ML17334B239
| ML17334B239 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/09/1988 |
| From: | Cheng C Office of Nuclear Reactor Regulation |
| To: | Scott W Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17325B069 | List: |
| References | |
| TAC-33288, TAC-68698, NUDOCS 8811170057 | |
| Download: ML17334B239 (4) | |
Text
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Docket No. 50-316 MEMORANDUM FOR:
FROM:
SUBJECT:
ENCLOSURE 2 UNITED STATES NUClEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 November 9, 1988 Wayne E. Scott, Jr., Acting Project Manager Project Directorate III-1 Division of Reactor'Projects -III, IV,'
and Special Projects Office of Nuclear Reactor Regulation C.
Y. Cheng, Chief Materials Engineering Branch Division of Engineering and Systems Technology REQUEST FOR TECHNICAL ASSISTANCE - CRACKING OF THE REACTOR COOLANT PIPING TO STEAM GENERATOR NOZZLE WELDS AT D.C.
COOK UNIT 2 (AITS 033288, TAC NO. 68698)
In accordance with a Region III request for technical assistance dated October 4, 1988, the Materials Engineering
- Branch, NRR, has evaluated the welding problems associated with the steam generator replacements at D.C.
Cook Unit 2.
Extensive cracking occurred during the welding of the reactor coolant piping to the replace-ment steam generator nozzles.
Our assessment of the issue was derived from the SER related to the licensee's topical report, a meeting with the licensee on September 19,
- 1988, a site visit between the period September 20-22, 1988 and the licensee's letter dated October 28, 1988.
NRR received technical assistance from two consultants from Brookhaven National Laboratory and P~rameters Inc.
Region III personnel participated in both meetings.
The D.C.
Cook replacement project was the first use of '.he flux cored arc weld-ing (flux core) process to apply a stainless steel butter on a cast carbon steel nozzle.
At the September 19, 1988 meeting the licensee concluded that the flux core process is equivalent to other flux processes and no ASME Code or regulatory restrictiors exist for this application.
The licensee encountered wetting and tie-in difficuties at the nozzle butter deposit.
The licensee contended that the cracking problem was resolved with a change in technique, i.e., electrode angle and welaing sequence.
Before the September 19, 1988 meeting the licensee haa removed all known defects and the welding was essentially completed.
The licensee concluded that nondestructive testing would demonstrate that the final weld con-figuration would meet all applicable Codes.
The staff considered the cracking to be a significant event because of the number and depth of repair excavations.
The site visit, review of records and interviews determined that factors, in adoition to those presented by the licensee, contri-buted to the problem as described in the attached SER.
NRR did not make a
specific root cause determination because of the limited scope of the SER, the short amount of time spent dt the plant site, and the absence of a cracked specimen for a failure analysis.
CONTACT:
M.
- Hum, EMTB, DEST X20932 f
'I
The staff made these findings:
The welding was performed based on the requirements of Section III,Section IX and Section XI of the ASME Code.
The licensee lost,control of the welding process ir, late August 1988 as a result of the tolerances in the essential variables and the non-essential variables.
The degree of cracking is illustrated in the SER.
2.
The licensee formed an experienced team to assess the problem and took corrective action.
Flaws were excavated and joints rewelded with a modified procedure.
3.
The structural integrity of the welds was addressed by the licensee with nondestructive examination methods that exceedeo the requirements of the ASME Code.
The SER has the following conclusions:
1.
The steam generator nozzle to primary piping welds are acceptable for service based on the nondestructive examinations that were performed.
2.
The mechanical properties of the completed welds were not significantly affected by the repair process.
3.
The nondestructive testing described in the licensee's Cctober 28, 1988 lette" will proviae adequate assurance that defects that could cause a loss of structural integrity will be identified.
4.
The staff did not find the automatic flux core arc welding process to be a prime contributing factor.
The licensee experienced significant dif-f;.ulties with the control of the welding parameters.
The licensee resolved f e problems, modified the welding procedure and repair ed the welds.
This riemorandum completes the requested task to provide technical assistance.
A SALP input is not provided for this SER because the Region III activities cover additional functional areas;
.thus, a regional assessment of the entire replace-rrent program woula be more comprehensivi.
cc:
L. Shao M. Virgilio H. Mill~r, RIII J. Jacobson, RIII E. Martindale, EHAR C.
- Cheng, Chief Materials Engineering Branch Division of Engineering and Systems Technclogy J.
Richardson J.
Stang D. Danielson, RIII H. Schuster, Bt'L H. Conrad