ML20217G858
| ML20217G858 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 07/29/1997 |
| From: | Hill W NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M96156, NUDOCS 9708080076 | |
| Download: ML20217G858 (2) | |
Text
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Northem States Power Company 4
Monticello Nuclear Generating Plant 2807 West Hwy 75 Monticello. Minnesota 5f'O 9637 July 29,1997 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Commitments Associated with Structural Design of ECCS Suction Strainers (TAC No M96156)
Telephone conference calls were held between the Staff and NSP on July 15,1997 and July 25,1997.
The intent of these calls was to discuss ECCS suction strainer structural design issues resulting from a recent NRC audit of the MNGP strainer design. The Staff concluded that the structurcil design of the ECCS suction strainers was adequate. Two technicalissues were discussed during these calls: 1) the application of hydrodynariiic mass coefficient, and 2) the adequacy of the stress analyses for the ECCS strainer design modification at MNGP.
In the design of the MNGP strainers, the hydrodynamic mass coefficient was derived from test data for a similar strainer and from the use of added factors to account for, among other things, extrapolation of the data to the MNGP strainers. These factors were conservatively applied. After discussions with the Staff, NSP has determined that it is prudent to verify these assumptions by testing a full-scale strainer. The goal of this testing will be to determine an empirical hydrodynamic mass coefficient that is independent of extrapolation and engineering judgment. The app!! cable commitment is described in (1) below, in regard to stress analyses, Staff informed NSP that the stress analyses for the affected torus components were adequate. After discussions with the Staff, NSP has determined that it is prudent to conduct additional analyses in order to refine the level of detail of the existing analytical models to include j
the local effects of strainer loading. These additional analyses will use data from the full-scale test;ng.
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The analyres will incorporate the reactions due to the strainer modifications into revised models and will jg quantify the resulting stresses at affected components in accordance with the Mark I program. The applicable commitment is described in (2) below.
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This letter contains the following new NRC commitments.
(1) Prior to startup from the ne::t scheduled refueling outage, NSP commits to conduct a test on a full-scale strainer to determine the hydrodynamic mass coefficient for the acceleration drag volume. The testing will be designed to determine an empirical value of the hydrodynamic mass coefficient that is not derived from extrapolation or engineering judgment. The test results will be reported to the Staff.
(2) Within 18 months of startup from the current maintenance outage, NSP commits to conduct additional analyses in order to refine the level of detail in the stress models. These additional analyses will use data from the full-scale testing. The analyses will incorporate the reactions due to the strainer modifications into revised models and will quantify the resulting stresses at affected components in accordance with the Mark I program.
I Please contact Joel Beres, Licensing Engineer, at (612) 295-1436 if you require further information.
1 4Ma~yh William J. Hill Plant Manager Monticello Nuclear Generating Plant c:
Regional Administrator-111, NRC NRR Project Manager, NRC Sr. Resident inspector, NRC State of Minnesota, Attn: Kris Sanda J. Silberg, Esq.
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