ML20198G555
| ML20198G555 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/17/1998 |
| From: | Richard Anderson SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9812290102 | |
| Download: ML20198G555 (4) | |
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Northern states Power Company 1717 Wakonade Dr. E.
Welch, MN 55089 Telephone 612-388-1121 December 17,1998 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Response to November 2,1998, Request for Additional Information on Proposed Revision to Main Steam Line Break Methodology dated June 26,1997 The information in the attachment to this letter is provided in response to an NRC staff request made in a teleconference on November 2,1998, for additional information related to our proposed revision to the Main Steam Line Break Methodology dated June 26,1997.
In this submittal we have made no new NRC commitments. If you have any questions related to this matter, please contact Jack Leveille at 651-388-1121, Ext. 4142.
Roger O Anderson Director Nuclear Energy Engineering
Attachment:
Response to November 2,1998, Request for Additional Information on Proposed Revision to Main Steam Line Break Methodology dated June 26,1997 c:
Regional Administrator-lil, NRC l \\ ;~O \\
NRR Project Manager, NRC 3
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Senior Resident inspector, NRC Kris Sanda, State of Minnesota J E Silberg 9812290103 981217 PDR ADOCK 05000282, P
PDR_
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i Response to November 2,1998, Request for Additional Information on Proposed Revision to Main Steam Line Break Methodology dated June 26,1997 i
Question "Give a detailedjustification why the WCAP-8822 analysis, as applied to the modeling ofentrainment during a MSLB, is applicable to the Prairie Island design. Discuss any adjustments made to the entrainmentprojiles usedfrom the WCAP-8822 in order to ensure their validityfor the two loop design. "
Summary This response provides the justification for the applicability of the entrainment curves in WCAP-8822 are applicable to the 2-loop design at Prairie Island. NSP has interpreted the question as " justify why the entrainment curves in WCA.P-8822 are applicable to the 2-loop design at Prairie Island when they were based in part on a 3/4 loop design". This interpretation is based on a phone conversation with the NRC reviewer.
l The use of these entrainment curves provides a more rigorous method of modeling entrainment than what 2
was used in our current design basis MSLB containment response analysis. The current analysis, which was approved as part of Prairie Island's Final Safety Analysis Report, credits entrainment as part of the justification for reduction of the mass and energy (M&E) release by 15%. Modeling of entrainment more explicitly (as is done in NSPNAD-97002-P Rev.1) removes some of the excess conservatism that is in this current MSLB analysis. In Generic Letter 85-16 "lligh Boron Concentrations", the NRC indicated a willingness to consider a relaxation of excess conservatism in MSLB analyses, so that it may be possible to remove the boron injection tanks. It is the intention of NSP to use the methods described in NSPNAD-97002 P Rev.1 (when approved) to perform the necessary analyses to remove the Boric Acid Storage Tanks (BAST) from the Safety Injection line flow path.
Response
The methodology described in WCAP-8822 consists of three parts. The first part which is described in Section 2 relates to 6e calculation of the entrainment profiles as shown in Figures 2.4-2 through 2.4-5 which are based on TRANSFLO calculations. The second part as described in Section 3 relates to the NSSS transient response as calculated with the MARVEL code. The third part relates to the calculation of the mass and energy release to the Containment for specific plants as described in Sections 4 and 6 (App.A).
The NSP MSLB methodology, as documented in NSPNAD-97002-P, is similar in nature to the approach in WCAP-8822, however the NSSS transient response is computed with the DYNODE-P code and utilizes the Prairie Island specific plant design and operational conditions along with entrainment profiles from the above referenced figures. Thus, the only aspect of the WCAP-8822 analysis that pertains to the NSP MSLB methodology is the usage of the entrainment profiles.
As discussed in Section 2 of WCAP-8822, the entrainment during a MSLB is dependent on the following parameters: break size and location, SG design, initial conditions, feedwater flow assumptions, Primary Coolant assumptions, and SG mass inventory. The following discussions demonstrate that the values of these parameters that have been chosen to generate the entrainment profiles in the referenced figures are applicable to the Prairie Island design and the methodology described in NSPNAD-97002-P.
c, NORTHERN STATES POWER COMPANY Dec mb;r 17,1998 Paga 2 of 3
. Break si:e and location The four break sizes and locations (break spectrum), as described in Section 2.1 of WCAP-8822, are the same ones as used in the NSPNAD-97002-P methodology.
Steam GeneratorDesign Although the emphasis of the analysis in WCAP-8822, Section 2.2.1 is for Model D SGs, the studies also include plants with Model 51 SGs - which is the Prairie Island design. The results of the TRANSFLO analyses shown in Figures 2.2.1-1 and 2.2.1-2 of WCAP-8822 demonstrate that the Model D entrainment results, which are shown in Figures 2.4-2 through 2.4-5 of WCAP-8822, are conservative for the Model 51 design. Thus the use of the Model D entrainment profiles introduces additional conservatism for the application to the Prairie Island design. No credit has been taken for this added conservatism in the methodology of NSPNAD-97002-P. Thus, the profiles are applicable and conservative for application to the SG design at Prairie Island.
