ML20148D951
| ML20148D951 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/31/1967 |
| From: | Thornburg H US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20148D950 | List: |
| References | |
| 50-010-67-04, 50-10-67-4, NUDOCS 8010100444 | |
| Download: ML20148D951 (10) | |
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U. S. ATOMIC ENERGY COMMISSION REGION III DIVISION OF COMPLIANCE May 31, 196'7 C0 REPORT No. 10/67-4
Title:
COMMONWEALTH EDISON COMPANY LICENSE NO. DPR-2 f 'G7' '
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By:
H. D. Thornburg, Senior Reactor Inspecto' /.
SUMMARY
Commonwealth Edison (CE) has essentially completed the f'.rst phase of the investigation of cracks and defects in the small diameter primary system piping. They have concluded that the small diameter piping weld heat af-fected zonem were sensitized by the welding procedure and methods of weld-ing application used.
Stress corrosion attack then occurred in the grain boundaries of the sensitized regions. The welding procedures used in the fabrication and erection of the large diameter primary system piping should not have been conducive to similar sensitization of the weld heat affected zones.
The available records of material chemical and physical properties, fabri-cation records, welding procedures, metallurgical test data, etc. tend to support CE-s conclusions. The opinions of staff metallurgists and our con-s'ultant alto tend to support CE's conclusions.
CE personnel have pointed out that stainless steel piping has never been known to fail in a brittle manner. The material in the heat affected zones of small diameter piping containing cracks has been chown to be duc-tile. Our consultant concurs in this also.
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TheDresden'1 leak'detectionprocedureandthelinebreakemergencyi}roce-dure have been reviewed and strengthened. A reanalysis of the full spec-trum of line break accidents for Dresden 1 is in process.
Work is progressing tavard further metallurgical examinations. Efforts are being made to obtain the detailed chemical and physical data on the small diameter piping.
A succesrful hydrote' t of the primary system at 1205 psig and 210 F was s
wittnessed by Region III personnel.
No items of noncompliance or immediate safety significance were noted.
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> DETAILS I.
Scope of Visit This report has been prepared to summarize the results of our review of Commonwealth Edison's investigation of cracks in the small diameter pri-mary system piping at Dresden 1.
CO Reports No.10/67-2 and 10/67-3 plus" :
this report should describe the Region III effort to investigate the matter to data.
A visit was made by the write: to the CE offices in downtown Chicago on April 4, 1967 to review the available records pertaining to the primary piping material and fabrication. A visit was made to the site by the writer, Mr. C. E. Jones, Reactor Inspector, Region III, and Mr. G. Fiore111, Reactor Inspector, Region III to wittness the hydrotest, review procedures, and obtain information on May 17, 1967.
During these visits, records were reviewed, operations in progress were observed, and interviews were held with the following Commonwealth Edison personnel:
W. B. Benke, Assistant to the President E. C. Bailey, Chairman, Dresden Review Board H. K. Hoyt, Superintendent, Dresden Nuclear Power Station (DNPS)
C. B. Zitek, Assistant Superintendent, DNPS R. Holyoak, Technical Group Supervisor, DNPS W. E. Kiedaisch, Chemist and Radiation Protection Engineer, DNPS II.
Results of Visit A.
Results of Commonwealth Edison's Investigation of Primary System Pipe Cracks Mr. Bailey stated that the Commonwealth Edison (CE) invertigation ameter p1, ping g noted in the heat affected zones of welds in the small di-of the crackin of Dresden 1,has disclosed the following:
1.
The small diameter piping became sensitized during the welding process.
2.
Stresses.were present in the seamless tubing due to the manu-facturing process and possibly from the welding procedure used.
3.
The above two conditions are necessary for initiation of stress corrosion attack.
(In most cases, intergranular attack mechan-isms include the presence of an ica such as C1".
(Writer's note)-
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IIThe small diameter piping ref erred to above,is Gra'de 304 stainless' steel seamless tubing, ranging from 3 to 10 inch'es in diameter, manufactured by Babcox and V11cox Company.
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Results of Visit (continued) 1I 4.
The large diameter piping had a known fabrication history which was not conducive to sensitization in the heat affected zones of the welds'.
For this reason and because a UT examina-tion of a representative number of the heat affected zones of large diameter pipe.. indicated no defects, it is CE's conclu-sion that the large diameter pipe will not be subjected to a similar attack.
B.
