ML20090M839

Nonproprietary Evaluation of Byron & Braidwood Units 1 & 2 Auxiliary Spray Lines Per NRC Bulletin 88-008

ML20090M839
Person / Time
Site:	Byron, Braidwood
Issue date:	02/29/1992
From:	Strauch P WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20034D376	List: ML20090M819 ML20090M823 ML20090M828 ML20090M834 ML20090M839
References
IEB-88-008, IEB-88-8, WCAP-13245, NUDOCS 9203250338
Download: ML20090M839 (24)

Text

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Westinghouss Class 3 WCAP-13245 k.

EVALUATION Of BYRON AND BRAIDWOOD

' UNITS 1 AND 2 AUXILIARY SPRAY

, LINES PER NRC BULLETIN 88-08 February 1992 P. L. Strauch

. VERIFIED BY: /k Nao D.-H7Roarty u Diagnostics & Honitoring Technology Approved by / 7 Y #'

S. S. falusamy, Manager

- Utagnostics & Honitotrng Technology l

i i.

WESTINGHOUSE ELECTRIC CORPORATION l Nuclear and Advanced Technology Division io P. O. Box 27 8 Pittsburgh, Pennsylvania 15230-2728 9203250338 920316 PDR ADOCK 05000454 s O PDR ,

l

TABLE OF CO'.iTENTS

. Section Titio Page 1.0 EXECUTIVE

SUMMARY

l-1

2.0 BACKGROUND

AND INTRODUCTION 2-1 l

3.0 THERMAL TRANSIENT DEVELOPMENT 3-1 4.0 STRUCTURAL INTEGRlTY AND FAilGUE ANALYS'S 4-1 5.0 INSERVICE INSI'ECilCN RECOMMENDATIONS 5-1

6.0 REFERENCES

6-1 4

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SECTION 1.0 EXECUTIVE SbMMRY ,

, This report provides an evaluation of the pressuriter auxiliary spray line for the effects of potential thermal stratification nd enling as described in NRC Bulletin 88-08 (reference 1). Inis avaluation included monitoring dsta review, transient development, structural integrity ard fatigue anaivis, and in.ervice inspection recommendations.

The monitoring data did not arovide any indicatico .:, uneialyzed thermal transients, including thermal cycling c- inloakage of cold fluid from the auxiliary spray line. However, for this enloation, e conservative therral transient was postulated, based on the experience of the safety injection piping at farley Unit 2. A structural integrity analysis was performed including fatigue crack grcath to determine an acceptable period of operation, assuming that the postult.ted trans bnt occurs, lhis analysis determined an acceptable period of power operatior of approsimately 39 months.

in con. lusion, an inservice inspection interva', of 39 manths of power oport. tion is recommended te provide continued assurance of the structural

. integrity of the pressurizar aur'liary spray piping. Therefore, it is judged that future monitoring of the auxiliary spray piping is not necessary.

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SECTION 2.0 j BACKGROUND AND M RN U UiON

,. Following the discovery of pipe cracks in the auxiliary lines of several nuclear cower plants, the United States Nuclear Regulatory Commission issued Bulletin 88-08 (Ref. 1). Action Item 1 of the Bulletir, requested utilities to idsntify systems connected to the Reactor Coolant System which are susceptible to adverse temper 6 turn distributions (not considered in the design analysis of  ;

the piping) tha', could be induced by leaking valves. The auxiliary ,

pressurizer spray line was identified as one such system at the Byron and Braidwood Units-(Ref. 2).

Action item 2 of Bulletin 88-08 requested that the identified systems be nondestructively examir.ed to provide assurance that there are no existing flaws. Recent inspection of the auxiliary spray lines at Syron Units 1 and 2 resulted in no indications of flaws. (The Braidwood Units are scheduled fo-inspection during the upcoming refueling cutage).

Action item 3 of the Bulletin requested that a program be implemanted to provide continuous assurance that aoverse temparature distributions are not

... occurring in unisolable piping sections. Accordingly, Commonwealth Edison Company has instrumented ths auxiliary spray line at Byron Units 1 and 2 with surface-mounted temperature sensors.

