ML19323C998

RO 2-80-8/1T:on 800417,preliminary Calculations Associated W/High Energy Line Breaks Revealed That Guillotine Failure of HPCI Steam Supply Would Result in Peak Pressure & Failure of Reinforced Concrete Block Wall.Mods Are Underway

ML19323C998
Person / Time
Site:	Peach Bottom
Issue date:	05/01/1980
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:
References
NUDOCS 8005190512
Download: ML19323C998 (3)

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• 6005190512 PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET P.O. BOX 8699 PHILADELPHIA. PA.19101 121SI 8414o00 May 1, 1980 Mr. Soyce H. Grier, Director Office of Inspection and Enforcement Region I United States Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

SUBJECT:

Licensee Event Report Narrative Description Information concerning the following occurrence was reported to Mr. C o w g i l '. , US Nuclear Regulatory Commission, Region I, Office of Inspection and Enforcement on April 17 and 22, 1980.

Reference:

Docket No. 50-277 and 50-278 Report No.: LER 2-80-8/lT neport Date: :tay 1, 1930 Occurrence Date: April 17, 1980 Facility: Peach Bottom Atomic Power Station RD 1, Delta PA 17314 Technical Specification

Reference:

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Technical Specifications 6.9.2.a(9) states in part

" Performance of structures, systems, or components that requires remedial action or corrective measures to prevent operation in a manner less conservative than assumed in the accident analysee in the Safety Analysis Report or Technical Specifications bases; or discovery during plant life of conditions not specifically considered in the Safety Analysis Report or Technical Specifications that require remedial action or corrective measures to prevent the existence or development of an unsafe condition." $f cO

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Mr. Boyce H. Grior Pago 2 Descripti'on of the Event Our prompt notification of April 17, 1980 reported that preliminary calculations resulting from development of the environmental conditions associated with high ener3y line breaks as requested in IE Bulletin 79-01B indicated that a guillotine failure of the HPCI steam supply piping in the outboard isolation valve room would result in a peak pressure (12 psig) within the room which is in excess of the ca p abi li tie s of the concrete block wall (7.2 psig). Unit 2 and Unit 3 are of similar design.

Additional investigation revealed that, as described on page 27 of Supplement No. 2 to the FSAR, restraints were added to the HPCI steam line upstream of the outboard isolation valve. These restraints restrict motion of the outboard isolation valve in the vertical or horizontal planes such that the failure of the HPCI stear lina upstream of the outboard isola tion valve is precluded and rupture of the pipe at the postulated break point down stream of the outboard isolation valve results in steam discharge into the torus compartment below.

More refined analysis shows that there will also be an upward flow of steam from the postulated break point which results in calculated peak pressures in the outboard isolation valve room of 5.01 psig (4.97 psig if the steam line isolation valves are throttled to 75% closed). Since the ultimate wall pressure capability based on the type of anchor bolts used is approximately 7.2 psig, a safety factor of only slightly greater than 1.4 exists.

Cause of Event The concern for the integrity of this wall uas a result of information developed and analyzed in' response to IE Bulletin 79-01B which requests, among other things, the use of core modern analytical techniques. Use of present day methods providing = ore accurate predictions indicate that the instantaneous oressures in the outboard isolation valve room resulting from a HPCI steam supply pipe break would result in a less than acceptable factor of safety for the type of anchor bolts used in the end restraints for these block walls.

Conseguences of Event The event as initially described in the LZR of April 17.1980 and as revised on April 22. 1980. would result in failure of the reinforced concrete block wall thus affecting the integrity of some engineered saf eguard cables contained in conduit supported on the face of the wall. The cabling involved affects the "3' Core Spray injection loop. the HPCI systen and some R3R (non-L?CI) couponents. However. the more refined analysis shows that this event will not occur.

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, . Mr. Boyco H. Grior Paga 3 Corrective Action Immediate corrective action on Unit 3 consisted of throttling the steam line isolation valves to greater than 75%

closed, proving HPCI quick start capability from this condition and performing immediate and daily visual inspection of the area to ensure that no steam leakage existed.

Based on the results of the additional investigation and

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more refined analysis, the isolation valves have been returned to their normally open condition. Daily visual inspections will be centinued until the final modifications are completed to achieve the desired factor of safety. If material can be procured as planned, the Unit 3 modification can be completed within 6 weeks.

Modification to Unit 2 will be completed prior to startup.

Very truly yours J

M. . n S perintendent G neration Division - Nuclear Attachment ec: Director, NRC - Office of Inspection & Enforcement Mr. Norman M. Haller, NRC -

Office of Management and Program Analysis 4

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