ML18094A503

Forwards Justification for Continued Operation of Plant for Period of at Least 2 Yrs While Fatique Analysis Being Prepared,In Response to NRC Bulletin 88-011 Re Potential Threat to Pressurizer Surge Line Integrity

ML18094A503
Person / Time
Site:	Salem
Issue date:	05/31/1989
From:	Labruna S Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-88-011, IEB-88-11, NLR-N89069, NUDOCS 8906070075
Download: ML18094A503 (9)

Text

Public Service Electric and Gas Company Stanley LaBruna Public Service Electric and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 609-339-4800 Vice President - Nuclear Operations MAY 3 l 1989 NLR-N89069 United States*Nuclear Regulatory Commission Document Control Desk Washington, .DC 20555

Gentlemen:

..NRC **:BULLETIN 8 8-1.1

.... JUSTIFICATION ~'FOR CONTINUE!) *:oPERA"TION

-SALEM GENERATING STATION UNIT NOS. 1 AND 2 .

DOCKET NOS. 50-272 AND 50-311 In our.March 6, 1989 response to NRC Bulletin 88-11 regarding the potential threat to pressurizer surge line integrity due to

• thermal stratification, Public Service Electric and Gas Company (PSE&G) indicated that a generic Justification for Continued Operation (JCO) was to be developed as part of a Westinghouse Owners Group (WOG) effort to respond to NRC concerns related to the bulletin. It was also indicated that a Salem Generating Station plant-specific application of this generic JCO would be developed.and submitted to NRC to support continued operation of Salem Units 1 and 2 while the required analyses on the pressurizer surge lines are being updated. This JCO is attached and concludes that continued power operation of the Salem Units for at least ten ..additional heatup-cooldown cycles per unit is acceptable.

Your letter of May 16, 1989 granted schedular relief for the submittal of our response to Action Item 1.b of NRC Bulletin 88-11 until May 31, 1989. Your letter also indicated that the product generated through the WOG*effort should provide sufficient information to allow bulletin closeout and that the alternate schedule proposed by WOG (and PSE&G) for preparation of a detailed fatigue analysis (2 years) was unacceptable. PSE&G f e~ls that the Staff may have misinterpreted the content of the bounding evaluation which is to be provided by WOG to the NRC by June 15, 1989 (as agreed to in the April 11, 1989 meeting between NRC and the WOG). The WOG bounding analysis along with the Salem specific information presented in the attached JCO, will be sufficient to permit continued.operation. The detailed fatigue analysis is being prepared by WOG and will be enveloped into the Salem calculations of record. This effort is to be completed within the time frame presented by WOG (2 years).

8906070075 890531 PDR ADOCK 05000272 Q PDC

Document Control Desk 2

• NLR-N89069 MAY 3 1 1989 Our involvement in and correspondence with Westinghouse related to the WOG effort has indicated that while currently available information will provide sufficient justification for continued operation, a more *detailed analysis will be required to address the requirements of Action Item.1.d of Bulletin 88-11.

The attached JCO has been prepared with the intent of justifying continued operation for both Salem Unit 1 and 2 for a period of at least two years while the fatigue analysis is being prepared.

Please notify us as soon as possible if you feel that this JCO, along with .the WOG boundary evaluation*to be'provided to you by

,.,,,,,,~ June 15, 19.89 are sufficient_ to *allow continued operation while

,* ..... the .. detailed _fatigue _an~lysiS...is.. being-_ prepared.

• ':.:Tf you**have :any.:~questions with regard-.to-this~tranSm:ittal.-., piease

. _,,,.,, .. *.do--not ..*hesitat.e-:to contact us *

.Sincerely, Attachment c Mr. J. c. Stone.

Licensing Project Manager

• Ms. K. Halvey Gibson Senior _Resident Inspector _

Mr.* w. T. Russell, Administrator Region I * ***"

Mr. Kent Tosch, Chief - ,.,,.

New Jersey Department of Environmental Protection Division of Environmental Quality Bureau* of.Nuclear Engineering

. CN 415 Trenton, NJ _ 08625 .'

REF: PSE&G letter NLR-N89069 STATE OF NEW JERSEY )

} SS.

COUNTY OF SALEM )

,_, .s *.LaBruna, .. being. duly. sworn according .-to :law deposes and says:

• :r a1n *Vice .President -  :.Nuclear Operations *of. :Public . Service Electric and.Gas Company, and as such, I find the matters set forth in our letter dated , concerning the Salem Generating Station, Unit Nos. 1 and 2, are true to the best of my knowledge, information and belief.

Subscribed and sworn to before me 1/ .,.:__/ --;,,

this,.**- day of /1-~ , 1989

\/_,

~/  : /'~ .. / !

