ML20210S227

Trip Rept of 860510-11 Site Visit to Participate in Licensee Cold Walkdown of Reactor Coolant Loop Piping & Components, Including Supports,To Assess Whether Cause of LER 85-013, Rev 1 Determined

ML20210S227
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	05/15/1986
From:	Terao D Office of Nuclear Reactor Regulation
To:	Ballard R Office of Nuclear Reactor Regulation
References
TAC-61405, NUDOCS 8605200466
Download: ML20210S227 (5)

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1. 4 gf UNITED STATES 8" NUCLEAR REGULATORY COMMISSION E -).tj WASHINGTON, D. C. 20555

.s EAY 151986 4.....

MEMORANDUM FOR: Ronald L. Ballard, Chief Engineering Rranch, PWR-A THRU: houtamBagchi,SectionLeader

/ Mechanical Engineering Section Engineering Branch, PWR-A FROM: David Terao, Mechanical Engineer Engineering Branch, PWR-A

SUBJECT:

TRIP REPORT

SUMMARY

OF THE TROJAN RCL COLD WALKDOWN (TAC #61405)

On May 10-11, 1986, the NRC staff (D. Terao, NRR, and J. Crews, RV) visited the Trojan Nuclear Plant and were accompanied by the NRC resident inspectors (S. Richards and G. Kellund). The purpose of the visit was to participate in the licensee's cold walkdown of the reactor coolant loop (RCL) piping and components including their supports to assess whether the cause of the events recently reported in Licensee Event Report (LER)85-013 Revision 1 has been reasonably detemined and whether appropriate corrective actions have been implemented. A list of attendees at the technical meetings is included in Attachment A to this memorandum. A copy of LER 85-013 Revision 1 is included

, as Attachment B.

Technical Discussions with Licensee A brief description of the background and events related to the LER was presented by the licensee, Portland General Electric (PGE), to the staff. The licensee addressed the following items:

the monitoring of the erratic thermal movements of the pressurizer surge line following the removal of the thennal sleeve in 1982, the structural failures (baseplate anchor bolt pull-out) of a pipe whip restraint bracing member on the Loop B hot leg, the failures of the 900 kip, Anker-Holth hydraulic snubbers on the four Trojan steam generators to meet lock-up test acceptance criteria.

The description, potential cause, and corrective actions of the above items I are described in detail in LER 85-013 Revision 1. In our discussions, the i licensee identified the root cause of the three events discussed in LER 85-013 l as the inoperability of the steam generator hydraulic snubbers. The licensee l l

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0605200466 060515 PDR S ADOCK 05000344 PDR

Ronald L. Ballard MAY 151996 discussed supplemental inspections and corrective actions which they have taken subsequent to the issuance of LER 85-013 Revision 1. These additional actions and the results of those actions already completed are described in a letter from B. D. Withers (PGE) to S. A. Varga (NRC) dated May 9, 1986 (Attachment C to this memorandum). The supplemental actions incluced the following:

1) inspection of each of the four RCL hot leg pipe whip restraints to verify the integrity of the horizontal pipe whip restraint bracing members and to check the clearances between the pipe and the whip restraint during both hot and cold conditions,

2) inspection of the vertical column supports on all four steam generators (including baseplate anchor bolts and support pad cap screws) and of the steam generator seismic support ring girder (upper lateral restraint) and bumper pads,

3) inspection of the pipe whip restraints and pipe hangers on the pressurizer surge line for both hot and cold conditions,

4) visual inspection of potential interferences on reactor coolant pump supports,

5) inspection of gaps between the RCL crossover piping and its associated pipe whip restraints under both hot and cold conditions,

6) visual inspection of the RCL cold leg pipe whip restraints including gaps in the cold condition,

7) visual inspection of the RTD bypass manifold piping and supports in the cold condition,

8) inspection of the gaps between the main steam line pipe whip restraints and the main steam line at the steam generator nozzle in the cold condition, and

9) a nondestructive examination (dye liquid penetrant) of the pipe-to-elbow weld on the RCL "B" hot leg.

In addition, the licensee has retained Bechtel Power Corporation to perform an independent review of the overall program initiated by the licensee since 1982 and to verify the conclusions and corrective actions to date. Furthermore, the licensee has retained Westinghouse Electric Corporation as a consultant for confirmation of NSSS related items.

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Ronald L. Ballard NAY 151996 The licensee provided the staff with the current status of the results of the cold walkdown inspections described above including the licensee's evaluations and conclusions to date and monitoring programs to be conducted during hot conditions. The cold walkdown inspections were being conducted by the licensee using several teams in the mechanical, civil / structural and NDE disciplines. The licensee's evaluations and conclusions presented to the staff are preliminary at this time. The final evaluation by the licensee of the cold walkdown results is anticipated to be completed by May 21, 1986 and will be provided to the staff.

