ML20084J938

Submits Addl Info to Suppl Re Structural Integrity of Torus.Vent Pipe Discharge Relocated to Optimize Mixing of Discharge

ML20084J938
Person / Time
Site:	Quad Cities
Issue date:	05/31/1972
From:	Butterfield L COMMONWEALTH EDISON CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084J932	List: ML20084J938
References
NUDOCS 8305190087
Download: ML20084J938 (2)

Text

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Commonwealth 3dison ompany ONE FIRST N A T IO N A L PLAZA 11r CHICAGO. ILLINOIS Aktess teely to.

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• CHIC G O. IL LIN OIS 6069 0

.s May 31, 1972 e k s t 4 Mr. Donald J. Skovholt k, TM/f

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Assistant Director for Operating Reactors C- q 8 t Directorate of Licensing .! ;g I8 I U.S. Atomic Energy Commission T @('jehgjg Washington, D.C. 20545 .

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Subject:

Additional information concerning the structural integrity of Quad-Cities tori

Dear Mr. Skovholt:

The purpose of this letter is to provide further infor-mation related to your letter dated March 13 pertaining to the structural integrity of the Quad-Citics tori and to supplement our response dated March 27, 1972. As indicated in this response, the modification to each torus in the Quad-cities Station is conceptually identical to that proposed for the Monticello plant. The concern associated with the baffle damage at Monticello due to relief valve discharge into the suppression pool is not relevant to the Quad-Cities Station. Units 1 and 2 do not have suppression pool baffles.

Due to coating problems an investigation was made and determined that the previous location of the relief valve discharge was not optimum and that better mixing of the discharge with the suppression pool water was feasible. This optimization was achieved 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 g pool surface near the inner wall.

feet below the water surface at the torus centerline, and making By moving the vent to about nine b the discharge tangential to the torus wall in both directions, the N momentum of the jets will promote good tangential mixing; also DE natural convection of heated water rising in the center of the pool

//1) will ensure strong radial convection to the torus walls, thereby thoroughly mixing in the radial direction as well.

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,a U Conunonwealth Edison Compy Mr. Donald J. Skovholt May 31, 1972 To relocate the discharge, one additional elbow and fifteen feet of pipe were required. This extension results in a somewhat higher pressure drop. An evaluation was performed to determine the '

losses and pressure at the discharge of the relief valve itself.

The h iculations show that the increase.in equivalent friction loss through the discharge piping would be about 0.4. The new piping represents less than a 10% increase in friction loss.

Therefore, with the flow choked at the valve, the slight increase in downstream loss coefficient will not affect relief valve capacity.

The added water in the relief valve piping which must now be accelerated when the valves open does not materially affect the time to reach full flou in the discharge piping. 'The total time required' to clear the discharge piping is less than one second. It should be noted that this does not mean there is no relief flow out of the vessel during this time, but rather that the relief flow is pressurizing the discharge piping volume. Therefore, the submergency effect on the relief valve operation is negligible. Verification of adequate valve flow capacities will be made during routine startup testing.

As described in the letter from L. O. Mayer to P. A. Morris dated December 15, 1971 on the Monticello docket, the modification included splitting the discharge fluid with a pipe and supporting this pipe to the torus ring girder. This design has the effect of reducing the reaction forces and minimizing the amount of bracing required to hold the pipe in place. The supports provided at the discharge piping c1 bow are designed to withstand up to 25,000 lbs.

of force produced along the 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. Additionally, stiffeners are placed at the piping " tee" as a precautionary measure to provide additional bracing against possible discharge differentials. Analysis shows that these differentials can never exceed 1000 lbs., which is well within the design capability of the supports (2000 lbs.).

As the preceding discussion demonst' rates, the modified dis-charge piping in Quad-Cities is provided with sufficient bracing to withstand all frees associated with relief valve discharges into the suppression pool.

Very truly yours,

&S ik L. D. Butterfield, Jr.

Nuclear Licensing Administrator