L **/;., -L . ...,. -

_.'/!J,,,rac.AJ;.~ / /[,Jc-<'~,, -"' -*

>Notary Fui{ic of New Jersey

• -~- . "!:_' . ,..,

. IARAINE Y. BEARD

• ~ Nota~ ~ublic o~ New J~mi'f . .

My Commission expires on .., . Commission ExpiresME;Jy 1, f9~f

JUSTIFICATION FOR CONTINUED OPERATION REGARDING PRESSURIZED SURGE LINE THERMAL STRATIFICATION SALEM GENERATING STATION UNIT NOS. 1 AND 2 BACKGROUND It was first reported in INPO SER 25-87 that temperature measurements at a German PWR indicated thermal transients different than design. Recent measurements at several domestic PWRs have indicated that the temperature difference between the pressurizer and the Reactor Coolant System (RCS) 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 **

, ... c';>oler .(RCS bot .leg .temp8rature)

• 0 The ~op-to~bottom temperature

• ,difference .can.. reach-250 F ..to. 30-0*F.:.during heatup. and .coQldown. * *

• * ** * *:surge '*rine****strat*i"ficat+/-on causes *t'Wo *effects~

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

Fatigue life of the piping could be reduced due to the global and local stress cycling resulting from '

stratification.

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

a) Conduct a visual inspection of the surge line b) Update stres~ and fatigue analysis to account for stratification c) Obtain thermal monitoring data, as necessary The bulletin encourages licensees to perform actions b) and c) above through collective efforts with other plants. In October 1988, PSE&G and other members of the WOG authorized a program to perform a generic evaluation of surge line stratification in Westinghouse PWRs 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, 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 specific analyses have been performed on five domestic.Westinghouse PWRs. In addition, NLR-N89069

twelve Westinghouse plants have completed or are currently performing an interim evaluation of surge line stratification This includes finit~ el_ement structural analysis of their specific configuration under stratified loading conditions.

(These analyses have not been performed for Salem Units 1 and 2).

WOG Program Status As part of the current WOG Program, surge line physical and operating data has been collected and summarized for all domestic Westinghouse PWRs (55 units). Information relating to piping layout, supports and restraints, components: size, material, operating history, etc., has been obtained. This data has 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,

._ ,,.. -.- .. .198.9. _ The _evaluation is being formalized into a Westinghouse

• ->,,-_Topical *:report .. (WCAP.J:22_77.,. ,P~oprietary-and -WCAP-12278,

.Non-proprietary version) .scheduled for submittal to-the NRC_on

_, ____ ,*"June -15,

• 1989. This topical *report"forms the basis* o-f the *I

.following justification for continued operation:

JUSTIFICATION FOR CONTINUED OPERATION A. Stratification Severity The~al stratification with temperature gradients greater than

.100 F has been measured on all surge lines for which monitoring has been performed and which have been reviewed by the WOG to date (eight surge lines).- (Surge line _temperature monitoring has not been performed at Salem).

The amount of stratification measured and its relation to time (cycling) varies. This variation has been conservatively enveloped and applied to plant specific analyses.

Var_ious surge line design parameters were tabulated for each monitored 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 parameters were used in a grouping evaluation which resulted in the definition of 10 monitoring groups corresponding to various combinations of these parameters at Westinghouse PWRs.

Approximately 40% of the plants ~all into one group for which the enveloping thermal transients, discussed above, are applicable.

Salem Units 1 and 2 are included in this group which includes five (5) plants for which surge line thermal monitoring data has been received. This volume of data is sufficient for the WOG to

_evaluate the effects of th~rmal stratification and apply the NLR-N89069

results to similar plants. Salem plant specific data was provided to.the WOG for the determination of group classification. The remaining 60% of Westinghouse PWRs 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 Signlf icant parameters which can influence the structural effects of stratification are: .

. a. *. Location and, *µesign o~ 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 variation 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 PWRs), 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 to date indicates that further evaluations will not resuit in a*more limiting configuration than those already performed.

c. Operating 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. A temperature difference between the pressurizer and reactor NLR-N89069

coolant system (RCS) hot leg of more than 300°F may result.

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 PWRs. A review of recent Salem Generating station heatup/cooldown data and interviews with Salem reactor operators has indicated that the temperatuf;e difference between the pressurizer and RCS hot leg is below 300 F. -

D. Pipe Stress and Remaining Life The Salem pressurizer surge line piping has been designed and fabricated in accordance with ANSI B31.1 - 1967 and ANSI B31.7 -

1969 power piping code requirements. The stress analysis has included primary and secondary stresses resulting from static and

.... dynamic loadings *...The .. static loads .. are internal pressure,

-...~ :~deadweight _and linear th~rmal e~ansion. .. The dynamic ...analysis . is ..

.*. .. - . :+/-he ,p_iping,:_respons~ .~to~:.a,,.design,.basis .,:earthguake..

