ML20086D075

Final Deficiency Rept Re NSSS Primary Loop Piping Welding Discrepancies.Initially Reported on 731024.Unauthorized Departure from Approved Procedures Corrected.Full Insp Revealed No Detrimental Effects

ML20086D075
Person / Time
Site:	Diablo Canyon
Issue date:	02/14/1974
From:	Searls F PACIFIC GAS & ELECTRIC CO.
To:	Knuth D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D064	List: ML20086D075 ML20086D098 ML20086D100
References
ISSUANCES-OL, NUDOCS 8311300118
Download: ML20086D075 (6)

Text

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PACIFIC GAS AND ELECTR,IC C O MPANY  !

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Dr. Donald F. Knuth, Director  %.3{6'3  ;

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U. S. Atomic Energy Commission I.7,= ",, E U'**-

Wachington, D. C. 20545 4

Re Docket No. 50-275-OL Diablo Canyon Unit 1

! Detr Dr. Knuth:

In our letter dated October 24, 1973, we provided a. pre-liminary report concerning the circumstances surrounding the apparent-diccrepancies found in work performed on the Diablo Canyon Unit 1

' nuclear steam supply primary loop piping. We have completed;our study, and this is our final report.

As we previously reported, PGandE, with assistance from-the contractor performing the work, Wismer and Becker, and Westinghouse Electric Corporation embarked on a comprehensive analytical' and physi-cal investigative program to. evaluate'the quality of the welds, both

-completed and partially completed, of the primary coolant loop piping.

This study included'an evaluation of any possible~ detrimental conse-

quences on other welds in which the preferential welding technique had.

bacn used.

The concerns resulting from the apparent. discrepant welding, Which were unresolved at the~ time of our preliminary report, with con-clucions of the investigative efforts thereon are provided below:

A. Concern: The possibility that preferential sequence welding for alignment purposes has introduced unusual-stresses in the ' reactor I

coolant pipe and/or weld joints.

Response: Weld joints in the .as-welded c'ondition will contain g intsrnal residual stresses which are considered acceptable as part of tho. welding. process _or processes. The technique. of welding for align- -

m:nt purposes has proven itself through experience at simlilar plants. - ,

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.2 February 14, 1974 DDr. Donald F. Knuth In the case at hand, the preferential sequence welding was l performed while the equipment on the end of the piping was free to lmova without restraint in the horizontal plane and vertically upward.  :

The only positive restraint was in the vertical downward direction. I iThe intent of the preferential sequence welding was to maintain the  !

lequipment level horizontally. As our records show, the equipment on i tha end of the piping did not remain level horizontally but rather ro-l ttted out of level, thus relieving stresses which might exist if this

movement had not occurred. ,

Under the direction of Westinghouse, a special investigative l program was undertaken. Extraordinary sensitive liquid penetrant and radiographic examinations were performed on portions of the weld joints

! which could have been subjected to unusual stress if the piping had been totally. constrained. While typical weld defects were-found by this macroscopic examination, no evidence indicative of any detrimental ef-

, fccts attributed to the preferential sequence welding was discovered.

The welding as performed was in accordance with the applicable design, fabrication and installation codes for this work, and the code considers stresses due to welding in its design requirements. On the <

basis of our investigations, the welding technique was acceptable.

In addition, the primary system weld joints are required to ,

1-ba non-destructively examined after hydrostatic and hot functional test-

, ing to ascertain that no failure condition developed due to the combined 4 rooidual and applied stress effects of these tests.

B. Concern: The possibility of material degradation within weld joints due to uncertainty of heat input rates during welding and the

. present linited evidence of interpass temperature control during prefer- ,

, ential welding.

Response: A review of records for the-primary coolant piping i revenis that the procedure used for welding, Wismer and Becker Welding Procedure 3500-1, produces welds with acceptable heat inputs. The j

walding on welds 3-5A and 3-5B was performed according to Wismer and

Becker Procedure 3500-1, and differed from other welds made using the

- procedure only in the welding sequence. Since welding sequence has'no- '

offect on heat input, no degradation of weld properties took _ place due

' to heat input effects.

