ML20203N940

Nuclear Safety Review Staff Investigation Rept I-86-131-SQN, Employee Concern 00-85-005-008, Seismic Supports Not Designed Properly Because They Are Rigid, on 850210-28

ML20203N940
Person / Time
Site:	Sequoyah
Issue date:	03/06/1986
From:	Kincaid J, Mashburn J, Stevens W TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML20203N908	List: ML20203N905 ML20203N911 ML20203N922 ML20203N940 ML20203N950 ML20203N964 ML20203N975 ML20203N986
References
I-86-131-SQN, NUDOCS 8605060231
Download: ML20203N940 (4)

Text

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TENNESSEE VALLEY AUTHORITY NUCLEAR SAFETY REVIEW STAFF NSRS INVESTIGATION REPORT No. I-86-131-SQN EMPLOYEE CONCERN: 00-85-005-008

SUBJECT:

SEISMIC SUPPORTS ARE NOT DESIGNED PROPERLY BECAUSE THEY ARE RIGID DATES OF INVESTIGATION: FEBRUARY 10-28, 1985 INVESTIGATOR: N

3. H. KINCATD DATE REVIEWED BY: h

. W. MAS!! BURN DATE APPROVED BY: [ _3/6 /JG W. D. STEVENS DATE B605060231 860502 PDR ADOCK 05000327 P PDR

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S I. BACKGROUND A Nuclear Safety Review Staff (NSRS) investigation was conducted to determine the validity of an expressed employee concern received by the Quality Technology company (QTC)/ Employee Response Team (ERT). The concern of record, as summarized on the Employee Concern Assignment Request Form from QTC and identified as 00-85-005-008, stated the following:

Sequoyah scismic supports are not designed properly.

They are rigid and will break loose during a seismic event and will fall down and damage other equipment, as well as failing to support their respectivo components.

II. SCOPE A. The scope of the investigation was datormined from the stated concern of record.

B. The technical evaluation was based on fundamental analysis and design ascumptions used in seismic analysis.

III. FINDINGS Field experience has shown that " rigid" supports can be more susceptible to shock loads than ficxible supportc. Shock loads can occur due to operational events cuch as water slugging or by impacting a cupport with a load. Rigid cupports have a natural tendency to " break loose" when overloaded rather than absorb or ecdictributo load through defocmation.

On the other hand, flexible supports can causo a significant incroaco in support load during a seismic event. One of the major rossons supports are designed rigid is because of the difficulty in calculating an accurate and realistic design load for a flexible support.

Seismic loading on a support does not occur as a shock (large step or impulse) but as an increasing response to multiple frequency sine wave inputs.

A ficxible support can cause amplification of sine wave inputs making the support load many timos higher than a more rigid cupport. In order to reduce and limit this amplified response, designers have deliberately attempted to design most seismic supports " rigid." Rigid has been used as a relative term. At Sequoyah Nucicar Plant (SQN) the flexibility of a support is controlled by limiting cupport deflection to 1/16 inch under design Joad.

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O 6 In piping scismic analysis, supports (including snubbers) are assumed to be absolutely rigid (zero deflection under load). Support loads are developed based on amplified response of flexibic piping. As long as supports are "more rigid" than piping or the dominant scismic frequencies, the zero deflection assumption in analysis does not causo a significant error in support load calculations. Any error is accommodated by cafety margins incorporated into design. In some casos in which the support of a component or pipe was obviously ficxible to an extreme, the ficxibility was modelled in the analysis or the support was stiffened. Seismic restraints are designed relatively rigid with a margin of safety sufficient to prevent them from breaking loose in a scismic event. In-service inspections are conducted over the life of the plant to detcet supports which may break in an unanticipated operational event.

IV. CONCLUSIONS AND RECOMMENDATIONS A. Conclusion The concern that supports will break loose in a seismic event because they are rigid has not been substantiated. Seismic supports are designed to carry loads which are computed based on piping and component analyses that assume the support is rigid (zero deflection under load). A safety margin has been incorporated in the design to accommodato variations in degrecs of rigidity. In some cases, in which the support of a component or pipe was obviously flexibic to an extremo, the ficxibility was modelled in the analysis or the support was stiffened. Seismic rostraints are designed relatively rigid with a margin of safety sufficient to provent them from becahing loose in a scismic event. In-service inspections are conducted over the life of the plant to detect supports which may break in an unanticipated operational event.

B. Recommendation None 0149T 2

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UNITED STATES GOVERNMENT , {g. . . , {

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2VICm0Tand um TENNESSEE VALLEY AUTHORITY To: H. L. Abercrombie, Site Director, Sequoyah Nuclear Plant FROM: K. W. Whitt, Director of Nuclear Safety Review Staff E3A8 C-K DATE:

MAR 0 51986 8 80 -

SUBJECT:

NUCLEAR SAFETY REVIEW STAFF INVESTICATION REPORT TRANSMIThAL c = :r s-~

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..q ifa 'dO Transmitted herein is NSRS Report No. I-86-110-SON Subject SEOUOYAH LOCATED ON EARTHOUAKE FAULT  !  ? b E s I .- 5 et Concern No. 00-85-005-009 ---r-W '. ,

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- . . i No response or corrective action is required for this repoft).[It-i g 2 i i '

transmitted to you for information purposes only. Should y@7ihCany -ii

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questions, please contact W. D. Stevens at telephone 6231 .

Reco:::nend Reportability Determination: Yes No X Aof GUfA

" Director, NSRS/ Designee WDS:CDM Attachment cc (Attachment):

W. C. Bibb, BFN W. T. Cottle. WBN James P. Darling, BLN R. P. Denise LP6U40A-C G. B. Kirk, SQN D. R. Nichols E10A14 C-K QTC/ERT, Watts Bar Nuclear Plant Eric Siiger, LP6N48A-C J. H. Sullivan, SQN

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