ML19312D480

LER 79-151/01X-1:on 791105,insp Per IE Bulletin 79-14 Showed Incorrect Amplified Response Spectrum Curve Was Used in Pipe Stress Analysis & Other Seismic Curves Were Used in Wrong Input Format.Cause Unknown

ML19312D480
Person / Time
Site:	North Anna
Issue date:	03/21/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19312D477	List: ML19312D476 ML19312D480 ML19312D482
References
IEB-79-14, LER-79-151-01X, LER-79-151-1X, NUDOCS 8003240468
Download: ML19312D480 (3)

Text

, NRC FQAM 386 U. S. NUCLE A"3 KEGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK: l l l l l lh 0

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O 4 l had been used in the wrong input fo rma t. During a stress review by Stone & Webster I o 5 l of the ARS problems, a further area of concern was discovered in the spreading of I D e l adjacent peaks for a limited number of ARS curves used in pipe stress analysis for i O 7 l North Anna Unit 1. The health and safety of the general public were not affected 1 0 s l by these events. Reportable pursuant to T.S. 6.9.1.8.h. I 7 89 E CO E $ BC E COMPONENT CODE SUB D'E SU t O 9 l WI Gl@ W@ W@ lP lI lP lE lX lX l@ y@ y@

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44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS 27 i o l '1he discrepancies were discovered as a result of review of valve weights in conjunc- I

, , l tion with the as-built inspection required by IE Bulletin 79-14. The cause of these I g'l discrepancies is not known at this time. An investigation of the Unit 1 ARS problems lias

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ItPDATE REPORT - PREVIOUS REPORT DATE 11-16-79 j i

Virginia l Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 2

. Docket NoJ S0-338 Report No. LER 79-151/01X-0 Description of Event On November 5,1979, with the unit in a refueling shutdown mode, Vepco was informed that during a review of valve weights in conjunction with-the as-built review of IE Bulletin 79-14, it was discovered that an in-correcc amplified response spectrum curve had been used in a pipe stress .

' analysis and that other seismic curves had used the wrong input format.

During a stress review of these ARS problems, a further area of concern was discovered ~ on March 7,1980 in the spreading of adjacent peaks for a limited number of ARS curves used in pipe stress analysis for North Anna Unit 1. When performing SHOCK III a eismic calculations the simul-taneous occurrence of the following four conditions resulted in the lesser spread peak.taking precedence over an overlapping high peak:

1. He ARS curve was not spread prior to being input to SHOCK III and the program option to perform the spreading internal to the program was selected.

2. He spreading zone of two or more adjacent peaks overlapped.

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3. Of the overlapped peaks, the minor peak (lower g-va1ue) precedes, in period, the major peak (higher g-value).

4. One or more significant modes falls within the overlap zone.

- Probable Consequences of Occurrence ,

The use of ~ this incorrect seismic input and the use of the faulty SHOCK III Computer Program could result in possible nonconservative pipe stresses, i .

pipe support loads, and equipment loads in certain safety-related systems in the main ' steam valve house, auxiliary building, service water pumphouse,

- fuel building and auxiliary feedwater pumphouse. The systems affected include main steam, auxiliary feedwater. service water, safety injection, quench spray, '

boron recovery, fuel pool cooling, component cooling, refueling purification, and containment hogger. Only portions of these systems are affected. No

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- portions of these systems within containment or. the reactor coolant system pressure boundary are affected. The health and safety of the general public were notDaffected by these events. He same pipe stress calculations were used on Unit 2 and the systems are similarly af fected. We ARS spreading problem, however, only applies to Unit I and does not affect Unit 2 piping.

Cause of Occurrence The cause of these discrepancies is unknown at this time.

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Attachment:

Page 2 of 2 Immediate Corrective Action An investigation of the ARS problems was performed to determine the extent of the discrepancies and the modifications required to correct them. Review of the ARS spreading problem revealed that all but two piping areas are unaffected, the ' two areas of concern being the main steam bypass piping around the non-return valves and the main steam decay heat release lines. Rerun of the pipe stress evaluation for the main steam bypass line shows that the pipe stresses exceed the normal condition code allowables but are within faulted allowables. As a result, the failure of main steam bypass piping is not predicted by the calculations. The review of supports for the main steam bypass line indicates they meet design limits except for two snubbers on each of the loops. These snubbers exceed normal design load, but are within the faulted allowables.

Therefore, the line will remain integral and adequately supported for a seismic event.

The stress on the main steam decay heat release lines exceeds normal design limits but meets faulted allowables. When utilizing actual material proper-ties of the pipe, normal design limits are met. Therefore, the line will

. remain integral with no yielding. The pipe supports have been reviewed and met original design allowables.

Scheduled Corrective Action Because it has been determined that the original design criteria was not k_ - fully satisfied by the installed restraint arrangement, system modifications will be made as determined necessary. The s".pport modifications and new support designs resulting from the ARS spreading problem are expected to be completed by March 31, 1980.

Actions Taken to Prevent Recurrence The cause of. the SHOCK III seismic calculation inconsistencies has been rectified by manually spreading the curves 15% prior to used in the analysis. Procedures have been established to prevent a similar occurrence in any further SHOCK III analysis.

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