ML19290F033

Forwards LER 80-005/03L-0

ML19290F033
Person / Time
Site:	Cooper
Issue date:	02/13/1980
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19290F034	List: ML19290F033 ML19290F041
References
CNSS800116, NUDOCS 8003170486
Download: ML19290F033 (2)

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COOPER NUCLEAR STAT 8oN

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CNSS800ll6 February 13, 1980 Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

Ihis report is submitted in accordance with Section 6.7.2.B.4 of "the Technical Specifications for Ccoper Nuclear Station and discusses a reportable occurrence that was discovered on January 16, 1980. A licensee event report form is also enclosed.

. Report No.: 50-298-80-05 Report Date: February 13, 1980 Occurrence Date: January 16, 1980 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

Degradation of the Reactor Equipment Cooling (REC) System piping.

Conditions Prior to Occurrence:

Steady state power operation at approximately 97% reactor power.

Description of Occurrence:

During a routine plant tour, two pin hole leaks were discovered in welds in the Reactor Equipment Cooling S stem in the north critical supply header.

Designation of Apparent Cause of Occurrence:

The apparent cause of the weld failure was intergranular cracking, characteristic of intergranular stress corrosion in an environment of NO 3 and /or CH . The presence of the backing ring crevice in cochination with the specialized water chemistry of this system is considered the m.ijor contribution to the failure.

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Mr. K. V. Seyfrit Fe~oruary 13, 1980 Page 2.

Analysis of Occurrence:

i The defect doea not prevent continued operation of this system or {

its associated systems. The north critical supply header provides cooling water to the Residual Heat Removal Pumps, A & C gland water coolers, and to the fan coil units it the northeast and northwest 4 Reactor Building quadrants. Operating experience with failures of  ;

this same type in non-essential portions of the Reactor Equipment i Cooling System and the Turbine Equipment Cooling System indicate the crack is tight and growth is very slow. There have been no complete failures of pipe welds in similar systems due to the same l failure mechanism.

In the event the indication accelerated its growth, daily surveil-lance by the operating staf f would detect this and corrective action would be taken. Should the failure go unnoticed during normal operation, plant indications such as the system surge tank ,

low level alarm or Reactor Building sump high level alarms would indicate the problem to the operators. In the event the failure occurred during operation of the critical header, the control room operators would receive a low flow alarm to the appropriate equip-ment. In this event, the redundant loop for the affected equipment would be supplied cooling water by the south critical supply header which is isolatable from the north header.

This occurrence presented no adverse consequences from the stand-point of public health and safety.

Corrective Action:

During the next shutdown of sufficient length, the subject welds will be replaced. The evaluation of the failure mechanism is being further analyzed by General Electric Company so that a recommended solution to this problem can be obtained. When their final recom-mendations are received, they will be reviewed and corrective action taken based upon their recom=endations.

Sincerely,

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L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.