ML20211F197

Final Deficiency Repts 86-03 by & 86-05 Bw Re Cold Leg Safety Injection Pipe Vibration & Cracks.Initially Reported on 860430.D Loops Changed to 5-D Bends & Support Added for Addl Stiffness

ML20211F197
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	06/05/1986
From:	Miosi A COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
1757K, 86-03-BY, 86-05-BW, 86-3-BY, 86-5-BW, NUDOCS 8606180252
Download: ML20211F197 (3)

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. Commonwealth We1 Adams Street,EdisonChicwo,Illinoi) j .1 A

• Mdress Reply to: Post Office Sox 767

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Chicago, tilinois 60690 0767 June 5, 1986 Mr. James G. Keppler Regional Administrator U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL. 60137

Subject:

Byron Station Unit 2 Braidwood Station Units 1 and 2 10 CFR 50.55(e) 30 Day Final Report Nos. 86-03 BY and 86-05 BW Cold Leg Safety Injection Pipu Vibration and Cracks NRC Docket Nos. 50-455 and 50-456/457

Dear Mr. Keppler:

On April 30, 1986, the Commonwealth Edison Company notified your office of a deficiency reportable pursuant to 10CPR50.55(e) concerning a crack in the cold leg safety injection line during ECCS full flow testing. The letter provides information to fulfill the thirty day reporting requirement and is considered to be a final report. An extension in submitting this report was discussed with W.S. Little of your office on May 30, 1986.

Description of Deficiency During ECCS Full flow testing for Byron Station, Unit.2, in February, 1986, a 1 1/2 inch socket welded-elbow on A (A loop) high head cold leg injection cracked and began leaking. The elbow was replaced and the test continued. The cracked elbow was metallurgically examined. The examination concluded there were micro-cracks which had propagated through the wall.

This elbow is downstream of a " pump runout" protection orifice which is flow limiting. At high flow rates during ECCS Full Flow, the small diameter orifice creates a high velocity flow and as a consequence high vibration.

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l Additional vibration testing, conducted with hand held instruments, showed high vibrational loads occurring at the elbow which exceeded Code allowable. The elbow was replaced with a five (5) diamete: bent pipe (5-D bend) and valve 2SI8810A was relocated to avoid a " lumped mass" near the point of stress concentration.

Testing with strain gauges confirmed the change was acceptable and was within Code allowable.

During this set of vibration tests, hand held instruments identified high vibrational loads at D (D loops) high head 1 1/2 inch cold leg injection elbow which exceeded Code allowables. The elbow was replaced with a 5-D bend and a support was added. Strain gauge testing again confirmed the change to be acceptable per Code allowables. The replaced elbow was subsequently metallurgically examined and micro-cracks were observed. These micro-cracks were initiated auring welding and grew as a result of service stresses.

At Braidwood Station, Unit 1, pipe vibration testing was conducted using strain gauges. This testing showed the pipe vibrational loads to be within the Code allowables. The Braidwood Unit 1 testing had D loop in its original configuration (socket welded elbow).

Safety Implications The high head cold leg injection is only put into operation during an S1 signal from the plant safeguards system. Only during a large break LOCA or ECCS Full Flow testing are these pipes subject to the high flow /high vibration conditions. During periodic testing or spurious SI actuation, these lines experience low flow and minor vibration due to the low pressure differential across the " pump runout" orifice.

Should a large break LOCA occur, which of itself is a low probability event and especially low probability on a new power plant, the high head cold leg injection provides a minor contribution to mitigating the effects. Since the micro-cracking occurs inside the containment there is no loss of borated water.

Corrective Action Taken Analysis was performed to determine the vibrational loadings and develop a revised acceptance criteria reflecting the stress intensification due to the presence of micro-cracks. Using the Braidwood Unit 1 testing results, the analysis showed that the unmodified D loop elbow was the highest vibrational load.

The D loop elbows on Byron Unit 2 and Braidwood Units 1 and 2 have been changed to 5-D bends and a support was added for additional stiffness. These lines were replicated.

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.. s The Braidwood Unit 2 A loop has been changed to replicate

'the Byron Unit 2 change. This change is not necessary for Braidwood Unit 1 since it is of a different configuration, which has been evaluated and found to be acceptable.

The B and C loops do not experience the high vibration loadings of D loop and they presently fall within the revised acceptance criteria. Therefore, no action is necessary on'these loops.

All design changes have been completed at Byron Unit 2 and Braidwood Unit 1. These changes are in progress at Braidwood Unit 2 and will be completed soon.

Please address any questions that you may have concerning this matter to this office.

. Very truly yours, if A. D. Miosi Nuclear Licensing Administrator

/klj cc: NRC Resident Inspector-Byron NRC Resident Inspector-Braidwood Director of Inspection & Enforcement U.S. Nuclear Regulatory Commission Washington, DC. 20555 1757K

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