ML17345A715

Forwards Justification for Continued Operation of Plant, While NRC Bulletin 88-011, Pressurizer Surge Line Thermal Stratification Issues Being Resolved

ML17345A715
Person / Time
Site:	Turkey Point
Issue date:	05/31/1989
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-88-011, IEB-88-11, L-89-194, NUDOCS 8906070164
Download: ML17345A715 (9)

Text

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AC CEM RATED 2 TRIBUTlON DEMONS TIO'.i SYSTEM REGULATO INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8906070164 DOC.DATE: 89/05/31 NOTARIZED: NO DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH.NAMEi 'UTHOR AFFILIATION WOODY,C.O: .. Florida Power & Light Co.

RECZP.NAM" RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Forwards justification for continued operation of plant, while NRC Bulletin 88-011 issues being resolved.

DISTRIBUTION CODE: IE30D TITLE: Bulletin COPIES RECEIVED:LTR 88-11 Pressurizer

+ ENCLStratification Surge Line Thermal

/ SIZE:

NOTES'ECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2,LA 1 0 PD2-2 PD 1 1 EDISONiG 1 1 INTERNAL,: AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB 1 1 NRR CHAN,T 1 1 NRR HOUIS 1 1 NRR KADAMBI,P 1 1

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NRR/DOEA/GCB 11 NRR S ILRB12 1

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TOTAL NUMBER OF COPIES REQUIRED: LTTR '4 ENCL 23

P.O. Box14000, Juno Beach, FL 33408.0420 MAY 3 1 1989 L-89-194 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Units 3 and 4 Docket Nos. 50-250 and 50-251 NRC Bulletin No. 88-11 Pressurizer Sur e Line Thermal Stratification NRC Bulletin No. 88-11, "Pressurizer Surge Line Thermal Stratification," issued on December 20, 1988, requested that licensees establish and implement a program to confirm pressurizer.

surge line integrity in view of the occurrence- of thermal stratification, and to inform the staff of the actions taken to resolve this issue.

By letter L-89-79 dated March 6, 1989 Florida Power & Light Company indicated that it would be participating in a program for partial resolution of this issue through the Westinghouse Owner's Group (WOG). The WOG program was discussed in that letter. A schedule for completion of the program was also provided.

Justification for continued operation of Turkey Point Units 3 and 4 while this issue is being resolved is provided in the attached evaluation.

Should there be any questions, please contact, us.

Very truly yours, C. O. W o Acting nior Vice President Nuclear WFC/TCG/gp Attachment cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, Turkey Point Plant 8906070264 890531 PDR ADDCK 05000250 8 PNU an fpI. Group cornpanr

ATTACHMENT 1 Turkey Point Units 3 and 4 Docket Nos. 50-250 and 50-251 NRC Bulletin No. 88-11 Pressurizer Sur e Line Thermal Stratification Back round It was first measurements reported in INPO SER 25-87 that temperature at a German PWR indicated thermal transients different than design. Recent measurements at several domestic PWR's have indicated that the temperature difference between the pressurizer and the hot leg results in stratified flow in the surge line, with the top of the flow stream being hot (pressurizer temperature) and the bottom being colder (hot leg temperature). The top-to-bottom temperature difference can reach 250 F to 300 F in certain modes of operation, particularly Modes 3, 4 or 5 during heatup and cooldown.

Surge line stratification causes two effects:

o Global bending of the pipe is different than that predicted in the original design.

o Fatigue life of the piping could be reduced due to the global and local stresses from stratification and striping.

More recently, the NRC has issued Bulletin 88-11 "Pressurizer Surge Line Thermal Stratification," December 20, 1988, identifying actions to be taken by licensees.

a) Conduct visual inspection walkdown.

b) Update stress and fatigue analysis to account for stratification and striping.

c) Obtain monitoring data, as necessary.

The bulletin encourages licensees to perform actions b) and c) above through collective efforts with other plants. In October, 1988, FPL and other members of the Westinghouse Owners Group (WOG) authorized a program to perform a generic evaluation of surge line stratification in Westinghouse PWR's that will address portions of Bulletin 88-11.

The WOG program is designed to benefit from the experience gained in the performance of several plant specific analyses on Westinghouse PWR surge lines. These detailed analyses included definition of revised thermal transients (including stratification) and evaluations of pipe stress, fatigue usage factor, thermal striping, fatigue crack growth, leak before-break, and support loads. The overall analytical approach used in all of these analyses has been consistent and has been reviewed, in detail, by the NRC staff.

