ML19273B213
| ML19273B213 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 03/13/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 7904030134 | |
| Download: ML19273B213 (6) | |
Text
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s UNITED SiaTES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
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VIRGINIA ELECTRIC AND POWER COMPANY
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Docket No. 50-281 (SURRY POWER STATION, UNIT 2)
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ORDER TO SHOW CAUSE I.
The Virginia Electric and Power Company (the licensee) is the holder of Facility Operating License No. DPR-37 which authorizes operation of the Surry Power Station, Unit 2 (the facility) at power levels up to 2441 megawatts thermal (rated power).
The facility, which is located at the Licensee's site in Surry County, Virginia, is a pressurized water reactor used for the commercial generation of electricity.
The facility is presently shut down for steam generator repairs.
II.
In the course of evaluation of certain piping design deficiencies in connection with the Beaver Valley Power Station, Docket 50-334, signifi-cant discrepancies were observed between the original piping analysis computer code used to analyze earthquake loads by Stone and Webster, the architect-engineer for that facility, and a currently acceptable computer code developed for this purpose.
In the course of a meeting on March 8,1979 to discuss these natters, the Beaver Valley Licensee informed the NRC staff that the difference in predicted piping stresses between the two computer codes is attributable to the fact that the piping analysis code used for a nu.,ber of piping 790403 013c[
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. systems in that facility uses an algebraic summation of the loads predicted separately by the computer code for both the horizontal component and for the vertical component of seismic events.
This incorrect treatment of such loads was not recognized at that time.
Such loads should not be algebraically added (with predicted loads in the negative direction offsetting predicted loads in the positive direction) unless far more complex time-history analyses are performed.
Rather, to properly account for the effects of earthquakes, as required by General Design Criterion 2 for systems important to safety, such loads should be combined absolutely or, as is the case in the newer codes, using techniques such as the square root of the sum of the squares.
This conforms to current industry practice.
The inappropriate analytical treatment of load combinations discussed above becomes significant for piping runs in which the horizontal seismic component can have both horizontal and vertical components on piping systems, and the vertical seismic component also has both horizontal and vertical components.
It is in these runs that the predicted earthquake loads may differ significantly.
Although the greatest differences in predicted loads would tend to be limited to localized stresses in pipe supports and restraints or in weld attachmer.ts to pipes, there could be a substantial number of areas of high s+.ress in piping, as well as a number of areas in which there is potential for. damage to adjacent restraints or supports, which could
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. have significant adverse effects on the ability of the piping system to withstand seismic events.
The NRC staff communicated with Stone and Webster, who was alsc the architect-engineer for the Surry facility, to ascertain whether the conditions identified for Beaver Valley were also applicable to Su r ry.
We were informed that since the same revision of the same computer code ~ had been used for both Beaver Valley and Surry, a similar problem may be anticipated.
The NRC informed the' Licensee these facts by phone on Friday, March 9 and on Sunday, Farch 11, 1979.
In order to ascertain the specific systems at Beaver Valley that could be potentially affected by this error, me.abers of the NRC staff op March 10,11 and 12 went to the offices of Stone and Webster, the architect-engineer of both Beaver Valley and Surry to review detailed designs and computations for some of the piping systems of principal potential Concurrently, on March 9,1979 the Beaver Valley Licensee suspended concern.
power operation of that facility.
Based on this more detailed review, the NRC staff has conc'luded that until full reanalysis of all potentially affected piping systems important to safety has been conpleted with a piping analysis computer code which does not contain the algebraic summation error, the potential for serious adverse effects at the Surry facility exists in the event of an earthquake and could be sufficiently widespread that the basic defense in depth provided by redundant safety systems may be compromised.
. In view of the safety significance of this matter as discussed above, the Director of the Office of Nuclear Reactor Regulation has concluded that the public health and safety requires that the present suspension of operation of the facility should be continued: (1) until such time as the piping systems for all affected safety systems have been reanalyzed for earthquake events to demonstrate conformance with General Design Criterion 2 using a piping analysis computer code which does not contain the error discussed above, and (2) if such reanalysis indicates that there are components which deviate from applicable ASME Code requirements, until such deviations are rectified.
III.
Accordingly, pursuant to the Atomic Energy Act of 1954, as amended, and the Commission's Rules and Regulations in 10 CFR Parts 2 and 50, IT IS HEREBY ORDERED THAT the Licensee show cause, in the manner hereinafter
- previded, (1)
Why the Licensee should not reanalyze the facility piping systems for seismic loads on all potentially affected safety systems using an appropriate piping analysis computer code which does not combine loads algebraically;
(2)
Why the Licensee should not make any nodifications to the facility piping systems indicated by such reanalysis to be necessary; and (3)
Why facility operation should not be suspended pending such reanalysis and completion of any required modifications.
In view of the importance to safety of this matter, as describcd hereir, the Director of the Office of Nuclear Reactor Regulation has determined that the public health and safety or interest require that this action be effective immediately, pending further Order of the Commission.
Ac cordingly, the facility shall remain shutdown until further Order of the Commission.
The Licensee may,.within twenty days of the date of this Order, file a written answer to this Order under oath or affirmation.
Within the same time, the Licensee or any interested person may request a hearing.
If a hearing is requested, the Commission will issue an Order designating the time and place for hearing.
Upon failure of the Licensee to file an answer within the time specified, the Director, Office of Nuclear Reactor Regulation wil'1, without further notice, issue an order suspending further activities under Operating License DPR-37.
. In the event a hearing is requested, the issues to be considered at such hearing shall be:
Whether operation under Facility License No. DPR-37 should be suspended until (1) the piping systems for all affected safety systems are reanalyzed for earthquake events using an dppropriate piping analysis Computer Code Which does not combine seismic loads algebraically, and until (2) any modi-fications required to restore the system to conformance with applicable ASME Code requirements are completed.
FOR THE NUCLEAR REGULATORY COMMISSION f kY$
Harold R. Denton, Director Office of Nuclear Reactor Regulation Dated at Bethesa, Maryland this 13th day of March,1979.
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