ML19262A237

Abnormal Occurrence 50-289/75-08:on 750318 & 21,snubbers Inoperative During Testing & Seal Replacement Program, Respectively.Caused by Improper Installation & Valve Design Deficiency.Defective Units Replaced

ML19262A237
Person / Time
Site:	Three Mile Island
Issue date:	04/02/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-0897, GQL-897, NUDOCS 7910260575
Download: ML19262A237 (4)

Text

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DATE OF DOC DATE REC'D LTR TWX >'T OTHER FROM: Metropolitan Edison Co.

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XXX 1 1 50-289 DESCRIPTION: ENCLOSURES:

Ltr. Pprt ibaorn. Occurr. # 50-289/08, on 3-1S-/3-21-75, concerning Inoperative Hyr'raulic _-

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METROPOLITAN EDISON COMPANY DCST OFFICE BOX 542 RE ADING. PENNSYLV ANI A 19603 TELEPHONE 215 - 929-3601 April 2, 1975 3G 0697 APR.9,L97r Director Division of Reactor Licensing U. S. Nuclear Regulatory Commission b'ashington, D. C . 20555

Dear Sir:

Operating License DPR-50 Docket #50-289 The following abnormal occurrence is submitted in accordance with the Technical Specifications for Three Mile Island Nuclear Station, Unit 1, and is being submitted at this time in accordance with the March 26, 1975, conversations between your office's Mr. D. Jaffe and our Mr. D. N. Grace.

(1) Report Number: A0 50-289/08 (2a) Report Date: April 2, 1975 (2b) Occurrence Date: March 18 and 21, 1975 (3) Facility: Three Mile Island Nuclear Station Unit 1 (4) Identification of Occurrence:

Title:

Inoperative Hydraulic Shock Suppressors I; pe : An abnormal occurrence as defined by the Technical Specifications, paragraph 1.8d, in that the inoperative hydraulic shock suppressors threatened to cause an Engineered Safeguards feature or system to be incapable of performing its intended function.

(5) Conditions Prior to Occurrence:

The reactor was at steady state power with major plant parameter as follows:

Power: Core: 99% 1484 213 Elec: 863 MW (Gross) ,p q

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RC Flow: 137 x 10 lb/hr

. t RC Pressure: 2155 psig RC Temp.: 579 F PRZR Level: 230 in.

PRZR Temp. : 655 F (6) Description of Occurrence:

During a routine inspection of hydraulic shock suppressors (snubbers) on March 18, one snubber (MS-288) , located outside the secondary shield in the Reactor Building on the "B" steam generator main steam line, was found to be inoperative in that the snubber ,iston was unable to move within the snubber cylinder. A rebuilt and tested replacement unit was then installed.

On another occassion on March 21, 1975, during performance of a scill in progress seal replacement program, it was found that one type of Grinnel snubber did not meet the design criteria of not permitting piston velocities in excess of eight inches per minute.

This deficiency was determined to be caused by Grinnel snubber valve model BH-1226. Eight valves on the main steam line inside the Reactor Building were determined to be of this type of valve, and all eight failed to lock up properly when tested: 15-204, MS-205, and MS-206 (A steam line , A steam generator) ; MS-202 (B steam line , B steam generator) ; MS-215 (C steam line, B steam generator) ; and MS-208,

}$-210, and MS-211 (D steam line , B steam generator) . All were replaced by rebuilt and retested units.

(7) Designation of Apparent Cause of Occurrence:

With regard to the MS-288 snubber unit , upon disassembly the piston rod was found to be f rozen to the bronze bushing. A pressure of 2500 pounds applied by a hydraulic press was necessary to free the piston rod. An investigation revealed that the piston rod had been painted during Unit 1 construction, in violation of the manufacturer's ins tructions . As the Main Steam Line moved due to thermal stresses ,

the painted area of the rod was drawn into the bushing, chipping and roughening the paint. The roughened paint and chips then " locked" the piston to the bushing. The re fore , the apparent cause of the occurrence was improper installation.

The apparent cause of the deficiency of the snubbers containing the BH-1226 valve is a deficiency in design of the valve.

(8) Analysis of Occurrence:

As the 24 inch main steam line would have moved due to thermal stresses, forces would have been exerted such that the piston rod would have been freed thus returning the MS-288 snubber to its normal operational mode.

in this manner, the snubber would have performed its intended design 1484 214

function. Also, as the sn ers are intended to be rigid supports during a seismic event wh_c: Allow only normal thermal movement, the

' rigid condition of the " frozen" snubber would not have precluded adequate performance during a seismic event. Based on this, this event is not considered to have threatened the health and safety of the public.

With regard to the eight snubbers containing valve model BH-1226, although the affected main steam line was not seismically acceptable, it is not believed that this situation could have threatened the health and safety of the public in that a steam line breat accident has been analyzed in the TMI-1 Final Safety Analysis Report, and even if a seismic event had led to a steam line break, the hypothetical accident would have not resulted in conditions more severe than thot '

already analyzed.

(9) Corrective Action:

Corrective action was taken as described above to replace the defective units and return the snubbers to service. The snubber seal replacement program (see the letter from R. C. Arnold to A. Giambusso dated February 14, 1974) will continue.

The Plant Operations Review Committee and the Station Superintendent reviewed and gave their approval of these actions.

(10) Failure Date:

Previous Failures: See Abnormal Occurrence Reports A0 50-289/74-14, 74-20, 74-23, 74-25, 74-30, and 75-03.

Eq uipment Identification:

Snubber Assembly Brand Cylinder Type Bore Stroke MS-288 Grinnel Miller 2 in. 5 in.

MS-204 Lindco MS-205 MS-206 MS-202 MS-215 MS-208 MS-210 MS-211 Sincerely,

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'R. Cr Arn'old "k Vice President-Generation RCA : RS B: pa ,

cc: Office of Inspection and Enforcement Ikh i

U.S. Nuclear Regulatory 631 Park Avenue King of Prussia, Pennsylvania 19406 File 20.1.1/7. 7.3.5.1