Data from the Byron Unit 1 auxiliary spray line has been evaluated for

.. evidence of adverse temperature distributions. Temperatures at the two monitored locations are steady, with no cycling observed. The temperatures are also within the expected range of temperatures during mode 1, therefore inleakage of cold fluid from the auxiiiary spray line into the hot main spray line-is not occurring. -

Plant operating practices have also been evaluated to determine the potential impsct on fatigue life of the auxiliary spray line and main spray line in the vicinity of the auxiliary sprey/cain spray connection if leakage as identified in the Bulletin occurs, m .. m m e 2I

• Based on tht results of insarvice inscection, tertperature moniterbs, plant '

operating practicct and fatigue analysis (astuming postulated transient), this evaluation provides justification for the elimination of monitoring the Syron and Braidnood 6uxilitry spray lines por fGC Bulletin 88-08 Iterr 3. Instead, periodic inservice inapection (with frequency determined by analysis results) will be performed. ,

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SECTION 3.0 THERHAL 1RANS!ENT DEVELQPMENT

. Adverse temperature distributions could occur in the auxiliary spray line and connecting main spray line if the auxiliary spray isolation valve admits l leakage flow under certain thermal hydreulic conditions. l l

4 Several possible scenarios must be cansidered for transient evaluation. The

., first, and most likely cond4 tion, consicers no leakage through valve 21ABBRE (see figure 3-1). This condition has been evaluated in the original design analysis, and therefore further consideration is not required. A second condition' assumes (

Ja,c.e This unlikely condition will not result in significant abnormal thermal transients, due to the small temperatura difference between the two fluids. A third condition is possible in whien (

Ja.c.e Due to the potential for excessive fatigue, this condition is evaluated in this report.

To develop a-thermal-transient for the assumed condition of cold leakage, it was necessary to evaluate the actual operating conditions of the spray line

. and determine the potential for thermal stratification, cycling and mixing.

e 3,1 Pressurizer Spray line Operation Tha flow rate in the main spray piping must be determined in order to evaluate the' potential for thermal stratification and cycling in the potentially

, affected piping. Typical flow conditions in the main spray piping are summarized in this section, based on actual operating experience at the Byron and Braidwood Units.

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The Byron and Braidwood pressuri:er spray systems are typically operated with a 10 to 20 percent demand on sprav valves 455B and 455C during 90 to 95 percent of the total time that the units are at normal operating conditions.

.. There is a diroct correlatiot, between percent demand and percent of rated  ;

travel .snd therefore typical flowrates may be calculated using figure 3-2.

.. The design flowrate for the main spray line is [

)a,c.e Therefore, during 90 to 95 percent of the normal operating period, the main l spray line flow rate is typically ( la.c.e l l

During the remaining 5 to 10 percent of the normal operating period, the main  ;

spray flow rate will vary depending on plant conditions. While this flow may be sufficient to cause turbulent mixing of the potential inleakage from the auxiliary spray line (thus eliminating the potential for thermal cycling), it ,

will be conservatively assumed that the flow conditions are such that thermal stratification and cycling dll occur.

3.2 Stettification Thermal Hydraulics d

Thermal stratification can occur in horizontal pipes when hot and cold fluids

, are present under certain thermal hydraulic conditions, including temperature, flowrate and pipe size. A measure of the potential for two fluids to stratify is given by the Richardson number, which is defined as follows:

2 Ri = gBAT0/V

. where: - g = acceleration of gravity _

B = volumetric expansion coefficient

-AT = fluid temperature difference 0 = pipe inside diameter V = fluid velocity ,

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Test data (reference 9) indicates that stratification is likely if the Richardt.on number is greater than or equal to aDproximately 1.0. Values much

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less than ( l It

l. is assumed that a Richarcison number of accronimataly (

)a,c.e Since the most likely location of thermal cyc'ing is [

3a.c.e This will provide the flow rate, and hence, fluid velocity for the calculation of the Richardson number, In addition to flow rate, it it, recessary to determine the fluid temperature t difference (AT). This will be used in the Richardson number calculation and the thermal transient definition for the fatigue analyses.

An evaluation of the thermal transient which caused the Farley pipe crack (reference 8) resulted in a maximum temperature difference (

ja.c.e Tb: anximum potential temperature difference for the auxiliary spray piping is

(

ja.c.e Based on a comparison of the maximum potential temperature differences for the farley safety injection line and the Byron /Braidwood auxiliary spray lines, a temperature difference of ( 'la,c,e is conservatively assumed for thermal transients on the auxiliary spray line,

, The potential for thermal stratification and cycling will be determined based upon the operating conditions defined in section 3.1 and the postulated transient, using the Richardson number.