Independent Review The writer reviewed the following sources of informatien in con-nection with Mr. Bailey's' arguments regarding the condition of the Dresden 1 primary system piping:
1.
Written welding procedures used by Southwest Fabricating and s
c Welding Company (SW), Inc. of Houston, T(xas, the firm which performed the shop fabrication of both the large and small di-ameter piping.
2.
Minutes of meetiegs held b3 tween representatives of General El'ctric Company and Southwest Fabricating and Welding Com-e pany regarding the welding and fabrication of the Dresden 1 primary system piping, 3.
Selected original radiographic films of the Dresden 1 piping.
4.
Chemical anslyses, destructive test data and weld qualifica-tions for the large diameter piping supplied by Taylor Forge and Pipe Works _(TP) of Chicago, Illinois.
5.
Previous reports pertaining to the problem; CO Reports No.
10/57-1, 10/67-2, and 10/67-3.
,6. The invoice for the shipment of seamless _, tubing from the.B&W Co., it.cluding heat numbers. The certified chamical analyses were not included.
7.
A report prepared by the General Electric Co. titled:
"Inves-tigation of Stainless Steel Pipe Failures at DNPS No. 1, APED -517 0.
8.
Miscellaneous correspondence from contractors and subcontrac-tors conccrning the erection and fabrication of the primary system piping.
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1 S The large diameter piping referred to above.vas annufactured from rolled and seam velded stainless steel plate pipe' manufactured by Taylor Forge and Pipe Works ranging from 12 to 22 inches in diameter.
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Results of Visit (continued)
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- 9. 'The results of meetings between Commonwealth Edison personne1' and General Electric welding engineers responsible for the
- fabrication of Dresden 1 primary piping.
- 11. The chemical-anclyses for the fittings and castings used in-
.the primary _ system fabricated by Bonney Floyd, Inc. of Columbus, Ohio.
12.
System piping prints and details.
The results of this review corresponding to the arguments advanced by Mr. Bailey are listed below. The information identified by lower case letters and as notes was obtained from the above review.
4 1.. The small diameter piping became sensitized during the welding process.
a.
The material (pipe and fittings) was fabricated from Grade 304 stainless steel.
It is known that this material can become sensicized by3phe fornation of chromium carbides in the grain boundaries; b.
Mr. Chyle,ourweldingandmetallurgpcalconsultant,has previously advanced the observation-that the macro photo-graphs of weld cross section showed evidence that sev;ral tungsten inert gas passes (TIG) were made in applying the weld. This would indicate that high interpass weld temper-atures had been experienced during application of the small diameter welds.
NOTE:
Chremium carbide takes place when stainless steel is heated in the sensitizing range of 900 to 1400 F.
A narrow strip ci base metal near the weld bead is heated into the sensitizing range duringjwelding and becomes sus-ceptible to intergranulat attack; c.
Photomicrographs of samples taken from the first two small diameter pipe failures at Dresden 1 are shown in a G-E re-port titled:
"Inve uresatDNPSNo.1.gyigationofStainlessSteelPipeFail-Electron micrographs of one of the
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gjStainless Steel Information Manual, DP-860, Vol.1, paragraph 3.2.2.
gjCO Report No. 10/67-2.
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- APED 5170.
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3 Results-of Visit (continued)-
cracks are shown in the same report.
CE personnel stated that the photomicrographs do not indicate gross precipita-tion of chromium carbide, while.the electron micrographs show distinct evidence of carbide precipitation.
G-E per-sonnel have indicated that they feel that the above indi-cations do not conclusively prove that sensitization has taken place.
d.
The welding procedure for the small diameter welds has l'
been reviewed. TIG processes were specified for each pass of the weld. The weld was qualified.
FOTE: Weld test tensile data indicates that the pipe may havebeen971d worked to a degree. Room temperature ten-sile tests-on parent metal near crack No. I showed simi-lar cold working, e.g., ultirate strength ~84 Ksi and elongation ~40%.
e.
No material certification data was yet available on small diameter tubing.
f.
It was noted that SW wrote Bechtel on August 8, 1958 and stated that the small diameter pipe would be sent to an outside concern for removal cf asphalt. substance on the outside of the pipe. It is known that the piping system received an acid wash following erection.
2.
Stresses were present in the seamless tubing due to the manu-facturing process and possibly from the welding. procedure used.
a.
A certain amount of cold working is inherent in the canu-facture of seamless tubing which has not received heat treatment following manufacture. Although the man.ufactur-ing history of the seam 1ces tubing has not been completely
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' developed, it'is believed that the f.ubing did not receive a post fabrication heat treatment.
b.