• -. ,, ., .;...aased upon -the* result:s *of *the stress. analysis 1 *the :surqe Tine was provided with high energy line break restraints to minimize the

. :effects of a postulated pipe* failure~ Seven (7) *restraints. were installed to mitigate the effects of pipe whip and jet impingement on adjacent equipm~nt.

Thermal stratification is self-limiting, i.e.,* the temperature gradient is finite and will not increase beyond the applied heat source. The resulting pipe stress caused by the strati-f ication mechanism is classified as a secondary stress. The primary stress analysis (those loads that are not self-limiting, i.e.,

the' seismic response) is not affected by the thermai stratification loading. Secondary stresses wiil not result in a catastrophe type failure but rather cause excessive deformation or fatigue loadings.

The surge line piping at both Salem 1 and 2 has been visually inspected for indications of abnormal piping movement as well as being ultrasonically inspected. No indications have been found on either Salem unit that would indicate that the surge line piping has been subjected to excessive thermal movement or .

fatigue induced cracking. The piping insulation does not show surface marring.and the pipe HEBA restraint clearances are in accordance with the design drawings. The NOE examinations on the pipl.ng welds have not indicated any material flaws.

The effects of secondary stresses on the remaining 1-ife of the surge line has been evaluated on a generic basis through the WOG program. The following summarizes the results of this evaluation.

NLR-N89069

All plant specific analyses performed as of March 1989 have demonstrated compliance with applicable ASME Codes.

• The fatigue evaluation has determined that the cyclic loading can be applied in excess of a 40 year ~lant life.

Review of plant specific 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 years) 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 50% of the fatigue life has been used at any Westinghouse plant to date.* To date, Salem Unit 1 has experienced 36 heatup/cooldown cycles while Salem Unit 2 has experienced 37.

This*may .. be extrapolated to less than 25% of.the available

- . :fat;i.gue life used to date.

...~

For a design life considering 200 heatup/cooldown *cycles* ('used in plant specific analyses) and considering the worst case condition noted above, this would indicate approximately 150 remaining cycles. This number of remaining cycles far exceeds the ten (10) postulated worst case number for the two year time frame needed to resolve the stratification issue.

E. Leak Before Break All plant specific analyses performed to date that have included the loadings due to stratification have validated the "leak-before-break" concept. Fatigue crack growth calculations, performed as part of these plant specific analyses, have demonstrated that an undiscovered crack as large as 10% 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. Visual Inspection The visual inspection of the pressurizer.surge line required by Action 1.a of NRC Bulletin 88-11 was performed on Salem Unit 2 during the recent Fourth Refueling Outage (Fall 1988). PSE&G has committed to the performance of both visual and ultrasonic examinations on both the Salem Unit 1 and Salem Unit 2 pressurizer surge lines during the next two consecutive refueling outages. This includes a field walkdown to verify support and HEBA restraint clearances. '

During the Salem Unit 2 Fourth Refueling Outage, the results of the NDE of the pressurizer surge line revealed no recordable indications of flaws. The support clearances and insulation were NLR-N89069

measured and compared against the design drawings. The piping ins~lation was intact and showed no signs of damage. No deviations were found that would' indicate abnormal pipe deflections. The Salem Unit 1 pressurizer surge line vis'1al and*

ultrasonic examination and field walkqown were perforll)ed in April 1989 during the Eighth Refueling Outage. The results of these examinations were similar to those of Salem Unit 2 in that no anomalies were disc*overed ~

These results provide additional support for continued operation of the Salem units.

summary of Conclusions from WOG Program

• Based on *information assembled on *surge *lines *for** al-1 *domestic

• -.-.- Westinghouse.PWRs,. and evaluation. of that information in

... :. co.!ljlinction with plan't;-specific and .pther interim .evaluation

... *~*"_results., :'.the:.: WOG~ ..concludes ,:.that:: *

- * * * -. *** -* * - ***~A *high .:degree* o*f:-confidence -"exists **that 'further

'.:evaluation will confirm that the worst combination has

-already been evaluated for stratification severity, structural effec~s and operating procedures.

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 PWRs, the worst case remaining life is approximately 100 heatup/cooldown cycles.

- Through wall crack propagation is highly unlikely, however, "leak-before-break" would permit a safe and orderly shutdown if a through-wall leak should develop.

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 PWRs may be safely operated while..additional data is obtained.

• Overall Conclusion Based on the above discussions, PSE&G believes that ~t is acceptable for s.alem Uni ts 1 and 2 to continue power operation for at least ten additional heatlip/cooldown cycles.,per unit without risk to pressurizer surge line.integrity. PSE&G has committed to update our existing calculations to include the fatigue analysis as required by Bulletin 88-11 within two years from the date of receipt of the bulletin.

NLR-N89069