ML13330A772
| ML13330A772 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/24/1979 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 7910050223 | |
| Download: ML13330A772 (11) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE J. T. HEAD, JR.
ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRESIDENT 213-572-1472 August 24, 1979 U. S. Nuclear Regulatory Commission Office of Inspection and EnforcEment Suite 202, Walnut Creek Plaza 1990 North California Boulevard Walnut Creek, California 94596 Attention:
Mr. R. H. Engelken, Director Docket No. 50-206 San Onfore Unit 1
Dear Sir:
By letter dated July 26, 1979, you forwarded IE Bulletin 79-17.
The Bulletin requires action by licensees concerning the potential for cracking in safety-related stainless steel piping systems containing stagnant borated water at PdR plants.
Submitted herewith as Enclosure 1 is our response to IE Bulletin 79-17.
The responses contained in Enclosure 1 correspond to the item nuxmbers given in the Bulletin.
If you have any questions or desire additional information concerning, please contact me.
Sincerely, Enclosure cc: Director, Division of Operating Reactors Office of Inspection and Enforcement 7910050OZ-
ENCLOSURE 1 RESPONSE TO IE BULLETIN 79-17 CONCERNqING PIPE CRACKS IN STAGNANT BORATED WATER SYSTEMS, ITEM 1 SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 A review has been conducted to identify those systems and portions of systems at San Onofre Unit 1 in which safetyrelated stainless steel piing is known to contain or may rt i;ts y-reltagnt, o
enated irated ater.
Piping systeus potentially within the scope of this bulletin include portions of the Reactor Colant System, Chemical and Volu e Control System, Auxiliary Coolant System (including Residual Heat Removal and Spent Fuel Cboling), Safety Injection System, Sapling System and Miscellaneous Water Systems (inclusive of the Recirculation and Containment Spray Systems).
No evidence exists that cracks in safety-related stainless steel piping at San Onofre Unit 1 may be attributed to the causes discussed in the subject bulletin; i.e.
cracks initiating on the piping I.D. surface of systems con taining stagnant or essentially stagnant brated water.
However, cracking attributed to chloride stress corrosion frm external contamination has oc curred in the weld heat affected zones and piping surfaces of stainless steel systexs.
Instances of this type of cracking have been previously reported to the NRC.
In the interest of competeness, information on cracking attri buted to externally caused chloride stress corrosion is included in the re sponses to Items l(a) through (d),
where appropriate.
Item 1. (a)
Response
Nondestructive testing of the Safety Injection, Residual Heat Removal, Reactor Coolant, Recirculation Chemical and Volume Control, and Containment Spray Piping SysttIs has been conducted on t\\j, occasions since 1975.
In re sponse to IE Circular 76-06, examinations were performed in February and March of 1977; as part of our canitnent to 10 CER 50.55a(g), examinations were conducted during the 1978 refueling outage.
Details of the procedures used, the extent of the inspections, and the results are provided below for each inspection period.
- 1.
IE Circular 76-06 Examinations.
Non-Destructive E xamination Procedures The ultrasonic examination procedures used conform to Appendix III of AS E B & PV Code,Section XI (through the Winter 1976 Addenda).
In addition, the examination area spans a distance of approximately six tismes the pipe wall thickness (but no less than 2 inches nor more than 2 incnes) on each side of the we-ld.
The visual examination Page 2 Item 1. (a) Response (Cont'd)
- 1.
IE Circular 76-06 Examinations (Cont'd) was performed per Article IWA-5000 of ASME Section XI.
The hydro static testing was performed per the San Onofre Unit 1 Appendix A Technical Specifications.
Procedure Qualifications No procedure qualifications were required since the NDT examination procedures conplied with ASME B & PV Code Section XI.
Acceptance Criteria The acceptance criteria used for the ultrasonic and visual examina tions are contained in ASME B & PV Code Section XI (through the Winter 1976 Addenda).
The leak rate limitations of the Technical Specifications were used as the acceptance criteria for the Recirculation System hydrotest.
Sampling Plan a)
Twenty-five percent (49 welds) of the total nu-nber of welds in the Safety Injection, Recirculation and Containment Spray Systems were ultrasonically inspected.
