ML20084G666

Submits Results of Torus Insp.Electromatic Relief Valve Discharge Piping Provided W/Sufficient Bracing

ML20084G666
Person / Time
Site:	Dresden
Issue date:	05/31/1972
From:	Butterfield L COMMONWEALTH EDISON CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084G655	List: ML20084G653 ML20084G657 ML20084G660 ML20084G666 ML20084G682 ML20084G724
References
3009, NUDOCS 8304220207
Download: ML20084G666 (2)

Text

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May 31,,1972 j ,

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$J Mr. Donald J. Skovholt

4 y 'yr 1

/7-Assistant Director for Operating Reactors \ ._

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Directorate of Licensing ,.N U.S. Atomic Energy Commission NJ Washington, D.C. 20545

Subject:

Results of Dresden Unit 2 Torus Insnection

Dear Mr. Skovholt:

The results of the Dresden Unit 2 torus inspection are provided in reply to your letter dated March 13, 1972 and supple-mental to our responses of March 24 and April 6, 1972.

The Dresden Unit 2 torus inspection was completed April 4, 1972. No indications of structural distress were discovered on the baffles, baffle support bolts, or electromatic relief valve piping supports. This inspection involved visual examination of every baffle support bolt for integrity and tightness. Only one broken bolt was discovered and it was replaced. On the basis of the satisfactory results of this inspection, the conclusion is the design of the baffles and supports are adequate and no further inspection is necessary.

The relief valve piping supports in the Dresden Unit 2 and 3 tori are similar in concept to the revised design used at the (h, Monticello plant.

The design of the relief valve piping was revised-in

?' spring 1971 to minimize any possible detrimental effects of relief

<- valve steam on the torus coating. This optimization was achieved

. /_ y by relocation of the vent pipe discharge to provide even further assurance of complete steam suppression in the torus. The discharge was originally located approximately three feet below the suppression pool surface near the inner wall. By moving the vent to about nine feet below the water surface at the torus conterline, and making the

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OCommonwealth Edison Com[hf Mr. Donald J. Skovholt May 31, 1972 f

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discharge tangent to the torus wall in both directions, the momentum  ;

of the jets will promote good tangential mixing; also natural convection of heated water rising in the center of the pool will l ensure strong radial convection of the torus wall, thereby l thoroughly mixing in the radial direction as well. I This design has the effect of reducing the reaction forces j and minimizing the amount of bracing required to hold the pipe in  !

place. The supports provided at the discharge piping elbow are designed to withstand up to 25,000 lbs. of force produced along the f

axis of the pipe immediately upstream of the " tee". Calculations show  :

that the maximum force which could be produced is less than 10,000 lbs. l Additionally, stiffeners are placed at the piping " tee" as a pre-  !

cautionary measure to provide additional bracing against possible {

discharge differentials. Analysis shows that these differentials can t never exceed 1000 lbs., which is well within the design capability  ;

of the supports (2000 lbs.). (

As the preceding discussion demonstrates, the modified j clectromatic relief valvo discharge piping in Dresden Station Unit [

2 and 3 tori are provided with sufficient bracing to withstand all-  !

forces associated with relief valve discharges into the suppression [

pool.  !

Based on the results of the Dresden 2 inspcction, the l program for inspecting the Dresden Unit 3 torus remains the first [

refueling outage, presently scheduled for the fall of 1973. This {'

is consistent with the schedule as submitted to you in our April 6, 1972 letter. l Should you require any additional information, please let [

me know.  !

I Very truly,yours, i s

\  !

Y v l

L. D. Butterfield, Jr.

l Nuclear Licensing Administrator k

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