NRC Generic Letter 79-20, Cracking in Feedwater Lines

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GL79020

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555

May 25, 1979

ALL PRESSURIZED WATER REACTOR LICENSEES

Gentlemen:

We have recently been informed of cracking in feedwater lines at D. C. Cook Units 1 and 2. The cracks were discovered after Unit 2 had been shut down to investigate leakage inside containment. Leaking circumferential through-wall cracks were identified in the piping heat affected zones of two feedwater nozzle to pipe welds for two steam generators in Unit 2. Subsequent radiographs revealed crack indications originating on the inside of the pipe, in similar locations in the two other steam generator feedwater lines in Unit 2. Four similar locations have been examined in Unit 1 and crack indications found in the locations examined.

You are requested to submit the information identified in the enclosure in accordance with 10 CFR 50.54

(f) of the Commission's regulations within 20 days of receipt of this letter. Compliance with this request does not, of course, relieve you from other reporting requirements of your license in connection with this matter.

Sincerely,

Victor Stello, Jr., Director Division of Operating Reactors Office of Nuclear Reactor Regulation

Enclosure:

Information Requested on PWR Feedwater Lines

cc w/enclosure Service List

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INFORMATION REQUESTED ON PWR FEEDWATER LINES

Design

• 1. Provide as-built piping or isometric drawings of the feedwater line to steam generator sparger within containment. Show details of the design such as dimensions, pipe schedule, support type and locations, pipe restraints, and valve(s).

• 2 Provide the results of any stress or fatigue analyses which was performed for this system.

Fabrication History

• 1. Supply a list of the materials for the steam generator sparger, steam generator feedwater nozzles and feedwater piping within containment.

• 2. Provide the details of the welding process(es) used to make the nozzle-

to-pipe, pipe to sparger and piping welds. Include details of welding such as preheat, joint configuration (include with or without backing ring), and post weld treatment, if any.

3. Provide the NDE performed during and after fabrication of the weld joints requested in question 2.

4. Provide the Code edition to which the feedwater piping system was fabricated.

5. State the fracture toughness requirements, if any, for the feedwater piping system.

Preservice/Inservice Inspection and Operating History

1. State whether the feedwater system welds received a preservice inspection in accordance with ASME B&PV Code,Section XI.

2. Provide the extent of inservice inspection performed on the feedwater pipe to steam generator nozzle welds. Include the results of the examinations, any corrective actions taken and causes of any failures.

3. Provide the schedule and extent of inservice inspection for the feedwater system for the next inspection interval.

4. Provide any history of water hammer or vibration in the feedwater system and design changes and/or actions take to prevent these occurrences.

5. Provide a description of feedwater chemistry controls and a summary of chemistry data.

• Provide the information available on these items within 20 days and any remaining information within 60 days of receipt of this letter.