ML20030D457
| ML20030D457 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 08/21/1981 |
| From: | Spencer W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, 511, NUDOCS 8109010419 | |
| Download: ML20030D457 (2) | |
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' August 21, 1981 N#
Mr. James P. O'Reilly, Director Serial No. 311 Office of Inspection & Enforcement PSE&C/WBR:bw
'J.S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Docket No. 50-404 Atlanta, Georgia 30303
Dear Mr. O'Reilly:
On July 24, 1981, a report was made under the provisions of 10CFR50.55(e) concerning the nonconservative calculation of seismic loads on the NSS equipment and supports.
f&W cses various mathematical models to generate seismic loads for NSS components and its supports and internals. Among them, the Loop Mathematical Model and Reactor Vessel Isolated Model take into consideration a dynamic coupling of the building internal structure with the NSS.
The Reactor Vessel Isolated Model, which is used for the calculation of loads on the reactor vessel internals, fuel and control rod drives, uses a full skewed representation of the building internal structure.
In the past, however, the Loop Mathematical Model from which seismic loads on NSS pressure retaining components and their supports were calculated, used a NSS half loop and a half wall (containment internal structure) representation.
The half wall was based on a symmetric approximation of the containment internal structure.
Since the containment internal structure is actually skewed and has mass and shear center eccentricity, a study was performed to investigate the imract of the skewed containment internal structure on NSS equipment and support loadings. For the study, a simplified full loop model of the NSS was used in conjunction with skewed and symmetric representations of the internal structure.
Corresponding NSS support loads from both representations were compared. Most loads for the symmetric representation were higher than the loads for the skewed representation ar.d thus were conservative.
However, in a few cases, the loads for the skewed representat'on were higher, by as much as 25%.
Based 0.1 this study, B&W will continue to use a NSS half loop and a symmetric half wall representation in the Loop Mathematical Model for calculating seismic loads; howt/er, all loads will be multiplied by a 1.25 factor to account for the eccentricity of the containment internal structure.
Since the Reactor Vessel Isolated Model already uses a full skewed internal structure representation, no change to this model, or any results from it, are necessary.
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IfD 8109010419 810822
{DRADOCK 05000404 PDR
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Mr.
'Reilly sneer No. 2
. VIRGINIA ELECT 9tC AND POWER COMPANY TO a
i We consider this to be both a 30-day and final report under the provisions of 10CFR50.55(e). Should you require additional information, please contact this office.
Very trul yours, 6
W.
Spencer Vice Presi ent - Power Station Engineering and Construction Services cc: Mr. Robert L. Tedesco i
Division of Licensing I
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