The discussions with the licensee focused on the results of the Impell RCL stress analysis; specifically, the RCL hot leg elbow where the maximum piping stress was predicted to occur. The staff expressed a concern that because a detailed finite-element plastic analysis of the elbow had not been performed, the surface examination of the Loop B hot leg pipe-to-elbow weld might not be sufficient to address the potential for crack initiation inside the elbow itself. As a result, the licensee discussed various alternatives to exan the elbow body usirg NDE techniques available and, at the same time, maintaining ALARA considerations. The licensee determined that a ultrasonic testing (UT) of the elbow material (centrifugally cast stainless steel) using a 41 degree refracted L-wave technique could be performed, and the work was initiated.

The UT would be perfonned by Westinghouse personnel. The accuracy of tFis technique would be confirmed by Westinghouse home office. The procedure used for the UT examination is described in Westinghouse Inspection Procedure 151-205, " Manual Ultrasonic Examination of Full Penetration Circumferential and Longitudinal Butt Welds", dated May 26, 1975 (Revision 2 - Issued April 29, 1977).

NRC Staff Walkdown of RCL The staff conducted an independent inspection of the four Trojan reactor coolant loops. Although all four loops were generally inspected by the staff, the staff inspection focused on the Loop B hot leg and its steam generator (including the Loop B pipe whip restraints and snubbers) because the findings to date appeared to indicate that the worst case failures found by the licensee which could be attributed to the locked-up steam generator snubbers were associated with Loop B. Furthennore, the pressurizer surge line is connected to the Loop B hot leg.

The staff inspection of the Loop B hot leg pipe whip restraint found the baseplate of the horizontal bracing member to be pulled away from the wall about 1 inch. A modification to the baseplate had been previously implemented i through an NCR which added shims between the beseplate and the wall and l provided additional steel and new anchor bolt locations. The failure of the l pipe whip restraint bracing appeared to have been caused by the binding of the pipe whip restraint to the hot leg piping during thermal expansion of the l

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Ronald L. Ballard MAY 15 E06 RCS. In the cold condition, the pipe whip restraint did not appear to move completely back to its original position as evidenced by 1) the pull'ed out condition of the baseplate of the horizontal bracing, 2) the raised concrete under the baseplate of the pipe whip restraint vertical legs, and 3) the uneven gaps in the shims between the pipe and the restraint.

The staff inspection of the Loop B steam generator and its supports identified the following. The structural steel used for the retention of the steam generator insulation around the man-way cover appeared to have been bent by the tilting of the steam generator. Although, according to the licensee, some tilting of the steam generator is expected under normal hot conditions (and as evidenced by the bent steel framing in Loops A, C, and D), the steel framing in Loop B appeared to have been bent approximately 5 degrees more than the framing in the other loops. It should not be construed that the Loop B steam generator tilted 5 degrees more than the other steam generators. However, the steel framing In Loop B which was bent 5 degrees more than the other steel framing should be evaluated to determine 1) if the deformation was caused by the tilting of the steam generator, and 2) if so determined, the relation between the angle of the bent steel framing and the angle of the steam generator.

The staff inspection of the Loop B steam generator vertical supports, baseplates, anchor bolts, cap screws, and upper ring girder identified no other signs of deformations which could have been caused by the lock up of the steam generator snubbers.

Furthermore, the staff did not identify any other potential interferences which might have caused unanticipated restraint of thermal expansion of the RCL (other than SG snubber lock-up and binding of the hot leg pipe whip restraint).

The staff inspected the pipe whip restraints on the Loop B cross over leg.

The staff found that the portion of the pipe whip restraint which is attached to the pipe with U-bolts appeared to have rotated around the pipe. Thus, in the cold condition, the gaps on one side of the pipe whip restraint (closer to the RPV) was considerably larger than the gap on the other side. The direction of rotation of the pipe whip restraint around the crossover leg piping is consistent with the direction of the tilting of the steam generator which would occur assuming a lock up of the steam generator snubbers.

Follow-up Actions Required The findings from the staff walkdown were discussed with the licensee during the exit meeting. The licensee will address the staff findings in its final report.

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Ronald L. Ballard MAY 151996 The staff discussed the schedule for completion of tasks associated with the inoperable steam generator snubbers. The licensee expects to complete its cold walkdown inspections and provide the results to the staff by May 21, 1986. The final report will document the results of the cold walkdown (including NDE results), monitoring plans for hot condition, conclusions drawn (including root cause and generic implications), corrective actions taken (including confidence in the modifications made to the hydraulic snubbers),

and any long term considerations.

The staff discussed the need for a follow-up meeting in order to finalize our evaluation. The staff will provide a written safety evaluation upon completion of nur review of the licensee's final report.

/s David Terao, Mechanical Engineer Encineering Branch Division of PWR Licensing-A cc: C. Rossi S. Varga T. Chan J. Crews, RV S. Richards, RV G. Kellund, RV E. Sullivan D. Jeng J. Fair, IE DISTRIBUTION:

Docket Files PAEB Reading PAEB Plant File GBagchi DTerao PAEB'(( PAE DTerao:ws GBacchi 5//y/86 5/)$I86

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