As of March, 1989, plant sp'ecific analyses have been performed on five domestic Westinghouse PWR's. In addition, twelve Westinghouse plants have completed or are currently performing an interim evaluation of surge line stratification which includes finite element structural analysis of their specific configuration under stratified loading conditions.

WOG Pro ram Status As part of the current WOG Program, surge line physical and operating data have been collected and summarized for all domestic Westinghouse PWR s (55 units). Information relating to piping layout; supports and restraints, components, size, material, operating history, etc., has been obtained. These data have been evaluated in conjunction with available monitoring data and plant specific analyses performed by Westinghouse. The results of this evaluation were presented to the NRC in a meeting on April 11, 1989. The evaluation is being formalized into a Westinghouse topical report (WCAP-12277, Proprietary and WCAP-12278, Non-proprietary version) scheduled for submittal to the NRC on June 15, 1989.

This topical report forms the basis for the following justification for continued operation.

Justification for Continued 0 eration A. Stratification Severit Thermal stratification (Q T > 100 F) has been measured on all surge lines for which monitoring has been performed and wh'ich have been reviewed by the WOG to date (eight surge lines).

The amount of stratification measured and its variation with time (cycling) varies. This variation has been conservatively enveloped and applicability of these enveloping transients has been demonstrated for plant specific analyses.

Various surge line design parameters were tabulated for each plant. From this, four parameters judged to be relatively significant were identified.

a. Pipe inside diameter,

b. Piping slope (average),

c. Entrance angle of hot leg nozzle,

d. Presence of mid-line vertical riser.

These paiameters were used in a grouping evaluation which resulted in the definition of 10 monitoring groups corresponding to various combinations of these parameters at Westinghouse PWR.'s. Approximately 40% of the plants fall into one group for which a large amount of m'onitoring data has already been received and for which the enveloping thermal transients, discussed above, are applicable. The remaining 604 of Westinghouse PWR's are divided among the other nine additional groups. Although monitoring data-has not yet been received representative of all these groups, in general, the combination of significant parameters of these nine groups is expected to decrease the severity of stratification below that of the enveloping transients. This conclusion is also supported by a comparison of available monitoring data.

B. Structural Effects Significant parameters which can influence-the structural effects of stratification are:

a) Location and design of rigid supports and pipe whip restraints, b) Pipe layout geometry and size, c) Type and location of piping components.

Although the material and fabrication techniques for Westinghouse surge lines are reasonably consistent and of high quality, the design parameters listed above vary among Westinghouse PWRs.

This vaiiation in design is primarily a result of plant specific routing requirements.

A preliminary evaluation, comparing the ranges of these parameters to those of plants for which plant-specific analysis and interim evaluations are available, (approximately 20% of Westinghouse PWR's), has been performed. This comparison indicates a high degree of confidence that, from a combined transient severity and structural effects standpoint, the worst configuration has most likely been evaluated. This conclusion is supported by plant-specific analyses covering five plants and interim evaluations of six additional plants (interim evaluation is in progress on six more plants as of March 1989). These analyses and evaluations have included various piping layouts, pipe sizes, support and restraint designs and piping components.

Although the full range of variation in these parameters has not been evaluated, experience gained from these evaluations indicates that further evaluations will not result in a more limiting configuration than those already evaluated.

C. Ooeratin Procedures The WOG currently has available the surveys of operating procedures performed in support of existing. plant-specific analyses. Experience indicates that heatup and cooldown procedures have a significant effect on stratification in the surge line. All conclusions reached by the WOG to date have assumed a steam bubble mode heatup and cooldown procedure which may result in a temperature difference between the pressurizer and reactor coolant system (RCS) hot leg of more than 300 F. In many cases, individual plant operating procedures and technical specifications provide limits on this value. It is also known that some procedures utilize nitrogen, during at least part of the,heatup/cooldown cycle, as a means of providing a pressure absorbing space'n the pressurizer. Based on information currently available to the WOG, a high confidence exists that the steam bubble mode heatup, assumed to date, is conservative with respect to Westinghouse PWR's.

D. Pi e Stress and Remainin Life The design codes for surge line piping have requirements for checking pipe stress limits and the effects of fatigue loadings.

These stress limits provide a means of controlling stress from primary loads such as pressure, deadweight, and design mechanical loading, as well as stress from secondary loads such as thermal and anchor motion effects.

Stratification in the surge line is a secondary load which will only affect the qualification of secondary stresses. The qualification of primary stresses is not affected by this loading.

