ML19225D051
| ML19225D051 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/17/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Groce R VERMONT YANKEE NUCLEAR POWER CORP. |
| References | |
| NUDOCS 7908060014 | |
| Download: ML19225D051 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION 7, y ' '". J REGION I S
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Docket No. 50-271 JUL 1713n Vermont Yankee Nuclear Power Corporation ATTN:
Mr. Robert H. Groce Licensing Engineer 20 Turnpike Road Westborough, Massachusetts 01581 Gentlemen:
This Information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities.
No response is requested at this time however liccnsees should be aware that the NRC is evaluating the issuance of a Bulletin to operating PWR's requesting information on previous inservice inspections of stagnant borated water systems and requesting inspection of systems which have not been inspected recently.
If you have questions or comments regarding this matter, please contact the Director or the appropriate NRC Regional Office.
Sincerely, C
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Bo ce H. Grier Director
Enclosures:
1.
IE Information Notice No. 79-19 2.
List of Information Notices Issued in 1979 cc w/encls:
W. F. Conway, Plant Superintendent Ms. J. Abbey, Technical Secretary A. Z. Roisman, Natural Resources Defense Council 421 114 790806D g y
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 IE Information Notice No. 79-19 Date:
July 17, 1979 Page 1 of 2 PIPE CRACKS IN STAGNANT B0 RATED WATER SYSTEMS AT PWR PLANTS Description of Circumstances:
During the period of November 1974 to February 1977 a number of cracking incidents have been experienced in safety-related stainless steel piping systems and portions of systems which contain oxygenated, stagnant or essentially stagnant borated water.
Metallurgical investigations revealed these cracks occurred in the weld heat affected zone of 8-inch to 10-inch type 304 material (schedule 10 and 40), initiating on the piping I.D. surface and propagating in either an intergranular or transgranular mode typical of Stress Corrosion Cracking.
Analysis indicated the probable corrodents to be chloride and oxygen contamin-ation in the affected systems.
Plants affected up to this time were Arkansas Nuclear Unit 1, R. E. Ginna, H. B. Robinson Unit 2, Crystal River Uni t 3, San Onofre Unit 1, and Surry Units 1 and 2.
The NRC issued Circular 76-06 (copy attached) in view of the apparent generic nature of the problem.
During the refueling outage of Three Mile Island Unit I which began in February of this year, visual inspections disclosed five (5) through-wall cracks at welds in the spent fuel cooling system piping and one (1) at a weld in the decay heat removal system.
These cracks were found as a result of local boric acid build-up and later confirmed by liquid penetrant tests.
This initial identification of cracking was reported to the NRC in a Licensee Event Report (LER) dated May 16, 1979.
A preliminary metallurgical analysis was performed by the licensee on a section of cracked and leaking weld joint frcm the spent fuel cooling system.
The conclusion of this analysis was that cracking was due to Intergranular Stress Corrosion Cracking (IGSCC) originating on the pipe I.P.
The cracking was localized to the heat affected zone where the type 30. stainless steel is sensitized (precipitated carbides) during welding.
In addition to the main through-wall crack, incipient cracks were observed at several iocations in the weld heat affected zone including the weld root fusion area where a miniscule lack of fusion had occurred.
The stresses responsible for cracking are believed to be primarily residual welding stresses in as much as the calculated applied stresses were found to be less than code design limits.
There is no conclusive evidence at this time to identify those aggressive chemical species which promoted this IGSCC attack.
Further analytical efforts in this area and on other system welds is being pursued.
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IE Information Notice No. 79-19 Date:
July 17,1979 Page 2 of 2 Based on the above analysis and visual leaks, the licensee initiated a broad based ultrasonic examination of potentially affected systems utilizing special techniques.
The systems examined included the spent fuel, decay heat removal, makeup and purification, and reactor building spray systems which contain stagnant or intermittently stagnant, oxygenated boric acid environ-ments. These systems range from 21/2-inch (HPCI) to 24-inch (borated water storage tank suction), are type 304 stainless steel, schedule 160 to schedule 40 thickness respectively.
