ML20087F922

Responds to NRC Re Violations Noted in IE Insp Repts 50-454/84-08 & 50-455/84-06.Corrective Actions:Leak on Snubber Repaired & quasi-static Structural Test Combined W/Fluid Stiffness Calculation Performed

ML20087F922
Person / Time
Site:	Byron
Issue date:	02/23/1984
From:	Swartz E COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20087F900	List: ML20087F922 ML20087F946
References
8161N, NUDOCS 8403190274
Download: ML20087F922 (5)

Text

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['N1 Commonwealth Edison

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)- one First NItionIl Ptiza CNcago, lihnois 4

( O j Addrtss Riply to: Post Office Box 767

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/ Chicago. Illinois 60690 February 23, 1984 Mr. James G. Keppler Regional Administrator U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137

Subject:

Byron Station Units 1 and 2 Steam Generator Snubber Qualification IE Inspection Report Nos. 50-454/84-08, and 50-455/84-06 NRC Docket Nos. 50-454/455 Reference (a):

W. S. Little letter to Cordell Reed dated February 6, 1984

Dear Mr. Keppler:

Reference (a) provided the Commonwealth Edison Company with the Region's concerns relative to steam generator snubber qualification

-testing performed by'the Boeing Company and acknowledges our recent commitment to perform additional snubber testing.

The purpose of this letter is to document the Commonwealth Edison Company position in this matter, and to request the Region's written acceptance of the enclosed preliminary specification for testing of these snubbers.

During the teleconference held on January 27, 1984 with Mr. Isa T. Yin of your office, we discussed our intentions of performing additional snubber qualification testing.

Mr. Yin was informed that a test specification would be developed encompassing his concerns and would be provided to the Region for comment and ultimata concurrence prior to its being released for bids.

Additionally, we emphasized our technical disagreement with Mr. Yin relative to the need for further testing.

For the reasons listed below, we continue to believe that the original snubber stiffness testing performed by the Boeing Company was adequate and that additional testing is not technically justifiable.

On January 17, 19 and 20, 1984, we met with Mr. Yin to review his concerns regarding the Byron Station steam generator snubbers.

The following addresses each of Mr. Yin's concerns as we understand them.

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,- Region Concerns:

1.

The leakage which was observed at Byron Station may change the characteristics of the snubber, even if corrected.- Mr.

' Yin stated that normally when there is leakage the snubber is replaced and tested.

Although the leakage has been corrected at Byron, no testing hcs been done.

(Mr. Yin

-pointed out that when the snubber is tested for operability, the spring rate can be determined at no extra cost.)

2.

The testing performed by the Boeing Company for snubber stiffness was,not based on a cyclic test of the entire snubber, including the control valve.

A quasi-static structural test combined with a fluid stiffness calculation was performed and this does not conform to the specification.

3.

The testing performed for the Byron Station snubbers was not acceptable because calculations, in addition to the tests, had been used to accept snubber stiffness.

(Mr. Yin does not accept analysis as a supplement to testing.)

4.

Stiffness testing was not completed at loads throughout the load range.

Stiffness at OBE, SSE and~ faulted load levels is required because snubber stiffness is nonlinear and

-varies with load level.

CECO Response to Concerns:

1.

-Leakage The leakage experienced at Byron Station has been repaired and the snubbers are now not experiencing any leakage.

Furthermore, the effect of such a leak on snubber stiffness is negligible because the loading rate for both seismic and pipe break loads are so high that leakage, both due to seal and piston bypass, contributes very little to total deflection of the snubber.

The repair to stop leakage does not change the seal details rnd consists only of a change to the

thread sealant.

A change in sealant will have no effect on snubber stiffness.-

2.

Adequacy of Testing Completed by the Boeing Company

-cnd 3.

.The snubber specification requirement is not intended to specify

-cyclic testing, but rather, it is intended to' require impact 1

testing.

This and other specification requirements were met by the Boeing Company test program.

The snubber stiffness testing performed to meet the specification requirements was based on three separate types of tests.

All three methods provided close results, met specification requirements, and are described as follows:

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The. stiffness of the' snubber bottomed out.in both tension and compression was-determined from'a test at.900 and~400 kips.

This stiffness accounted for' play in fittings and results in the (same: load path as'when the snubber is in its hot position with r

fluid.in place.- This stiffness was combined ~in series, with the fluid = stiffness which was;obtained using the bulk modulus of the

,; fluid;atroperating~ temperature.

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B.

.The snubber with control 1 valve.was tested both in tension and j, [t f

icompressioniusing1.a-drop weight test.

Loads above 2400 kips

'1)within;.005 seconds were obtained both in compression and tension.

The snubber stiffness was obtained through correlation

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oft the defle'ction time history measured 1from the test with the Ldeflection response of an~ analytical.model including an assumed

'snubberustiffness'and subjected to the measured loads.

Because

'ofxthe~ relative. simplicity of: the test set'up for the compression case,-the' stiffness obtained from the analyses are y; -

' valid, and at18200 kips / inches.are within'the spacification

. required-range.

R The tension stiffness does-not correlate well due to the fact

~

-that_the analytical model:Used didfnot accurately represent the

,more: complex load 1 path for the. tension test.. Due to the good af

correlation in compression,---the-additionalfanalytical' work required to obtain correlation was deemed-unnecessary.

Thus,.the-drop weight test predictably supports the quasi-static tests.

'C.

The fluid' bulk modulus used in the quasi-static approach described above wasLverified at 400 and 900 kips'using

' deflections from tests of the snubber with the piston in the hot

' position, thus' making the' fluid: effective.. The bulk modulus u' sed in "A"nabove compared with the bulk modulus determined from

-these tests.isowithin~11% inLthe worst csse.

Since the fluid stiffness.is in series with the snubber structure stiffness, s

.this variation. corresponds to 5% difference, which is negligible,

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4.. !Stif fness Testing Required Only at Faulted Load StiffnessEtesting was required:at faulted load levels because the

.effectior'snubberistiffnessrvariation on total stiffness is small

enough toLbe; neglected'.':TheEfaulted' condition is critical;for system

= design due;to high load level.

Therefore, the stiffness was.

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. determined at--faulted:loadflevels.

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During.Mr. Yin's. audit, Sargent.& Lundy produced reduced cyclic test

/ y data-provided in the Boeing test report for load levels less than'0BE d[ - o and ativarious frequencies.

The, average-stiffness obtained was 7000 kips / inch,.which is"close to the specification required 9000 4

-kips / inch.. Th s' demonstrates the validity of'the stiffness' i

.determinationfrequired-in the specification.

This data was reviewed by;Mr.-Yin during the. inspection.

,Notwithstanding the above and'our continuing technical

. disagreement;in this matter,nenclosed for your immediate review and Twritten concurrence is a copy-of the preliminary steam generator snubber-test specification._ :Your immediate attention to this matter is. requested.

Very truly yours,

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r-E. Douglas Swartz Nuclear Licensing Administrator

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