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For 90 percent of the operating time, the flowrate of [

Ja c.a Therefore, fatigue is not a e concern for at least'90 percent of the ncemal cporating period, for the remaining 10 percent of the time, a [ Ja.c.e stratification

, transient will be considered in the fatigue avaivatio,. i l

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Figure 3-1. Flow ~ Schematic and Typical 1sowetric Layout of Spray Piping i

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Figure 3-2. Valve % Rated Travel Versus % of Rated Flow for Main Spray Valve ,

40189/110388 10 3.g

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SECTION 4.0 STR!!CTURAL INTEGR!TY AND FATlGUE ANALYSES As described in the previous sectier, thermal cycling is possible during at.

much as ten cercent of the time the Byron and Braidwood units are at normal operating cenditions, should worst case auxiliary spray isolation valve leakage occur.

4.1 Thermal Lea,dino Since the transient for the assumed auxiliary spray line leskage is postulated, rather than actual, a conservative transient, based on the Farley safety injection experience was used in this evaluation. Based on torperature data from Farley and the expected low flow loakage conditions .i 16ernal profile was defined to be used in finite element thermal and stress enalyris (see figure 4-1).

Assuming the thermal conditions shown in figurc 4-1 are (

3a c.e This temperature loading assumed a conservative transient period of

( Ja,c.e minutes Aur cycle. Finite element analysis has shown that if the actual 7 u*p time it shorter than ( Ja,c.e minutes, the resulting stresses

, wili J. ;s; ievere, since heat transfer through the pipe thickness requires a certa:n o.s .nt of time, li the cycle time is longer than ( la.c.e minutes, the local thermal stresses will be identical to the ( la.c.e minute cycle, but the piping will be subjected to fewer cycles.

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i 4.2 Stress Analysis _

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A thermal stratification loading will typically have two stress effects on

.. piping, a "lecal" ot fa.'t and a "gicbal" offact. Local stresses can be i obtained [  :

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)a,C,e Glcbal stresses result from [  :

)a,c.e

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The local stress for this evaluation is conservatively obtained using the ,

, (' la.c.e The heat transfer elements '

used in the thermal aaalysis model were replaced with (

)8'C and loaded with nodal-temperature

, input from the heat transfer analysis, r 4.3- Fatigue Analysis A' fatigue analysis was performed using fatigue ersck growth methods, to ensure i the structural integrity'of the auxiliary spray and main spray piping, should

.: the postulated transient occur. This fatigue evaluation will be used only to determine.an acceptable period of operation between inservice inspection intervals.

The ASME Section XI method is based on stress analys+s results and material crack growth laws. The stress intensity factor (K y) required for.the-fatigue crack growth calculations is obtained from the Kg expression given sou, morse ,s 4.g

h in reference 3 for an aspect ratio (2a/t) of 1:6, The fatigue crack greath  :

law fer stainless steel in a pressurized water enviror. ment was obtained frc:n f reference 4. The crack growth per cycle da/cN (inches / cycles) is

, a,c,c i l

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i The stress intensity range input to the fatigue crack growth analysis was obtained from the maximum axial stress.

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. . The results of the fatigue crack growth analysis indicate that approximately

( Ja,c.e cycles of the p stulated transient would be required to-

1. .

prcpagate an initial [ Ja,c.e percent through wall crack to ( Ja c.e percent of the wall thickness. This cycling has been postulated to occur only during a maximum of ten percent of the time the plant is at normal operating conditions, should auxiliary spray line isolation valve leakage occur. -Based ,

upon the conservative transient period of ( Ja,c.e minutes, this translates to 39 months of power operation. The inservice inspection interval is therefore recommended to be two refueling cycles,-or approximately

. 39 months of power operation.

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Figure 4-1. Thertal Loading Based on farley SI Pipe Incident

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SEC11CN 5.0 INSERV!CE INSPECilCN RECCMMENDATIONS d

This section surearites recommencations for inservice inspection on the Byron

and Braidwood p essuri:er spray and auxiliary spray lines for those lccations susceptible to culd inloakage from the auxiliary spray line. This updetes the recommendations provided in letter CAC-89-324 (reference 7), based on the

. evaluation summarized in this recort.

. 5.1 inservice inspection Locations Figure 5-1 illustrates the two general locations required for inservice inspection, The locat hn Icteled as (

3a,c,o The other location is a { jd'C s figure 5-2 illustfates the most, critical zones for potential crack indications

, in tbn vicinity (

p.c,o .

