level changes). This introduces limitations because the calculation is not accurate if temperatures are rapidly changing or if there is significant boration or dilution to control power. Therefore, the NRC staff believes that the RCS inventory balance would not be accurate for a few days during and after startup and for several hours after power changes. The containment radiation monitors (R-11) also may not be effective for the first few days during and after startup because the source term is low. The containment sump would provide leakage detection during this period, but it probably is not sensitive enough to detect a 0.2 gpm leak in part because of leakage evaporation.

a) In light of the above discussion, justify your conclusion that the RCS leakage detection systems have a detection capability of 0.2 gpm in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

b) Explain how a substantial margin to the postulated leakage flaw would be maintained considering uncertainties in the release of water and radioactivity from the postulated crack, the potential for the crack to be plugged by particulate debris over time, the response time and accuracy of the leakage detection method, the method of operator identification that the leakage threshold has been exceeded, and the rate of crack growth during the period required for detection.

4. Concerning the licensee's October 8,2010, response to E1-2 Page 7 (Page 1 of 12 of Enclosure 1 with question repeated):

The licensee stated that when LBB was applied to the RCS loop piping in an LBB evaluation in 1986, a criterion of 1 gallon per minute (gprn) in one hour for RCS leakage was used for the leak detection system capability. However, for the current submittal, the licensee used a leakage detection limit of 0.2 gpm. The use of O. 2 gpm in the proposed LBB evaluation is an improvement in the leakage detection capability from the original licensing basis of 1 gpm. However, discuss whether the design basis for the RCS leak detection system needs to be changed in the Updated Final Safety Analysis Report and plant technical specifications via a license amendment process. If not, provide justification.

The requirements regarding Technical Specification (TS) content are provided in 10 CFR 50.36(c)(2), but the licensee does not address these requirements in its response. The

-3 licensee cites Generic Letter (GL) 84-04 as not specifying T8 content. However, the GL states that having leak detection capability consistent with RG 1.45 guidelines maintains a large margin against unstable crack extension, and RG 1.45 calls for T8 addressing the availability of leak detection instruments and limits on unidentified leakage. The licensee has identified a leak detection capability more sensitive than that provided in RG 1.45 and considered in development of the current Prairie Island T8, so the licensee's reference to GL 84-04 and the bases of the current Prairie Island T8 does not adequately justify the lack of a proposed revision to the T8s. Therefore, the NRC staff requests the licensee clarify its response to address applicable regulations and guidance.

M. Schimmel -2 If circumstances result in the need to revise the requested response date, please contact me at (301) 415-4037.

Sincerely, IRAJ Thomas J. Wengert, Senior Project Manager Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306

Enclosure:

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