Results of these examinations were reported to the NRC on June 30, 1979 as an update to the thy 16, 1979 LER.
The ultrasonic inspection as of July 10, 1979 has identified 206 welds out of 946 inspected having UT indications characteristic of cracking randomly distributed throughout the aforementioned sizes (24"-14"-12"-10"-8"-2" etc. )
of the above systems.
It is important to note that six of the crack indications were found in 21/2-inch diameter pipe of the high pressure injection lines inside containment.
These lines are attached to the main coolant pipe and are nonisolable from the main coolant system except for check valves.
All of the six cracks were found in two high pressure injection lines containing stagnated barated water.
No cracks were found in the high pressure injection lines which were cccasionally flushed during makeup operations.
The ultrasonic examination is continuing in order to delineate the extent of the problem.
Enclosures:
1.
List of Information Notices Issued in 1979 42i ii6
i.
November 26, 1976 IE. Circular No. 76-06 STRESS CORROSIO CRACKS IN STAGNAh"r, LOW PRESSURE STAINLESS PlPING CCNTAINING BORIC ACID SOLUTION AT FWR's DESCRIPTION OF CIRCUMSTANCES:
During the period November 7,1974 to November 1.1975, several incidents of through-wnll cracking have occurred in the 10-inch, schedule 10 type 304 stainless steel piping of the Reactor Building Spray and Decay Heat Removal Systems at Arkansas Nuclear Plant No. 1.
On October 7,1976, Virginia Electric and Powcr also reported through-wall cracking in the 10-inch schedule 40 type 304 stainless discharge piping of the "A" recirculation spray heat exchanger at Surry Unit No. 2.
A recent inspection of Unit 1 Containnent Recirculation Spray Piping revealed cracking similar to Unit 2.
On October 8, 1976, another incident of similar cracking in 8-inch schedule 10 type 304 stainless piping of the Safety injection Pump Suction Line st.the Cinna fac1*1ty was reported by the licensee.
Information received on the metallurgical analysis conducted to date indicates that the failures were the result of intergranular stress corrosion cracking that initiated on the inside of the piping.
A cocmonality of f actors observed asucciated with the corrosion mechanism were:
1.
The cracks were adjacent to and propagated along wcld zones of the thin-walled low prensurn piping, not part of the reactor coolant system.
2.
Cracking occurred in piping containing relatively stagn t boric acid solution not re red for normal operating con ' ~ "
s.
3.
Analysis of surface products at this time indicate a s..oride ion interaction with oxide formation in the relatively stagnant boric acid solution as the probable corrodant, with the state of stress probably due to welding and/or fabrication.
The source of the chloride ion is not definitely known.
However,.at ANO-1 the chlorides and sulfide level observed in the surface tarnish film near welds is believed to have been introduced into the piping during testing of the sodium thiosulf ate discharge valves, or valve leakage.,Similarly, at Ginna the chlorides and pctential oxygen 421 117
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IE Circular No. 76-06 November 26, 1976 availability were assumed to have been present since originni construction of.the borated water storage tank which is vented to atmospherc.
Corrosion attack at Surry is attributed to in-leakage of
, chlorides through recirculation spray heat exchange tubing, allowing buildup of contaminated water in an otherwise normally dry spray piping.
ACTION TO BE TAKEN 3Y LICENSEE:
1.
Provide a description of your program for assuring continued integrity of those safety-related piping systems which are not frequently flushed, or which contain nonflowing liquida.
This program should include consideration of hydrostatic testing in accordance with ASME Code Section XI rules (1974 Edition) for all active systems required for safety injection and containment spray, including their recirculation modes, from source of water supply up to the second isolation valve of the primary system.
Similar tests should be considered for other safety-related piping systems.
2.
Your program should also consider volumercic examination of a representative number of circumferential pipe welds by non-destructive examination techniques.