Lines with diameters of 4 inches or less were not included in this inspection in accordance with IWC-1220(d).
b)
The Residual Heat Removal System was visually inspected.
c)
A hydrostatic test of the Recirculation System was conducted in accordance with Section 4.3.111 of the San Onofre Unit 1 Appendix A Technical Specifications.
Results of the Examinations and Corrective Actions Taken The results of the above examinations were reported to the NRC by letter (J.
B. More to USNRC Region V) on May 12, 1977.
The examinations disclosed no indications of defects similar to the failures identified in IE Circular 76-06.
Specifically, a)
The results of the ultrasonic examinations indicated that all welds were acceptable.
Page 3 Item 1. (a) Response (Cont'd)
- 1.
IE Circular 76-06 Examinations (Cont'd)
.b)
No abnormalities were found during the visual inspection of the Residual Heat Removal System.
c)
The hydrostatic test of the Recirculation System was satis factorily co 1
leted.
Tvo leaks were noted during the hydrostatic test of the Recircula tion System.
These leaks were located in the heat affected zone of welded joints.
Metallurgical analysis showed that the welded joints had been sensitized to intergranular stress corrosion, probably due to the weld technique ealployed.
The welding procedure used for the replacement pipe was designed to limit the metal temperature during welding and thus eliminate the possibility of sensitization.
Terperature sensing devices were used in the heat affected zone of the new welds and metal teperature limited to 350 0F.
In addition, a welded joint intended for use in the re placement pipe was subjected to metallurgical analysis.
The results of the analysis showed no signs of sensitization.
The replacement pipe is fabricated from low stainless steel and is highly resistive of intergranular stress corrosion.
In sunmary, the changes made in fabrication technique and metal composition have minimized the possibility of intergranular stress corrosion of this line.
The recirculation line was replaced in its entirety and successfuly hydrostatically tested in accordance with Section 4.3.111 of San Onfore Unit 1 Technical Specifications.
[See response to Bulletin Item 1. (d)].
- 2.
1978 Inservice Inspection Nondestructive Examination Procedures The ultrasonic and liquid penetrant examination procedures used conformed to the ASME B & PV Code Section XI and V through the Sumer 1975 Addenda.
The Code Class 2 hydrotests were performed in accordance with Articles IWA-5000 and IWC-5000 of the ASME B & PV Code Section Xl.
The Recirculation System hydrotest was performed per the San Onofre Unit 1 Appendix A Technical Specifi cations.
Procedure Qualifications No procedure qualifications were required since the ultrasonic and liquid penetrant examination procedures used conformed to the ASME B & PV Code Sections XI and V.
Page 4 Item 1. (a) Response (Cbnt'd)
- 2.
1978 Inservice Inspection (Cont'd)
Acceptance Criteria The acceptance criteria used for the ultrasonic, liquid penet.rant and ASME Code Class 2 hydrotests are contained in the ASME B & PV Code Section XI.
The acceptance criteria of the Technical Speci fications were used for the RacircuIation Systemn hydrotest.
Sampling Plan a) Per the San Onofre Unit 1 Inservice Inspection Program and as it applies to this bulletin, 14 welds were penetrant tested and 8 welds were ultrasonically tested on lines in the Safety Injection, Residual Heat Removal, Reactor Coolant System, Con tainment Spray, and Chemical and Volume Control Systems.
This represents 16% of the applicable welds scheduled to be examined by the ISI Program during the current 10 year inspection in terval.
b) Portions of eight ASME Code Class 2 lines in the Chemical and Volume Control System and within the scope of this bulletin were hydrotested per the San Onofre Unit 1 Inservice Inspec tion Program.
c)
A hydrotest of the Recirculation System was conducted in accordance with Section 4.3.111 of the San Onofre Unit 1 Appendix A Technical Specifications.
Results of the Examinations and Corrective Actions Taken The results of the Inservice Inspection were reported to the NRC by letter (H. L. Ottoson to USNRC Region V) on January 25, 1979.
