ML19325D235
| ML19325D235 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/12/1989 |
| From: | Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| P-89349, NUDOCS 8910190252 | |
| Download: ML19325D235 (3) | |
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October 12, 1989-
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Unit No. 1-P-89349
.U.'S. Nuclear: Regulatory' Commission
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. ATTN:
Document-Control Desk Washington, D.C.
20555 Docket No. 50-267
SUBJECT:
-De-rating of Steam Generator Main' Steam Ringheaders Gentlemen:
l Please be advised of our intention to> eliminate the ASME Sec. III,
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Class A status of-the Main Steam Ringheaders on each of~th 12 steam i
- generator modules.at Fort St. Vrain. The NRC !s already aware of the multiple linear 7;;dications that were receatly documented on.
The following is.ourl basis-for eliminating the.ASME Sec. III,. Class A.
requirements-for these components:
1.
Fort St.
Vrain has. ceased operation effective August 29, 1989.
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The reactor will not be re-started.
t 2.
The Main Steam Ringheaders will be removed from their existing ASME :Sec.
III, Class A requirements.
Existing multiple indication,s in base metal make it impossible to meet code y
requiremants (including ANSI B31.1).
. Preliminary conversations with ASME Code Inspectcrs have indicated that this would be permissible based on NRC approval.
3.
Prior.to discovery of the leak in the module B-1-4 header, the
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i ringheaders had been subjected to steam conditions of 2400 psig and-1025 -F during normal plant' operation.
These ~ components will now be part of the Condensate circulating system during the defueling process. This is a water system at
. maximum conditions of 400 psig and 300* F, which is a substantial reduction in service.
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Th'e ring' header integrity has maintained during the plant.
b operation, with the exception ~of leaKege which was documented B
'recently in NCR 89-144 This leakage w:s limited to one area and.
was driven by 2400 psi,1000? F' main steam conditions.
Given the l
ring. header past nerformance 'at ' main steam conditions, it is reasonable to cxpect that the header integrity can be maintained.
1 at' the-much reduced operating conditions (following repair of the one ;1eak).
4.
Public Service. Company of Coloradr (PSC). t s evaluated the,new operating requirements of water at 400 psig and 300* F.
A wall I
thickness calculation per B 31.1 para. 104.1 (based on original material minimum strength) gives a required wall _ thickness of w.
0.0758".
-A thickness of 0.250" (nominal) was chosen for the NCR-repairs in ordar to be conservative, account, for base ~ metal defects, and to be. similar to industry specificaticns. for 5" 4 SCH 40-pipe, which has wall-thickness of 0.258".
PSC 'non-destructive examination technicians have performed a liquid penetrant inspection on the steam ring headers.
The areas of concern are the locations where nozzles were welded into the main header.
Each header has 18 nozzles.
The.5" ( header has a
' nominal wall thickness of 3/4 inch.
i PSC crafts worked under the direction of Engineering and Quality Centro 1_ to perforrr grinding on several of these indications in
-.o rde r to determine extent of indications and possible repair methods.. Grinding operations-followed by addicional liquid penetrant' examination revealed continued propagation of linear indications. Grinding operations were stopped since PSC QA Metallurgy and Engineering had decided t! at excessive weld repair on this:SB407 header material would induce further damage with possible cracking.
The following course of action was taken:
1.
Weld repai-the existing through crack on the module B-1-4 header which resulted in leakage.
2.
Inspect all areas where grinding had taken place.
Measure the wall thickness and perform weld repairs as needed to obtain a minimum nominal thickness of 0.250" of metal in the pipe wall.
Liquid penetrant examination will be performed on the added weld metal.
l All of the above work is currently in progress.
At the reduced operating conditions, pSC would not expect that degradation of headers, 1# any would be mainifested by leak before break and catestrophic failure wculd be extremely remote.
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PSC wi11 perform weekly surveillances whenever these heed"rs are-K in se rvi ce'.
Visual._ inspection will assure safety and reli abili ty.~
It :thould be noted that failure of a ring header -
- dos not-result in conditions adverse to public health and.
sa fety.;;
6.
Plant Operations will assure that the maximum -operating l conditions of 400 psig and 300 F will not be exceeded.
.Your prompt consideration of this matter is appreciated. 'If you have any questions, please contact Mr. M. H. Holmes at (303) 480-6960.
Sincerely 0-/Y W Y D. W. Warembourg Mar.ager, Nuclear Engineering Division DW/JD:jmb.
cc::Regionsi-Adn,inistratior, Region IV ATTN: Mr. T. F. Westerman Chief, Projects Section B Mr. Robert Farrell
' Senior Resident Inspector
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