Secondary stresses are controlled to prevent excessive displacements and gross plasticity and to prevent excessive fatigue loadings in the pipe. The basic characteristic of a secondary stress is that it is self limiting; thus, a failure from a single application of a secondary loading is not expected.

For the stratification issue, the potential effects of excessive displacements have been investigated through a detailed visual observation of the surge line during the walkdown required per Bulletin 88-11 action 1.a. The following are the results of the walkdowns:

Unit 3 The results of the walkdown performed by FPL personnel indicated some crushed insulation at two of the pipe whip restraints. The movement of the surge line resulting in 'he crushed insulation is consistent with the thermal expansion of .the line during power operation and startup. There is no evidence of abnormal movement "or interference of the surge line piping'ith any of the whip restraints.

The walkdown also indicated that the spring hanger had bottomed out both of its spring cans. This movement is consistent with the maximum predicted movement with stratification. The resulting loads have been determined to remain within the capacity of the spring hanger components.

Unit 4 The results of the walkdown performed by FPL personnel indicated some crushed insulation at two of the pipe whip restraints. The movement of the surge line resulting in the crushed insulation is consistent with the thermal expansion of .-the line during power operation and startup. There is no evidence of abnormal movement or interference of the surge line piping with any of the whip restraints.

The walkdown also identified cracks in three pipe to saddle tack welds in spring hanger SR-400. These welds serve only to locate the saddle relative to the pipe; they are not required to maintain the capacity of the hanger. The spring assembly showed no signs of damage.

The effects of secondary stresses on the remaining life of the surge line have been evaluated on a generic basis through the WOG Program. The following summarizes the results of this evaluation.

All plant specific analyses performed as of March, 1989, have demonstrated compliance with applicable ASME Codes and a surge line fatigue life in excess of a 40 yr. plant life. Review of plant specific, fatigue calculations indicates that the surge line fatigue life is primarily dependent on the number of heatup and cooldown cycles, rather than years of operation.

Considering the worst case years of operation (28.5 yr.) in combination with the worst case number of heatup-cooldown cycles (75, at a different plant) at any Westinghouse PWR, and assuming a 40 year life for all surge lines, it is estimated that no more than approximately 504 of the fatigue life has been used at any Westinghouse plant to date.

For a design life considering 200 heatup-cooldown cycles (used in plant specific analyses), this would indicate approximately 100 remaining cycles. This number of remaining cycles the postulated worst case number for the two year time far'xceeds frame needed to resolve the stratification issue.

E. Leak Before Break All the plant specific analyses performed to date that have included the loadings due to stratification and striping have validated the "leak-before-break" concept and have substantiated a 40-year plant life. Fatigue crack growth calculations, performed as part of these plant specific analyses, have demonstrated that any undiscovered crack as large as 104 of the wall thickness would not grow to cause leakage within a 40 year plant life. Nevertheless, any postulated through wall crack propagation would most likely result in "leak-before-break" and thus permit a safe and orderly shutdown.

F. Ins ection Histor The NDE inspection history at Turkey Point Units 3 & 4 as well as all other domestic Westinghouse designed PWR's, has not revealed any service induced degradation in the surge line piping that has been attributed to thermal stratification.

Summar of Conclusions From WOG Pro ram Based on information assembled on surge lines for all domestic Westinghouse PWR s, and evaluation of that information in conjunction with plant-specific and other interim evaluation results, the WOG concludes that:

0 A high degree of confidence exists that further evaluation will confirm that the worst combination has already been evaluated for stratification severity, structural effects and operating procedures.

o All plant specific analyses, to date, have demonstrated a 40 year life of the surge line. Assuming that further evaluation leads to. the same conclusion for the remaining Westinghouse PWR s, the worst case remaining life is approximately 100 heatup-cooldown cycles.

Through wall crack propagation is highly unlikely, however, o

"leak-before-break" would permit a safe and a through wall leak should develop.

orderly shutdown if NDE inspection history demonstrates the present day integrity of Westinghouse PWR pressurizer surge lines.

6

o While additional monitoring, analyses, and surveys of operating procedures are expected to further substantiate the above conclusions, the presently available information on surge line stratification indicates that Westinghouse PWR's may be safely operated while additional data is obtained.

t Overall Conclusion Based on the above discussions, FPL believes it is acceptable for Turkey Point Units 3 & 4 to continue power operation for at least ten additional heatup-cooldown cycles. FPL has committed to address the requirements of Bulletin 88-11 by January, 1991.