These examinations and the Recirculation System hydrotest dis closed no indications of defects similar to the failures identi fied in the subject bulletin. However, a linear indication was found in a socket weld on line 2090 (Safety Injection Fecircula tion).
This indication was a shallow surface defect and appeared to be related to fabrication.
The defect was removed by grinding and weld build-up applied to restore wall thickness. Four addi tional Safety Injection indications were found in these welds.
Item 1. (b) Response:
Station Order S-E-2, entitled "Operation, Maintenance and Chemical Control of Heat Exchange Equipnent", sets forth the water chemistry control program for San Onofre Unit 1. This station order assigns responsibility Page 5 Item 1. (b)
Response (Cbnt'd) and sets limits for the operating integrity, chemical treatment and chemical maintenance of all controlled plant systems.
Plant systems containing stagnant, oxygenated borated water which are routinely sampled for chemical content are the Safety Injection System and the Refueling Water Storage Tank.
The sampling parameters, limits and fre auencies are as follows:
Recircu System Parameter Limit Frequency lation
- 1.
Refueling Water Boron 3775-4275 ppn WeeKly Refueling Storage Tank Chlorides
<.15 ppn Weekly Interval Fluorides
<.1 ppn As neces sary
- 2.
Safety Injection Boron 3775-4275 ppn Mbnthly anthly System The above sampling schedule has been in effect since the current re visions to Technical Specification Sections 3.3.3 and 4.2 were incorporated on April 1, 1977.
Current Technical Specifications require the boron concentra tion of the Refueling Water Storage Tank to be maintained at 3750 to 4300 ppn whenever the Safety Injection System or the Containment Spray System is re quired to be operable.
Weekly data reported since April 1, 1977 shcws the boron concentration in the Refueling Water Storage Tank to have been within Technical Specification limits during all periods of plant operation.
A low value of 3683 ppn and a high value of 4994 ppn were recorded during plant outages.
Prior to April -1, 1977, Technical Specifications required the boron con centration in the Refueling Water Storage Tank to be maintained above 2900 pp-n.
Available data shows the boron concentration in the Refueling Water Storage Tank normally in the range of 2900-3000 ppn.
Formal reporting of chloride concentrations in the Refueling Water Storage Tank began in March, 1977.
Sample analysis data shows that chloride concentra tions in the tank have reached or exceeded the Station Order S-E-2 limit of
.15 ppn on 20 occasions; however, in only 4 of these instances did the concen tration exceed.20 ppn.
The highest concentration of chlorides recorded was 1.10 ppn.
Out of limit conditions result in the contents of the Refueling Water Storage Tank being processed through an ion exchanger until the require ments for chloride concentration in Station Order S-E-2 are met.
Chemical sampling and analysis on the Refueling Water Storage Tank con tents performed to measure chloride concentrations vDould additionally indicate Page 6 Item 1.
(b) Response (Cont'd) fluoride concentrations in excess of Station Order S-E-2 limits.
Fluoride concentrations in the Refueling Water Storage Tank have been determined not to be a problem at San Onofre Unit 1.
7Tebrn concentration of the Safety Injection System is checked during the monthly system operational test.
The boron concentrations have been within the limits specified by Station Order S-E-2 except on three occasions, when values below the minimun concentrations were recorded.
In accordance with Operating Instruction S-3-3.3, Hot Operational Test of Safety Injection and Containment Spray, the Safety Injection System was recirculated on these occasions and subsequent sampling showed the boron concentration to be within limits.
Prior to April 1, 1977 the boron concentration in the Safety Injection System was normally in the range of 2900-3000 ppm.
No design changes relating to the maintenance of water chanistry with respect to pH, B, CL, F, or 02 in safety related stainless steel lines con taining stagnant oxygenated borated water have been processed at San Onofre Unit 1.
Most of the lines identified as potentially within the scope of this bulletin are in use, flushed or recirculated at least on an occasional basis.
As described in a letter (J. T. Head to USNRC Region V) dated May 12, 1977, all portions of the Safety Injection, Recirculation, Containment Spray and Residual Heat Removal Systems are flushed at least once per refueling in terval.
