ML20210B037

Responds to AEC 721213 Questions Re Torus Ring Header & Forwards Special Rept 31, Torus Ring Header Support Mod, Describing Ring Header Insps & Repairs

ML20210B037
Person / Time
Site:	Dresden, 05000000
Issue date:	07/11/1973
From:	Abel J COMMONWEALTH EDISON CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20209J032	List: ML20209J028 ML20209J102 ML20209J362 ML20209J414 ML20209J428 ML20209J450 ML20209J504 ML20210A204 ML20210A316 ML20210A365 ML20210A410 ML20210A454 ML20210A522 ML20210A538 ML20210A585 ML20210A633 ML20210A720 ML20210B005 ML20210B037 ML20210B073 ML20210B140 ML20210B165 ML20210B193 ML20210B233 ML20210B262 ML20210B269 ML20210B312 ML20210B376 ML20210B424
References
FOIA-87-40 5566, NUDOCS 8705050219
Download: ML20210B037 (4)

Text

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Commonwealth Edison One First National Plaza. Chicago. Ilhnois d% rg A ,

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July 11, 1973

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Mr. D. J. Skovholt Assistant Director for n

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JUL 19 1973 -* '

Operating Reactors d Directorate of Licensing b dQek[ h U.S. Atomic Energy Commission Of Washington, D.C. 20545 61

Subject:

Dresden Units 2 and 3 Torus Ring Header Analyses, AEC Dkts 50-237 and 50-249

Dear Mr. Skovholt:

In response to your letter dated December 13, 1972, concerning this subject, answers to your specific questions are furnished below and Special Report No. 31, describing the ring header inspections and repairs are attached.

Question 1:

Provide a summary of a dynamic analysis of the torus ring header system subjected to blowdown forces resulting from operation of the automatic pressure relief valve. Include information on the mathematical model, natural frequency of the system, and the forcing function of blowdown forces.

l Resoonse:

A dynamic analysis of the General Electric Mark I Torus Ring Header has been performed. In addition, experimental ,

verification of the model employed has been accomplished by means of the tests performed on the Quad-Cities Unit 2 Torus during October,1972. General Electric has issued a report "NEDO - 10859 which covers the theoretical and experimental program.

l I This report describes the parametric models used to perform the analysis, and the response of the torus'to the relief valve discharge forcing function. The maximum experimentally

, determined blowdown loads on the vertical suction ring header hangers recorded was 10,200 pounds and the maximum horizontal load recorded was 3,400 pounds.

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Commonwealth Edison Company Mr. D. J. Skovholt July 11, 1973 Question 2:

Provide the basis for determination of forcing function as derived from either test data or analytical methods.

Response

"The forcing function used for the response calculation was derived from the study of an envelope of experimental data..."

Quote from G.E. Report NEDO - 10859, see this report for further information.

Question 3:

Provide a summary of (a) the stress analysis of the torna ring header system, including the interaction of torus wall and hanger supports under static and dynamic loads, and (b) fatigue analysis of the ring header, hangers, and component parts that are subjected to cyclic load during blowdown.

Response

The stress analysis has been performed and can be found in the NEDO - 10859 report. The calculated dynamic loads for Dresden are discussed in Section 5.2 of Special Report No. 31.

The fatigue analysis has been performed and the conclusion as presented in the NEDO - 10859 report is that the

1. ,,) torus can accommodate (f56 reliet valve actuativu ,per year for y3, the forty years lifetime of the plant without fatigue failure l

occurring in the torus.

l l The torus shell region above the vertical ring header attachment was judged to be the most critical area from the standpoint of fatigue life, therefore this region was the only one analyzed for fatigue, due to cyclic loading.

Question 4:

In the event the above analysis demonstrates stresses in excess of code allowable design values, provide your plans and schedules for corrective actions, and confirmatory tests.

l

Mr. D. J. Skovholt July 11, 1973

Response

The analysis presented in NEDO - 10859.has shown that no excessive stresses exist or will exist, in the torus structure, during the life of the plant due to combined static, seismic, and electromatic relief valve actuation induced loads.

Question 5:

Describe any provisions that may be available in the plant design which would allow the emergency core and containment cooling systems to function for long-term effective-ness in the event of failure of the suction header.

Response

This hypothosized situation involves two simultaneous class I failures and therefore is incredible, but if the event is assumed to occur the feedwater system can be used to pump an' unlimited amount of river water into the core by means of '

the(standby (coolant.kupply' system. (Dresden Unit 2 and ,3 FSAR Section 6.3)

This system will pump water into the reactor until the torus room is filled with water. This watar is assumed to reach the torus room throudithe postulated leak in the primary piping which required the use of the emergency core and containment cooling systems. When this room is filled the HPCI and LPCI pumps can again take their suction from this room even though the ring header is assumed to be broken off the torus.

All improvements to the Dresden torus suction ring headers are completed. They were completed on Dresden Unit 2 November 8, 1972 and on Dresden Unit 3 May 25, 1973. These improvements result in systems with a conservatively calculated minimum load carrying capability which is approximately two (2) times the calculated maximum combined (static, seismic, and relief valve induced) load.

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b' Mr. D. J. Skovholt Commonwealth Edison Company July 11, 1973 One signed original and 39 copies of this letter and Special Report No. 31 are provided for your use.

Very truly yours,

/

J. S. Abe Nuclear Licensing Administrator -

Boiling Water Reactors l

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