L-PI-11-038, Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures from the Licensing Basis Based Upon Application of Leak-Before-Break Methodology

Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures from the Licensing Basis Based Upon Application of Leak-Before-Break Methodology

ML110970101
Person / Time
Site:	Prairie Island
Issue date:	04/06/2011
From:	Davison K Xcel Energy, Northern States Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-11-038, TAC ME2976, TAC ME2977
Download: ML110970101 (7)

Text

APR 0 6 2011 L-PI-I 1-038 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Supplement to License Amendment Request to Exclude the Dvnamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodoloav - Support for Containment Particulate Monitor Response Calculation (TAC Nos. ME2976 and ME29771

References:

1. Letter from M. A. Schimmel, Northern States Power Company, a Minnesota corporation (NSPM), to Document Control Desk (Nuclear Regulatory Commission, NRC), "License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology,"

L-PI-09-134, dated December 22, 2009, ADAMS Accession Number ML100200129.

2. Letter from M. A. Schimmel (NSPM) to Document Control Desk (NRC), "Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Request for Additional Information (TAC Nos. ME2976 and ME2977)," L-PI-11-006, dated January 14, 201 1, ADAMS Accession Number M L I 10140367.

3. Letter from M. A. Schimmel (NSPM) to Document Control Desk (NRC), "Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Requests for Clarification (TAC Nos. ME2976 and ME2977),11 L-PI-11-019, dated February 23, 201 1, ADAMS Accession Number ML110550582.

1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651,388.1121

Document Control Desk Page 2 8 In Reference 1, Northern States Power Company, a Minnesota corporation (NSPM),

doing business as Xcel Energy, submitted a License Amendment Request (MR)to 1

6 apply Leak-Before-Break (LBB) methodology to certain piping at the Prairie Island d

t Nuclear Generating Plant (PINGP), in References 2 and 3, NSPM submitted additional 9

information regarding calculated response times for the containment particulate I

4 radiation monitors to detect Reactor Coolant System (RCS) leaks.

b During informal telephone discussions held on March 7 and 14, 2011, the NRC staff requested historical information and other suppoFting documentation for the leakage detection response time calculation described in References 2 and 3. The enclosure to this letter provides the requested information, consistent with additional informal discussions held with the NRC staff on March 28, 2011. NSPM submits this supplement in accordance with 10 CFR 50.90.

The supplemental information provided in this letter does not impact the conclusions of

! the Determination of No Significant Hazards Consideration or Environmental a Assessment presented in the Reference Isubmittal.

I In accordance with 10 CFR 50.91, NSPM is notifying the State of Minnesota of this LAR supplement by transmitting a copy of this letter to the designated State Official.

If there are any questions or if additional information is needed, please contact Sam Chesnutt at 651-267-7546.

Summarv of Commitments This letter contains no new commitments and no revisions to existing commitments.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on ##+a 0 6 2011 Kevin Davison Plant Manager, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC State of Minnesota

ENCLOSURE This enclosure provides supplemental information from the Northern States Power Company, a Minnesota corporation (NSPM) doing business as Xcel Energy, associated with a License Amendment Request (WR) submitted December 22,2009 (Reference 1). This LAR requested approval to use Leak-Before-Break (LBB) methodology on certain piping at the Prairie Island Nuclear Generating Plant (PINCP).

The supplemental information in this enclosure provides support for the Reactor Coolant System (RCS) leakage detection response time calculation previously described in NSPM letters dated January 14 and February 23, 201 1 (References 2 and 3). The PINGP RCS leakage detection response time calculation was discussed during informal telephone discussions on March 7, 14, and 28, 201 1.

Referenced documents are identified at the end of this Enclosure.

Support for R - I I Response Calculation In References 2 and 3, NSPM described a calculation that demonstrates the response time capabilities for containment particulate radiation monitors 1R-I Iand 2R-11 for Units 1 and 2, respectively, to detect RCS leaks. In Reference 3, NSPM stated that the calculated response time of newly installed R - I Iinstrumentation has not been tested or benchmarked to actual plant leakage events because an active leak of sufficient magnitude and duration has not been experienced since installation of the monitors.

