ML20235E679

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Supplementary Ro:On 711116,structural Damage to Torus Baffles Discovered.Caused by Initial Transient Dynamic Loading.Listed Repair Work,Including Catwalk Bracing & Insps Completed.Updated Diagrams Encl
ML20235E679
Person / Time
Site: Monticello, 05000000
Issue date: 02/15/1972
From: Mayer L
NORTHERN STATES POWER CO.
To: Morris P
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20235B311 List: ... further results
References
FOIA-87-111 NUDOCS 8709280223
Download: ML20235E679 (6)
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Text

.

%!cte"! Flie Cy; N O R T'M E R N STATES POWER COMPANY M I N N E A PO LI S. M I N N E S'OTA 5 5 401

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February 15, 1972  %

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USAtc Dr. Peter A Morris, Director

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OM * '

2 8 Division of Reactor Licensing REGllLATORY 3 ~

United States Atomic Energy Commission Washington, D C 20545 hEMC k y I" $c

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Dear Dr. Morris:

g T "9 M017fICELLO NUCLEAR GENERATING PIANT Docket No. 50-263 License No. DPR-22 Supplementary Report on Damage to Toms Baffles A letter reporting the anmnge to torus baffles and the status of repair work was transmitted on December 15, 1971, in compliance with the 30-day reporting requirement of Section 6.6.C.1 of Appendix A, Technical Specifications of Provisional Operating License DPR-22. The following infomation supplements the December 15,1971, letter and summarizes the completion of inspection and repair work.

At the time of the prior report, all torus baffles had been removed. The re-lief valve discharge lines vem being modified as recommended by the General Electric torus design engineers. Repairs ve m in progress on small lines and catwalk bracing. Consideration was also given for repair of the painted sur-faces.

Since the last report, all small lines have been restored to their original condition. Likewise, the structural support bracing for the torns catvalk has been repaired. The modifications to the relief valve discharge lines have been completed as described in the previous report. The lines were extended under the torus water level'and terminated with a ram's head type tee as shown on the attached sketches.

Special tests were conducted to assure the integrity of the torus metal. All significant scratches attributed to baffle movement on the torus valls were subjected to a magnetic particle test; the test showed the base metal to be of satisfactory integrity in all cases. Areas where paint was removed by steam discharged from the relief valve lines against the torus vall were magnetic particle tested and found acceptable. In addition, the vall thickness was mea-sured; it was found that no measurable metal erosion had occurred. A group of original pipe connection and structural velds on the inside and outside of the torus were magnetic particle tested. All velds were satisfactory with the ex-ception of two velds connecting each relief valve discharge line brace to the 8709280223 870921 ,

FOIA 7 ([F/ 2 [(d _>s. / y' t

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NORTHERN ' STATES POWER COMPANY P A )brris February 15,.1972 1

. torus skin. A small crack was found at the end of each veld which penetrated

. slightly into the surface of the torus metal. In each case, the weld was re-paired in accordance .with applicable code. requirements. . That brace is no long-er used. The design modification called for bracing to be connected between two

- torus ring girders rather than. welded to the ' torus skin. A stress analysis shows-that a similar failure is not expected in the modified design.

Paint was earlier reported to be damaged in a number of places. All loose paint was removed and a base primer was. applied as necessary. Affected areas were re-

- painted to restom. the original quality of metal surface protection.

The Safety Audit Committee reviewed the work completed and plans for additional torus work at the December 15 and 16, .1971, meeting. . They discussed final-res-olution'of all work at the January 19 and 20,1972, meeting. All torus work was essentially completed at this time. The consnittee saw no safety consideration restmining continued plant operation in light of the removal of'the baffles, modifications of the relief valve discharge lines, and other torus repair work.

All quality assurance supervision and documentation was done under the direction and supervision of the Quality Assurance Section of the Northem States Power Corpany, Plant Engineering and Construction Department.

A. detailed report of all torus repair work done including quality assurance doc-umentation is available at the Monticello site for Compliance Inspectors.

Yours very truly, W O.

L 0 Mayer, P.E.

Director-Nuclear Support Services LOM/MEV/br cc: B H Grier Attachments l

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