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3a,c.e 9

av.sewa 51 l

5.2 jnservice,InsoectionGuidelines e The type of indications expected from this type of loading are generally ID initiated and circumferentially oriented cracks, for zone B, the orientation of potential indications is not known, except that they are axpected to be ID

. initiated.

The followirg generai UI guicelines previvwsi, pre.ided ir, esfcccr.:c ' r:# lect the experience of the inspection of the Farley Unit 2 safety injection line as

- discussed in NRC Bullet 4n 88-08, Supplement 2.

Larger Diemeter Lines (4 to 6 inch)

Performing a 45 degree refracted shear wave examination using a 2.25 Mhz 0.5 to 0.25 inch diameter transducer, calibrating out to a one anc one-half vee exam for all of the above welds.

Performing an additional 60 degrec refracted shear wave examination using a 0.50 to 0.25 inch diameter, 1.5 MH.2 transducer, calibrating out to a one and

, one-half vee exam fur all of the above wolds.

Scanning sensitivities should be at 14 dS above reference sensitivity with a noise level of less than 10% full screen height for the 45 and 60 degree exams. If the noise 16"sl exceeds the above limit, reduce the scanning

- sensitivity in one dB increments until the noise level drops to below the above level, and record this . c' on on the applicable data sheet.

Record and evaluate all indications that traveled in time, are not attributed to componer6t geometry and have an amplitude of greater than or equal to 207. of the distance amplitude correction curved.

Smaller _DiameterLines(lesstnan4inchesl As a result of the NRC bulletin 88-08, a number of smaller diameter pipes are

. now requiring inspection. It should be noted that these lines were not

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w_- . . .. =- . - . . . - . .

. designed for such inspection, and some locations may require advanced volumetric inspection techniques. Volumetric inspection can be either a ultrasonic testing or radiographic testing. -

L, Ultrasonic testing may involva use of miniature or specialized transducers with specific procedures for examining the volume of interest.

2. Radiographic techniques should te considered when unusual component goometry or large areas require inspection. These techniques should be qualified to ensure that proper coverage of the comnonent volume of concern. Access for positioning the radioactive source is also an important consideration.

In some cases, it may be practical to use a combination of radiographic and ultrasonic testing techniques.

if an' *dications or suspect. indications are detected during the above exam ar., it is recommended that suoplemental radiographic examination of

. tht: Mc a performed.

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a figure 5-1. Inservice Inspection Locations

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') Figure 5-2. Inservice Inspection Location - Branch Connection

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SECTION 6.0 '

REFERENCES 3

1. Uni'ed States NRC Bulletin 88-08, " Thermal Stresses in Piping Cornected l

. ts Reactor Coolant Systems," 6/22/88; Supplement 1, 6/24/88; Supplement 2, 8/4/88 and Supplement 3, 4/11/89.

2. Westinghouse letters CAE-88-324 and CCE-88-464, 9/21/88.

. 3. McGowan, J. J. and Raymund, M. " Stress Intensity Factor Solutions f or Internal Longitudinal Semi-Elliptical Surface Flans in a Cylinder Under _

Arbitrary Loadings," Fracture Mechanics, ASTM STP 677, 1979, pp. 365-380.

4. James, L. A., and Jones, D. P., " Predictive Capabilities in Environmentally Assisting Cracking," Special Puolications, PVP-Vol. 59, ASME, Nov. 1985.

5. Program WECAN, version date 9/3/02A, cycle 22, 4/11/89 Westinghouse Proprietary.

6. Program FCG, cycle 3, 8/2/89, Westingnouse Proprietary.

\ 7. Westinghouse letter CAE88-324, 9/21/B8, " Commonwealth Edison Company.

Byron /Braidwcod Huclear Stations, Response to NRC Bulletin 88-08."

.. 8. WCAP-11786, Rev. 1, "J. W. Farley Unit 2, Engineering Evaluation of the J

Weld Joint Crack in the Six inch Saftty injection and Residual Heat Removai

. Piping," July, 1989, Westinghcuse Proprietary.

9. J. S. Turner, Buoyarcy Effects in Fluids, Cambridge Press, London,1973. '

10. ASME Boiler and Pressure Vessel Code,Section III, Division 1, eppendices, 1977 Edition, throuijh Summer 1979 Addendum, and Section XI, Division 1, 1983 Edition th ough Summer 1933 Addendum.

g 11. Bamford, W. H., " Fatigue Crack Growth of Stainless Steel Reactor Coolant Piping in a Pressurized Water Reactor Environment," ASME Trans. Journal of Pressure Vessel Technology, Feb. 1979.

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