Such examinations should be perforned generally in accordance with Appendix I of Section XI of the ASME Code, except that the examined area should cover a distance of approximately six (6) times the pipe wall thickness (but not J ess than 2 inches and need not exceed 8 inches) on cach side of the weld.
Supplementary examination techniques, such as radiography, should be used where necessary for evaluation or confirmation of ultrasonic indications resulting from such examination.
3.
A report describing your program and schedule for those inspec-tions shculd be submitted within 30 days after receipt of this Circular.
4.
The NRC Regional Of fice should be informed within"24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, of any adverse findings resulting during nondestructive evaluation of the accessible piping welds identified above.
5.
A summary report of the examinations and evaluation of results should be submitted within 60 days f rom the date of co=pletion of proposed testing and examinations.
421 118
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IE Circular No. 76-06
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November 26, 1976 This summnry report should also include a brief description of plant conditions, operating procedures or other activities which previde assurance that the effluent chemistry vill maintain low levels of potential corrodants in such relatively stagnant regions within the piping.
Your responses should be submitted to the Director of this office, with a copy to the NEC Office of Inspection and Enforcement, Division of Reactor Inspection Programs, Washington, D.C.
20555.
Approval of NRC requirements for reports concerning possible generic problems has been obtained under 44 U.S.C 3152 fram the U.S. General Accounting Of fice.
(GAO Approval B-180255 (K0062), expires 7/31/77.)
421 119 4
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ENCLOSURE 2 IE Information Notice No. 79-19 Date:
July 17,1979 Page 1 of 2 LISTING OF IE INFORMATION NOTICES ICSUED IN 1979 Information Subject Date Issued to Notice No.
Issued 79-01 B rgen-Paterson Hydraulic 2/2/79 All power reactor Shock and Sway Arrestor facilities with an Operating License (OL) or Coastruction Permit (CP) 79-02 Attempted Extortion -
2/2/79 All Fuel Facilities Low Enriched Uranium 79-03 Limitorque Valve Geared 2/9/79 All power reactor Limit Switch Lubricant facilities with an OL or CP 79-04 Degradation of 2/16/79 All power reactor Engineered facilities with an Safety Features OL or CP 79-05 Use of Improper Materials 3/ 21 /79 All power reactor in Safety-Related Components facilities with an OL or CP 79-06 Stress Analysis of 3/23/79 All power reactor Safety-Related Piping facilities with an OL or CP 79-07 Rupture of Radwaste Tanks 3/26/79 All power reactor facilities with an OL or CP 79-08 Interconnection of 3/?8/79 All power reactor Contaminated Systems with facilities with an Service Air Systems Used OL and Pu Processing As the Source of Breathing fuel facilities Air 79-09 Spill of Radioactivity 3/30/79 All power reactor Contaminated Resin facilities with an OL 79-10 Nonconforming Pipe 4/16/79 All power reuctor Support Struts facilities with a CP A21 120
IE Information Notice No. 79-19 Date:
July 17,1979 Page 2 of 2 LISTING OF IE INFORMATION NOTICES ISSUED IN 1979 Information Subject Date Issued to Notice No.
Issued 79-11 Lower Reactor Vessel Head 5/7/79 All power reactor Insulation Support Problem facilities with an OL or CP 79-12 Attempted Damage to New 5/11/79 All Fue. Facilities, Fuel Assemblies Research Reactors, and Power Reactors with an OL or CP 79-13 Indication of Low Water 5/29/79 All power reactor Level in the Oyster facilities with an Creek Reactor OL or CP 79-14 Safety Classification of 6/11/79 All applicants for, Electrical Cable Support and holders of a Systems power reactor CP 79-15 Deficient Procedures 6/7/79 All power reactor facilities with an OL or CP 79-16 Nuclear Incident at 6/22/79 All research and Three Mile Island test reactors with an OL 79-17 Source Holder Assembly 6/20/79 All holders of reactor Damage from Misfit Between OLs and cps Assembly and Reactor Upper Grid Plate 79-18 Skylab Reentry 7/5/79 All holders of reactor OLs 421 121
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