ML19273B214
| ML19273B214 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/13/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 7904030136 | |
| Download: ML19273B214 (6) | |
Text
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NRC PUBLIC DOCUMENT ROOM UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
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MAINE YANKEE ATOMIC POWER COMPANY
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Docket No. 50-309 (Maine Yankee Atomic Power Station)
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ORDER TO SHOW CAUSE I.
The Maine Yankee Atomic Power Company (the licensee) is the holder of Facility Operating License No. DPR-36 which authorizes operation of the Maine Yankee Atomic Power Station, (the facility) at power levels up to 2630 megawatts thermal (rated power).
The facility, waich is located at the Licensee's site in Lincoln County, Maine, is a pressurized water reactor used for the commercial generation of electricity.
II.
In the course of evaluation of certain piping design deficiencies in connestion 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 ourse of a meeting on March 8,1979 to discuss these matters, the Beaver Valley Licensee informed the NRC staff that the. difference in predicted piping stresses between the two computer ccdes is attributable to the fact that the piping analysis code used fo, a number of piping 70040301%:
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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 algebr;ically added (with predicted loads in the negative direction offsetting predicted loads in the positive direction) unless far more complex time-history analyses are perfonned.
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 confonns 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 woald tend to be limited 'o localized stresses in pipe supports and restraints or in weld attachments to pipes, there could be a substantial number of areas of high stress in piping, as well as a number of areas in which there is potential for damage to adjacent restraints or supports, which could
, 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 also the architect-engineer for the Maine Yankee facility, to ascertain whether the conditions identified for Beaver Valley were also applicable to Maine Yankee.
We wore infomed that since the same revision of the same computer code had been used for both Beaver Valley and Maine Yankee, a simil ar problem may be anticipated. The NRC infomed the Licensee of these facts by phone on Friday, March 9 and on Sunday, March 11, 1979.
In order to ascertain the specific systems at Beaver Valley that could be potentially af,fected by this error, members of the NRC staff on March 10,11 and 12 went to the offices of Stone and Webster, the architect-engineer of both Beaver Valley a.id Maine Yankee to review detailed designs
- M 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 concluded that until full reanalysis of all potentially affected piping systems important to safety has been completed with a piping analysis computer code which does not contain the algebraic summation error, the potential for serious adverse effects at the Maine Yankee 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 natter as discussed above, the Director of the Office of Nuclear Reactor Regulation has concluJed that the public health and safety requires that an orderly suspension of operation of the facility should be effected immediately and that, in order to provide adequate protection of public health and safety the facility operation should be suspended:
(1) until such time as the piping systems for all affected safety systems have been recnalyzed ' or earthquake events to demonstrate conformance with General Design Criterion 2 using a piping analysis computer code which does nor contain the error discussed above, and (2) if such reanalysis indicates that there are conponents which deviate from applicable ASME Code requirements, until such deviations are rectified.
III.
Accordingly, pursuant to the Atomic Energy Act o' 1954, as amended, and the Commission's Rules and Regulations in 10 CFR Parts 2 and 50, IT IS HERELY ORDERED THAT the Licensee show cause, in the manner hereinafter
- provided, (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 ccde which does not combine loads algebraically
, (2) Why the Licensee should not make any modifications 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 modi fications.
In view of the importance to safety of this matter, as described herein, the Director of the Office of Nuclear Reactor Regulation has detennined that the public health and safety or interest require that this action be effective immediately, pending further Order of the Connission. Accordingly, within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of the receipt of this Order, the facility shall be placed in cold shutdown condition, and shall remain in such mode 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 en 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 will, without further notice, issue an crder suspending further activities under Operating License DPR-36.
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.., In the event a hearing is requested, the issues to be considered at such hearing shall be:
Whether operation under Facility License fio. OPR-36 should be suspended until (1) the piping systems for all affected safety systems are reanalyzed for earthquake events using an appropriate piping analysis computer code which does not combine seismic leads 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 ph,* s2L Harold R. Denton, Director Office of Nuclear Reactor Regulation Dated at Bethesa, Maryland this 13th day of March,1979.
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