Initial Conditions As described in Section 2.2.2 of WCAP-8822, the four SG initial conditions (0%,30%,70%, and 102%
of nominal power) are the same ones used in the NSPNAD-97002-P methodology with the exception that the Prairie Island SG primary and secondary initial conditions used in the analysis correspond to the 5
actual plant design and operating conditions. The primary differences in initial condition are due to the difference between the Model D and Model 51 steam generator designs. These differences have been factored into the comparative analyses between the Model D and Model 51 results as shown in Section 2.2.1 of WCAP-8822. The attached table 1 provides the numeric comparisons between the initial conditions presented in table 2.2.2-1 of WCAP-8822 (which are the initial conditions used in generating the quality versus tirne plots in figures 2.4-2 through 2.4-5 of WCAP-8822) and the limiting containment pressure case in NSPNAD-97002-P Rev.1. This table illustrates that the initial SG conditions assumed in 3
NSPNAD-97002-P Rev. I are very close to those used in generating the quality versus time plots in WCAP-8822.
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Feedwater Gowassumptions The feedwt er assuinptions discussed in WCAP-8822, Section 2.2.3 have been made to minimize the feedwater flow in order to minimize the entrainment; whereas the NSPNAD-97002-P methodology maximizes the feedwater flow to maximize the mass and energy release to the containment, see Table 1 below. Thus, the NSPNAD-97002-P methodology conservatively assumes maximum feedwater for M&E release while utilizing the minimum feedwater entrainment profiles. Although these are contradictory assumptions, they are consistent with the WCAP-8822 methodology as discussed in Section 3.1.5 of WCAP-8822 and are conservati"e.
Primary Coolant assumptions The Primary Coolant assumptions as discussed in Section 2.2.4 of WCAP-8822 are applicable to the Prairie Island design and the methodology of NSPNAD-97002-P, since the primary system as calculated by DYNODE-P behaves in the manner as described in that section. It is important that the SG secondary side response as calculated by TRANSFLO and NSSS system code (MARVEL for the WCAP-8822 and DYNODE-P for the NSPNAD-97002-P methodologies) be self consistent as discussed in Section 3.2.1 of WCAP-8822. It is not possible for NSP to make this type of comparison for the NSPNAD-97002-P methodology, since the TRANSFLO results are not available. Ilowever comparisons of the Primary
e Attachment i NORTHERN STATES POWER COMPANY Dec;mber 17,1998 Pags 3 of 3 temperature responses for equivalent cases between 3/4 loop (as analyzed in WCAP-8822) plants and the Prairie Island plant, as modeled using the NSPNAD-97002-P methodology, would provide an indirect validation of self consistency. This type of comparison is important, since the Primary temperature response is a key input to TRANSFLO from MARVEL to determine the heat transfer from the Primary to Secondary side. NSP has provided the NRC staff with this information (in a letter from NSP to the NRC dated October 16,1998) for the case of a 1.4 ft break at liFP conditions to be used in their evaluation.
2 SG mass inventory The SG mass inventory assumption discussed in Section 2.2.5 of WCAP-8822 has been made to minimize the inventory to minimize entrainment while the NSPNAD-97002-P methodology maximizes the inventory to maximize the mass and energy releases to containment, see table 1 below. Thus, the NSPNAD-97002-P methodology conservatively assumes maximum SG mass inventory for M&E release while utilizing the minimum SG mass inventory entrainment profiles. Although these are contradictory assumptions, they are consistent with the WCAP-8822 methodology as discussed in Section 3.1.6 of WCAP-8822 and are conservative.
Adjustments to Entrainment Profiles No adjustments were made, nor needed, to the entrainment profiles to ensure their validity for the Prairie Island two loop desir '.owever, there was an adjustment made consistent with Section 3.2.2 in WCAP-8822. An adjustment was made to the entrainment profiles in Figures 2.4-2 through 2.4-5; whereby, an addition of 0.1 to the effluent quality was included for all time points. This adjustment is consistent with the manner in which the profiles are input to MARVEL as described in Section 3.2.2 of WCAP-ES22 which provides added conservatism and eliminates the sensitivity of the results to possible inaccuracies in the TRANSFLO steam generator and steam separator modeling. This adjustment ensures that the entrainment is treated in an identical manner to the WCAP-8822 methodology with respect to the coupling between the Primary and Secondary side responses.
Table 1 0% Power Table 2.2.2-1 DNP case WCAP-8822 c960081 Core Power (Mwt) 0 8+
Primary Coolant AT( F) 0 0.6 Circulation Ratio Steam Pressure (psia) 1106 911*
Total Fluid Mass (lbm) 165,600 187,887 Water Mass (lbm) 159,410 181,930 Initial Feedwater Flow (lbm/sec) 0 10+
Note that DNP case c960081 includes decay heat. Thus, there is an initial heat load on the sG.