We have calculated that.the maximum interpass temperature i attainable after 65 weld passes, the maximum number of passes on either l

wald 3-5A or 3-5B on' any one day, was 220 degrees F, a temperature .well 4 below the maximum specified interpass temperature of 350 degrees 'F.

Ths calculation was based on temperature measurements made in~the' field, utilizing six thermocouples, during the welding of similar weld 2-4A -

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m Dr. Donald F. Knuth 3 February 14, 1974 (

t after the resumption of work. For evaluation of the adequacy of our -

4 investigative efforts on this subject and the interpretation of con- .

clusions derived, Wismer and Becker retained the advice of an engineer- 4 4 ing consultant, Jacobs Associates of San Francisco, to review all the collected data and to provide independent judgment. Their report con- 7 firmed the validity of our investigation and conclusions. PGandE has 7

' approved and implemented changes to Specification 8752 which, with  ?

associated drawings, defines the scope of the installation of the  ;

primary loop pipe; Wismer and Becker's work procedures have likewise  : _,

been changed, approved and implemented to provide improved guidelines y for accomplishment of work on this system. '

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Although the welding of joints 3A and 5A deviated from the -

procedures then in use, the welding techniques employed did not con- C flict with ASME code technical requirements or those of the engineer, Westinghouse Nuclear Energy Systems, and there was no evidence or -

indication of detrimental effects from which to conclude that any f degradation of material existed because of the preferential sequence .-

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welding technique employed. Therefore, welding of the primary coolant [

loop pipe, recommencing with joint 2-4B, was resumed November 9, 1973.

Welding of joint 3-5B was resumed January 31, 1974 and welding of joint .-

3-5A will resume about February 18, 1974. PGandE Deviation Report ,

No.182 and Wismer and Becker Non-conformance Report No.12 document

the discrepancy and are available for review by your inspectors at . I the site. j The circumstances surrounding the unauthorized departure from .)

approved procedures and subsequent documentation thereof has been cor- f rected, and we have utilized this discrepancy as a teaching vehicle in )

our special training program for on-site field engineering and inspect- L ing personnel to refamiliarize them with the quality assurance require- .

i ments of on-site activities. We will continue to monitor the applica-

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tion of field procedures to ensure that our people are informed and ,

that work is in full compliance with applicable quality assurance re- .

quirements.

Very truly yours, ._

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CC: Mr. R. H. Engelken, Director Directorate of Regulatory Operations Region V 5 l

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Dr. Donald F. Knuth, Director @)),6"={',fF' Directorate of Regulatory Operations D::, ;*. "22,"- -

Office of Regulation ""l*;.'e";"1

U. S. Atomic Energy Commission l"*6~,, y [C" Washington, D. C. 20545 Re: Docket No. 50-275-OL Diablo Canyon Unit 1

Dear Dr. Knuth:

In our letter dated October 24, 1973, we provided-a pre-liminary report concerning the circumstances surrounding the apparent discrepancies found in work performed on the Diablo Canyon Unit 1 i

nuclear steam supply primary loop piping. We have completed our study, and this is our final report.

As we _previously reported, PGandE, with assistance from the contractor performing the work, Wismer and Becker, and Westinghouse Electric Corporation embarked on a comprehensive analytical and physi-cal investigative program to evaluate the quality of-the welds,-both

completed and partially completed, ' of the primary. coolant loop piping.

This study included an evaluation of any :possible detrimental conse-l quences on other- welds in which the preferential welding . technique had 4

been used.

The concerns resulting'from the apparent discrepant welding, '

which were unresolved at the time of our preliminary report, with con-

.clusions of the investigative efforts thereon are provided below:

A. Concern:- The' possibility that preferential sequence welding

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for alignment purposes has -introduced unusual' stresses in the reactor coolant pipe and/or weld. joints.

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Response: . Weld joints in the as welded condition will'contain-

. internal residual. stresses which are considered acceptable'as part of- '

the welding process or processes.- The; technique of welding for align-L . ment purposes has proven itself through experience'at' similar plants.?

