05000312/LER-1981-041, Forwards LER 81-041/03L-0.Detailed Event Analysis Submitted

Forwards LER 81-041/03L-0.Detailed Event Analysis Submitted

ML20031H188
Person / Time
Site:	Rancho Seco
Issue date:	10/16/1981
From:	Walbridge W SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20031H189	List: 05000312/LER-1981-041, Forwards LER 81-041/03L-0.Detailed Event Analysis Submitted 05000312/LER-1981-041-03, /03L-0:on 810916,found That Pipe Supports Could Be Overstressed by Thermal & Seismic Loads.Caused by Design Deficiency.Pipe Supports Redesigned & Modified to Conform to ASME Code Allowables
References
NUDOCS 8110270233
Download: ML20031H188 (2)

LER-1981-041, Forwards LER 81-041/03L-0.Detailed Event Analysis Submitted

Event date:
Report date:
3121981041R00 - NRC Website

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esuun SACF'AMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, Box 15330, Sacramento, California 95813; (916) 452-3211 October 16, 1981 y

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WALNUT CREEi< CA 94596 DOCKET N0. 50-312 LICENSE NO. DPR-54 REPORTABLE OCCUPRENCE 81-41 in accordance with Rancho Seco Nuclear Generating Station Technical Specifications Section 6.9.4.2.b and Regulatory Guide 1.16 Section C.2.b.(2), the Sacramento Municipal Utility District hereby submits a thi rty-day report of Reportable Occurrence 81-41, and correct ion to the 24-hour Licensee Event Report dated September 16, 1981.

After a more detailed review of the analysis provided by Bechtel, the situation was found to be reportable on a thirty-day report, per the sections cited.

The following discussion was initially presented in summary to the NRC resident inspector.

This occurrence is being down graded to a thirty-day report for the fol lowi ng reasons.

a.

Only one of the supports or jinally identified as out-of-spec (32120-11PS) was on the Class I si de o f ti.e mai n stop val ve.

Therefore only one loop of the Class l piping was involved d i rec t l y.

b.

No failure of piping was predi ted by Bechtel even if the supports had been overstressed.

Following is a discussion of the details of this occurrence.

An analysis was performed by Bechtel at the request of Nuclear Ope rat ions personnel to provide data for a new flux to feedwater 5

flow anticipated i. actor trip system.

During this analysis it j

l was discovered that the original Bechtel analysis did not take into account moments due to thermal and seismic loads on pipe supports PS-11 (32120-11PS) and PS-25 (3213L-25PS).

When considering the effect of these forces two pipe supports were found to cxceed allowable limits.

These were PS-13A (32125-13APS) which reached E110270233 811016 P.)R ADOCK 05000312 S

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R. H. Engelken October 16, 1981 39 KSI and PS-25 which reached 46 KSl (average stress). The allowable stress is 36 KSI, per ASME Code, Section 111, NC 36.50.

To correct this problem, it was necessary to change the supports to reduce the stress. Therefore, designs were developed to strengthen supports PS-13A, PS-25, and PS-26 (32126-26PS). The modification of these supports brings the support system within acceptable stress limits under the combined therm'al and seismic loads, and relieves the out-of-spec condition originally found on PS-11 and PS-25.

This modification w.'s completed under ECN A-3699 and Work Request 64821 before startup.

There were no transients associated with this occurrence and since no piping failure was predi:ted by Bechtel, the safety of the public was unaffected.

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.n Wm C. Walbridge General Manager cc:

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