During informal telephone discussions on March 14 and 28, 201 1, data from historical RCS leakage events using the previous R - I Imonitors was discussed. In addition, information available in open literature which supports the leakage detection response time calculation was discussed. Particular considerations included the following:

The presence of particulate daughter products of noble gas decay, Rubidium-88 (Rb-88) and Cesium-138 (Cs-138) which are included in the source term for the R - I Iresponse time calculation, in sufficient quantities for detection on R - I I radiation monitors The behavior of particulate aerosols in containment and plateout in the sample tubing, and their effect on detection by the R-I Iradiation monitors Page 1 of 5

Enclosure NSPM RCS Leakage Detection Supplemental Information Prevalence of Daughter Products The use of daughter products of noble gas decay for evaluating the capabilities of radiation monitors to detect coolant leakage from the Reactor Coolant Pressure Boundary (RCPB) has been described in industry references, as discussed belaw ISA Standard, ISA-S67.03-I982 (Reference 4)) Section 7.2.1, "Air radioparticulate and radiogas activity monitors," includes the following:

"c) Assumptions for design computations These assumptions provide a uniform design basis and shall be used to estimate the capabilities of radiation monitors to detect coolant leakage from RCPB...

2) For particulate monitors, owing to differences in source terms in PWRs, only Rb-88 which is in secular equilibrium with its parent isotope Kr-88 need be considered. ..."

An IEEE paper titled "Enhancement of Reactor Coolant Leakage Measurement Using Radiation Instrumentation," also addresses the importance of daughter products of noble gas decay in detection of RCS leakage (Reference 5). Regarding daughter products, this paper states in Section I.B, "Particulate Monitor Model Considerations":

"a. 8 8 ~Source r of 8 8 ~ b The most important consideration for particulate monitoring of RCS leakage is the 8 8 ~daughter b generated by 8 8 ~ .r..I1 Regarding plateout, Section 1.B of this paper also states:

"c. Plateout Particulates are removed from the containment atmosphere by more mechanisms than those which remove gases. In addition to radioactive decay and purge, particulates are removed by plateout on internal containment surfaces and by operation of the recirculation cleanup system or the containment cooling units. Such factors are not readily quantifiable for a complex structure like the containment.

These plateout rates have little effect on the 8 8 ~concentration b because the plateout removal constants considered are much less than the 8 8 ~decay b constant. Plateout does have an effect on the build up of the other particulates because of their much longer half-lives. This limits the build up of the particulates over longer periods."

Page 2 of 5

Enclosure NSPM RCS Leakage Detection Supplemental Information These referenced documents confirm industry experience that Rb-88 will be present in sufficient concentrations for detection, and also that particulate transport to the R-I I detector will not be significantly affected by plateout. As described in Reference 3, the NSPM calculation conservatively accounts for aerosol removal mechanisms that could affect particulate transport.

Historical Examples of R-I IResponse to RCS Leakas Several RCS leakage events at PlNGP have been identified based, in part, on increased R-I Iindications. Two leakage events described bslow demonstrate the ability of the containment radiation monitoring sampling system to transport airborne particulates to the R-I Iradiation detector, despite the effects of plateout in containment or the sample line. In addition, containment grab sample analyses from one of these events demonstrate the presence of Rb-88 and Cs-138 in sufficient concentrations for detection.

I 1995 Unit 2 Reactor Coolant Pump Flancle Leak i

I In 1995, Unit 2 experienced a leak on the 22 Reactor Coolant Pump (RCP) main flange.

R-I Icount rate and containment grab sample analysis data include the following (note that radionuclide concentration data are only provided for particulates, to identify material that would contribute to the R-1Icount rate):

August 19, 1994:

R-I Iindication 3,202 counts per minute (cpm)

Bromine-82 (Br-82) 3.72 x 10-lomicrocuries per cubic centimeter (pCilcc)

Rb-88 3.28 x 10-' pCi/cc March 22, 1995:

R-I Iindication 1,829 cpm Count rate prior to increase April 5, 1995:

R-I Iindication 10,281 cpm Br-82 3.89 x 10-lopCi/cc Cs-I 37 3.43 x lo-" pCi/cc Cs-138 3.73 x lo- pCi/cc Na-24 9.14 x lo-" pCi/cc Rb-88 7.70 x 10-' pCi/cc Y-92 4.56 x lo- pCi/cc April 24, 1995:

R-I 1 indication 14,335 cpm Br-82 4.01 x lo-" pCi/cc Cs-I 38 6.76 x 10-lopCi/cc Rb-88 8.49 x lo-' pCi/cc Page 3 of 5

Enclosure NSPM RCS Leakage Detection Supplemental Information This Unit 2 RCP main flange leak demonstrated that the particulate daughter products of noble gas decay, Rb-88 and Cs-138, were present in sufficient quantities for detection. In addition, this event demonstrated particulate transport between the containment air and the detector despite the effects of plateout in containment or the sample line.

1994 Unit 1 CRDM Canopy Seal Leak In 1994 a leak in a control rod drive mechanism (CRDM) canopy seal weld in Unit 1 was detected by the R-I Imonitor. On July 13, 1994, the R - I 1 instrument was logged as indicating 2,000 cpm. A containment air grab sample conducted on the same day indicated 6.18 x 10-lopCi/cc of containment particulate activity. These values were recorded prior to the onset of the leak and represent baseline values.

A step change in the R-I Icount rate to 5,000 cpm was noted on July 19, 1994, By July 28, 1994, the R-11 count rate had reached 10,000 cpm. A containment air grab sample conducted on July 21, 1994 indicated 3.44 XIO-' pCi/cc of containment particulate activity.

In this instance, a very small leak resulted in an increase in the containment particulate activity of over five times the baseline and resulted in an increase in R - I 1 count rate of 8,000 cpm. It is also noted that RCS total radiogas and particulate source term for this event was low, less than 4 x 1om2pCi/cc gas and 7.5 x 10" pCi/cc particulates.

This Unit 1 CRDM canopy seal leak verifies that changes in the containment airborne particulate activity level resulting from a small leak were transported to the previous R-I I radiation detector despite the effects of any plateout in containment or the sample line.

For comparison between the new and previously installed R-I Iinstrument responses, the new R - I Isensitivity in terms of cpm per pCi/cc of source activity is at least double that of the previous R-I Iinstruments. In addition, the new R-I Iuses a much lower flow rate through the sample tubing than the previous R-I I , which will further minimize any losses due to deposition in the sample line. The previous R-I Isample flow rate was approximately 10 standard cubic feet per minute (scfm), whereas the current sample flow is conservatively limited to approximately 1.4 scfm to maintain laminar flow conditions. ANSI N13.1 (Reference 6) recommends laminar flow conditions in the sample tubing to minimize interactions between entrained particulates and tubing surfaces.

Conclusion A review of historical leakage events at PlNGP and open literature supports calculation assumptions regarding the prevalence of Rb-88 and Cs-138 as contributors to R-11 Page 4 of 5

Enclosure NSPM RCS Leakage Detection Supplemental Information count rate. This review also justifies that particulate transport behhreen the containment air and the detector is consistent with calculation assumptions, References

1. Letter from M. A. Schimmel (NSPM) to Document Control Desk (NRC), "License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology," L-PI-09-134, dated December 22, 2009, ADAMS Accession Number ML100200129.

2. Letter from M. A, Schimmel (NSPM) to Document Control Desk (NRC),

"Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Request for Additional Information (TAC Nos. ME2976 and ME2977)," L-PI 006, dated January 14,201I, ADAMS Accession Number MLI 100140367.

3. Letter from M. A. Schimmel (NSPM) to Document Control Desk (NRC),

"Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Requests for Clarification (TAC Nos. ME2976 and ME2977)," L-PI-11-019, dated February 23,201 1, ADAMS Accession Number MLI 10550582,

4. Standard for Light Water Reactor Coolant Pressure Boundary Leak Detection, ISA-S67.03-1982, Instrument Society of America.

5. Enhancement of Reactor Coolant Leakage Measurement Using Radiation Instrumentation, Daniel G. Weis, PhD, PE, IEEE Transactions on Nuclear Science, Vol. 46, No. 3, June 1999, pp. 438-443.

6. Guide to Sampling Airborne Radioactive Materials in Nuclear Facilities, ANSI N13.1, American National Standards Institute, February 19, 1969.

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