Weld tensile test data and destructive tests performed on parent material near the first crack detected in C loop tend t'o support the conclusion that the seamless tubing was cold worked (see item 1.d above).
c.
The GE welding engineer responsible for the Dresden 1 pip" ing described the implementat, ion of the welding procedure.
The welds in the small diameter piping were applied by a team of two welders.
In eany cases the beads overlapped which was conducive to overheating and stressing.
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1IStainicas Steci Information Manual, DP-860, paragraph 3.2.2.
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, Resultw'of Visit (continued) 3.
The above two conditions are necessary for the initiation of stress corrosion attack.
NOTE: There are instances where the presence of Cl contri-butes to intergranular attack at the grain boundaries.
In-stances of Cu+t ion contributing to intergranular attack FTve also been reportec, according to Mr. Chyle.
a.
The average concentration of C1" ior in the primary ' system duringtg7 year 1963,1964,1965and1966hasaveraged~
0.04 ppm-b.
The Cu-Ni feed water heater and condenser tubes have un-dergone corrosion. The best data available indicates that the concentration range for Cu++ in the primary system has been 0-20 ppb. over the same four year period. Other cor-rosion product average concentrations in the primary sys-cem are:
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Fe @ 20-900 ppb.
Ni @ 30-550 ppr.
4.
The large diameter piping had a known fabrication history which was not conducive to sensitization in the heat affected
- ones of the welds. For this reason and because a.
The mill data on the plate for the large diameter pipe in-dicates that the plate was in the annealed condition fol-lowing forming, seam welding, and solution heat treatnient at TF. The yield strength of a test sample was 39,600 psi, the tensile strength was 82,710 psi, and the clonga-tion in 2" was 58.0%. The destructive test data : cross the seam welds indicated <10% cold working.
b.
The large diameter pipe was heat treated at d9500F for 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, depending on the thickness of the plate and cooled by forced air following forming and welding, c.
CertaJn of the'16" pipe sections were returned to TF by SW for removal of scale by pickling. Reportedly, precautions were taken against overexposure to I!C1.
d.
The shop
- welding procedure for the large diameter pipe contained the following elements.
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.I 8/This is an estimate' based on summary information and does not' represent an exact average of the analytical data, t
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> Results of Visit (continued)
(1) The root pass was deposited using the TIG process. A space was lef t in the weld preparation so t: hat the root pars could be observed for proper fusion and pen-q etration.
1 (2) All succeeding passes were applied using the TIG pro-Cess.
(3) The G-E welding engineer responsible for the Dresden 1 primary system piping stated that a stray ring water header was used inside the large diameter pipe for cooling purposes while the circumferential shop welds were applied. The inspector has found a refer-ence to the possibic use of artificial cooling meth-ods in a document which repottedly summarized several meetings between G-E, TF, and Bechtel personnel con-cerning pipe fabrication. The G-E welding engineer retconsible for the Dresden 1 piping reported to Mr.
Bailey that a spray ring header and a system of dams in the piping were used to cool the large diameter pipe ss the passes following the first two passes were applied.
(4) 1he use of Temple stichs sensitive.to temperaures of
< 800F at-pipe walls during application of large di-ameter circumferential welds.
It was specified that surfa e metal temperatures be maintained below 800 F.
e.
Mr. Bailey stated that he followed the field weldfag of the large diameter pipe.
(1) Root' pass was applied using the TIG process under ob-servation.
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(2) Succeeding passes were applied using stick electrodes to maintain low interpass temperatures.
(3) Bechtel personnel rade the field welds.
f.
Mr. Bailey summarized his argarents with respect to the sensitization of the large diameter pipe as follows:
(1) The q 3/4" to ~ 1-1/2" walls of the large diameter pipe provide a more extensive heat sink than for the thinner walled pipe.
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Results of Visit (continued)
(2) In the case of the shop welds, artificial cooling was
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used. Temperature sensing (gross) was employed by use of the Temple sticks.
(3) Interpass overheating was avoided in the application of the large diameter field uelds by the use of stick electrode passes.
(4) No cracks have been detected in the large diameter piping.
C.
Hydrostatic Tast-9 On May 17, 1967, the Dresden 1 primary system was hydrotested at 1205 psig and 210 F.
The portions of the system tested were as follows, 1.