Item 1 (c) Response:
San Onfore Nuclear Generating Station Unit 1 was designed and constructed prior to the establish1ent by regulating agencies of a required code for pre service or inservice inspection.
Preservice Inspections undertaken for San Onofre Unit 1 were conducted in accordance with ASA B.31.1-1955 inclusive of the acceptance criterion therein; however, records of these inspections are no longer available.
Item 1. (d) Response:
The following listing identifies the new materials utilized in the repair or replacement of safety-related stainless steel lines containing borated water having previously experienced cracking at San Onofre Unit 1.
Page 7 Item 1 (d)
Response (Cont'd)
Line Replacement System Designati SpecificationRemarks
- 1.
Miscellaneous 734-6"-HP ASME-SA-31 2 Entire line re Water Systems GR 304L, Sche-placed in 1977.
trtem dule 40S Through wall spray) cracking attri buted to stress corrosion resulting from manufacturing and fabrication deficiencies.
Reported to NRC in LER 77-02 and LER 77-04.
Normally stagnant.
- 2.
Chemical 2014-3"-151R ASTM A-312, A 20 ft.
section and Volune TP 316 was replaced in control Schedule 40S 1978.
Through wall System cracking attributed to chloride stress corrosion from ex ternal. containa tion.
Reported to NRC in LER 78-012.
Normally flowing.
2002-2"-2502R ASTM A-312, Same as above.
TP 316 Schedule 160S 2005-4"-2502R None Surface cracks of sane general pattern as above were ground out.
Reported to NRC in LER 78-012.
Normally flowing.
1/2" north
- None, bld Repaired in 1979 as charging pup Repaired the result of through seal water wall cracking attri injection buted to pump vibra line tion.
Normally flowing on alternate weeks.
Page 8 Item 1 (d)
Response (Cont'd)
Line Replacement Systen Designation Specification Remarks Chemical &
2054-1"-15lN None, Weld Through wall cracking Volume pai red in 1979 attributed Control to apparent chloride Systen stress corrosion from (Cbnt'd) external contamination.
Flow established in this line once per shift for borated water make up.
2054-1"-150N ASTM-A-312 A 6" section was TP 304 replaced in 1978 as Schedule SOS a result of through wall cracking attri buted to apparent chloride stress cor rosion.
Flow is established in this line once per shift for borated water make up.
2052-2"-151N Sleeved over Through wall cracks 2044-2 "-151N with ASTM A-312 attributed to ap TP 316L, Sche-parent external dule 40S chloride stress cor rosion were observed near union of lines sleeved over in three 8" sections in 1979.
Flow verifica tion once per week in line 2062; re circulation once per shift in line 2044.
Page 9 Item 1 (d)
Response (Ont'd)
Line Replacement System Designation Specification Remarks 2046-2"-151N ASME SA-376, Through wall cracks
-1/2"-15LN TP 304, Sdhe-in 1978 were attri 2049-2"-151T du e 40S buted. to aooarent 2064-2"-15N chloride stress 2048-2"-151N corrosion on exterior 2051-2"-151N surface of piping 2053-1"-15N which led to replace ment of line 2046 and portions of others.
The line is in fre quent use and as a minimun is recircu lated once per shift.
2044-2 "-151N ASTM-A-312 Through wall cracks TP 304 attributed to chloride Schedule 40S stress corrosion on exterior surface led to replacement in 1976 of a 2 ft.
sec tion.
Flow is es tablished in this line once per shift.
Boric Acid None, Vbld Minor surface Storage repaired indications in tank Thnk parent metal in (Item D-3) heat affected zone of exterior weld joining drain line socket weld nipple to bottom of tank.
Repaired in 1978.
Item 2. (a) Through (c)
Response
Inservice inspection examinations of normally accessible portions of systems identified under Item 1 which have not been previously examined will be examined within 90 days in accordance with this Bulletin.
Page 10 Iten 3.
ResMnse:
This item is not applicable to San Onofre Unit 1.
Item 4, 5, 6 and 7
Response
The requirements of Items 4, 5, 6 and 7 of this Bulletin, where appropriate, wiM be met by San Onfore Unit 1.