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Dr. Donald F. Knuth 2 February 14, 1974 1 j i In the case at hand, the preferential sequence welding was -}

performed while the equipment on the end of the piping was free to t move without restraint in the horizontal plane and vertically upward.

The only positive restraint was in the vertical downward direction.

The intent of the preferential sequence welding was to maintain the  ;

equipment level horizontally. As our records show, the equipment on j the end of the piping did not remain level horizontally but rather ro-tated out of level, thus relieving stresses which might exist if this movement had not occurred.

Under the direction of Westinghouse, a special investigative program was undertaken. Extraordinary sensitive liquid penetrant and radiographic examinations were performed on portions of the weld joints which could have been subjected to unusual stress if the piping had been totally constrained. While typical weld defects were found by this macroscopic examination, no evidence indicative of any detrimental ef-fects attributed to the preferential sequence welding was discovered.

The welding as performed was in accordance with the applicable design, fabrication and installation codes for this work, and the code considers stresses due to welding in its design requirements. On the basis of our investigations, the welding technique was acceptable.

In addition, the primary system weld joints are required to be non-destructively examined after hydrostatic and hot functional test-ing to ascertain that no failure condition developed due to the combined residual and applied stress effects of these tests.

B. Concern: The possibility of material degradation within weld joints due to uncertainty of heat input rates during welding and the present limited evidence of interpass temperature control during prefer-ential welding.

Response: A review of records'for the primary coolant piping reveals that the procedure used for welding, Wismer and Becker Welding Procedure 3500-1, produces welds with acceptable heat -inputs. - The-welding on welds 3-5A and 3-5B was performed according to Wismer and Becker Procedure 3500-1, and differed from-other welds made using the procedure only in the welding sequence. Since welding sequence has no effect on heat input, no degradation of. weld properties took place'due to heat input effects.

We have calculated that the~ maximum _interpass temperature  :

attainable after 65 weld passes, the maximum number of passes on'either- I weld 3-5A on 3-5B .on any one day, was 220 degrees F, a temperature 'vell-below the maximum specified interpass temperature of 350 degrees F.

The calculation was based on temperature measurements'made'in the_ field, utilizing six thermocouples, during-the welding of similar weld 2-4A' L_ . _ - _ _ . _ _ . . . ~ .

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Dr. Donald F. Knuth 3 February 14, 1974 4

after the resumption of work. For evaluation of the adequacy of our investigative efforts on this subject and the interpretation of con-clusions derived, Wismer and Becker retained the advice of an engineer-ing consultant, Jacobs Associates of San Francisco, to review all the collected data and to provide independent judgment. Their report con-firmed the validity of our investigation and conclusions. PGandE has approved and implemented changes to Specification 8752 which, with associated drawings, defines the scope of the installation of the primary loop pipe; Wismer and Becker's work procedures have likewise

been changed, approved and implemented to provide improved guidelines for accomplishment of work on this system.

Although the welding of joints 3A and 5A deviated from the procedures then in use, the welding techniques employed did not con-flict with ASME code technical requirements or those of the engineer, Westinghouse Nuclear Energy Systems, and there was no evidence or indication of detrimental effects from tihich to conclude that any degradation of material existed because of the preferential sequence i

welding technique employed. Therefore, welding of the primary coolant loop pipe, recommencing with joint 2-4B, was resumed November 9,1973.

Welding of joint 3-5B was resumed January 31, 1974 and welding of joint 3-5A will resume about February 18, 1974. PGandE Deviation Report No. 182 and Wismer and Becker Non-conformance Report No. 12 document the discrepancy and are available for review by your inspectors at the site.

4 The circumstances surrounding the unauthorized departure from approved procedures and subsequent documentation thereof has been cor-rected, and we have utilized this discrepancy as a teaching vehicle in j our special training program for on-site field engineering and inspect-j ing personnel to refamiliarize them with the quality assurance require-ments of on-site activities. We will continue to monitor Ehe applica-tion of field procedures to ensure that our people are informed and

that work is in full compliance with applicable quality assurance re-quirements.

Very truly yours,

/

CC

Mr. R. H. Engelken, Director Directorate of Regulatory Operations Region V 1

. - - _- -. .