IR 05000312/1978008

IE Investigation Rept 50-312/78-08 on 780609.No Noncompliance Noted.Major Area Investigated:Allegation That Bechtel Neglected to Correct Significant Design Error in 1972

ML19319E026
Person / Time
Site:	Rancho Seco
Issue date:	06/19/1978
From:	Albert W, Spencer G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
Shared Package
ML19319E024	List: IR 05000312/1978008 ML19319E023
References
50-312-78-08, 50-312-78-8, NUDOCS 8003270787
Download: ML19319E026 (5)

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U. S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT

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REGION V

S'-312/78-08 Report No.

f Docket No.

50-312 License No.

DPR-54 Safeguards Group

. Licensee:

Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Facility Name: Rancho Seco Unit I Investigation at: Bechtel Power Corporation, L.A. Power Div., Norwalk, Calif.

Investigation Conducted:

June 9,1978 Inspectors.

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1. G. Albert, Reactor Ihspector

' Date Signed Date Sigr.ed

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Approved by:

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G. 5. Spe$ter, Chief, Reactor Construction Date Signed and Engineering Branch Special Investigation on June 9,1978 (Report No. 50-312/78-08)

Reopened investigation (Report 78-07) of ari allegation by an NRC employee which stated that'Bechtel neglected to correct a significant design error

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which the alleger discovered in 1972 while an employee of Bechtel.

Results: The investigation confirtned that an error in a supplemental calculation had been made. However, the error was not found to be

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significant nor were any design deficiencies evident.

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DETAILS 1.

-Individuals Contacted

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Bechtel Power Corporation (Bechtel)

W. A. Brandes, Chief Civil-Structural Engineer

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-A. H.'Hadjian, Principal Engineer j

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R. B. Fa11gren, Engineering Group Supervisor

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2.

Allegation

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In a report issued May 26, 1978 (50-312/78-07), Region V reported on findings from an initial investigation of two allegations.

Subsequent to the completion of this initial investigation, the alleger was able to provide, from personal files, copies of design calculations which showed the decimal point error stated as the basis for Allegation No. I in report 50-312/78-07. Based on this'

new information, the investigation of Allegation No. I in report 50-312/78-07 was reopened. No basis was found for reopening the investigation of Allegation No. V of the original report (78-07).

ThecalculationsofconcernassociatedwithdilecationNo.I

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were examined within the NRC and at Bechtel. Ar'ditional design analyses were also performed by Bechtel.

3.

Additional Findings - Allegation No. I

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a.

A Decimal Point Error was Evident in the Calculations The calculation of concern was a supplemental calculation consisting of a dynamic analysis performed to assure that seismically induced accelerations and resulting overturning

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moments on the upper fuel pool wall would not exceed the structural capability of the wall as designed. The design had been based on a seismically induced acceleration of 0.28 g horizontal for the case of the Operating Basis.

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Earthquake.

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The decimal point error was found by the alleger on pp 5.10 of the supplemental calculations for the Fuel Storage Building._ The error resulted in the calculations of record i

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for this particular analysis showing a natural period of 2:56 seconds and a corresponding acceleration value (with Basis Earthquake (g) of 0.056 g for the case'of the Operating 2% critical dampin 0BE). The OBE is the design controlling event rather than the larger Safe shutdown Earthquake (SSE).

Correction of the error would result in a period of approximately 0.8 seconds and an acceleration of 0.18 g (irispector's review). The design, based on 0.28 g horizontal, was not changed.

A corresponding change in acceleration values would also be applicable to the accelerations produced by the SSE (formerly DBE) in the supplemental calculations.

b.

The Design was not Based on the Calculations in Question

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The original designer utilized an acceleration value of 0.28 g for the OBE which is essentially the maximum value on the curve for 2% critical damping. This conservative value of accelera-tion is shown on the calculations of record. The supplemental calculation in question had been performed to investigate the effect of lower order vibration modes and assure that the more simplified assumption used in the design was conservative.

c.

The Calculations of Record Represented Corrected Calculations which Had Not Been Referrad Back to the Original Designer

The original designer, R. B. Fallgren, provided his initial version of these e,upplemental calculations from personal files.

This initial version showed an acceleration value of 0.191 g.

During a period when he was not employed by Bechtel, the calculations had been checked and changed. These changes produced the error referred to in the allegation.

The inspector found from records and discussion that, contrary to Bechtel procedures in effect at the time (May 1970), the original calculations had apparently been changed by the checker without reference back to the original designer. The engineer who perfor1ned the checking is no longer employed by Bechtel and was not contacted.

Bechtel procedures dated November 1969 stated in part:

'All errors and deficiencies detected through checking shall be discussed with the designer and corrections made to the satisfaction of the checker."

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Bechtel personnel stated that in the absence of the original designer, supervisory personnel should have checked the corrections or appointed an independent designer to work with the checker.

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d.

Bechtel Performed New Calculations Which Demonstrated that the Upper Wall of the Fuel Storage Building was Conservatively

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Designed Innediately prior to the NRC visit on June 9,1978, Bechtel performed check calculations for the loadings induced by the operating basis earthquake (OBE). This earthquake is the design controlling event since the safe shutdown earth'1uake (SSE) uses acceleration loadings with greater damping and structural capabilities greater than the working stresses used for the OBE. From these calculations, Bechtel determinea that an upper fuel storage building wall section was capable of resisting an overturning moment of 242,000 ft. Ibs. without exceeding working stresses and that the moment induced by the OBE on that section was 151,500 ft. lbs. Therefore, the existing structure was at least 60% over designed. The acceleration value calculated utilizing a current structural computer code (B-SAP) was 0.187 g which corresponds closely O

to the original acceleration calculated in 1968 before the supplemental calculation was revised by the checker.

Bechtel personnel also noted other conservative assumptions such as a damping value of 2%, neglecting certain restraints and internal steel, which made the design even more conserva-tive.

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The New Information on Allegation No. I Did Hot Change any Positions Bechtel had Previously Taken with Regard to the Allegation Mr. Brandes stated that pinpointing the alleger's concern did not result in any changes in Bechtel's position or provide any aid to recollection of such an incident. There was still no evidence that the alleger had ever been assigned work on the fuel storage building.

4.

Management Interview At the conclusion of the visit to Bechtel-Norwalk, the inspector

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stated that the finding regarding the revised calculations not being

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checked indicated a soft spot in QA practices at that time.

Bechtel stated that practices in this regard had been tightened i

during the past eight years.

Region.[IV - ViB of NRC routinely examines design practices at Bechtel.

The item was-brought to their attention should any followup regard-ing current practice be advisable.

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