The primary side of all four recirculating loops, including the 6" diameter bypass loops around the inboard steam genera-tor outlet isolation valve, where a significant number of the defects and cracks in the small diameter piping have been found.
2.
The pressure vessel and the communicating risers and downcom-ers to and from the steam drum. The steam drum was also pres-surized.
3.
The 6" dawncomer header equalizing line, where defects were also found and which was subsequently replaced.
4.
The small diameter piping to the first isolation valves for the following systems:
a.
Emergency condenser.
b.
Both reactor cleanup loops.
c.
Both shutdown cooling loops.
d.
Reactor druins.
5.
The poison system.
6.
The control drive system back to the block valves.
7.
The primary steam lines to the containment isolatien valves.
Two groups composed of representatives from P.cgion III, Traveler's Indemnity Company, and CE toured all of the reactor compartments for a vis-ual inspection of the primary system piping' under 1205 psig, including:
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-G Results of._Yisit (continued) 1 - Each steam generator.
2.
All instrument rooms.
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3.
Both reactor cleanup loop compartments.
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The steam drum compartment.
5.
The vicinity of the poison tank.
6.
The downcomer and riser cavities.
7.
The steam line tunnel.
8.
The sub pile room.
9.
The vicinity of the control drive piping manifolds.
During the course of the above visual inspection, several valve packing leaks and one drum level sensor leak were detected. No piping leaks were detected.
It was observed that CE and Traveler's Indemnity personnel were very thorough in their inspection efforts. The hydrotest was considered successful by personnel at the site.
D.
Safety Analysis The CE analysis of the significance of the cracks and defects found to date in the small diameter piping is as follows:
1.
The mechanism for the occurrence of pipe cracks in the small diameter piping is thought to be fairly well known and cannot be identified at present as an indication of the impending failure of the large diameter pipe.
2.
The parent material at the ends and edges of the crack is ductile, which tends to preclude the possibility of a rapidly propagating brittle fracture.
3.
The propagation of cracks in stainless steel is a rather slow process,whichcanbedetectedfarinpdvanceoftheexistence g
of a catastrophic primary system leakT 4
Present leak detection methode etaployed at the site are rensi-
- t. iv e.
(See Section E below.)
5.
Eccrgency procedures are in existence for coping with a pri-mary system leak.
It should be noted that studies performed by G-E have shown that y
j the double ended break of a 4" primary system if ne (which is not isolatable) is the maximum sized break which can be tolerated with the loss of off-site l
power.
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4 E! essrs. Chyle and A. Holt of DRS generally support this statement.
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> Results of Visit (continued)
E.
Leak Detection The writer performed a study of the Dresden 1 leak detection scheme in May, 1966, which is attached as Appendix A.
It should be noted thec the activity detection methods are the most sensitive (~2 to 20 cc/ min with pri-mary cystem activity in the vicinity of 1 pc/cc); The humidity detection system, ventilation continuous particulate monitor and containment vessel activity monitors are continuous and alarm in the central control room.
L The leak detection procedure has been updated in Operating Order 6-67 by personnel at the site and uas reviewed by the inspector on May 17, 1967. Essentially, it states that operation of the reactor will be discon-tinued if the leak is nog isolatable and the' airborne activity in the con-tainment reaches 1.5x10~ pc/ce, which roughly corresponds to a leak rate of 40 ml/ min. Specifications f or the availability of instrumentation are now included in the procedure, which are considered to be adequate by the writer.
F.
Follow-up Items e
As o,f the date of this report, the following i tems have ne c been fully pursued essentially either because of the unavailabi ity of records or the necessary laboratory work has not yet been completed:
1.
The certified chemistry of the small diameter seacless tubing.
At present G-E and B& Wart attempting to locate the records.
6 2.
The physical properties of the small diameter seamless tubing l
G-E and B&W are also attempting to locate these-recordo.
I 3.
The metallurgical study of the first axial crack.
G-E is pre-i sently working on this in their hot laboratories.
4.
Micro probe analysis of a cracked section of small diameter piping in an attempt to identify ions which"may,have assisted the grain boundary attack. Arrangements have been made with Battelle Memorial Institute to perform a micro probe analysis.
5.
Re-examin,ation of all of the available radiographs of prinary system welds. This work will require correlation of film iden-tification with print veld numbers followed by an examination j
of the films.
These matters as well as the general performance.of the leak detec-ll tion scheme and the primary system piping during future service willi be followed closely.
Attachment:
Appe6 dix A
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