ML19257A316

Submits Addl Info Re 791207 Rept of Nonconservative Calculation of Seismic Response Spectra.Analysis of Switchover to New Computer Code Revealed Error Calculating Inertial Forces.Caused by B&W Error.Mod Underway

ML19257A316
Person / Time
Site:	North Anna
Issue date:	12/12/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
REF-PT21-79-183-000 NUDOCS 8001030722
Download: ML19257A316 (3)

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VIRGANI A El.ECTRIC AND POW ER COMP ANY, RICHMONQ, VIRGINI A 23261 I"' id .o

. yqcember 12, 1979 Mr. James P. O'Reilly, Director Serial No. 1119 Office of Inspection & Enforcement PSE&C/HJFjr/CES:mac: wang U.S. Nuclear Regulatory Commission Region II Docket Nos. 50-404 101 Marietta Street, Suite 3100 50 405 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

On December 7, 1979 a report was made under the provisions of 10CFR50.55(e) concerning the Nonconservative Calculation of Seismic Resoonse Spectra for North Anna Units 3 and 4.

In accordance with the reporting requirements of 10CFR21, the following information is submitted:

A. Name and address of reporting individual:

Mr. E. A. Baum, Executive Manager Licensing and Quality Assurance Virginia Electric and Power Company P. O. Box 26666 Richmond, Virginia 23261 B. Facility, activity and/or component affected:

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Seismic Response Spectra for the NSSS and Connecting Piping (Including Supports and Restraints)

North Anna Power Station, Units 3 and 4 C. Name of firm constructing the facility.or supplying the component, activity or service:

Babcock & Wilcox Company P. O. Box 1260 Lynchburg, Virginia 24505 D. Description of defect, deficiency, or failure to comply:

, In the past, the ST3DS, LUMS and RESPECT computer codes have been

- used by B&W to calculate seismic response spectra as input to their customers' A/E for piping analyses. The latest reanalysis submitted for use on North Anna Units 3 and 4, however, used the STALUM and RESPECT computer codes. STALUM was developed by B&W's Technical Staff to replace ST3DS and LUMS.

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B&W has informed us that the STALUM code has been found to have an error in the way the signs of the inertial forces were calculated.

Essentially, through an inappropriate application of the SRSS method of combining forces, all of the signs on the forces were " lost";

i.e., forced to be positive. Since the calculation of response spectra involves a time history analysis, wherein the signs of inertial forces, as well as their magnitude, are important, this error has affected some of the response spectra submitted for use on North Anna Units 3 and 4.

It has also been determined that this error has had no effect on any of B&W's seismic loading analyses since the response spectra method rather than time history method is used.

E. Date of determination of reportai,ility:

December 7, 1979 F. Similar components, activities, or services:

None G. Corrective action which has been, is being or will be taken, the individual responsible and the length of time to complete the action:

The A/E has been informed of the error and instructed not to use

,previously submitted B&W spectra for design. B&W has modified the inertial force calculation in STALUM to preserve the sign of the inertial force thereby making the inertial force output accurate for use in time history analyses. B&W has generated revised seismic response spectra for North Anna Units 3 & 4 and is in the final process of incorporating this data into a specification revision.

H. Other information:

None Since no other actions are required t'o correct the problem described in Section D of this report, we consider this to be the final report under the provisions of 10CFR50.55(e).

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Should you require further information, please contact this office.

.Very truly yours,

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' am C. Brown, Jr.

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Senior Vice President - Power' Station Engineering and Construction cc: Director,, Office of Inspection and Enforcement (3)

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